Diagnostic field guide by Plantwise

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Plantwise Diagnostic Field Guide recommendations for their management make Compiled by Phil Taylor www.plantwise.orgORE


The Plantwise Factsheet Library USB The Plantwise factsheet library USB allows you to access content from the Plantwise knowl- edge bank even when you are offline. On the USB card, you will find a variety of content, including Plantwise factsheets for farmers, pest management decisi▯ es, Plantwise technical factsheets, and more. To access the Plantwise factsheet library: 1. Unfold the USB connector and insert the card into the USB port of your computer 2. The USB will load a USB drive and a CD-ROM drive, labelled ‘PWKB’, in your list of devices. Open the PWKB CD-ROM drive to view the Plantwise factsheet library 3. Click on ‘Menu.htm’ to open the Plantwise factsheet library Navigating the Plantwise factsheet library: • Select a category to view the list of pest or host species • To find a particular pest or host, press Ctrl + F and type the name you wish to search for • Click the name of your chosen pest or host to access content on th▯ iesec • Click on a factsheet title to view the factsheet or clic▯ begin a new search • Click back in your browser at any time to return to the previous list www.plantwise.org/kb For more information, please contact: plantwise@cabi.org


Plantwise Diagnostic Field Guide recommendations for their management make Compiled by Phil Taylor www.plantwise.orgORE


CABI is a trading name of CAB International CABI Nosworthy Way Wallingford Oxfordshire OX10 8DE UK T: +44 (0)1491 832111 F: +44 (0)1491 833508 E: info@cabi.org www.cabi.org Published by CABI on behalf of Plantwise www.plantwise.org plantwise@cabi.org © CAB International 2015. The copyright holder of this work is CAB International (trading as CABI). It is made available under a Creative Commons Attribution-Noncommercial Licence (CC BY-NC). Reproduction of this publication for educational or other non-commercial purposes is authorised without prior permission from the copyright holder provided the source is fully acknowledged. Reproduction for resale or other commercial purpose is prohibited without prior written permission from the copyright holder. A catalogue record for this book is available from the British Library, London, UK. ISBN-13: 978 1 78064 676 3 Production editor: Tracy Head, CABI Line drawings in Table 2: Robert Reeder, CABI Cover design and typesetting by Sarah Hilliar, CABI Printed and bound in the UK by Intaglio Ltd, www.intaglioltd.co.uk


CONTENTS Foreword 5 Preface 6 Acknowledgements 8 INTRODUCTION 9 FIELD DIAGNOSIS: A PROCESS OF ELIMINATION 11 Field visits 14 READY RECKONERS FOR PEST IDENTIFICATION 15 Insect and mite pests 15 Plant pathogen pests 15 Mineral deficiencies 15 The principal symptoms and their causes 23 Wilt 23 Leaf spot 30 Witches’ broom 38 Canker 40 Mosaic 41 Yellowing of leaves 43 Distortion of leaves 49 Little leaf 53 Galls 55 Drying/necrosis/blight 58 POTENTIAL SOURCES OF CONFUSION 61 MAKING RECOMMENDATIONS 72 ‘BIG 5’ Key considerations when making a recommendation 72 BIG 5 Economic 72 BIG 5 Effective 73 BIG 5 Safe 73 BIG 5 Practical 74 BIG 5 Locally available 74 Biology of the pest 75 Integrated pest management 76 Field diagnosis and recommendation overview 79 ANNEXES 83 Annex 1: Scientific names of crops mentioned 83 Annex 2: Plantwise Policy on the Use of Pesticides 84 Annex 3: Plantwise Pesticide Red List 85 Annex 4: Glossary of terms 87 Annex 5: Photographic glossary of symptoms 90 Contact us 113 3


Plantwise is supported by Ministry of Agriculture People’s Republic of China 4 Plantwise Diagnostic Field Guide


Foreword Continuous advances in global agricultural knowledge and technology have increased food production massively, but there are several factors that make it difficult for farmers to maintain yields and▯ produce high-quality food. Plant health problems are an ongoing issue for farmers due to pest outbreaks (pathogens, insects, rodents, weeds, etc.), climate change (e.g. unpredictable rainfall), the decline of many natural resources (e.g. poor soils) and limited access to important inputs (e.g. plant protection products, water). When farmers encounter new or unfamiliar plant health problems they need support. Plantwise is an innovative global programme, led by CABI, which aims to connect farmers to the services and information they need to maximise yields and improve the quality of their crops. Working in close partnership with relevant actors, Plantwise strengthens national plant health systems from within, enabling countries to more effectively develop sustainable solutions in agriculture. This approach initially focuses on establishing sustainable networks of local plant clinics, owned by national partners and run by trained plant doctors, where farmers can find practical plant health advice. Plant clinics are reinforced by the Plantwise knowledge bank, a gateway to online and offline actionable plant health information, including diagnostic resources, pest management advice and pest data for effective global vigilance. The establishment of plant clinics with national partners improves the frequency and quality of interaction between advisory services (extension) and farmers. Plant doctors receive requests from farmers to diagnose diverse crop problems and to provide management recommendations. At the same time, plant doctors are gathering data from the field that can stimulate action by different members of the plant health system to investigate and solve the crop problems that farmers have. As plant doctors play such a critical role in giving advice to farmers, it is important that they are selected from existing extension and/or plant protection services and have the right knowledge for the job. The Plantwise programme tries to ensure that they are equipped with the basic resources they need to run a simple, yet effective, plant clinic. Plantwise facilitates the training of plant doctors through two short courses that encourage the trainees to think about the general principle▯ of diagnosing plant health problems and giving good advice. To support plant doctors in their work, a variety of information tools, such as the online Plantwise knowledge bank (freely available at www.plantwise.org) and offline documents, are produced through the programme to improve the quality of diagnoses and crop management advice given. The Plantwise Diagnostic Field Guide is an important companion document for plant doctors running plant clinics. It provides images and short descriptions, which make it a useful resource for plant doctors at the plant clinic, but it also contains additional information that ▯ nt doctors can absorb during quieter moments. Furthermore this diagnostic field guide is a handy resource for anyone wanting to learn more about how to diagnose plant health problems and to explore the kinds of challenges with which plant doctors commonly have to deal. The Plantwise Diagnostic Field Guide contains content that is the result of years of concept development and field testing, involving a number of CABI staff and partners around the world. The actual creation of this work was the result of tireless efforts by Dr Phil Taylor, with significant support from Dr Matthew Cock. It is important to also recognise the many others within CABI who provided content and feedback on earlier drafts of the document. Finally, this type of resource would not be possible without the strong support from the Plantwise donors. Dr Ulrich Kuhlmann Plantwise Programme Executive 5


Preface The Plantwise Diagnostic Field Guide is intended for all plant doctors and other plant health advisors around the world. The job of being a plant doctor is not an easy one. Since farmers can bring any crop with any type of problem to a plant clinic, there are many different kinds of plant disorders that a plant doctor will be asked to diagnose and give advice on. It is not possible for a plant doctor, or anyone else for that matter, to be an expert on all crops and all plant health problems. This diagnostic field guide is designed to provide support to agricultural advisory staff as a field tool to assist in diagnosis of plant health problems prior to making management recommendations. Since 2011, the Plantwise programme has been developing locally adapted information materials to support plant doctors, recognising that it is not always easy to obtain useful and up-to-date information about plant protection and production. These information materials are available both online (Plantwise knowledge bank) and offline (in the form of both digital and printed documents). Furthermore, Plantwise emphasises the importance of information networks to make sure that plant doctors and others involved in agriculture are connected to the right people to get the information and services they need. Much of the work that Plantwise does is based around strengthening linkages among plant health system stakeholders, such as extension, research (including diagnostics), policy, input supply and, of course, the farmers themselves. Although the Plantwise Diagnostic Field Guide supplements training Modules 1 and 2 on ‘How to become a plant doctor’, it is not intended to be a manual for use in the plant doctor trai▯ning courses, nor is it a substitute for taking the modules. The Plantwise plant doctor training courses have been designed with a discovery learning approach to get participants thinking about the broad principles of symptom diagnosis and giving good advice, as well as providing a detailed introduction to the operation of a plant clinic. Therefore, attendance at Modules 1 and 2 training is considered an important minimum requirement prior to operating a plant clinic as a plant doctor. Moreover, it is very important that candidates for plant doctor training should already have considerable experience and knowledge in plant health. The plant doctor training modules contain only limited information on th▯e biology of pest organisms because the aim of the training is to raise awareness of the diverse causes of plant disorders and to stimulate participants to think logically and critically when diagnosing plant health problems and giving appropriate advice. In contrast, this diagnostic field guide contains more information on the biology of the pest groups mentioned in the training. It is written so that most sections of it could be helpful to a plant doctor at a plant c▯linic. More information on diagnosing plant health problems and methods for maintaining healthy crops can be obtained through various knowledge resources that may be available, such as pest management decision guides, factsheets and other extension materials, text books, a▯nd Internet tools such as the Plantwise knowledge bank. 6 Plantwise Diagnostic Field Guide


1 It is hoped that plant doctors and others dealing with plant health problems will find this diagnostic field guide useful in the years to come. Comments on the Plantwise Diagnostic Field Guide are welcome. To provide feedback, please send it in an e-mail to the following address: plantwise@cabi.org. Dr Phil Taylor Compiler, Plantwise Diagnostic Field Guide 1 Plant doctors: the name plant doctor is widely used in many countries b▯ut not all. For those countries that have adopted Plantwise but use different terminology for the operators of plant clinics, please read this document mentally replacing ‘plant doctor’ with the chosen terminology of your country. 7


Acknowledgements Any publication of this nature builds on the work of others. The Plantwise approach and some of its training materials grew from an earlier CABI-led project, the Global Plant Clinic, funded by DFID to provide a diagnostic and advisory service for crop protection in developing countries. Under Dr Eric Boa’s leadership, the plant clinic concept was developed and tested from about 2002 with support from Jeffery Bentley, Solveig Danielsen, Rob Harling, Paula Kelly and Robert Reeder. Dr Phil Taylor was responsible for developing the Plantwise Diagnostic Field Guide and he must be thanked for his enthusiasm and dedication to complete this book ▯project. Special thanks must go to Dr Matthew Cock (editing and reviewing, entomology inputs), Dr Wade Jenner (editing and reviewing, plant clinic insights) and Dr Robert Reeder (reviewing, pathology inputs, pictures). Other CABI staff who made important contributions in terms of pictures, information, text, editing and review include: Dr Melanie Bateman, Alex Brook, Dr Claire Beverley, Katherine Cameron, Dr Malvika Chaudhary, Erica Chernoh, Dr Yelitza Colmenarez, Dr Jayne Crozier, Claire Curry, Dr Steve Edgington, Dr René Eschen, Muhammad Faheem, Dr Tim Haye, Dr Shaun Hobbs, Dr Elizabeth Johnson (now with IICA), Peter Karanja, Julien Lamontagne- Godwin, Dr Aamir Malik, Efa Negussie, Dr MaryLucy Oronje, Dr Washington Otieno, Shamela Rambadan (now with FT FARFAN Ltd, Trinidad), Abdul Rehman, Dr Mike Rutherford and Dr Stefan Toepfer. Individuals who have made photographs available, either directly or via the Internet, include, Kalule Okello David (NaSARRI,Uganda), Yubak Dhoj (Department of Agriculture, Nepal), Paul Van Mele (Agro Insight) and Scot Nelson (University of Hawaii). The diagnosis of mineral deficiencies has been enormously improved by the use of information and illustrations from Prakash Kumar and Manoj Kumar Sharma’s Nutrient Deficiencies of Field Crops: Guide to Diagnosis and Management published by CABI in 2013. Organisations that have made pictures available either directly or via Creative Commons license on the Internet include The Bugwood Network (www.bugwood.org), CIMMYT and Wikimedia Commons (http://commons.wikimedia.org/). Individual and corporate photographers are acknowledged with each photograph. The Plantwise programme has been funded through a consortium of donors and their support has made it possible to prepare, print and distribute the Plantwise Diagnostic Field Guide to the plant doctors worldwide. Many thanks to all who have injected energy and ideas into this publication. Ulrich Kuhlmann Plantwise Programme Executive 8 Plantwise Diagnostic Field Guide


INTRODUCTION One of the focal activities of the global Plantwise programme is to support local agricultural advisory services (extension and plant protection organisations) in establishing plant clinics. Based on the human health care system with doctors, medical clinics, prescriptions, etc., a plant clinic is a place where farmers can meet with local plant health advisors, called ‘plant doctors’, to get management advice for their crop problems. Farmers might ask for assistance on many different kinds of problems concerning the crops they grow, so plant clinics generally accept ‘any problem on any crop’. Plant clinic sessions are usually held in public places. Farmers attending a plant clinic are encouraged to bring samples of the affected crops from their farms for the plant doctor to inspect. While inspecting each plant sample brought, the plant doctor also interviews the farmer about the crop problem, which helps the plant doctor to understand the nature of the problem on the farm and make a ‘diagnosis’ (identify the cause). Once a diagnosis is made, the plant doctor can explain to the farmer what should be done to minimi▯se yield loss, and a written recommendation (‘prescription’) is usually provided as well. It is important that a crop problem is diagnosed correctly because that diagnosis will determine the best plant health management advice to be given in the prescription. The Plantwise Diagnostic Field Guide is intended to support plant doctors to make diagnoses by showing relationships between common symptoms on plants and the various possible causes. It also provides a short overview of important principles for giving good advice, which is also underpinned by an integrated pest management (IPM) approach. This document provides images and descriptions of many typical symptoms (indications that ▯ the plant is unhealthy) and signs (observations of pest organisms) associated with biotic and abiotic factors that harm plant health. Among the biotic factors, the major pest▯ groups are represented. Please remember that throughout the Plantwise Diagnostic Field Guide, the term ‘pests’ will refer to all animals, microorganisms and weeds that damage plants.The most common abiotic factors of plant health decline are also highlighted.This diagnostic field guide does not attempt to show all possible symptoms or causes of plant disorders; therefore, it is important to understand the different types of symptoms caused by each factor and to use that knowledge to make a field diagnosis. This diagnostic field guide consists of ‘ready reckoners’ (simple information tables for quick and easy reference) that serve as reminders of symptom–cause associations and therefore can assist in diagnosing plant health problems. While several biotic and abiotic factors create characteristic symptoms in plants, many others lead to very similar symptoms. There is also a table (‘Potential sources of confusion’) that identifies these areas of overlap and provides methods to differentiate between the possible causes. The Plantwise Diagnostic Field Guide concludes with a short section on important points to remember when providing management advice to farmers for crop problems. These few, simple considerations will ensure that each farmer gets the best advice for him or her. 9



FIELD DIAGNOSIS: A PROCESS OF ELIMINATION The process of diagnosing a plant health problem without any specialised laboratory equipment is called ‘field diagnosis’. This is the situation at a plant clinic and when making a farm visit. Field diagnosis involves careful observation of the symptoms on a plant and linking those symptoms with possible causes. While some plant health problems are relatively easy to diagnose, others can be very difficult for a number of reasons. For instance, there may be multiple factors that cause similar symptoms or the sample provided by the farmer may not show very clear symptoms. As a result, it will often not be possible to make a highly specific field▯ diagnosis, such as giving the name of a nutrient that is deficient or the pest▯ cies causing the problem. However, in many cases a very specific diagnosis is not necessary. A diagnosis of a pest group, such as fungus or stem-boring insect, will provide a lot of useful information for developing a good recommendation for the farmer. The precision and accuracy of the plant doctor’s diagnosis ultimately depends on his or her knowledge of the crops and crop problems in the area, with additional support from tools like this diagnostic field guide. Precise versus accurate These two terms are often used interchangeably but they are different. A precise diagnosis is very specific, perhaps naming a pest species (as opposed to a pest group like virus or mite). An accurate diagnosis is one that is correct. If someone claimed she weighed 62.64932 kg, that would be very precise but hopelessly inaccurate if she actually weighed 67.5 kg. It is sometimes better to settle for lower precision (specificity) to ensure higher accuracy. In this example about body weight, it would have been far better for the person to have said she weighed about 65 kg. A field diagnosis of Fusarium oxysporum race 4 would be very precise but very inaccurate if the cause was nematode attack. Do not try to be precise unless you can be sure you are also accurate (correct). The first step in narrowing down the cause of a plant health problem is to determine if the symptoms are caused by a living organism (biotic) or by a non-living factor (abiotic). Abiotic factors usually affect the whole plant and often (but not alway▯ there is not a defined line between healthy and affected tissue, although exceptions will be discussed later in the section on potential sources of confusion (Table 6). Many abiotic causes of poor plant health are associated with the soil environment (compaction, pH, nutritional deficiencies, etc.). These tend to affect all of the upper parts of the plant since they are all connected to the same root system. Other abiotic factors, such as heat, wind, cold, hail, etc. have direct effects on the above-ground parts of the plant and lead to symptoms that are often distributed symmetrically within the plant and within individual leaves. Field Diagnosis: A Process of Elimination 11


The huge variety of pests that attack crops gives rise to a great variety of symptoms. Where the pest is active there may be a clear line between the healthy and the affected tissue, with more general symptoms of stress elsewhere on the plant. Much of the remainder of this field guide provides information on how to link symptoms with cause. Once the cause of the crop problem has been narrowed down to either a biotic or abiotic factor, it will usually be possible to take the diagnosis to the next level of detail. For biotic causes this would mean identifying the pest group (virus, weed, mite, etc.), and for abiotic causes this would mean determining whether the problem is associated with water, nutrients, temperature or some other environmental factor. It may be possible to take the diagnosis even further, such as naming a specific nutrient that is deficient or naming a type of virus, weed or mite, or even giving a species name. The more precise a diagnosis is, the better it is because it means that a more specific and effective recommendation can be given. However, making a very precise diagnosis is more difficult (for instance, many pest species look very similar) and the risk of making a mistake is higher compared to making a general diagnosis. Whenever you are unable to provide a full diagnosis to the pest species level or of the specific abiotic factor, make as precise a diagnosis as you can with confidence. As a diagnosis, ‘insect’ is useful but not particularly informative. ‘Maize stem borer’ is more helpful and ‘Lepidoptera maize stem borer’ is better still; however, avoid going further unless you know which stem borer it is because, depending on where you work, it could be one of several species that are difficult to distinguish. Remember to ALWAYS eliminate all the alternative causes before pronouncing your final diagnosis. Even if you cannot determine the exact cause, a general diagnosis (e.g. pest group) may be enough to provide the farmer with some good advice and a recommendation that will help him or her overcome the problem. Don’t be in too much of a hurry. Slow down, cut open the plant and have a look inside. Use a hand lens to look for fungal fruiting bodies or small insects. Most importantly, talk to the farmer and ask questions relating to what you are looking at and the ideas that are forming in your mind. It is better to tell a farmer that you are unfamiliar with the problem presented than to make a complete guess at the diagnosis (although be sure to tell them as much as you do know, e.g. what is NOT causing the problem). If you are too cautious you will never make a diagnosis, but equally you should not try to give a diagnosis for a plant health problem if there is not enough information to make the diagnosis. In many cases, the plant sample and information provided by the farmer may not be enough to make a diagnosis, in which case a visit to the farm may be required. 12 Plantwise Diagnostic Field Guide


Example: Field diagnosis of spots on leaves This cashew leaf has leaf spots, which are clearly defined and are all a similar size. This clear delineation between healthy (green) and unhealthy (tan brown) tissue indicates that there is a biotic cause. If the cause were an abiotic one you would expect to see a much more general yellowing or browning of the leaf without the sharp divide between healthy and unhealthy plant materi▯al. We can eliminate certain biotic causes through a mixture of experience and observation because the symptoms they generally produce do not fit in with the evidence presented. Robert Reeder, CABI • This symptom is not caused by insect or mite damage; there is no evidence of chewing, no webbing seen and no presence of insects or mites. • This symptom is not caused by a nematode, virus or phytoplasma, as these▯ organisms do not cause leaf spots. • This symptom is not caused by a mammal or parasitic plants or weeds, as ▯there is no evidence of it having been eaten (mammal) or of decline caused by competition by weeds or pa▯rasitisation by another plant. • This symptom could be caused by a bacterial pathogen but you would expec▯t the spots to have a water-soaked margin, to be bound between the leaf veins and generally associated with th▯e edge of the leaf. • This symptom could be caused by a water mould but the leaf spots are not spreading aggressively (they are all of a similar size), have a clearly defined border and show no evidence of fluffy sporulation. All of these characteristics together indicate that a water mould is not the causal a▯gent. By the process of elimination it can be concluded that this symptom has a fungal ▯cause. They are known to cause leaf spots with these characteristics. More detailed examination of the material with a hand lens reveals fungal fruiting bodies (arrowed), making this diagnosis definitive. A tool to diagnose crop pests and make recommendations for their management 13


Field visits Extension workers often have a limited amount of information available to them, especially if the farmer brought the plant sample to the extensionist: they may have collected the wrong part of the plant or the sample may have deteriorated in transit. It may be necessary to visit the field to see fresh symptoms and to gain other information on the pest. If you intend to send a sample to a colleague or a formal diagnostic support service, it is usually a good idea to visit the field yourself and to select a fresh sample of your own. The following is a summary of what to do when visiting a field to observe the symptoms in the context of the entire crop. (All of the information gathered would be of interest to a diagnostic support service if a sample were to be sent.) STEP 1: GET IN CLOSE • What parts are affected? • Describe symptoms using the correct terminology. • Observe changes in shape, colour and growth. • Look for visible signs of insects, fungi or other pests. STEP 2: LOOK AT THE WHOLE PLANT (INCLUDING ROOTS) • Where are the symptoms within the plant? • Which growth stages are affected? • How do the symptoms progress from early to late stages? • How severe is the attack? STEP 3: EXAMINE GROUPS OF PLANTS • Incidence: how many plants are affected? • Distribution: random, edge of the plot only, in patches, pattern caused by use of machinery? • Remember: consider plant variety, age and how it is grown. STEP 4: SPEAK TO FARMERS AND OTHER LOCAL EXTENSION WORKERS • When did the problem appear? Is this the first time? • Record local name for the problem. • Consider soil type and climate (patterns). • Obtain information on the varieties used, recent history of chemical inputs used, etc. 14 Plantwise Diagnostic Field Guide


READY RECKONERS FOR PEST IDENTIFICATION The following tables (ready reckoners) provide a rapid method of linking plant symptoms and signs with possible causes. In order to use the ready reckoners effectively, some experience of diagnosing plant health problems is required by the observer. There is one table for insect and mite pests and one for pathogens, and the latter is then expanded to dea▯l with each symptom group in more detail. Insect and mite pests The body shape and general appearance are often sufficient to identify many insects (Tables 1 and 2) to a group level, so no additional text is supplied in this diagnostic field guide. Plant pathogen pests As microorganisms are generally not visible, diagnosis is primarily based on symptoms, so additional information (Table 3) is provided focusing on the symptoms that different types of microorganisms can produce. Mineral deficiencies The ready reckoner (Table 4) summarises the major symptoms that many plants show when short (deficient) of a mineral. It provides only general information and shortage of a mineral is just one of many causes that can produce some of these symptoms. Not all crop plants display the same symptoms even when deficient in the same mineral (especially true for zinc). Some plants are more susceptible to shortage of minerals than others (e.g. molybdenum shortage in brassicas). Photographs of mineral deficient plants are provided in Table 5. It is unlikely that the mineral deficiency will be so acute that the se▯edlings die (the seed carries limited amounts of mineral). In most cases the shortage is chronic and the plants will survive but show symptoms that can be severe or mild. Chronic symptoms generally include slow growth (possibly stunting) and poor flowering and fruit production (where relevant). Yields can be affected even when symptoms are not seen. The more commonly deficient minerals are listed on the left of the table and the less commonly deficient ones o▯n the right. While field symptoms may be sufficient to provide an accurate diagnosis by an experienced agronomist who is familiar with local soil conditions, it is usually essential to h▯ave the field diagnosis confirmed with a laboratory soil analysis. This is especially important if the farmer is intending to spend a significant amount of money or effort on correcting the problem. 15



Table 1. Ready reckoner for insect and mite pest diagnosis APPROX SIZE METAMORPHOSIS ADULTS WITH WINGS EXTERNAL FEEDERS? LARVA/NYMPH OR ADULT PREDATORY OR PARASITIC LEGS OBVIOUS? BODY SHAPE DO THE YOUNG LOOK (TWO PAIRS EXCEPT AS CAUSES DAMAGE GROUPS OCCUR DIFFERENT FROM ADULTS? INDICATED) APHIDS 2-5mm No Some individuals Yes, but often in curled leavesBoth No Yes Pear-shaped MEALYBUGS 2-4mm No No Yes, but often in curled leavesBoth No No Oval SCALE INSECTS 2-4mm No No Yes Both No No Oval or round PSYLLIDS 2-5mm Young look very different Yes Yes, except gall-formers Both No Yes Varied; adults elongate THRIPS 1-2mm Paler, but similar Yes, limited flight Yes, but often in curled leaves or Both Yes Yes, but very small Elongate gall-formers PLANT BUGS 5-15mm No, but nymphs have reduced Yes, forewings more rigid, Yes Both Yes Yes Varied or no wings membranous hind wings underneath are for flying PLANT HOPPERS 3-15mm No, but nymphs have reduced Yes Yes Both No Yes Tube-like or no wings WHITEFLIES 2-3mm Yes, similar but lack developeYes, limited flight mostly witYes Both No Hidden beneath wings to some Early stages oval; adults with wings crop extent (usually white) wings held at an angle GRASSHOPPERS 20-40mm Young (nymphs) resemble Yes, may be strong fliers Yes Both No Yes Adults are grasshoppers; young AND LOCUSTS adults without wings lack wings WASPS 3-15mm Yes Yes Most wasp pests are gall- Larva Yes Yes on adults; usually not on Larvae grub-like (SAWFLIES) formers larvae except sawflies MOTHS Larvae Yes Yes, strong fliers Internal and external Larva Almost none Yes on larvae and adult Larvae are caterpillars (CATERPILLARS) 2-35mm Larvae Yes Yes, forewings form a rigid Internal and external Both Yes Yes on larvae and adult Larvae are grubs; adults varied, BEETLES (GRUBS) 5-30mm protective cover, membranous but have hard forewings (wing- hind wings underneath are for cases) flying; limited flight FLIES Larvae Yes One pair of wings only; can bePests are internal Larva Yes Yes on adult only Larvae are maggots (MAGGOTS) 2-12mm strong fliers MITES 1mm No No, but do parachute on threadExternal except gall-formers Both Yes Yes but small Rounded 17


Table 2. Line drawings of the major insect pest groups APHID MEALYBUG SCALE PSYLLID THRIPS PLANT BUG PLANT HOPPER 5 5 5 5 5 5 5 10 15 20 25 30 35 40 45 50 55 60 65 70 7510 15 20 25 30 35 40 45 50 55 60 65 70 7510 15 20 25 30 35 40 45 50 55 60 65 70 7510 15 20 25 30 35 40 45 50 55 60 65 70 7510 15 20 25 30 35 40 45 50 55 60 65 70 7510 15 20 25 30 35 40 45 50 55 60 65 70 75 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 mm mm mm mm mm mm mm WHITEFLY GRASSHOPPER WASPS (SAWFLY LARVA) MOTH (LARVA) BEETLE (GRUB) FLY (MAGGOT) MITE 5 5 5 5 5 5 5 10 15 20 25 30 35 40 45 50 55 60 65 70 7510 15 20 25 30 35 40 45 50 55 60 65 70 7510 15 20 25 30 35 40 45 50 55 60 65 70 7510 15 20 25 30 35 40 45 50 55 60 65 70 7510 15 20 25 30 35 40 45 50 55 60 65 70 7510 15 20 25 30 35 40 45 50 55 60 65 70 75 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 mm mm mm mm mm mm mm The size of the insect is indicated by the green scale on the left of each drawing. There can be great variation in the sizes between species. Upper limits are generally provided. 18


Table 3. Ready reckoner of pest and detrimental environmental conditions based on symptoms SYMPTOM FUNGUS WATER MOULDS BACTERIA VIRUS PHYTOPLASMA NEMATODE INSECTS MITES MAMMALS & BIRDS NUTRIENT DEFICIENCIES PHYSICAL & HERBICIDE Wilt YES Very common. Usually YES Common. Often YES Common. Often (NO) although some viruses (NO) except one example: YES Very common. YES Common. The larval NO (NO) although mammals (NO) but copper deficiency YES Very common. Shortage Fusarium or Verticillium sp.caused by root-attacking seen in Solanaceae, e.g. of tomato, pineapple and Coconut lethal yellowing Seen in a wide range of stages of stem borers and and birds that damage the can cause wilting in some of water (drought) and its phytophthoras. Water Ralstonia on tomatoes and broad bean cause wilting crops the larvae and adults of bark of trees or roots can plants. Extremely rare excess (waterlogging) are a moulds are a common cucurbit crops root feeders commonly produce this symptom common cause of wilt as is cause of damping off in cause wilts. Not usually physical damage to the roots, seedlings associated with sucking e.g. through weeding. Some insects unless extremely herbicides can induce this severe effect too Leaf spot YES Very common, many YES Common. Generally YES Very common. (NO) although there are (NO) although leaf markings (NO) but can occur on YES Not common. NO NO YES Not common. Necrotic YES Common. types involved on a wide rapidly spreading, may have On many types of crop exceptions. Ringspots are can occur ornamental plants, do not Some sucking insects inject spots on leaves can indicateCareless spraying with range of crops. Rust water-soaked appearance more common occur on crop plants a toxin when they feed nutrient deficiencies. contact herbicides such pustules are included as and sporulation around that can cause necrotic or Shortages of potassium, as diquat can lead to leaf spots here edges. White rusts and yellow spotting zinc, manganese and spots. Sunscald can lead downy mildews can produce copper can all lead to this to damaged patches often pustules with little necrosis symptom if severe on fruit Witches’ YES Common. In woody NO NO NO YES Very common. NO NO YES Very common. NO NO YES Common. broom plants only, not so in Generally associated with They are usually far too Only where plants have (many herbaceous plants little leaf small to be seen even with grown back after treatment branches) a hand lens with glyphosate Canker YES Very common NO YES Common NO NO NO NO NO NO NO NO Mosaic NO NO NO YES Very common NO NO (NO) although the feeding (NO) although as with NO YES Common. The mottling NO of tiny insects with piercingnsect feeding, mites can caused by deficiencies mouthparts such as thrips produce an effect that of several minerals can and whitefly can produce a resembles a mosaic produce a mosaic type of mosaic-like effect symptom Yellowing of YES Common. YES Common. General YES Common. YES Not common. YES Common. Relatively YES Common. A general YES Common. A general YES Common. Low (NO) although mammals YES Very common. YES Very common. leaves Often indicates symptoms stress caused by root death A general or non-specific Mosaics are much more rare pathogen BUT they do or non-specific symptom or non-specific symptom populations of mites can and birds that damage the Depending on the pattern Can be due to a variety or infection in other parts often the cause. Downy symptom indicating general likely, unusual for the entireften cause yellowing when noting general decline of caused by damage to the cause many leaves to turn bark of trees or roots can of yellowing can give an of abiotic factors, some of plant e.g. roots, cankersmildews may create defined decline of the plant leaf to turn yellow they do occur the plant due to root feedingoots or a general decline inellow produce this symptom indication of which mineral herbicides will generate on stem yellow patches on leaves the plant may be deficient but a yellow leaves on the treated prior to the production of definitive field diagnosis islant the downy spores masses difficult Distortion of (NO) although there is one YES Not common. NO YES Very common YES Not common. Usually NO YES Very common. YES Common. NO YES Not common. Cupping YES Common. leaves spectacular example and a Downy mildews can cause associated with witches’ Can be due to feeding Due to the mites damaging of leaves as well as reducedSome herbicides induce few others that can produce unusually shaped leaves broom and little leaf damage by sucking insects the developing leaves leaf lamina, can indicate unusual patterns of growth mild distortion or leaves rolled by web mineral shortage formers Little leaf (NO) reduced growth should YES Not common. (NO) reduced growth should YES Not common YES Very common. NO (NO) reduced growth should YES Common. NO NO YES Common. not be mistaken for this Downy mildews can cause not be mistaken for this Often considered to be the not be mistaken for this They are usually far too Only when plants have symptom leaves to develop severely symptom classic symptom of this symptom small to be seen even with grown back after treatment reduced in size group a hand lens with glyphosate Galls (NO) although on woody NO YES Common. NO NO YES Very common. YES Very common. YES Very common. NO NO NO plants they can occur. Often at the base of Swellings appear on root, asSeen on many types of plant Seen on many types of plant Bunts and smuts could be broadleaved plants (not well as general distortion of considered galls grasses, banana or palms) root systems Drying/ YES Very common. YES Common symptom YES Very common. (NO) although there are (NO) although there are YES Many types of YES Common. NO (NO) although mammals YES Not common. YES Not common on crops. necrosis/ Associated with many types of foliar attacking Associated with many types exceptions such as Maize exceptions, this is not nematode cause death and Stem boring and root eating and birds that damage the In extreme cases the plants Due to gross misuse of blight phytophthoras lethal necrosis and Cassava a symptom commonly decay of the roots but not larvae can cause these bark of trees or roots can will dry and die prematurelyrapidly acting herbicide brown streak associated with those that produce galls symptoms leading to death produce this symptom such as diquat or paraquat phytoplasmas or cysts of the plant 19


Table 4. Ready reckoner for common mineral deficiencies Nitrogen (N) Phosphate (P) Potassium (K) Magnesium (Mg) Manganese (Mn) Iron (Fe) Zinc (Zn) Sulphur (S) Calcium (Ca) Boron (B) Copper (Cu) Molybdenum (Mo) Notes Lower leaves Pale and yellowing Dark green and dull Light coloured ‘Bronzing’ and Not so affected Not usually affected Affects upper and No effect Hollowing and rotting of No effect Generally mottled Lower leaves will Often fall early with a bluish green tint necrotic patches necrosis often with unless severe lower leaves stems in brassicas Yellowing cotyledons naturally yellow and leaf fall Intermediate and die as they get older Often more severe in Remain dark green in due to age and shade mature leaves show the younger leaves brassicas symptoms Upper leaves Generally remain green Dark green with Generally remain Not usually Yellowing especially Yellow at leaf base but May fail to expand Small Small and misshapen Light green and with except in severe cases purpling healthy between veins remainder of leaf stays Often seen early in the properly reduced lamina in green growth of plants May be darker green brassicas White flecks can develop Tip of plant Green Dark green Green No effect No effect Bleached yellow No effect Pale Blackened and stunted Shoot dieback and Small, misshapen, Necrosis Stem borers and cold development of many side wilted damage shoots Shoot dieback Root tips swell Leaf distortion No effect No effect Leaf rolling in fruit Leaf curling may occur Frizzle top (stunted No effect In extreme cases fern No effect New leaves may stick Leaf curling of young leaves Leaf curling and Leaf cupping or rolling Make sure that no trees and deformed) in leaf or little leaf together and not cupping insects or pathogens Zig-zag leaf in palms Appear thicker or palms Small, pointed leaves expand properly Lodging in cereals whiptail in brassicas are at work in fruit trees Leaf hooking may (no lamina) occur Reddening Occasionally mostly Yes Possible Can occur especially No Not usually Possible No No No No No Reddening is common as a sign of stress in cotton if severe in response to many kinds of stress Leaf veins Not different from Dark green Near midrib remain Mostly remain green Remain green Remain green/ Not different from No effect May be more prominent than No effect More prominent due remainder of leaf green especially close to Leaf veins remain prominent remainder of leaf usual especially in trees to reduced lamina midrib green but not such a Interveinal Not different from Dark green with a Yellow/necrotic Yellowing or necrosis clear distinction as for Producing a stark net Yellow/necrotic Not different from No effect No effect Yellowing and necrotic See leaf distortion regions remainder of leaf bluish green tint iron deficiency of green on a yellow remainder of leaf patches can develop above background Leaf edges No different from Reddening Yellow/necrotic Necrosis spreading No different from Yellow Occasionally crinkly Not different from Necrosis on expanding Fail to expand and curl the Tips of young leaves Can cause browning Wind, chemical or salt remainder of leaf from margins of leaf remainder of leaf or wavy remainder of leaf leaf edges leaf withered and white in damage when severe cereals Plant size Stunted Severely stunted; Shortened internodes Unlikely to be a major Small with slender White if severe Severe stunting can Stunted Unlikely to be a major Stunted, shortened Unlikely to be a major Stunted Mineral deficiency will looks like a miniature symptom stems occur symptom internodes symptom always slow down the plant growth of a plant but many other things can do this too Fruit Small and likely to fall Generally poor Poor flowering and Quality and quantity Necrosis with seeds No different from Formation of fruit bud Small and likely to fall Often do not develop but Flavour, storage and Uneven development Bitter pit of apple flowering and fruiting fruiting reduced such as ground nut remainder of leaf inhibited Necrotic patches may be small, misshapen, sugar content all of grapes within the (Ca) and distortion of and pea lumpy, corky and cracked affected same bunch pawpaw (Bo) common Thick rinds in citrus Fruit is elongated, within fruit or seeds if P/N fertiliser ratio misshapen and wrong cracked Blossom end rot in tomatoes and Necrotic patches No No Light coloured fleck Yes between veins In severe cases Unlikely to be a major Yes No cucurbits Cracks and necrosis of stems Yes they can occur on No Typically symmetrical on leaves often reddish symptom leaves if severe across the mid rib in Curd of cauliflower can appear brown at edges the case of mineral deficiencies pH effects Not applicable Not applicable Not applicable Less available at low Less available at Quality and quantity Less available at Less available at Less available at Less available at high pH Less available at Less available at Agricultural soil pH 6.0-7.5 pH and sandy soils high pH reduced high pH low pH low pH high pH low pH should be maintained between these ranges Very common Common Common Common Common No Common Common Rare Not common Rare Locally these Likelihood Common deficiencies can be important Can be confused Many types of stress Young plant Wind scorch/drought/ Pathogen attack Pathogen attack Less available at Phytoplasma or Nitrogen deficiency Fungal infection Frost damage Pathogen attack Nitrogen deficiency in Mineral deficiencies with leaf spots high pH glyphosate damage in legumes are some of the most fruit trees Herbicide damage difficult symptoms to Manganese deficiency Magnesium or diagnose manganese deficiency Common in All crops Carrot, spinach, Potato, tomato, Tomatoes Onion, apple, peas, Common Citrus Ground nut, Tomatoes, lettuce Papaya, brassicas Wheat, sugarbeet, Brassicas, legumes lettuce, maize cabbage beans amaranthus legumes, sweet potato Note: this table provides general advice with regard to the kind of symp▯toms that mineral deficiencies produce. There are always exceptions to▯ the rules; some of these are highlighted but there are others that are ▯not mentioned. It is not meant to be a definitive guide but it should ▯provide assistance in the field. 20


Table 5. Photographic ready reckoner for the symptoms associated with lack of some common nutrients Nitrogen Phosphate Potassium Manganese Magnesium Iron Sulphur Zinc Maize Rice Pigeon pea Castor bean These photos show the symptoms of the shortage of various minerals in fo▯ur different crops. Compare the photographs for each mineral and try and▯ spot the pattern, e.g. the pictures of iron deficiency all appear ver▯y different but in each case the leaf veins have remained green contrast▯ing strongly with the yellow lamina. Similarly all of the photos of phosphate shortag▯e show reddening and each of those of potassium shortage show the leaf e▯dge is yellowing and turning brown at the edges. While field symptoms ▯may be sufficient to provide a definitive diagnosis by an experience▯d agronomist, it is usually essential to have the field diagnosis confirmed with a▯ laboratory soil analysis, especially if the farmer is intending to spen▯d a significant amount of money or effort on correcting the problem. A▯ll photos are from Kumar and Sharma Nutrient Deficiencies of Field Crops, CABI, 2013, except for rice deficient in manganese and magnesium, which were supplied by IRRI▯. 21



WILT The principal symptoms and their causes The ready reckoners above are single page summaries of the types of insect and mite pests (Table 1) and the symptoms commonly associated with many pest groups and other plant health problems (Table 3). In the sections below we take the symptoms from Table 3, and treat LEAF SPOT each in turn, providing additional information on the symptoms and their causative agents. Wilt Wilt is a very common symptom of plants in distress. Plants rely on the water in leaves and WITCHES’ BROOM stems to hold them up; without the water the plants will wilt, i.e. the ▯green parts of the plant will hang down limply. Unless water is restored to a wilted plant it will die. The roots or stems or base of the stem may be the affected area of the plant although the symptom will mostly be seen in the leaves. Sometimes it can be just one region of the plant that is affected (indicating CANKER a problem in the stem) but more usually the whole plant will wilt. Wilts can be temporary whereby the plant will recover at night but wilt again the next day, this can be normal if the sun is strong and the ground dry but it may also indicate a problem. SYMPTOM FUNGUS Wilt YES Very common. Usually Fusarium or Verticillium sp. MOSIAC YELLOWING OF LEAVES DISTORTION OF LEAVES Fusarium wilt on banana. Note the internal discolouratiVerticilliumwilt on sunflower. Leaves are severely short of water. a common symptom associated with this pathogen. Upper leaves are wilted and the lower ones are dead. Scot Nelson, University of Hawaii Howard F. Schwartz, Colorado State University, Bugwood.org LITTLE LEAF Fungi commonly produce wilts in plants by preventing water from flowing up the tubes (xylem) in the stems, resulting in the leaves becoming starved of water. Wilt-inducing fungi are mostly soil borne pathogens and they attack the roots and the base of the stem. There is often discolouration of the xylem. The main fungal groups that produce wilts are Fusarium and Verticillium. Whereas Fusarium can produce a pink colouration inside the stem, Verticillium produces dark streaks. Cut the stem open and look for discolouration, making sure you compare it to a healthy plant. GALLS The Principal Symptoms and their Causes 23


WILT SYMPTOM WATER MOULDS Wilt YES Common. Often caused by root-attacking phytophthoras. Water moulds are a common cause of damping off in seedlings. LEAF SPOT WITCHES’ BROOM CANKER Base of dry bean seedlings having damped off after attack by Phytopthora capsici attacking the roots of capsicum pepper, the Pythium. plant is severely wilted due to the damage to the roots. Gerald Holmes, California Polytechnic State University at San Luis Obispo, Howard F. Schwartz, Colorado State University, Bugwood.org Bugwood.org MOSIAC YELLOWING OF LEAVES DISTORTION OF LEAVES Phytopthora infestans attacking the upper stem of tomato. NoticePhytophthora katsurae causing yellowing and wilt. Heart rot of that that the plant is not wilting despite extensive damage to tcoconut. stem. Phil Taylor, CABI Scot Nelson, University of Hawaii LITTLE LEAF Wilt is associated with damping off of seedlings and root-attacking phytopthoras. Damping off occurs where the base of the seedling rots quickly and the plant wilts and dies. It can be caused by a variety ▯ f true fungi but Pythium (water mould) is often involved as well. Downy mildews and foliar-attacking phytophthoras do not generally wilt plants unless the attack i▯ s extremely severe. GALLS 24 Plantwise Diagnostic Field Guide


WILT SYMPTOM BACTERIA Wilt YES Common. Often seen in Solanaceae, e.g. Ralstonia on tomatoes and cucurbit crops LEAF SPOT WITCHES’ BROOM CANKER Ralstonia on potato. This wilt has occurred suddenly as therInternal discolouration due to Ralstonia on capsicum pepper. no symptoms other than the wilt. Phil Taylor, CABI Scot Nelson, University of Hawaii MOSIAC YELLOWING OF LEAVES DISTORTION OF LEAVES The papaya has turned yellow and is severely wilted due Capsicum pepper with bacterial wilt. Note the complete to Pseudomonas solanacearum infection. collapse of the plant in the foreground relative to the healthy one at the rear. Scot Nelson, University of Hawaii Phil Taylor, CABI Bacteria are a common cause of wilting in plants. Unlike in the case of fungi (whe▯re the cause is usually localised in the base of the stem) bacteria occur throughout the stem and the prevention of water moving up the plant is due to the LITTLE LEAF presence of the huge numbers of bacteria (and the gums they produce) in the water-carrying tubes. If you cut open a bacteria-infected stem, as you pull apart the cut ends it is sometimes possible to see strands of gum stretching between the two sides. It is also possible to put the cut stem into still GALLS water and observe bacterial streaming (see below). As for fungi they too can produce discolouration within the stem. Bacteria commonly associated with wilting are PseudomonR as,lstonia and Xanthomonas. The Principal Symptoms and their Causes 25


WILT Bacterial streaming A plastic bottle, a sharp knife and a matchstick are all that are required for the bacterial streaming test. Fill the bottle with clean water and leave it in a place where it will be kept completely still but can be viewed. Cut a 15 cm section of stem with a sharp knife close to the LEAF SPOT base of the plant. Remove any leaves and put the lower end into the water as shown. Insert a matchstick through the top end so as to hang the cut stem portion in the bottle. Do not disturb the bottle or stem. Put a drop of water on the top cut section of the stem to prevent it from drying out. Observe for bacterial streaming after about 5 minutes against a dark background - you may see thin wisps of white fluid flowing from the cut end of the stem down into the water. These could be the millions of bacteria oozing from the cut stem. Make sure WITCHES’ BROOM you test healthy stems as some plants produce latex that looks similar to bacterial streaming. Do not disturb the bottle or stem, otherwise the movement of the water will prevent a visible stream of bacteria appearing. CANKER MOSIAC YELLOWING OF LEAVES Bacterial streaming in field using a plastic bottle and matBacterial streaming from cut eggplant stem. Thin white wisps of bacterial ooze emerge from the cut stem. The container must be Phil Taylor, CABI kept still and a black background helps visualise it as it can be difficult to see. Robert Reeder, CABI DISTORTION OF LEAVES LITTLE LEAF GALLS 26 Plantwise Diagnostic Field Guide


WILT SYMPTOM VIRUS Wilt (NO) although some viruses of tomato, pineapple and broad bean cause wilting. LEAF SPOT WITCHES’ BROOM CANKER Don Ferrin, Louisiana State University Agricultural Center,Scot Nelson, University of Hawaii Notice the reduced size as well as the wilt of this tomato plant (left) infected w▯ith Tomato spotted wilt virus. Symptoms on fruit (right). It is extremely unusual for viruses to cause wilting. There are exceptions, the most common one being Tomato spotted wilt virus. Often the virus will produce other symptoms in addition to wilting. MOSIAC SYMPTOM PHYTOPLASMA Wilt (NO) except one example: Coconut lethal yellowing. This is not a symptom that is usually associated with phytoplasma infecti▯ on but there is an exception: phytoplasmas reach such YELLOWING OF LEAVES high numbers in coconut (Coconut lethal yellowing) that the water-carrying tubes become blocked, causing wilt in much the same way as bacteria do in other hosts. Witches’ broom and little leaves are much more typical of this group of pathogens. SYMPTOM NEMATODE Wilt YES Very common. Seen in a wide range of crops. DISTORTION OF LEAVES Root loss due to nematode feeding causes the plant to be more susceptible to water stress as they are simply unable to take up enough water to replace that lost through the leaves. Nematodes eat the fine root hairs which are responsible for the uptake of water so, even if the roots seem to be mostly intact, the water uptake part of the root system may be missing. Nematodes can be extremely damaging but produce only general symptoms above ground and unless the roots LITTLE LEAF are examined it will be almost impossible to diagnose nematode infection. GALLS The Principal Symptoms and their Causes 27


WILT SYMPTOM INSECTS Wilt YES Common. The larval stages of stem borers and the larvae and adults of root feeders commonly cause wilts. Not usually associated with sucking in▯sects unless extremely severe. LEAF SPOT WITCHES’ BROOM European corn borer-induced wilt on Lepidoptera larvae: the damage caused Stink bug damage on tobacco. The insect CANKER cotton. is an access point for pathogens. Stem injects a toxin into the plant causing borers often have reduced legs and extensive damage. The leaf is wilted, prolegs and may superficially appear likeyellow and showing signs of necrosis. a fly larva (maggot). William Lambert, University of Georgia, Bugwood.org IRRI Images R.J. Reynolds Tobacco Company, Bugwood.org MOSIAC Wilt induced by insects is common. It is often the larval stages that ca▯use this symptom, and they may be present in the soil or in the stem. Consider which part of the plant is wilting – is it the whole plant or just a part of it? Split the stem open and look for stem borers. The insect may be providing access for pathogens which rot the plant so when you see a rot, consider whether it is associated with insect damage. SYMPTOM MAMMALS & BIRDS Wilt (NO) although mammals and birds that damage the bark of trees or roots can YELLOWING OF LEAVES produce this symptom. Many large bark-eating animals can gnaw the bark off trees. They may wilt immediately or this symptom may be seen with yellowing and drying as the plant dies. DISTORTION OF LEAVES LITTLE LEAF GALLS 28 Plantwise Diagnostic Field Guide


WILT SYMPTOM NUTRIENT DEFICIENCIES Wilt (NO) but copper deficiency can cause wilting in some plants. Extremely rare. LEAF SPOT WITCHES’ BROOM Wheat showing wilting and leaf deformity due to copper deficiency. CANKER Dr Prakash Kumar and Dr Manoj Kumar Sharma SYMPTOM PHYSICAL & HERBICIDE Wilt YES Very common. Shortage of water (drought) and its excess (waterlogging) are a common cause of wilt as is MOSIAC physical damage to the roots, e.g. through weeding. Some herbicides can induce this effect too. Both a shortage of water and too much water (waterlogging) are abiotic causes of wilting. If the wilt is over a large area then consider whether this may be the cause. If wilted plants are close to healthy ones in well watered soil then there is probably a biotic cause. YELLOWING OF LEAVES DISTORTION OF LEAVES LITTLE LEAF GALLS The Principal Symptoms and their Causes 29


WILT Leaf spot Leaves are exposed to a great range of potentially damaging agents. Once a leaf is damaged a mark of some sort will always remain, not all of these marks are considered leaf spots. A true LEAF SPOT leaf spot is the site of an infection by a pathogen. It will start small and enlarge with time. It is an extemely common symptom and experience is required to identify the cause. In this section other spots on leaves are included as leaf spots. SYMPTOM FUNGUS Leaf spot YES Very common, many types involved on a wide range WITCHES’ BROOM of crops. Rust pustules are included as leaf spots here. CANKER MOSIAC Leaf spots of Venturia inaequalis on apple in Nepal. Yubak Dhoj, Department of Agriculture, Nepal The leaf spot is a classic symptom of many groups of fungi. The leaf is generally unaffected except for the area of the leaf spot and immediate surrounding area. The margins of the leaf spot may be a different colour to the inside. Bacteria and water moulds (see below) can produce similar symptoms. Leaf spots on grasses often turn into streaks because of the geometry of the leaf, YELLOWING OF LEAVESe. the leaf veins direct the pathogen along the length of the leaf. Fungal lesions will spread but will generally not consume the whole leaf. They appear to reach a certain size and then stop growing; this is not the case for some foliar pathogens, especially Phytophthora (a water mould) and bacteria, which can spread aggressively across the whole leaf. An indication that the leaf spots are caused by a true fungus is that they are all of similar size (or go on to grow to a similar size) and the older ones may have fungal fruiting bodies within them (see below). Visible fruiting bo▯ are not produced by bacteria or water moulds (although water moulds may produce fluffy spores). The fungal fruiting bodies are not always present (even in fungal infections) and are difficult to see with the naked eye but are often visible with a hand lens. DISTORTION OF LEAVES LITTLE LEAF GALLS Correct use of a hand lens will enable you to see great detail within a leaf spot (as well as mites and other small pests)▯. Hold the lens close to the eye and move the plant material back and forth until it is in focus (left). The same technique ca▯ ase the to incre magnification of a compact camera (right). All the photographs in th▯is section were taken using this technique. Phil Taylor, CABI 30 Plantwise Diagnostic Field Guide


WILT Pictures of fungal fruiting bodies in leaf spots. The presence of the fruiting bodies is a sure indication that the pathogen is a fungus, but if they cannot be found then this does not mean that it▯ is not a fungus causing the problem. In the top pair of photographs only the two spots arrowed (right) contain fruiting bodies (left). Some fungi do not produce fruiting bodies in this form. All of these photographs were taken with a compact camera and a hand lens, so the magnification is▯ no greater than that achievable in the field. LEAF SPOT WITCHES’ BROOM CANKER MOSIAC YELLOWING OF LEAVES DISTORTION OF LEAVES LITTLE LEAF GALLS All images: Phil Taylor, CABI The Principal Symptoms and their Causes 31 DRYING/NECROSIS/BLIGHT


WILT LEAF SPOT WITCHES’ BROOM Natural features of the leaf could be mistaken for fungal fruiting Insect frass can appear like fungal fruiting bodies but will appear bodies. both within and outside the leaf spot. CANKER Phil Taylor, CABI Phil Taylor, CABI Ensure that the ‘fruiting bodies’ are not natural features of the leaf (left) or some artefact like insect frass (right). Older lesions may have been colonised by secondary microorganisms. These secondary invaders may produce fruiting bodies that could be mistaken for those of the disease-causing pathogen. When l▯ooking for fruiting bodies, try to find them in the younger lesions. MOSIAC YELLOWING OF LEAVES DISTORTION OF LEAVES Phil Taylor, CABI Phil Taylor, CABI What appeared to be fungal fruiting bodies (left) were removed by wiping with a wet thumb (right) indicating that they LITTLE LEAF were insect frass and not of fungal origin. GALLS 32 Plantwise Diagnostic Field Guide DRYING/NECROSIS/BLIGHT


WILT SYMPTOM WATER MOULDS Leaf spot YES Common. Generally rapidly spreading, may have water-soaked appearance and sporulation around edges. White rusts and downy mildews can produce pustules with little necrosis. LEAF SPOT WITCHES’ BROOM CANKER Leaf spot caused by Phytophthora infestans on tomato. Note the Leaf spot caused by Phytophthora capsici on capsicum pepper. zone of lighter coloured leaf around the darker necrotic area: The symptoms are characterised by rapid death of the leaf is the area where spore production may be taking place. material. Phil Taylor, CABI Gerald Holmes, Bugwood.org MOSIAC Leaf spots caused by water moulds are often rapidly spreading (especially in wet weather) and may not have a clearly defined border. They are usually not limited by the leaf veins and may have a water-soaked region around the spot, which may have fluffy white material (spores) on the surface. YELLOWING OF LEAVES DISTORTION OF LEAVES LITTLE LEAF GALLS The Principal Symptoms and their Causes 33 DRYING/NECROSIS/BLIGHT


WILT SYMPTOM BACTERIA Leaf spot YES Very common. On many types of crop. LEAF SPOT WITCHES’ BROOM CANKER Bacterial infection of cabbage (left) and bean (right). Notice how i▯n both cases the spots usually begin at the leaf edge. Howard F. Schwartz, Colorado State University, Bugwood.org Bacteria cannot penetrate a leaf in the same way as fungi and so bacteri▯ l leaf spots (in the early stages of attack) are often associated with the edge of the leaf or minor damage. As the bacterial n▯ mbers increase you will see the spots spread across the leaf. Bacterial leaf spots are more likely to be limited by the leaf veins in the initial stages but when t▯ he infection is growing rapidly, the expanding numbers of bacteria will push the infection past leaf vei▯ ns. The edges of a bacterial leaf spot are often MOSIAC water-soaked, the plant tissue leaks material and the bacterial gums fill▯ the air spaces that are usually within the leaf. You will never see structures within a bacterial leaf spot as bacteria do not produce fruiting bodies which are characteristic of fungi. Bacteria often colonise stressed plants and the leaf spots will carry on spreading, especially if the leaf is under stress or is old. SYMPTOM VIRUS Leaf spot (NO) although there are exceptions. Ringspots are more common. YELLOWING OF LEAVES DISTORTION OF LEAVES LITTLE LEAF Citrus ringspot virus – not what would normally be called a trSpots caused by Tomato spotted wilt virus are not considered leaf spot. true leaf spots. Stephen M. Garnsey, USDA-ARS, South Atlantic Area, Bugwood.orgScot Nelson, University of Hawaii GALLS Viruses can produce a type of leaf spot on some occasions but they are usually in a ring or crescent pattern. Remember that viruses generally do not often cause the plant tissue to die, so▯ iral leaf spot will not usually have much dead tissue associated with it, but it will be a different colour (almost always yellow) from the remainder of the leaf. 34 Plantwise Diagnostic Field Guide


WILT SYMPTOM PHYTOPLASMA Leaf spot (NO) although leaf markings can occur. LEAF SPOT SYMPTOM NEMATODE Leaf spot (NO) but can occur on ornamental plants; do not occur on crop plants. SYMPTOM INSECTS WITCHES’ BROOM Leaf spot YES Not common. Some sucking insects inject a toxin when they feed that can cause necrotic or yellow spotting. CANKER MOSIAC Insect feeding can produce damage that looks like bacteriaCoconut plant bug damage on cashew. fungal infection. This may be due to the physical action of feeding YELLOWING OF LEAVES or due to toxins injected into the plant. Mirid damage on cacao. Robert Reeder, CABI Robert Reeder, CABI Feeding damage by insects that have sucking mouthparts can leave marks that look like fungal or bacterial spots and damage by biting insects that do not perforate the leaf can look similar.▯ DISTORTION OF LEAVES LITTLE LEAF GALLS The Principal Symptoms and their Causes 35


WILT SYMPTOM NUTRIENT DEFICIENCIES Leaf spot YES Not common. Necrotic spots on leaves can indicate nutrient deficiencies. Shortages of potassium, zinc, manganese and copper can all lead to this symptom, if severe. LEAF SPOT WITCHES’ BROOM Potassium deficiency in lucerne: the Zinc deficiency in wheat: a pale grey spot Blossom end rot on tomato: this disorder marginal yellowing is associated with on the middle of the leaf. is common on tomato and is seen when CANKER scattered white necrotic spots. the fruits are rapidly expanding. It looks like a bacterial or fungal rot but is due to a shortage of calcium. Dr Prakash Kumar and Dr Prakash Kumar Dr Manoj Kumar Sharma Shamela Rambadan, CABI MOSIAC A severe deficiency of any mineral will lead to poor growth but it is unusual for a plant to suffer such extreme shortage that would lead to cell death. The main exception is rapidly expanding tissue, such as the ends of tomatoes or courgettes. If calcium is in short supply the ends of the fruits will break down and appear like a fungal or bacterial rot (not ‘leaf spot’ but something similar on a fruit). YELLOWING OF LEAVES DISTORTION OF LEAVES LITTLE LEAF GALLS 36 Plantwise Diagnostic Field Guide


WILT SYMPTOM PHYSICAL & HERBICIDE Leaf spot YES Common. Careless spraying with contact herbicides such as diquat can lead to spots. Sunscald can lead to damaged patches, often on fruit. LEAF SPOT WITCHES’ BROOM Strong sunlight can cause burnt patches Strong sunlight can cause burnt patches Paraquat damage on Phaseolus bean. on fruit (pepper). on leaves (tobacco). Notice how the areas of damage are next to areas of healthy leaf with little transition CANKER between the two. University of Georgia Plant Pathology ArchiR.J. Reynolds Tobacco Company Slide Set, Howard F. Schwartz, Colorado State University, Bugwood.org Bugwood.org Bugwood.org Bright sunshine can produce patches of dead tissue on leaves and fruit which may appear as spot▯ s. Wilted leaves exposed to bright sunshine and succulent fruits that are undergoing a period of rapid growth are the most susceptible. Shaded portions of wilted leaves exposed to the sun generally recover at night. Any type of stress that causes wilting will make plants more MOSIAC susceptible to sunscald. Paraquat and diquat (and other less common herbicides) can cause what a▯ppear to be leaf spots: the otherwise healthy leaf is covered in small tan-coloured spots within which the tissue is dead. These symptoms are produced rapidly following herbicide application. YELLOWING OF LEAVES DISTORTION OF LEAVES LITTLE LEAF GALLS The Principal Symptoms and their Causes 37 DRYING/NECROSIS/BLIGHT


WILT Witches’ broom In this condition, a biotic or abiotic factor causes the plant to lose co▯ntrol of the correct growth pattern and it grows in an uncontrolled way. The pathogen is either producing (or LEAF SPOT causing the plant to produce) the wrong balance of chemicals that regulate its growth. The clustered growth of many branches all emerging from a central point is not an especially common symptom: it usually occurs on woody plants and is often associate▯d with ‘little leaf’. SYMPTOM FUNGUS WITCHES’ BROOM Witches’ broom YES Common. In woody plants only, not so in herbaceous (many branches) plants. CANKER MOSIAC Fungal witches’ broom on silver birch. Extreme proliferation of branches from a single point creates a witches’ broom. Phil Taylor, CABI SYMPTOM PHYTOPLASMA YELLOWING OF LEAVES Witches’ broom YES Very common. Generally associated with little leaf. (many branches) DISTORTION OF LEAVES LITTLE LEAF Witches’ broom caused by a phytoplasma on lime. J.M. Bové, INRA Centre de Recherches de Bordeaux, Bugwood.org This is a classic symptom of phytoplasma. The dormancy of the side buds ▯is broken and the cluster of tiny shoots all competing with each other is the result. GALLS 38 Plantwise Diagnostic Field Guide


WILT SYMPTOM MITES Witches’ broom (many branches) YES Very common. They are usually far too small to be seen even with a hand lens. Mites can get into the growing point of the plant and cause witches’ broom symptoms. The constant feeding on the material at the very tip of the plant causes it to produce multiple shoots. It is not possible to see the mites at the tip as▯ LEAF SPOT the kind of mites that cause this symptom are too small to be seen, even with a hand lens. SYMPTOM PHYSICAL AND HERBICIDE Witches’ broom (many branches) YES Common. Only where plants have grown back after treatment with glyphosate. WITCHES’ BROOM CANKER MOSIAC If glyphosate does not kill a plant the regrowth can appear as witches’ brooms (associated with little leaves). Nettle (left) and coffee (right), showing regrowth symptoms following glyphosate treatment. Eric Boa, CABI (nettle) and Scot Nelson, University of Hawaii (coffee). Glyphosate can produce witches’ brooms in many plants. If you spray with glyphosate, much of the upper par▯ts of YELLOWING OF LEAVES the plant will appear dead, however sometimes, a while later, the lateral buds will break dormancy and small witches’ brooms will develop. DISTORTION OF LEAVES LITTLE LEAF GALLS The Principal Symptoms and their Causes 39


WILT Canker This refers to an open wound that does not heal readily. Usually, cankers are found on woody plants. The host plant is attempting to limit the pathogen by producing additional woody LEAF SPOT material to enclose it and the pathogen is attempting to grow into living tissue. This ongoing battle of host and pathogen produces raised sides to the wound which gives the canker its shape. It is not the same as a stem infection on green stems as they do not have the ability grow additional material around the infection site to limit the pathogen. SYMPTOM FUNGUS WITCHES’ BROOM Canker YES Very common. SYMPTOM BACTERIA Canker YES Common. CANKER MOSIAC YELLOWING OF LEAVES Phil Taylor, CABI Phil Taylor, CABI DISTORTION OF LEAVES LITTLE LEAF GALLS Eric Boa, CABI Phil Taylor, CABI Fungal cankers on ash and Jatropha (top); a bacterial canker on ash (bottom left). Physical damage▯ can produce a similar effect once the damage has healed (bottom right). Notice how the dead plant materi▯al is compensated for by additional growth around the edges of the canker. 40 Plantwise Diagnostic Field Guide


WILT Mosaic Many words can be used to describe the uneveness in the colour of a leaf and it can be difficult to convey the extent and severity of the unevenness. The word ‘mosaic’ is often used to describe such a symptom. It is a common symptom of viral infection (see below); however, LEAF SPOT other pests as well as nutrient deficiencies can produce similar symptoms. SYMPTOM VIRUS Mosaic YES Very common. WITCHES’ BROOM CANKER MOSIAC Robert Reeder, CABI Scot Nelson, University of Hawaii YELLOWING OF LEAVES DISTORTION OF LEAVES LITTLE LEAF Robert Reeder, CABI Phil Taylor, CABI Mosaic caused by plant viruses. Note that the areas of green and yellow are distinct and do not blend to a great extent. Viral symptoms of areas of green and yellow on leaves vary greatly - from a vague mottle through to a stark mosaic with extreme contrasts in colours in adjoining panels of leaf. This distinguishes it from ‘yellowing’ where the yellowed area of the leaf is continuous. The mosaic caused by viruses is often associated▯ with rugosity (this is where the leaf does not lie GALLS flat between the veins). The Principal Symptoms and their Causes 41


WILT SYMPTOM INSECTS Mosaic (NO) although the feeding of tiny insects with piercing mouthparts such as thrips and whitefly can produce a mosaic-like effect. LEAF SPOT SYMPTOM MITES Mosaic (NO) although in the same way as insect feeding, mites can produce an effect that resembles a mosaic. WITCHES’ BROOM CANKER The superficial damage of mites can produce symptoms similar to viruses. This speckling on cassava could be mistaken for MOSIAC Cassava mosaic virus. Robert Reeder, CABI The superficial feeding by mites and thrips can resemble viral symptoms. The surface layer of cells have their contents sucked out and this creates a silvery appearance in some cases. This flecking of silver can ▯give the impression of mosaic (viral infection), especially if leaf distortion (a symptom of mite, thrips and viral attack) is present. YELLOWING OF LEAVSYMPTOM NUTRIENT DEFICIENCIES Mosaic YES Common. The mottling caused by deficiencies of several minerals can produce a mosaic type of symptom. DISTORTION OF LEAVES LITTLE LEAF Zinc-deficient maize plant with bands or Iron-deficient pearl millet with faded vManganese-deficient pearl millet plant streaks of yellow and green. in more advanced stage. showing stripes on the leaves. GALLS Dr Prakash Kumar Dr Prakash Kumar and Dr Manoj Kumar SharDr Prakash Kumar There are many nutritional disorders of plants that can give rise to areas of leaves turning yellow adjacent to green areas, creating a kind of mosaic pattern. Experience is required to determine if the symptoms are those of a virus or mineral deficiency. Note that mineral deficiencies rarely distort leaves and cause mosaic/stripes symptoms at the same time whereas following virus infection, the two (distortion and mosaic) are often associated. 42 Plantwise Diagnostic Field Guide


WILT Yellowing of leaves All pests weaken and stress plants and this often induces yellowing, however the pattern of yellowing can be important and indicate a cause. Plants can go into decline, where yellowing and reduced growth leads to further reduction in growth and so the problem continues. Even LEAF SPOT on a healthy plant the lower leaves will naturally grow old and will die; a yellowed leaf can be a normal sign of aging on a healthy plant and such leaves should not be considered a symptom. SYMPTOM FUNGUS Yellowing of leaves YES Common. Often indicates symptoms or infection in other parts of the WITCHES’ BROOM plant, e.g. roots, cankers on stem. SYMPTOM WATER MOULDS Yellowing of leaves YES Common. General stress caused by root death often the cause. Downy CANKER mildews may create defined yellow patches on leaves prior to the production of the downy spores masses. SYMPTOM BACTERIA MOSIAC Yellowing of leaves YES Common. A general or non-specific symptom indicating general decline of the plant. SYMPTOM NEMATODE Yellowing of leaves YES Common. A general or non-specific symptom; general decline of the plan▯t due to root feeding. YELLOWING OF LEAVES SYMPTOM VIRUS Yellowing of leaves YES Not common. Mosaics are much more likely, unusual for the entire leaf to turn yellow. DISTORTION OF LEAVES It is unlikely that a viral infection will make the whole leaf turn gene▯rally yellowish. Yellow and green regions next to each other (see mosaic) is much more typical of virus infection. SYMPTOM PHYTOPLASMA LITTLE LEAF Yellowing of leaves YES Common. Relatively rare pathogen BUT they do often cause yellowing when they do occur. Yellowing is a common symptom and may occur without other symptoms. Plant▯s may be considerably smaller as well as yellowed (and sometimes red) when suffering from phytoplasmas. Usually much more striking features (witches’ broom, little leaves) are present in addition to the yellowing. GALLS The Principal Symptoms and their Causes 43


WILT SYMPTOM INSECTS Yellowing of leaves YES Common. A general or non-specific symptom caused by damage to the roots or a general decline in the plant. Heavy infestation of sucking insects can weaken the plant sufficiently▯ so that it turns yellow; the plant is unable to sustain LEAF SPOT the insect population and it goes into decline. The reduced growth of a plant under stress will prevent it from growing away from insect pest damage and the insect numbers will increase, which further increases the stress on the plant. Remember that insects attack the roots too and a yellowed plant may have insects attacking the roots. SYMPTOM MITES WITCHES’ BROOM Yellowing of leaves YES Common. Low populations of mites can cause many leaves to turn yellow. CANKER MOSIAC A. Elizabeth Johnson, CABI B. Phil Taylor, CABI C. Elizabeth Johnson, CABI Male and female palm mites (A). Yellowing of palm leaflet associated with palm mite (B). T▯ duce toxic saliva that causes the trees to go into decline and die. The numbers of mites may be relatively low but will do severe damage and ultimately kill a mature tree. Yellowing and decline associated with palm mite in mature coconut trees (C). YELLOWING OF LEAVES SYMPTOM MAMMALS & BIRDS Yellowing of leaves (NO) although mammals and birds that damage the bark of trees or roots can produce this symptom. The removal of bark from trees will lead to the death of the tree; prior to death the leaves will turn yellow. DISTORTION OF LEAVES LITTLE LEAF GALLS 44 Plantwise Diagnostic Field Guide


WILT SYMPTOM NUTRIENT DEFICIENCIES Yellowing of leaves YES Very common. Depending on the pattern, yellowing can give an indication of which mineral may be deficient but a definitive field diagnosis is difficult. LEAF SPOT WITCHES’ BROOM CANKER Nitrogen-deficient pale green lentil leaflet. Nitrogen-deficient maize: lower leaves are yellow. Dr Prakash Kumar Dr Prakash Kumar MOSIAC YELLOWING OF LEAVES DISTORTION OF LEAVES Nitrogen-deficient wheat: yellowing of older leaves. Nitrogen-deficient cluster bean: general yellowing. Dr Prakash Kumar and Dr Manoj Kumar Sharma Dr Prakash Kumar Older leaves of nitrogen-deficient plants are yellow. LITTLE LEAF GALLS The Principal Symptoms and their Causes 45 DRYING/NECROSIS/BLIGHT


WILT SYMPTOM NUTRIENT DEFICIENCIES Yellowing of leaves Mineral deficiency commonly causes leaves to turn yellow. The position of those leaves and the colour of the leaf veins can give an indication as to which mineral is LEAF SPOT deficient. WITCHES’ BROOM CANKER Iron deficiency in wheat: severe yellowing between veins. Green veins contrast sharply against the yellowed iron-deficient sweet potato leaf. Dr Prakash Kumar and Dr Manoj Kumar Sharma Dr Prakash Kumar and Dr Manoj Kumar Sharma MOSIAC YELLOWING OF LEAVES DISTORTION OF LEAVES Severely iron-deficient green gram: white leaf lamina while veinIron-deficient lentil plant: upper leaflets are yellow. remain green. Dr Prakash Kumar and Dr Manoj Kumar Sharma Dr Prakash Kumar LITTLE LEAF Iron deficiency generally makes leaves turn yellow but characteristicall▯y the veins remain green. GALLS 46 Plantwise Diagnostic Field Guide DRYING/NECROSIS/BLIGHT


WILT SYMPTOM NUTRIENT DEFICIENCIES Yellowing of leaves Sulphur deficiency is shown in the upper leaves first because this element is less mobile within the plant than other nutrients and the plant is unable to remobilize it to LEAF SPOT the tip of the plant. WITCHES’ BROOM CANKER Sulphur deficiency in pea: yellowing of upper leaves. Sulphur deficiency in ground nut: uniformly pale young leaves. Dr Manoj Kumar Sharma Dr Prakash Kumar MOSIAC YELLOWING OF LEAVES DISTORTION OF LEAVES Sulphur-deficient sugarcane plant. Sulphur deficiency in potato: the pale yellow sulphur-deficient plant (left) compared with dark green normal plant (right). Dr Manoj Kumar Sharma Dr Prakash Kumar Symptoms of sulphur deficiency are similar to those of nitrogen deficiency but the younger leaves are the first to turn yellow. LITTLE LEAF GALLS The Principal Symptoms and their Causes 47 DRYING/NECROSIS/BLIGHT


WILT SYMPTOM PHYSICAL AND HERBICIDE Yellowing of leaves YES Very common. Can be due to a variety of abiotic factors, some herbicides will generate yellow leaves on the treated plant. LEAF SPOT WITCHES’ BROOM CANKER This oil seed rape plant was damaged by a herbicide used to This oil seed rape plant has temporarily yellowed due to sudden control weeds. cold weather. Phil Taylor, CABI Phil Taylor, CABI. MOSIAC Herbicide damage often makes leaves lose their green colour and become yellow without other symptoms. The symptoms of herbicide on a crop could be drift from nearby spraying or from carryover from the previous crop. Many abiotic factors can cause plants to become stressed and turn yellow. If the environment changes so that the plant is in less than optimum conditions, it will stress the plant, which may turn yellow or pale green. YELLOWING OF LEAVES DISTORTION OF LEAVES LITTLE LEAF GALLS 48 Plantwise Diagnostic Field Guide


WILT Distortion of leaves The leaves of all plants have a characteristic shape. Many kinds of problem can distort the shape of leaves; this can be a local effect where the distortion is only around the site of infection, or it could be a more general effect where the whole plant (or section of it) is affected. A general reduction in leaf LEAF SPOT size is not generally considered as distortion. Leaves can grow into a distorted shape as they develop or may become distorted after they have fully grown. SYMPTOM FUNGUS Distortion of leaves (NO) but there are exceptions and there is one spectacular example and a few others that can produce mild distortion. WITCHES’ BROOM CANKER The fungus that distorts leaves more so than any other is Taphrina deformans, the cause of peach leaf curl. This fungus distorts the leaves of peach and plum in a dramatic way that is difficult to miss; however for those who manage to overlook the hugely distorted leaves, it usually turns the leaves bright red too. It is difficult to imagine a plant pathogen with more dramatic and distinctive symptoms. Other fungi can distort leaves but this is MOSIAC not an especially common symptom. Paul Bachi, University of Kentucky Research and Education Center, Bugwood.org SYMPTOM WATER MOULD Distortion of leaves YES Not common. Downy mildews can cause unusually YELLOWING OF LEAVES shaped leaves. DISTORTION OF LEAVES LITTLE LEAF Leaf distortion by blue mould on tobacco caused by Plasmopara halstedii causing leaf distortion in sunflower. Peronospora tabacina. GALLS R.J. Reynolds Tobacco Company Slide Set, Bugwood.org Howard F. Schwartz, Colorado State University, Bugwood.org If the downy mildew just causes a leaf spot there is little distortion of the leaves, but sometimes it can become systemic, in which case the whole of the leaf material is infected with the pathog▯en and leaves grow in a distorted manner (often with a waxy appearance). The Principal Symptoms and their Causes 49


WILT SYMPTOM VIRUS Distortion of leaves YES Very common. LEAF SPOT WITCHES’ BROOM CANKER Leaf distortion in tomato. Contrast the infected leaf (left) The lettuce has severe leaf distortion; in this case the leaf veins healthy leaf (right). The infected one is smaller, twisted anare unusually large, distorting the whole appearance of the leaf. blistered (rugose). Gerald Holmes, California Polytechnic State University at San Luis Obispo, Central Science Laboratory, Harpenden Archive, British Crown, Bugwood.org Bugwood.org Viruses can distort leaves into weird and peculiar shapes. They are often puckered (also called blistered or rugose) MOSIAC because the leaf lamina has grown at a different rate to the leaf veins or the leaf lamina may be severely reduced giving the appearance of a leaf that has been eaten. Beware that aphids and other sucking insects can distort leaves just by their feeding so do not assume the presence of a virus just because you see distorted leaves and insects (see below). SYMPTOM PHYTOPLASMA Distortion of leaves YES Not common. Usually associated with witches’ broom YELLOWING OF LEAVES and little leaf. They can distort leaves but by far more obvious is the small leaf size (see later) or the witches’ broom usually associated with phytoplasma infection (see previously). DISTORTION OF LEAVES LITTLE LEAF GALLS 50 Plantwise Diagnostic Field Guide


WILT SYMPTOM INSECTS Distortion of leaves YES Very common. Can be due to feeding damage by sucking insects or leaves rolled by web formers. LEAF SPOT Aphids, mealybugs and other sucking insects can distort leaves: WITCHES’ BROOM the leaves are unable to expand properly as the sap is being sucked from them and this distorts the leaf. Notice that it is the developing leaves that are distorted: once produced, the leaves do not often become distorted. Mealybugs causing damage to Plumeria leaves. Scot Nelson, University of Hawaii CANKER SYMPTOM MITES Distortion of leaves YES Common. Due to the mites damaging the developing leaves. MOSIAC YELLOWING OF LEAVES Mites commonly cause leaf distortion. Currant mites causing damage to currant. DISTORTION OF LEAVES Whitney Cranshaw, Colorado State University, Bugwood.org LITTLE LEAF GALLS The Principal Symptoms and their Causes 51 DRYING/NECROSIS/BLIGHT


WILT SYMPTOM NUTRIENT DEFICIENCIES Distortion of leaves YES Not common. Cupping of leaves as well as reduced leaf lamina can indicate mineral shortage. LEAF SPOT WITCHES’ BROOM Pigeon pea showing leaf deformity due to copper deficiency. CANKER Dr Prakash Kumar SYMPTOM PHYSICAL & HERBICIDE Distortion of leaves YES Common. Some herbicides induce unusual patterns MOSIAC of growth. YELLOWING OF LEAVES Tomato showing extreme leaf distortion due to herbicide exposure. DISTORTION OF LEAVES Rebekah D. Wallace, University of Georgia, Bugwood.org LITTLE LEAF GALLS 52 Plantwise Diagnostic Field Guide


WILT Little leaf The point about this symptom is the severe reduction in leaf size, hence the name ‘little leaf’. As for ‘yellowing’, there are many things that will cause the leaf size to be reduced: this can be a response to the stress the plant is under and is not directly a symptom. If a stressed plant is LEAF SPOT struggling to grow, the leaves it will produce will be smaller than those of a healthy plant. This is not the severe reduction of size seen in ‘little leaf’ that we are describing here. Little leaf here really means miniature leaf; the leaf is often perfectly formed but just on a miniature scale. SYMPTOM WATER MOULDS WITCHES’ BROOM Little leaf YES Not common. Downy mildews can cause leaves to develop severely reduced in size. When the downy mildews enter the ‘systemic phase’ the leaves that ▯are produced are waxy and thick, and generally smaller than healthy leaves. See ‘water mould distortion of leaves’ on page 49. CANKER SYMPTOM VIRUS Little leaf YES Not common. MOSIAC YELLOWING OF LEAVES DISTORTION OF LEAVES Potato leaf roll virus: the potato leaves are rolled and sGroundnut rosette virus. The ground nut plant is small partially due to reduced in size on the infected plant on the right. the stem length but also because of the severe reduction in leaf size. Eugene E. Nelson, Bugwood.org Kalule Okello David, MoA Uganda Not as common as infection by phytoplasmas, but viruses can cause someth▯ing similar. The distortion caused by the virus can result in smaller leaves but the symptom is often associated with other t▯ypes of distortion, such as rolling. LITTLE LEAF GALLS The Principal Symptoms and their Causes 53


WILT SYMPTOM PHYTOPLASMA Little leaf YES Very common. Often considered to be the classic symptom of this group. LEAF SPOT WITCHES’ BROOM Infection by phytoplasma often causes a proliferation of small leaves. They can be in the form of a witches’ broom with all the little shoots growing together with tiny leaves on them. This symptom may affect only a portion of the plant (sectoring) or it can affect the whole plant. Here we see phytoplasma infection on pigeon pea causing little leaf symptoms. CANKER Phil Taylor, CABI SYMPTOM MITES Little leaf YES Common. They are usually far to small to be seen MOSIAC even with a hand lens. YELLOWING OF LEAVES Witches’ broom of longan. The exact cause is not known but there appears to be a mite involved and possibly a microbial component. Notice how ‘little leaf’ can be a symptom with the DISTORTION OF LEAVES witches’ broom. Phil Taylor, CABI Mites are often associated with little leaf and witches’ broom but the kind of mites associated with these symptoms are too small to be seen, even with a hand lens. Little leaf symptoms often ▯resemble witches’ brooms because the leaves are clustered together; the two symptoms are often closely associated. LITTLE LEAF SYMPTOM PHYSICAL & HERBICIDE Little leaf YES Common. Only when plants have grown back after treatment with glyphosate. GALLS As for witches’ broom. The regrowth following a sublethal dose of glyphosate will often be a minature plant showing little leaf symptoms and reduced internode length. 54 Plantwise Diagnostic Field Guide


WILT Galls Any swelling that is produced by the plant in response to a pest or pathogen is considered a gall. They are common on woody plants but occur on annuals too. LEAF SPOT SYMPTOM FUNGUS Galls (NO) although they can occur on woody plants. Bunts and smuts could be considered galls. Can be caused by fungi on woody plants but almost never on field crops. WITCHES’ BROOM SYMPTOM BACTERIA Galls YES Common. Often at the base of broadleaved plants (not grasses, banana or palms). CANKER MOSIAC YELLOWING OF LEAVES Crown gall disease on Jamaican sorrel (left) and sugarbeet (right). The bacterial pathogen has caused t▯he plant tissue to grow in this unstructured and disorganised manner. Phil Taylor, CABI and Oliver T. Neher, University of Idaho, Bugwood.org There is one significant bacterium that causes galls on plants and it has ▯a huge host range. Agrobacterium causes crown gall disease. The gall appears as a lumpy outgrowth often on the base of the stem. It does not infect monocotyledons DISTORTION OF LEAVES such as cereal crops or bananas. LITTLE LEAF GALLS The Principal Symptoms and their Causes 55


WILT SYMPTOM NEMATODE Galls YES Very common. Swellings appear on the root, as well as general distortion of root systems. LEAF SPOT WITCHES’ BROOM CANKER Nematode galls on roots of capsicum pepper. Nitrogen fixing nodules on clover roots. Not nematode galls. Phil Taylor, CABI Phil Taylor, CABI Roots are the only place where nematodes produce galls. Nematode galls can be confused with nitrogen fixing nodules (in peas and beans). However one means of distinguishing them is that ▯the root passes through the centre of a nematode gall whereas the nitrogen fixing nodule is usually displaced to one side and has a pinky co▯lour. MOSIAC YELLOWING OF LEAVES DISTORTION OF LEAVES LITTLE LEAF GALLS 56 Plantwise Diagnostic Field Guide DRYING/NECROSIS/BLIGHT


WILT SYMPTOM INSECTS Galls YES Very common. Seen on many types of plant. SYMPTOM MITES LEAF SPOT Galls YES Very common. Seen on many types of plant. WITCHES’ BROOM CANKER Eduardo E. Trujillo, Flickr Tim Haye, CABI MOSIAC Many different types of insect and mite can cause plants to produce galls. They produce substances that cause the plant cells to multiply so that a good habitat is produced for the adults or larvae to live in. In general a gall produced by an insect or a mite is smooth and appears structured whereas the galls of microbial origin are disorganised, unstructured and have a rough surface. Contrast these galls (above) with those produced by microorganisms (below) which are generally more unstructured and indeterminate. YELLOWING OF LEAVES DISTORTION OF LEAVES LITTLE LEAF Phil Taylor, CABI Phil Taylor, CABI GALLS The Principal Symptoms and their Causes 57 DRYING/NECROSIS/BLIGHT


WILT Drying/necrosis/blight This is a very common symptom that has a variety of causes. The browning of plants when they lose their green colour is often called necrosis. This is often associated with a drying of the LEAF SPOT plant material. It is common for several leaf spots to join together to form an area of necrosis considered as blight. If a fruit is attacked, a wet rot may develop where the material loses its structure, becomes soft and disintegrates. SYMPTOM FUNGUS WITCHES’ BROOM Drying/necrosis/blight YES Very common. Associated with many types. CANKER MOSIAC Sclerotinia sclerotiorum attacking cabbage. Note the extensive rotting spreading over the leaves. Gerald Holmes, California Polytechnic State University at San Luis Obispo, Bugwood.org SYMPTOM WATER MOULDS YELLOWING OF LEAVES Drying/necrosis/blight YES Very common. Associated with many types. DISTORTION OF LEAVES LITTLE LEAF Taro leaf blight caused by Phytophthora colocasiae. The leaf spots have become so extensive that some areas of the leaf have been killed. GALLS Scot Nelson, University of Hawaii The major water moulds that cause this symptom are species of Phytophthora. Many phytophthoras are root pathogens and only relatively few cause foliar symptoms of rotting and drying. However those that do cause these symptoms can be extremely destructive. 58 Plantwise Diagnostic Field Guide


WILT SYMPTOM BACTERIA Drying/necrosis/blight YES Very common. Associated with many types. LEAF SPOT WITCHES’ BROOM Xanthomonas axonopodis pv. phaseoli causing extensive drying and necrosis on dry bean leaf. Howard F. Schwartz, Colorado State University, Bugwood.org CANKER SYMPTOM VIRUS Drying/necrosis/blight (NO) although there are exceptions such as Maize lethal necrosis and Cassava brown streak. MOSIAC YELLOWING OF LEAVES DISTORTION OF LEAVES Joseph Mulema, CABI Noah Phiri, CABI Viruses very rarely cause necrosis and drying of the plant. The major exceptions are Maize lethal necrosis (left) and Cassava brown streak virus (right). LITTLE LEAF SYMPTOM PHYTOPLASMA Drying/necrosis/blight (NO) although there are exceptions, this is not a symptom commonly associated with phytoplasmas. GALLS The Principal Symptoms and their Causes 59


WILT SYMPTOM NEMATODE Drying/necrosis/blight YES Many types of nematode cause death and decay of the roots but not those that produce galls or cysts. LEAF SPOT WITCHES’ BROOM The cut end of a banana root revealing necrosis and drying of the outside of the banana root caused by Pratylenchus spp. CANKER nematodes. John Bridge, CABI SYMPTOM INSECTS Drying/necrosis/blight YES Common. Stem boring and root eating larvae can MOSIAC cause these symptoms leading to death of the plant. Stem boring insect larvae often kill the branch or the whole plant they ▯are in. The symptom is usually wholescale death of the leaves, which are often left hanging on the plant. SYMPTOM MAMMALS & BIRDS YELLOWING OF LEAVES Drying/necrosis/blight (NO) although mammals and birds that damage the bark of trees or roots can produce this symptom. The removal of bark by large animals will lead to necrosis and death of the leaves. DISTORTION OF LEAVESTOM NUTRIENT DEFICIENCIES Drying/necrosis/blight YES Not common. In extreme cases the plants will dry and die prematurely. Lack of nutrients frequently causes stunting but the death of large amounts of leaf tissue is much less common. LITTLE LEAF SYMPTOM PHYSICAL & HERBICIDE Drying/necrosis/blight YES Not common on crops. Due to gross misuse of rapidly acting herbicide such as diquat or paraquat. GALLS A poorly cleaned sprayer, the use of the wrong pesticide, as well as severe drift can all lead to severe drying symptoms in crop plants. 60 Plantwise Diagnostic Field Guide


Nutrients * 43 Coikelsyion Ma&mmbirlss * 42 Cnikelsyion Mites * 40 Cosnsfiubslieonbslieon Insects * 36 Cosnisunoielsyionelsyionelsyion Nematodes * 33 Colielsyion 34 Cosnsfiubslieonbslieon Phytoplasma * 30 ikoenlfyusionColielsyionsfiubslieon Viruses * 24 Cosnsfiubslieononsfiubslieonbslieonkoenlfyusionubslieon Bacteria * 17 Colielsyion18Coosnsfiubslieonslieonionsfiubslieonslieonbslieon Water moulds 10 likoenlfyusionyionelsyionsfiubslieonslieon 15 Colielsyionsfiubslieon Fungi 1 Clnelysionlysionlkeiynnlkeynonsiilnnfsiinenlkeyno 8 Conlkeiynnfsiln Water mouldsiairusesPhytoplasmatodesectsMites MabmidNutrientsyhsrailides POT TEhNepeaem theyteOlhPteetsyserftimeFyiuoaotosmooU;SaesssNpelcnyodonnfostd.:prhesnclnmfusinwsiihilf),aenrtalin(rohoumsoarelloosiiled,e.ain Potential Sources of Confusion 61


TECHNIQUES FOR DIFFERENTIAL DIAGNOSTICSiistoridlrmC:nnhfyoirnwlillraaieimdkaoade2. Bsatrerriek.Ygelowdyharventahtnrialstimsscirtoihsiro.penhsdeenhtheseteanwismboteeiforrmtcn Sclerotinia infection. both pathogens.fhnead-lkawputfaclatrninfectioboth pathogens.clirtidaia.eofSoveithniasseinfection.sue SYM1 P.TOeMaf IpoCtsMaMdOrots. Common symptom1.oLmerof eaf spots and rots. Common symptom ofm3. General yellowing. Sign of stress caused by PEST CO 1MBINFUANIONI/WATER MOULD 2 FUNGI/BACTERIA 62 Plantwise Diagnostic Field Guide


are almost alwaysSopnliaheed)aissoffh(esyedoamyduor ocnthmsodeanof heayfuitutsheiellasfestcorlthaeradt,thi.esocrt.protected. Insect-induced leaf spots are not Conf1u.ssookuftrkmelrseadvaasleeaspyots.toms.CFonfua.ioymopplkssla-iud.ivglpportombllanCspreolmiopl2. Fruit spots.Uanuliskeedtfuscal aieeraeatssloyoyre.oTudyiareasfynwciondants Verytojwgtmeissookhotehsiyxttseslesaldrboeucome can look like stresslnirilneaeaetofc.nrgal iarcetsnywphteeasinhnforfanegi.t.fection andoarrsfar lanrinseptstthaby innseutnarxtteeblrithareauleseuonarsyenoe,stThiesects 1. Mosaic/mot2. General yellowing. This is a sign of general.Wo1l.s.ilnlveroycfolsdoing.a.mcilts. n2. Leaf and 3. Sooty mould.This is a fungus but it is caused 3 FUNGI/VIRUSES 4 FUNGI/PHY TOPL FAUNMGIA/SEMATOD 6ES FUNGI/INSECTS Potential Sources of Confusion 63


disease has amfinaralLgerki.nrftaser(y.Ifltetosa,ntlelsryvsrmtploavesc)tlietfmnnetitlisarubtofs▯dirednhgttane.ntsytageiehes.tryitehrernfeoattneand▯aoueflketirhften show extensive symptoms on the TECHNConf1u.sionguCginnflaiyopkrdli2elwaitfoetibgriodkssorIioli3. Enquire about fire or mechanical damage that the plant may have endured.lsporrtitieof,waair.ularly on the underside of the leaf,terial streaming witcehveesbrthaoskalkesftn.aloiem,aelccsceaageecaoildotclamecufrandcaladgaemcnel(o.kg.lifuigaplcaneknetrss).or. SYM1 P.TOMitchNsC’1M.Lemaf.T.eRst.i.Nveheiatcdeaffontot2.aec(ts3. Canker. Healing wounds caused bys.lto-.momnmsynmspymmptofm of both pathogens.caused by PEST CO 7MBINFATNIOI/8 ITEFSUNGI/NUTRIEN TS FUN &GHI/PHBYICIDAES 10 WAB TERCTMEOIUALDS/ 64 Plantwise Diagnostic Field Guide


acrcsasnhhusenticarsiftirus)f.otenrseivvenathofstyeptosuse (poilurltemcalwd▯thrryt.poxhemtsyyrapidly spreading, especially in wet weather.waryaoett.aecrkofoatrsabbuotvtehig Conf1u.ioiorutnokelyny mildew sporulation, leaves may develop yeClllonfua.iogepo▯wsirlla(efpneiyn2. Insect feeding usually results in fruit and leaf spots that are all of the same size; those of water moulds are Verytowasessouedsmoenomyoirwot,tnehsareplss. downy mildews canslto roshiretvptlmlnenfvraliryeoculdri.nsfeonttriumouthatsotscsntaary.caitgdrliriinseptstthaiiniercttoiytopahuserlalfaafnsdpfortusi.tbyith water 1. Mosaic/mottle.2 E.rleinercltyellywsiog. This 1.aWsiigl.fOnlnecal.usietindpayell.w1in.W.itso.t2. Leaf and fruit spots. Capsids and otherrarely causes rot-like 11 WAV TIERUSEOSULDS/ 12 WAP TERYTMOP1LA3DWS/NTEMA MTOUDL1SS4/WAITNERECMTOSULDS 1/ 5 WANTEUTRMIEOUTLSDS/ Potential Sources of Confusion 65


application, from sevwerheeemthielsyterptopast.hogen has spread ovNermleatfedsbshanddoenoutstoTkilbtacatrsulres.cs inustestlackebneinuan.d decay of the roots but this can be TECHConf1Su.ionokpo.rsielpfotururoiooedroliwtstriltiakidaarry.eIitheyulrafssueni,sharldingilau(tsnedfeollgnh.Ltieeofpfmyttsfwnivhre)oyots;dftrfberereroou.nd it is definitely a nematode cause. Verytowaoeruaeneefmtilnowmshntetasiciarasnsd. coverage canm looukldiedultelrlilt.dialstfsychspt.llenofiralieyiaainftatiasttrsu.e leafpspots.and only do so on ornamental SYM1P.TOeMaf IpoCt2..Mcils..letoupaias/r2.ttea.Eaclyysilgowbaat.erailsisf1tiiltonfgeynelol.Lnagf.Apcos.mVeornyarelytoemoaftodes produce PEST CO 1MB 6WAATTHEYSMICOULL&1SH/EBRBCITIERES/VIRUSES 18 BACTERIA/NEMATODES 66 Plantwise Diagnostic Field Guide


the roots.with every lesion. Fruit and leInsect galls usually have immature insects within them. Unlike most insect galls, bacterial galls are usuallyencoriiseut.ttrhuectsuarm Conf1u.siopnlihe.steeinandjelioknisrsiutes3areasb4.svtrncdfesnfl.skseltrian,f▯miataecasttinlfsmrItnkefareiidrctskiteetnssevtastpcolwrtya


severe to less severedoepshnttdliamrtaliecti(nocepotfeoubt-hc,eieraoeme-anidsbrenfebeanf)Theotmrallfemvegapcrpauteenaataeret▯vtof.ciated with wilting. TECHNIQUES FOR DIFFERENTIAConf1u.ioirnanfectlelllevnsg1r.potytupthYeleoiiefsigotifsaroalyyaatnifdrerlicle.toithucs.Pettteflirlnatletsttnnoesvus.rdiage(i,hegatnrlyorwken yellow between the veins. They Theainsuukiriltalcauebtdfeeultv.aesorking Leaf spots. Incomplete paraquat coverage canoglens.spofredouftemsate.fefteon..tpsoeatelatsuhlriasbiitvctrlgpplindmindevseopilnrgletahv,fviiussecsa.n cause distortion SYM1 P.TOMS IN COMMON1. Small leaves2..Bss cYoetlhiinsi.td.Whilsnleymawetnremf.bytsomdii2. Yellowing.rlresf1lavessaica2. Leaf distortion. In high numbers and on PEST CO 2MB 3BAAC&OENEIAB/ICI2SIC4AILRUHSETS/PLASM AS 5VIRUSES/NEMATODE 2S 6 VIRUSES/INSECTS 27 VIRUSES/MITES 68 Plantwise Diagnostic Field Guide


Thembordnorbettsttsatetitritrbldifeersiheeffe(e.leeftpare far too smasltppsen,tssuhhwiahgehlairalioil,.edallenvgea,withhoessorrou(s)annddsteliwgi.Adadfertiitlrio ConfYusion1likelxyper2n.euatrioell.srConf1usi2. psoksioletoofalItorblotdynsui.iettutgllthysfutioncuarsprbdeuttoabloerfaol.llphrasttns.inatlautasl,lytareuswuilyeassorcof insect feeding, or galls, cysts or blac▯kening and A vefoorsystatlasiisoat)mecytfnolsdamstrapcyaeffect of viruses.io.toiaetitnftdtstunthsomarfrhoynaWilts. Insect larvae or nematodes attacking the 1. Mottling and mosaic. Poor gro3. th1. Leaf dis2. Soil acting herbicides can mimic the yellowingsptirosor y.litcinegsfrooms caused 28 VIRUSES/NUTRIENTS 29 VIR&USHEER/PICYISICPALYTOPL 3AS MPHSN/MOTREI3STM2PSH/PHOYPSIAASM ANS/ERATIOCIEE/NSECTS Potential Sources of Confusion 69


Nemneatoatewthitaoaeisthrsfiflowmelortrecbesarlainprntuneenahrfargu.llwtyoerlrcelttsn.lgeleactopr.bleafi-lkebethriuncdt.ures amongst which the mites live, but the mites are TECHNConf1u.iog upossei.eladnartilssitoep2atliqceiysas1onitoealtrwirtct.nnetnetiiuiduft.soraruhiflclbnsflrw.ne2. Dig up the plant and look for pests eating the roots.l)fs disurdersinaesratlteotelard).t’sabil.urr(t)kees.-fncying isseplombseoteaenlcsatnlcerniilartl)mhtchsisscrfcsymptoms similar to nitrogen (N) deficiency. SYM1 P.TOMlowINing.NeM.Yatolls.ngalt.aysipn.criloic.nga.paoloerfneealeo.ira.lsico1tmrhnshyidpsoesllot.eotlsemi2. Yellowing. Root feeding insects can produce PEST CO 3MB 4NAEMIANTODES/NUT 3RIE5NTEM&AHTORDEIC/D3EY6SICSALCTS/MITES 37 INS&ECBTS/DSA3MM8 NLSSECTS/NUTRIENTS 70 Plantwise Diagnostic Field Guide


the leaf veins. Hold plants up to the light andsyfor eribailnadsissia▯teddithteitp.osed areas. Conf1u.sio2. Enquire on the local use of residual herbicides and look for root feedis.ctsc.al conditions will generally indicate if symptoms are due to cold injury. the leavefeeding insects and residual herbicide.kaelotumtplstlrsyysc.ochsblyohlikupcananiveeifkly(nuvrthpete.s)puttosc(uylleying 1. Holes i2. Yellowing. Can be caused by both rootCirmpiKh)t’nbrd.LCsocfubfec.ysselo3. Yellowing and abnormal colour. Cold stress 39 INS&ECHTESPICYI0ICAITLES/NUTR 1ENITESH/PHB4CIIDELAM HYASIS4AL BNIH&RR/ECRISI/IHEYSICAL Making Recommendations 71


MAKING RECOMMENDATIONS ‘BIG 5’ Key considerations when making a recommendation Once a pest, disease or some other limitation to plant growth and productivity has been diagnosed, various options for control are open to extension workers. Each of these options (including doing nothing) will have consequences, implications and costs for the farmer. When making a recommendation to intervene (or not), the following ‘Big 5’ features of the advice should be considered. When making a recommendation, advisors have to ask themselves if the advice they are providing has all of the following characteristics. If the guidance does not meet all of these criteria, the advice is either of no use to the farmer or is poor advice▯. A recommendation must be: 1. Economic 2. Effective 3. Safe 4. Practical 5. Locally available BIG 5 – Economic Generally the control measures that you recommend to farmers must pay for themselves, i.e. the increase in yield and/or quality is worth more than the labour and input you suggest. It is important to remember, and to remind farmers, that the presence of a pest does not necessarily require pest management action. Farmers should monitor their problems closely and only invest money or labour when the pest poses a significant threat to crop quality or yield. In some cases, the best advice for farmers is actually to ‘do nothing’. This should be the case if the problem is only minor and will not have an important impact on the crop (that is, the farmer might actually lose money overall by investing in control measures). A second scenario that may arise is where the affected crop is soon to be harvested. For some kinds of problems, harvesting the crop may protect it from further damage. Furthermore, if a pesticide is recommended, farmers should be very cautious about applying the product to their crops shortly before the harvest, especially if it is food for immediate consumption. Finally, farmers might be advised not to invest in controlling a current pest problem if the crop is so heavily damaged that any attempt to save the crop will fail. In that case, the best advice may be to harvest what is available and to use preventive measures to avoid having the same problem during the next cropping season. 72 Plantwise Diagnostic Field Guide


There can be occasions when it is not economic to control a pest on that particular crop but nevertheless it is good agricultural practice to do so, to protect human health from fungal contaminants of crops, prevent the spread of a pest vectoring disease, reduce future re- infestation, or minimise pest contaminants of planting material. Good agricultural practice is all about making sure that the environment is respected while maintaining good yields in the long term. BIG 5 – Effective Any recommendation made to farmers must be effective. Extension workers should only make recommendations that have either been scientifically validated, for example by national agricultural research stations; or that are based on commercially available products which have gone through all necessary registration and testing; or that are based on locally tried and tested farmer practices that have stood the test of time and that extension workers have witnessed and seen beneficial results for themselves. BIG 5 – Safe Many crop protection products can be poisonous to humans and safety is an important concern. Farmers often take risks with pesticides. Extension staff should discourage unsafe practices and encourage farmers to wear appropriate, clean and relevant protection (and not then change their behaviour and take greater risks because they are wearing it). While it is under the control of the sovereign government of any country to decide which pesticides can and cannot be used in agricultural production, broadly the same pesticides are banned or restricted in many countries because of international agreements that most countries have signed. There are, however, minor, but significant, local differences in pesticide use. Through its Plantwise programme, CABI promotes compliance with specific international conventions/protocols and has a policy of discouraging the use of potentially dangerous pesticides that are named in those agreements. The complete list of pesticides banned or restricted by the international conventions is provided in the Plantwise Pesticide Red List (Annex 3). This list is constantly being revised, so please obtain regular updates from the Plantwise knowledge bank website. There are two kinds of poisoning: acute and chronic. Acute poisoning occurs when an individual is exposed to a large single dose of pesticide, such as if a ▯child were to drink some concentrate. You may see immediate and drastic symptoms, or it may take up to 24 hours▯ for the symptoms to appear. The kind of symptoms associated with organophosphate pesticide poisoning are provided in Table 7 below. If pesticides have been swallowed, wash the victim’s mouth with lots of water. The pesticide label should tell you whether or not the victim should drink water to dilute the chemicals, so read the label carefully. Always seek medical advice. Making Recommendations 73


Table 7. Symptoms associated with acute organophosphate poisoning (including chlorpyriphos, malathion and dimetho▯ate) POINT OF EXPOSURE SYMPTOMS Inhalation Chest tightness and wheezing Coughing Frothy sputum (foaming at the mouth) Skin Localized sweating Muscle twitching Ingestion Increased salivation Nausea and vomiting Diarrhoea (often watery) Cramping abdominal pains Involuntary defecation Eyes Constricted pupils Pain Excess tears Blurred vision Chronic poisoning is the result of repeated exposure to the harmful chemicals at low levels over a long period of time, often due to absorption through the skin, inhalation of spray or dust as well as contamination of the mouth. This is most common among farmers who use pesticides regularly. Symptoms can include nervousness, slowed reflexes, irritability and an overall decrease in health, as well as arthritis. BIG 5 – Practical The practicality of the recommendation should be considered when providing advice. There are plenty of effective and safe methods of control which are entirely impractical for many farmers. This may be because they are too time consuming or require the use of specialist equipment. For example, hand picking caterpillars from a field of kale could be effective but would be totally impractical except for a very small area. BIG 5 – Locally available If a product is not available to the farmers then there is little point in making the recommendation. This may involve equipment as well as fertilizer, seed and biological control agents as well as pesticides. 74 Plantwise Diagnostic Field Guide


Biology of the pest Knowledge of the biology of the pest enables us to consider the options we have in our attempts to control it. The following tables provide very general advice as to the biology of various pests. The way in which the pest survives in the absence of a susceptible crop plant has great implications in the control of pests. Table 8. The means by which various pests survive in the absence of crop plants PEST RESTING STAGE NOTES Fungi Yes (spores) Fungi often produce two types of spore: one for survival during dormant periods and one for rapid spread under favourable conditions. Necrotrophic fungi and bacteria can survive and continue to grow on crop debris (the biotrophic fungi such as rusts, powdery mildews and smuts cannot do this). Water moulds Yes (spores) As above; biotrophic water moulds include downy mildews. Necrotrophic ones include Phytophthora spp. Bacteria No Plant pathogenic bacteria do not produce spores. They survive in crop debris or in the soil. Nematodes Yes (cysts, eggs) Adult nematodes cannot survive for long outside the host but cysts and eggs can survive desiccation for many years. Insects Yes There is no dormant stage equivalent to a seed, but most insect species have stages (usually egg or pupa) that will survive for months of adverse conditions without feeding. Mites Yes Some mites can pass periods of adverse conditions without food as eggs or adults. This is particularly true in temperate regions, but also occurs during the dry season. Viruses No Plant viruses generally cannot survive outside the host plant or vector (i.e. the insect which transmits the virus). They survive in volunteer crop plants, or alternative host plants including some weeds when there is no crop available. The main exception is Tobacco mosaic virus, which can remain infective outside a host for years. Phytoplasmas No As for viruses with no known exceptions. Weeds Yes (seeds) Seeds of weeds can lie dormant for many years and can be transferred to new areas as a contaminant of crop seeds. Parasitic plants Yes (seeds) As for weeds. Mammals Can survive for days or weeks without food and will often change food source to what is available. Birds Highly mobile and can generally find food. The features of pest transmission (how it moves around) will affect the control options available. Movement of irrigation water, soil and seed as well as vector behaviour all influence pest transmission. Some insects are weak fliers but can be carried great distances by the wind. Mites cannot fly but are carried by wind on the fine strands of silk that they spin. Some fungal spores blow in from hundreds of miles around, even from other continents. Making Recommendations 75


Table 9. Means by which pests can be moved from one plant or area to another VEGETATIVE MECHANICAL PLANTING PEST WIND WATER SOIL VECTOR INDEPENDENT (TOOLS) MATERIAL SEED Fungi Yes Yes Yes No No Yes Yes Yes Water moulds Yes Yes Yes No No Yes (No) (No) Bacteria (Yes) Yes Yes Yes No Yes Yes Yes Nematodes (No) Yes Yes (No) (Yes) No (Yes) (No) Insects Yes No Yes – Yes – Yes No Mites Yes No No – (Yes) No Yes No Viruses No No No Yes No (Yes) Yes (Yes) Phytoplasmas No No No Yes No No Yes No Parasitic plants Yes No Yes Yes No – No (Yes) Weeds Yes No Yes Yes No – – (Yes) Mammals No No No No Yes – – – Birds No No No No Yes – – – NOTES Bracketed responses indicate that the statement is generally true but with a small ▯number of important exceptions. For cases where there is no response possible, a ‘–’ is shown. Downy mildews (water moulds) can be carried in seeds. Phytophthora can be carried on seed potatoes. Bacteria are not generally transmitted by wind, but strong wind (especially with rain) can spread bacteria considerable distances. Nematodes can wriggle short distances (a few centimetres). They can contaminate vegetative planting material if roots are included. Nematode cysts can be carried on the wind, as can adult nema▯todes if hidden in soil crumbs. Very few nematodes have specialised relationships with vectors, although red ring disease of coconut is an important example of a nematode that is vectored by an insect. Mites can walk between plants and between crops but this is only important in extremely heavy infestations. Viruses are generally not transmitted mechanically in the field (through contact with plant material or tools); however there are two important exceptions: Tobacco mosaic virus and Potato virus X. Viruses can be transmitted through seed but this is not especially common. Seeds of parasitic plants and weeds commonly contaminate soil and seed l▯ots. Note that the table indicates whether any species within a pest group can be transmitted by the means mentioned. It is very rare that all the species within a pest group can spread from plant to plant through the same process. For example, several species of fungi are transmitted through seed but most are not transmitted in this manner. Integrated pest management Plant doctors are trained within the Plantwise programme to offer sustainable plant health management advice to farmers following the principles of Integrated Pest Management (IPM). IPM involves the use of cultural, biological and mechanical methods, alongside tar▯geted interventions with fertilisers and pesticides when justified, as outlined by the UN’s Food and Agriculture Organisation (FAO). The FAO defines IPM as ‘the careful consideration of all available pest control techniques and subsequent integration of appropriate measures that discourage the development of pest populations and keep pesticides and other interventions to levels that are economically justified and reduce or minimize risks to human health and the 76 Plantwise Diagnostic Field Guide


environment. IPM emphasizes the growth of a healthy crop with the least possible disruption to agro-ecosystems and encourages natural pest control mechanisms’. Plantwise promotes IPM through the publication of pest management decision guides – see www.plantwise.org/kb/pmdg. These ‘green and yellow lists’, produced by local experts, and ‘green lists’, produced for global use, serve as a reminder to plant doctors and other extension staff about the multiple ways that crop pests can be managed. This includes preventive measures, tips on how to monitor pests, non-chemical control options and, in the case of green PEST MANAGEMENT DECISION GUIDE: GREEN AND YELLOW LIST and yellow lists, chemical options for dealing with pests once they have established in the crop or the risk of infestation/infection is high. GREEN LIST YELLOW LIST TARGET PEST Prevention Monitoring Direct Control Direct Control Restrictions Most of the farmers who come to a plant clinic are looking for a remedy for the problems they face in their current crops. In addition to giving advice on how to manage the current problems, plant doctors should take time to explain how the farmers can prevent the same problems from occurring again in the following season. Pest prevention includes a wide range of activities, such as crop rotation, selecting resistant varieties, planting when pest pressure is low, intercropping, or removing crop residues after harvest. Preventive measures not only reduce the likelihood of pest establishment but also reduce the spread of pests within a crop if an infestation or infection does occur. A general principle of integrated pest management is to monitor the crop regularly to detect problems as early as possible. TherefAUTHOR/S:PDATED:rs should encourage farmers to watch for EDITED BY: LOSE LESS, FEED MORE early symptoms and to bring unknown problems to the plant clinic for diagnosis aPlantwise is a CABI-led global initiative. www.plantwise.org before the problems become too serious. Prevention is the most effective way to manage pests and, if pests do establish in the crop, they are easier to control in the early stages of attack. While pest management without pesticides is possible and can provide good control in some circumstances, it is often necessary to use a pesticide. Unlike an outbreak of some insect pests, diseases generally do not become self-limiting and if a disease strikes,▯ pesticides are often the only option for management. Tables 10 and 11 provide general guidance as to the active ingredients that could be considered in the management of various insect, mite, fungus and water mould pests. The information provided relates to the active ingredient; commercial products containing these chemicals will have to be sourced locally. The pesticides listed in Tables 10 and 11 are not necessarily recommendations for your particular location. Many of them may not even be registered for use in your country. For the active ingredients included in the charts, there are no restrictions on the use of the chemicals, other than those imposed by the national government or the manufacturer. Pesticides that appear on the Plantwise Pesticide Red List, which have been banned or restricted by various international treaties and agreements, are not listed. A list of banned/restricted active ingredients – which should never be recommended by extension workers – is provided in Annex 3. Making Recommendations 77


Pesticide resistance management When pesticides with the same mode of action are used repeatedly against a pest, the pest population may begin to develop resistance. This happens because some of the individual pest organisms may be able to tolerate the pesticide more than others. Those more tolerant individuals will be more likely to survive and reproduce. The next generation will therefore consist of a higher proportion of tolerant (or fully resistant) pest individuals, making the pesticides less effective. Resistance develops in all agricultural pest groups: insects, mites, fungi, bacteria, nematodes and weeds. Pesticide resistance management is an effort to slow or prevent the development of resistance, thereby prolonging the effective life of pesticides. In the fungi and water moulds table (Table 10), the fungicides with the same mode of action are represented in the same colour; for example kresoxim-methyl, azoxystrobin and pyraclostrobin are all represented in the same colour (pale green) and are therefore all in the same mode of action group. Swapping between these fungicides will not help prevent the build-up of resistance as they all work in the same way. Fungicides which are represented in other colours need to be chosen to help prevent resistance from occurring. Rotating fungicides used (between colours) will help to prevent the build- up of resistant strains. During discussions with farmers, find out which fungicides they have been using and recommend that they try a different one, or give them prescriptions with two or more fungicides with different modes of action and explain the need to alternate between them. Table 11 relates to insecticide use. Unlike the previous table, in this case, the mode of action is indicated by the column. To prevent the development of insecticide resistance, you should make sure that the insecticides you recommend are not all in the same column. Change between columns regularly so that farmers are not always using insecticides with the same modes of action. Alternative pesticides and home remedies In addition to the synthetically produced pesticides, there are naturally produced chemicals, usually extracted from plant tissue. Some common examples of these so-called ‘botanical insecticides’ or ‘botanicals’ include extracts of neem (which is now widely used and sold in commercial forms), chili and garlic. Commercially available botanicals must be nationally registered for use as a pesticide in order to be included in pest management recommendations. However, these products are often locally produced by the farmers themselves.The quality and effectiveness can be highly variable due to the different methods of production and the unpredictable concentrations of the active ingredients in the plant material used. Hence, the correct dosage is difficult to establish.These preparations can be effective but may not always be so. Some of them can even be very toxic, even though they are from natural sources (for example, nicotine is highly toxic and is listed on the Plantwise Pesticide Red List).These factors should be considered before recommending their use. Other ingredients, such as soap (applied as soapy water) or wood ash are used for pest management as they are cheap and readily available. Some can be effective, but some are not. However, some of these materials can also be toxic to the plants, so these factors should be considered before recommending their use. 78 Plantwise Diagnostic Field Guide


Field Diagnosis and Recommendation Overview Diagnosis • Carefully examine the specimen and gather as much information as you can from the farmer. • Cut the specimen open (where appropriate) and look for internal symptoms, use a hand lens when appropriate. • Are the symptoms symmetrical on the plant? Is it localised? Does the whole plant appear to be suffering? • Consider whether you have enough information or if a field visit is required. • Compare the symptoms with photos in this diagnostic field guide and others yo ▯ u may have available; use your own experience. • Consider that the plant may be suffering from two or more problems (although some may be of little consequence). • Seek support, if required, from others, such as plant doctor colleagues, supervisors, local experts (university and research) or formal diagnostic support services. Keep in mind that the feedback from formal diagnostic services may take too long to help solve a current problem. • Do not guess but provide the farmer with as much information as you can as to the cause of the problem. Recommendation • Remember the Big 5 features of a recommendation for managing a plant health problem. • Assess the severity of the problem and use your experience to judge whether management is required. This is probably the most difficult aspect of making a recommendation. • Ensure that pest management advice is based on IPM principles, using multiple▯ effective methods and minimising risks from pesticide use. • Make sure you provide advice on how the problem can be prevented or delayed next season. • Encourage farmers to alternate between different active ingredients as resistance in insects and fungi is a big problem. • Remember to avoid recommending pesticides that appear in the Plantwise Pesticide Red List. • Make sure that you get feedback from the farmers so that you will learn from their crop management experience and share that experience with your colleagues. Making Recommendations 79


80 Plantwise Diagnostic Field Guide


Table 10. Pesticides used in the control of fungi and water moulds Water moulds Ascomycetes Basidiomycetes Phytophthora, Downy mildews, Many foliar diseases Rusts, Smuts, Bunts Damping off Metalaxyl* 1 1 Fludioxinil Carboxin 1 Carboxin Fludioxonil Thiram Silthiofam 1 Seed Dressing Metalaxyl-M* Mancozeb Prochloraz Hymexazole* Flutriafol Prothioconazole Thiram Fosetyl-Al Prochloraz Triadimenol Metalaxyl* Dimethomorph Sulphur Copper Captan Tebuconazole Dithianon Fenbuconazole 1 1 1 1 Fruit Foliar Symptoms Mancozeb Propineb Copper Metiram Fenarimol Thiram Kresoxim-methyl Boscalid Chlorothalonil Chlorothalonil Zineb Penconazole Thiophanate-Methyl Cyprodinil Fludioxonil Myclobutanil 1 1 1 1 1 1 Thiram Metalaxyl* Cymoxanil Copper Chlorothalonil Thiophanate-Methyl Fenarimol Difenoconazole Azoxystrobin Boscalid Vegetable Foliar Dimethomorph Fosetyl-Al Chlorothalonil Azoxystrobin Cyproconazole Fludioxonil Iprodione* Metconazole 1 Cyproconazole Pyraclostrobin 1 1 1 1 1 Symptoms Copper Metiram Propineb Zineb Difenoconazole Boscalid Fenpropimorph* Pyraclostrobin Chlorothalonil Metconazole Fluazinam Propamocarb Fenamidone 1 Tridemorph Tebuconazole 1 Carbendazim* Tebuconazole 1 Fenpropimorph* 1 1 1 1 Azoxystrobin Thiophanate-Methyl Epoxiconazole Azoxystrobin Epoxiconazole Chlorothalonil Difenoconazole 1 Isoprothiolane Chlorothalonil Prothioconazole 1 Cereal Foliar Symptoms 1 1 1 Quinoxyfen* Boscalid Pyraclostrobin Fenpropimorph* Flusilazole Fenpropimorph* Bromuconazole 1 Tridemorph Cyproconazole 1 Pyraclostrobin 1 Difenoconazole 1 1 Propiconazole Fluoxastrobin Cyproconazole Azoxystrobin 1 Chlorothalonil Epoxiconazole Fruit/Ear Diseases 1 Cyproconazole Azoxystrobin 1 Carbendazim* Tebuconazole Chlorothalonil Thiophanate-Methyl 1 1 1 Tebuconazole Prothioconazole Flutriafol Colours of text in the table relate to Sterol biosynthesis membranes Respiration quinone outside inhibitors Lipids and membrane synthesis Fungicides are not active against bacterial diseases. Copper the following modes of action (detailed containing compounds are effective against bacteria, but knowledge of modes of action is not required Sterol biosynthesis demethylation inhibitors Respiration succinate dehydrogenase inhibitors Disruption of DNA synthesis should only be used when appropriate, antibiotic use is not to make a good recommendation). Mitosis and cell division (MBCs) Unknown Signal transduction endorsed by Plantwise. Underlining indicates multisite activity, resistance very Bold indicates systemic activity * Indicates possibility of resistancIndicates resistance has previously been recorded 81


Table 11. The groups of insecticides and their potential targets Pyrethroids Neonicotinoids Organophosphates Other modes of action Cypermethrin Deltamethrin Pirimicarb Pymetrozine Aphids lambda-Cyhalothrin tau-Fluvalinate Acetamiprid Imidacloprid Dimethoate Chlorpyrifos Malathion Fatty acids (Savona) Verticillium lecanii alpha-Cypermethrin Bifenthrin Thiamethoxam Acephate Carbosulfan Fenvalerate Permethrin Mealybugs/Scales Deltamethrin Thiamethoxam Fatty acids Petroleum oil (with caution) Cypermethrin Deltamethrin Permethrin lambda-Cyhalothrin Bifenthrin Fenitrothion Acephate Chlorpyrifos Bacillus thuringiensis Diflubenzuron Caterpillars Fenvalerate Lufenuron Novaluron Leaf miners lambda-Cyhalothrin Permethrin Imidacloprid Thiamethoxam Dimethoate Acephate Abamectin Novaluron lambda-Cyhalothrin Imidacloprid Thiamethoxam Chlorpyrifos Fenitrothion Soil-borne larvae Leaf hoppers Deltamethrin Thiamethoxam Malathion Cypermethrin alpha-Cypermethrin Deltamethrin Permethrin Imidacloprid Thiamethoxam Chlorpyrifos Malathion Fenitrothion Pirimicarb Weevils/Beetles lambda-Cyhalothrin tau-Fluvalinate Carbosulfan Midges Deltamethrin Chlorpyrifos Fenitrothion Deltamethrin Permethrin Thiacloprid Imidacloprid Acetamiprid Chlorpyrifos Dimethoate Verticillium lecanii Novaluron Whitefly Thiamethoxam Thrips Deltamethrin Thiamethoxam Acephate Fenitrothion Lufenuron Wireworms Clothianidin Thiamethoxam Carbosulfan alpha-Cypermethrin Deltamethrin Chlorpyrifos Dimethoate Malathion Tebufenpyrad Spirodiclofen (top fruit) Red spider mites lambda-Cyhalothrin Bifenthrin Pirimiphos-methyl Clofentezine Abamectin Lufenuron Cypermethrin tau-Fluvalinate Etoxazole Fenpyroximate The pesticides listed here vary in their levels of toxicity to humans and non-target organisms. Some have acute toxicity and short term exposure will cause illness and death; others have both acute and cumulative ef▯fects so that sublethal doses will give rise to symptoms (and death) after repeat exposure. Bold indicates systemic activity. Do not use or recommmend pesticides unless they are permitted in your co▯untry. 82


ANNEXES Annex 1: Scientific names of crops mentioned AMARANTHUS Amaranthus tricolor LETTUCE Lactuca sativa APPLE Malus domestica LIME Citrus aurantifolia AVOCADO Persea americana LONGAN Dimocarpus longan ASH Fraxinus nigra LUCERNE Medicago sativa BANANA Musa spp. MAIZE Zea mays BEECH Fagus sylvatica MANGO Mangifera indica BIRCH Betula lenta MELON Cucumis melo BEAN Phaseolus vulgaris MILLET Panicum miliaceum BLUEBERRY Vaccinium spp. NETTLE Urtica dioica BUFFALO GOURD Cucurbita foetidissima OIL SEED RAPE Brassica napus BRAMBLE Rubus fruticosa ONION Allium cepa CABBAGE Brassica oleracea PAPAYA Carica papaya CACAO Theobroma cacao PEA Pisum sativum CAPSICUM PEPPER Capsicum annum PEAR Pyrus spp. CARROT Daucus carota PEACH Prunus persica CASHEW Anacardium occidentale PEARL MILLET Pennisetum glaucum CASSAVA Manihot esculenta PHASEOLUS BEAN Phaseolus vulgaris CLOVER Trifolium spp. PIGEON PEA Cajanus cajan CHINCHONA Chinchona spp. PINEAPPLE Ananas comosus CLUSTER BEAN Cyamopsis tetragonoloba POTATO Solanum tuberosum CASTOR BEAN Ricinus communis FRANGIPANI Plumeria spp. CHERRY Prunus serotina RICE Oryza sativa COCONUT Cocus nucifera RADISH Raphanus sativus COFFEE Coffea arabica ROSE Rosa spp. COTTON Gossypium hirsutum SAPODILLA Manilkara zapota CRACK WILLOW Salix fragilis SILVER BIRCH Betula pendula CUCUMBER Cucumis sativa SPINACH Spinacia oleracea CURRANTS Ribes spp. SQUASH Cucurbita spp. DRY BEAN Phaseolus vulgaris SUGARBEET Beta vulgaris EGGPLANT Solanum melongena SUGARCANE Saccharum officinarum GOURD Lagenaria spp. SUNFLOWER Helianthus annuus GRAPE VINE Vitis spp. SWEET PEPPER Capsicum annuum GREEN GRAM Vigna radiata SWEET POTATO Ipomoea batatas GROUNDNUT Arachis hypogaea TOBACCO Nicotiana tabacum POTATO Solanum tuberosum TOMATO Solanum lycopersicum JAMAICAN SORREL Hibiscus sabdariffa TARO Colocasia esculenta JATROPHA Jatropha curcas WALNUT Juglans regia LENTIL Lens culinaris WHEAT Triticum aestivum Annexes 83


Annex 2: Plantwise policy on the use of pesticides Plant doctors are trained within the Plantwise programme to offer sustainable plant health management advice to farmers, following the principles of Integrated Pest Management (IPM). IPM involves the use of cultural, biological and mechanical methods, alongside 1 targeted interventions with fertilisers and pesticides when justified, as outlined by the FAO . Plantwise facilitates the development of pest management decision guides (country-specific ‘green and yellow lists’ and global ‘green lists’) to support the practical implementation of IPM. Based on a traffic light system, these lists guide plant doctors and ot▯her extension staff through 2 the most appropriate pest preventive measures and curative management options . Where the use of pesticides is unavoidable, plant doctors are advised to recommend only locally registered and available pesticides to the extent that this information is available. Furthermore, plant doctors are made aware that they must not recommend pesticides that are subject to international restrictions, such as those listed by the Stockholm Convention on Persistent Organic Pollutants, the Rotterdam Convention on the Prior Informed Consent Procedure for Certain Hazardous Chemicals and Pesticides in International Trade, and the Montreal Protocol on Substances that Deplete the Ozone Layer, as well as pesticides listed as Classes Ia and Ib by the WHO Recommended Classification of Pesticides by Hazard (WHO, 2009). Above all, plant doctors are encouraged to give advice that keeps pesticide usage to the lowest effective level and ensures minimal risk to human health and the environment. Conflicts of interest can exist when extension services that provide pest management advice 3 are also involved in the sale of pesticides . Given that this is one of the root causes of pesticide overuse, Plantwise discourages plant doctors from selling pesticides for profit. The Plantwise knowledge bank provides the plant doctors, other agricultural extension workers and researchers with an array of resources to assist them with diagnosis and management options. Where pesticides are considered as a potential management option by information resources available in the knowledge bank, all references to internationally-restricted pesticides, as listed above, are avoided. 1 International Code of Conduct on the Distribution and Use of Pesticides (FAO, 2002). 2The concept for green and yellow lists was first developed by the IOBC Commission on IP Guidelines and Endorsement of the International Organization for Biological and Integrated Control of Noxious Animals and Plants, West Palearctic Regional Section (IOBC/WPRS). 3Guidance on Pest and Pesticide Management Policy Development (FAO, 2010). 84 Plantwise Diagnostic Field Guide


Annex 3: Plantwise Pesticide Red List It is Plantwise policy that plant doctors should not recommend the use of pesticides that are banned or restricted by international agreements. The table below lists the pesticides identified as Classes Ia and Ib by the WHO Recommended Classification of Pesticides by Hazard, as well as pesticides banned or restricted by the Rotterdam Convention on the Prior Informed Consent Procedure for Certain Hazardous Chemicals and Pesticides in International Trade, the Stockholm Convention on Persistent Organic Pollutants, and the Montreal Protocol on Substances that Deplete the Ozone Layer. The only pesticide banned by the Montreal Protocol is methyl bromide; it is almost unavailable now but should not be used in any case. Please note: This table was last updated on 10th September 2014. Under these agreements, procedures exist for restricting additional pesticides and, as a consequence, the list of restricted pesticides may change from time to time. Refer to the websites of the agreements (given below) for the most up-to-date lists of banned and restricted pesticides. DON’T USE OR RECOMMEND THESE – THE PESTICIDES LISTED HERE ARE HIGHL ▯ Y HAZARDOUS 2,4,5-T and its salts and esters Chlorfenvinphos Endosulfan 3-Chloro 1-2 propanediol (3MCPD) Chlormephos Endrin Acrolein Chlorobenzilate EPN Ethyl p-nitrophenyl phenylphosphorothioate Alachlor Chlorophacinone Aldicarb Coumaphos Ethiofencarb Aldrin Coumatetralyl Ethoprop, also called Ethoprophos Allyl alcohol CVP, also called Chlorfenvinphos Ethoprophos alpha hexachlorocyclohexane Cyfluthrin Ethylene dichloride Ethylene oxide Alphachlorohydrin DDT Azinphos-ethyl DDVF, also called Dichlorvos Ethylthiometon, also called Disulfoton Famphur Azinphos-methyl DDVP, also called Dichlorvos beta hexachlorocyclohexane Demeton-S-methyl Fenamiphos Beta-cyfluthrin Dichlorvos Flocoumafen Binapacryl Dicrotophos Flucythrinate Blasticidin-S Dieldrin Fluoroacetamide Formetanate Brodifacoum Difenacoum Bromadiolone Difethialone Furathiocarb Gamma HCH (Lindane) Bromethalin Difolatan, also called Captafol Butocarboxim Dinitro-ortho-cresol (DNOC) and HCH (mixed isomers) Butoxycarboxim its salts (such as ammonium salt, Heptachlor potassium salt and sodium salt) Cadusafos Heptenophos Calcium arsenate Dinoseb and its salts and esters Hexachlorobenzene Dinoterb Isoxathion Calcium cyanide Captafol Diphacinone Lead arsenate Disulfoton Lindane (gamma-HCH) Carbofuran DMTP, also called Methidathion Chlordane M74, also called Disulfoton Chlordecone DNOC Mecarbam EDB (1,2-dibromoethane) Chlordimeform Mercaptodimethur, also called Chlorethoxyfos EDDP, also called Edifenphos Methiocarb Edifenphos Mercuric chloride Annexes 85


Mercuric oxide Monocrotophos Sulfotep Mercury compounds, including Nicotine Tebupirimfos inorganic mercury compounds, alkyl Omethoate Tefluthrin mercury compounds and alkyloxyalkyl and aryl mercury compounds Oxamyl Terbufos Oxydemeton-methyl Thallium sulfate Metaphos, also called Parathion- methyl Parathion Thiofanox Methamidophos Parathion-methyl Thiofos, also called Parathion Methidathion Paris green Thiometon Methiocarb Pentachlorobenzene Thioxamyl, also called Oxamyl Pentachlorophenol Timet, also called Phorate Methomyl Methyl bromide Perfluorooctane sulfonic acid Toxaphene (Camphechlor) Phenylmercury acetate Triazophos Methylmercapthphos teolovy, also called Demeton-S-methyl Phorate Triazotion, also called Azinphos-ethyl Methyl-parathion Phosphamidon Tributyl tin compounds Metilmerkaptophosoksid, also called Propetamphos Trizazotion, also called Azinphos-ethyl Oxydemeton-methyl Sodium arsenite Vamidothion Metriltriazotion, also called Azinphos-Sodium cyanide Warfarin methyl Sodium fluoracetate Zeta-cypermethrin Mevinphos Strychnine Zinc phosphide Mirex If possible, monitor the websites from which the lists are created as they are regularly updated. The Plantwise Pesticide Red List is available on the Plantwise knowledge bank: www.plantwise.org/pesticide-restrictions Rotterdam Convention on the Prior Informed Consent Procedure for Certain Hazardous Chemicals and Pesticides in International Trade: www.pic.int Stockholm Convention on Persistent Organic Pollutants: chm.pops.int Montreal Protocol on Substances that Deplete the Ozone Layer: www.ozone.unep.org The WHO Recommended Classification of Pesticides by Hazard and Guidelines to Classification 2009: www.who.int/ipcs/publications/pestici... 86 Plantwise Diagnostic Field Guide


Annex 4: Glossary of terms Term Definition Active ingredient The part of a pesticide mix that has the effect of killing an organism. Acute The opposite of chronic, a one-off severe event (which may of course reoccur after a period of absence). Annual A plant that will grow from seed and produce more seed in less than one year. Arthropods Jointed legged animals covered with a hard external skeleton, including insects, mites, spiders, crabs, millipedes, etc. Bactericide A product that kills bacteria. Antibiotics are occasionally used in agriculture but are costly, are often not readily available and increase the risk of drug resistance in bacteria. Copper is the most widely used bactericide. Bacterial gums Glue-like material produced by bacteria. Blight A widely used term that is quite confusing as it can mean different things. Generally involves death and necrosis of large areas of tissue. Biological control The use of living organisms (e.g. insects, nematodes, fungi) to suppress populations of (or biocontrol) pests. Bore hole A small tunnel eaten into a plant (stem, fruit, tuber, etc.) by an insect or insect larva. Canker Open wound on the woody part of a tree caused by a pathogen, often has raised edges. Cell A tiny enclosed part of the plant which is far too small to be seen. Chronic Long term and ongoing (cf. acute). Concentric Rings of circles one inside the other so that it appears like a target. Cyst (nematode) The swollen body of a nematode full of eggs and attached to the root system. Deficiency To have a shortage of something. Deformed Not in its usual or expected shape. Determinate Will grow to a certain (pre-determined) size and no more, the opposite of indeterminate which describes things that will continue to grow. Diagnosis The process of determining what the cause of one (or more) symptom is. Disease Abnormal growth of a plant caused by microorganisms. Dormancy/dormant Remaining alive but not active. Dose Quantity of pesticide applied per individual or per unit area or weight. Drift Spray or dust carried by natural air currents beyond the target area. Economic injury level The lowest pest population density that will cause economic damage. Economic threshold The pest population level at which control measures should be started to prevent the pest population from reaching the economic injury level. Frass Particulate faeces/excrement of insects. Formulation The blend of chemicals in a pesticide. Fungicide Pesticides intended to kill fungi, usually prior to infection. Gall Abnormal growth (swelling) of plant tissue in response to a pest. Grub Beetle larva which is thick bodied with a well-developed head and true l▯egs, no pseudo legs and usually sluggish in behaviour. Herbaceous The non-woody parts of a plant. Herbicide A pesticide intended to kill weeds. (also called weedicide) Honey dew Sugary material excreted by sap sucking insects often collected by ants. When it falls on leaves, it promotes the growth of sooty mould. Host The organism in or on which a parasite lives; the plant on which an insect fee▯ds. Annexes 87


Identification (of a pest) Identification (of a pest) to species (or as near as possible) –▯ compare with diagnosis. Infect (plants) To enter and establish a pathogenic relationship with a plant. Infection The process of being infected (with a pathogen or parasite). Infestation Being infested (covered in); usually by insects, mites or weeds. Insect Six legged arthropods. Insecticide A poison effective against insects. Integrated pest The management of pests using techniques that complement each other rath▯er than work management (IPM) against each other. Invertebrate An animal without a backbone or spine, e.g. arthropods, molluscs. Knowledge bank (KB) A large store of information held electronically. The Plantwise KB is on plant pests. Larva (plural, larvae) The part of a life cycle for many insects between the egg and the pupa. Leaf lamina Areas of the leaf between the leaf veins. Leaf vein Ribs of material fanning out into the leaf providing support and a plumbing system. Lesion Discrete area of necrotic host tissue caused by a pathogen or the toxic saliva of some insec▯ . Localised Restricted to limited areas. Maggot Fly larva (without a head capsule and with no legs). Mammals Warm blooded animals with fur. Metamorphosis The life cycle: egg-larva-pupa-adult or egg-nymph-adult in insects. Microorganism An organism too small to be seen with a hand lens. Mildew Visible fungal growth on plant surfaces. Mildew (downy mildew) Diseases that are usually characterised by the production of downy growth on the lower surface of leaves (usually pink or cream). They are caused by water moulds. Mildew (powdery Diseases characterised by the production of white powdery growth on the upper surface of mildew) leaves. Caused by true fungi. Mite A tiny eight-legged, spider-like animal; those on plants include pest and predator species. Monocotyledons A group of plants that includes bananas, palms, gingers, as well as maize, s▯orghum and all other grasses. Mosaic Mottled pattern on leaves often used to describe viral symptoms. It does▯ not describe any malformation of the leaf although leaf distortion may be associated with mosaic. It is similar to mottled but in a mosaic, the regions of different colours are more clearly defined. Mode of action The way in which a pesticide works, that is, how it kills the target pest. Mottled Used to describe the pattern of yellow and green on a leaf surface. Very similar to mosaic but the areas of different colours are less distinct in a mottle. Natural enemies Living species (including insects, mites, spiders and pathogens) that ▯kill pests. Necrotic Browning and cell death. Nematode A kind of tiny worm that cannot be seen in the field and causes plant ▯disease. Nitrogen fixing Those plants that (together with a bacterium) can convert nitrogen gas into usable nitrogen fertilizer. Nodule A small lump or bump (in this case a swelling that houses nitrogen fixing bacteria). Nutrients Sustenance and minerals. Nymph A young instar of an insect that does not go through complete metamorphosis. Oomycetes See water moulds. Ornamental A plant grown to look attractive and not for eating. Pathogen A microbial parasite. Pest Any organism that will reduce crop productivity, including fungi, bacteria, viruses and weeds as well as insects, mites, birds and mammals. Pesticide Any product used to kill pests. 88 Plantwise Diagnostic Field Guide


Parasite An animal or plant that forms an intimate relationship with a host, from which it obtains material (essential for its existence) to the detriment of that host. Predator An animal that eats others, e.g. an insect or mite that eats other insec▯ts or mites. Pustule Discrete area on a plant with fungal material swelling from it. Phytoplasma An infective agent that can cause disease in plants. Transmitted via insects (like a virus), it has no survival outside the host. Phytotoxic Poisonous to plants or part of plants. Recommendation Detailed advice on what action to take to overcome a particular problem. Resistance The natural or induced capacity of a plant to avoid or repel attack by pests. The ability of a pest to withstand the toxic effects of a pesticide intended to kill it. Rot A disease symptom in which plant material is softened and putrefied. Rust A group of biotrophic fungi that are characterised by the production of reddish orangey or yellow dusty pustules on plant surfaces. Rugose The leaf surface does not lie flat and is uneven and bumpy. Sawfly A class of insect pests whose larvae resemble caterpillars but are related to wasps. Sclerotia Tough resting bodies produce by Sclerotinia fungi. Sign The physical presence of a pest or its by-products. Smut A type of fungus that infects the developing seed and turns it into a bl▯ack powdery mass. Spore (plural, spores) The reproductive body of a fungus or water mould that can give rise to a new organism. Spores are small and can often remain dormant for prolonged periods. They serve similar roles (but are not the same) as seeds of higher plants. Sporulation The production of spores. Superficial On the surface only but can also mean not serious. Susceptible Capable of being infected; not resistant. Symmetry/symmetrical Left and right side appearing the same. Symptom The way in which a plant responds to a pest. Systemic Spreading throughout the plant. Target The region (or organism or species) intended to receive treatment. Threshold The level at which intervention is appropriate. Tissue The mass of plant material that makes up the plant organs: leaf tissue, root tissue, etc. Transmission The spread of an organism from one host to another. Toxic Poisonous. Toxin Naturally produced poison. Tuber Swollen underground storage organ often used as means of propagation, e.g. potato, yam. Vegetative planting materialMaterial used to increase the number of plants without the use of seed. Viral Pertaining to a virus. Virus Sub microscopic organism that can replicate in plants and cause disease. Volunteer plant A crop plant growing where the farmer did not intend it to grow, usually self-seeding, late germinating or growing from crop remnants. Water moulds Oomycetes; previously considered to be fungi but are now seen as a separate group of organisms (they are fungus-like). Webbing Layers or linings made of silk threads produced by insects or mites. Weed A plant that is limiting crop production by competing with the crop for light, water or nutrients. Xylem The tubes that carry water up stems to the leaves. Annexes 89


Annex 5: Photographic glossary of symptoms Invertebrate pests (usually insects but also slugs, snails and mites) are generally large enough to be seen and their presence is a diagnosis in itself. In contrast, pathogens which cause disease, such as fungi and bacteria, are generally too small to be seen and it is usually the symptoms that are used to identify the cause.There are exceptions to this and sometimes you can see the pathogen (e.g. fruiting bodies of witches’ broom on cacao) or fail to see the invertebrate pests (e.g. if the pest is no longer on the damaged plant or it is too small or too well concealed). Use your skill and training to interpret the photographs here and compare them with samples brought to you by farmers or which you find in the field. Note that no images are provided for some symptoms such as fruit drop or leaf fall as these are considered sufficiently self-explanatory. 90 Plantwise Diagnostic Field Guide


Leaves and young stems droop down due to lack of water WILTED reaching them. Woody parts of plants cannot wilt, only the attached leaves. Bean plants wilting and yellowing, these two symptoms are Squash plants wilting due to shortage of water. The leaves are commonly seen together. drooping but the plants have not yet collapsed. Robert Reeder, CABI Gerald Holmes, Valent USA Corporation, Bugwood.org Sweet potato wilting. The leaf will not survive in this wilted statSingle capsicum pepper plant wilting. Note fully healthy and will become dried and necrotic. neighbouring plants. Gerald Holmes, California Polytechnic State University at San Luis Gerald Holmes, Valent USA Corporation, Bugwood.org Obispo, Bugwood.org Annexes 91


Leaves are normally green but when they lose their green colour they often become yellow. The cause of the yellowing may be on a different part of the plant to YELLOWED the yellowed leaves. Although yellowing is an extremely common symptom, the pattern of yellowing, e.g. older leaves or leaf veins can be diagnostic. Leaves can turn yellow or can be yellow when they are produced. The yellow peach leaves contrast strongly with the healthy one below. Notice how the leaf veins have remained green, this can be a diagnostic feature in some cases. Eric Boa, CABI L.S. Murphy, International Plant Nutrition Institute Dramatic contrast between the healthy wheat on the left and the Yellowed leaves at the top of the plant are often smaller than diseased on the right. green ones; this is because the plant is under stress. Keith Weller, USDA Agricultural Research Service, Bugwood.org Eric Boa, CABI 92 Plantwise Diagnostic Field Guide


Leaves have changed colour from green (but are not yellow). ABNORMAL COLOUR They often turn purple or red. This can be a sign of stress and the cause of the stress may be some way from the symptom. Some plants have colour in the leaves even when healthy, make sure Reddening of the leaves may be associated with loss of the green you know what a healthy plant looks like before looking at symptoms.colouration. It may also be a sign of aging. In this pineapple the red colouration is more pronounced than usual. Paul van Mele, Agro Insight Julien Lamontagne-Godwin, CABI Reddening of banana can be a sign of stress. Some plants may turn red much more readily than others and for some ornamental plants the abnormal colours can be part of their appeal. International Plant Nutrition Institute Julien Lamontagne-Godwin, CABI The lower leaves have gained the red colour, the upper leaves are Note that it is the borders of the leaf that are turning red and the only slightly coloured. middle remains green. This may be diagnostic. D. Janaki, International Plant Nutrition Institute Dr Prakash Kumar, CABI Annexes 93


Stunted plants are usually at the same developmental stage STUNTED but smaller due to conditions (caused by pests, nutrients etc.). If a plant has been eaten by a mammal then although it is smaller, it is not considered to be stunted. These two wheat plants are about to produce an ear but the one on theYoung Brassica seedlings; those on the left are smaller but with right will produce only a small yield. The whole plant (including the just as many leaves as the healthy plants on the right. roots) is small compared to the healthy one on the left. Phil Taylor, CABI Phil Taylor, CABI The taro plant on the right is the same age as that on the left but muchAs these plants were all grown from the same seed, it is clear smaller. The leaf stalks, the leaf lamina and the roots are not showingthat there is something different about the soil that is reducing any obvious symptoms but the whole plant is stunted. the growth of the wheat plants on the left, relative to those on the right. They are smaller, have fewer leaves and the tips of the leaves have turned yellow. Scot Nelson, University of Hawaii CIMMYT 94 Plantwise Diagnostic Field Guide


The tip of the plant is dead and the effect may spread DIEBACK down the stem affecting the immature leaves. Dieback does not include symptoms that spread up the plant. There are no other symptoms on this avocado except for the The very end of this coffee branch is wilting and the leaves are dying; drying/necrosis at the tip. the leaves further down the stem are beginning to show symptoms. Eric Boa, CABI Scot Nelson, University of Hawaii Severe blackening and death of the very tip of this citrus shoot. The tip of this sugarbeet plant is unable to grow, and the leaves There are no other symptoms on the plant. are not developing. Phil Taylor, CABI L.S. Murphy, International Plant Nutrition Institute Annexes 95


Patterns of yellow or brown and green stripes on the leaves STREAK or stems. These are common on grasses but can occur on bananas too, the pattern of leaf veins create the effect. These leaf spots have spread up and down the leaf creating a Commonly seen on banana, these brown and yellow streaks are streak-like pattern. running at right angles to the midrib of the leaf. Phil Taylor, CABI Phil Taylor, CABI The maize leaf is showing alternate white and green stripes The discolouration on the maize leaf runs up and down the leaf which are considered to be streaks. creating a streak. Phil Taylor, CABI Dr Prakash Kumar and Dr Manoj Kumar Sharma 96 Plantwise Diagnostic Field Guide


A discrete zone on a leaf that is a different colour from LEAF SPOT the remainder of the leaf. Most leaf spots are caused by a fungal, water mould or bacterial infection. Leaf spots on cassava clearly seen contrasting against the green These discrete leaf spots on coffee consist of a pale interior leaf. surrounded by a dark border with a yellow zone around that. Robert Reeder, CABI Scot Nelson, University of Hawaii Note that these leaf spots are all of a similar size and they have a Circular leafspots with a clearly defined border. Notice how they yellow border, partially limited by the leaf veins. These observations reach a maximum size. can be important in diagnosis. Scot Nelson, University of Hawaii Scot Nelson, University of Hawaii In some cases the leaf spots are creating such a drain on the leaf These leaf spots have no yellowing around them; pale material is that the areas between the leaf spots turn yellow, as is happening in the centre of the leaf spot and brown dead material is around here on the leaf of this rose. the outside, directly against the green healthy material. Phil Taylor, CABI Phil Taylor, CABI Annexes 97


A discrete zone on a leaf that is a different colour from PUSTULES the remainder of the leaf. Most leaf spots are caused by a fungal, water mould or bacterial infection. Dusty pustules on bean leaf, yellow regions are infection sites that Pustules appear more waxy on leek. have not yet broken through the leaf surface. Phil Taylor, CABI Phil Taylor, CABI Pustules are often brightly coloured (orange and brown), but can be Pustules are elongated and in chains along the length of the leaf black or white as shown in this photo. due to the leaf veins. Scot Nelson, University of Hawaii Scot Nelson, University of Hawaii Minor host reaction around these pustules on coffee. Dusty brown pustules on ground nut. Robert Reeder, CABI Scot Nelson, University of Hawaii 98 Plantwise Diagnostic Field Guide


Many pests eat leaves leaving characteristic marks where the leaf material has been eaten away. Note that many small insects (including aphids, scales, whitefly, CHEWED mealybug, thrips) and mites do not chew leaves. Look for frass near the damage as that can often assist in diagnosing the pest. The damage caused has not made holes through the leaf but has This eggplant leaf has been eaten. The holes are mostly between just eroded the surface. The brown regions are due to the healing the veins, and although the leaf has been extensively eaten, it is reactions of the leaf and are not a rot. not considered to be distorted. The leaf is normal in shape and size but with portions eaten. Phil Taylor, CABI Phil Taylor, CABI This banana leaf was attacked by two boring insects when The very edges of these bean leaves have been chewed. immature, i.e. the insects ate through the leaf when it was still rolled up in the pseudostem. Once the leaf unfolds, the lines of holes appear. Phil Taylor, CABI Phil Taylor, CABI Annexes 99


This phrase includes buckled, wrinkled or puckered leaves BLISTERED where the leaf is not truly blistered but it will not lie flat. The correct term for this symptom is ‘rugose’ but here we include it under blistered. This distorted cotton leaf has a blistered appearance. The blistered regions may be a different colour to the remainder of the leaf as in this photo. Gerald Holmes, Valent USA Corporation, Bugwood.org Phil Taylor, CABI The blistering can be associated with other forms of distortion Blistered and misshapen tomato leaf. whereby the leaf has folded or twisted as well as blistered. Gerald Holmes, California Polytechnic State University at San Luis IITA Image Library Obispo, Bugwood.org 100 Plantwise Diagnostic Field Guide


DISTORTED Leaves or fruits grow into an unusual shape due to a pest OR the leaves are manipulated into an unusual position once formed. In this severe leaf distortion, notice The leaves appear normal except that they This cassava leaf has grown distorted and how some leaflets are severely affected are curled at the edges, forming these has developed yellow areas. whereas others close by are healthy. boat-like cupped structures. Phil Taylor, CABI Phil Taylor, CABI Julien Lamontagne-Godwin, CABI This potato plant has very small, distorted The leaf lamina is extremely reduced on Tiny, curled and distorted leaves leaves. this papaya giving the appearance that it clustering around the tip of the plant. may have been eaten but the plant has grown into this shape. Julien Lamontagne-Godwin, CABI Robert Reeder, CABI Robert Reeder, CABI This lime appears healthy except for the It is not just the above-ground regions These limes are misshapen and lopsided. lumps covering the surface. of the plant that can become distorted. Here the lower cassava tuber appears to be constricted at various points along its length. This is a very distinctive symptom. Phil Taylor, CABI Robert Reeder, CABI Phil Taylor, CABI Annexes 101


Small and clustered leaves. Remember that a leaf has to be much smaller than normal (but otherwise appearing LITTLE LEAVES healthy) to be considered a ’little leaf’. Leaves which are smaller due to a plant being under stress are not considered to be ‘little leaves’. The symptoms of little leaf and witches’ broom are similar and The symptom can affect the whole plant or just a section of it. often go together. In each of the these cases, notice how the leaves appear healthy but extremely small. Eric Boa, CABI Eric Boa, CABI Phil Taylor, CABI Eric Boa, CABI 102 Plantwise Diagnostic Field Guide


An unevenness in the greenness of the leaf, with yellow areas mixed with green areas, giving a mottled or patchwork pattern effect (unlike ‘yellowed’▯ where the colour tends to be a uniform block across large areas of the leaf). The whole leaf may turn yellow or the yellowing may start from the margins inwards or the LEAF MOSAIC centre outwards. Sometimes the regions are not so distinct and the patches of yellow and green fade into each other. Flecking and silvering of leaves (often from insect or mite feeding) can produce symptoms that look superficially like a mosaic but are generally not considerd such if the colouration is only in the surface layers, and a hand lens may be required to see this. This taro leaf has patterns of yellow and On close inspection this leaf is seen This citrus shoot has a marbled effect, green within it. Not a typical mosaic but can to be made up of small areas of yellow which can be considered mosaic. be considered in this category. Often called surrounded by green and is not an even feathering due to the ‘feather-like’ pattern. yellow colour. Phil Taylor, CABI Robert Reeder, CABI Phil Taylor, CABI The symptoms here are of stange yellow The patches of yellow and green on this An extreme mosaic with clearly defined patterns especially around the leaf veins. leaf are not a typical mosaic but may be lines between the green and yellow zones. Not a typical mosaic but can be classed considered as such. Mosaics are rarely this contrasting; more as one. often the transition between green and yellow areas is more diffuse. Robert Reeder, CABI Julien Lamontagne-Godwin, CABI Scot Nelson, University of Hawaii Annexes 103


The edges of the leaf become brown and die (necrotic). LEAF EDGE SCORCH This condition always has an abiotic cause. Bacterial infections spreading from the edges of the leaf are not considered leaf edge scorch. The tips of these leaves have died and become necrotic. Note the very sharp divide between the healthy leaf and the dead region near the tip. Eric Boa, CABI Eric Boa, CABI The very edge of this lettuce leaf has turned brown and died. The edge of this leaf is under stress; the edge is brown but there is a yellow zone between it and the healthy green area. Phil Taylor, CABI M.K. Sharma and P. Kumar, International Plant Nutrition Institute The edges of this mango leaf have dried up and died. The blistering of this leaf is natural and is unrelated to the leaf edge scorch. Phil Taylor, CABI Daren Mueller, Iowa State University, Bugwood.org 104 Plantwise Diagnostic Field Guide


The growing tip splits into many smaller competing WITCHES’ BROOM shoots or branches that cluster together. Often associated with little leaf. The shoots are competing with each other, creating a small This tree is full of witches’ brooms; each clump on the branches witches’ broom on this bramble. is a bundle of small leaves forming a broom. Robert Reeder, CABI Phil Taylor, CABI This small bundle of branches is a witches’ broom; they are all This longan tree is full of witches’ brooms, all of which are growing from the same point. showing little leaf. Phil Taylor, CABI Phil Taylor, CABI Annexes 105


This is a sign rather than a symptom as you are not only able to see the symptoms but the microorganism is present in such numbers that it is visible SURFACE GROWTH to the unaided eye. Not all surface growth is a problem and can be a secondary problem caused by something else. It is all on the leaf rather than in the▯ leaf and if it is true surface growth, it is possible to wipe it off with a wet finger. The light green material growing on the leaf This white growth over the surface of A very common problem usually associated is not causing the damage to the edge of these grapes is a common problem in with insect attack. This is sooty mould the leaf. grape production. growing on the sugar excreted by insects on the surface of the sapodilla. Phil Taylor, CABI Julie Beale, University of Kentucky, Bugwood.orgPhil Taylor, CABI The white powdery material can be wiped This growth is pink and fluffy and found This reddish surface growth can be wiped off easily. on the underside of leaves. from the upper surface of the leaf. Gerald Holmes, Valent USA Corporation, Bugwood.org Phil Taylor, CABI Phil Taylor, CABI This orange is almost completely This papaya fruit has a whiteish growth This onion leaf has a purple coloured consumed by the the pathogen, seen as spreading over the surface. downy material covering certain areas. white and green areas on the surface. Robert Reeder, CABI Scot Nelson, University of Hawaii Phil Taylor, CABI 106 Plantwise Diagnostic Field Guide


CANKERS (STEM LESIONS) An open wound in woody or semi-woody stems. This cherry tree has a classic canker in the side. Notice how the This is a very early canker that is just beginning to form on edges of the canker are bulging. blueberry. The stem has split and the characteristic shape is beginning to form. Phil Taylor, CABI Gerald Holmes, Valent USA Corporation, Bugwood.org An old and mostly dead canker on beech; the swollen edges of Young canker developing on walnut. The infection may girdle the the canker remain although the canker does not appear active. stem in which case the shoot will die. Alternatively the plant will seal it off so that it will become a canker. Phil Taylor, CABI Curtis Utley, Colorado State University Extension, Bugwood.org Annexes 107


The entry or exit hole of an insect pest, sometimes BORE HOLES (STEM/FRUIT) surrounded by frass. It is often the laval stages that produce the bore hole, but it can be the adults too. Insect bore hole in banana stem. Insect bore hole in avocado. Julien Lamontagne-Godwin, CABI Eric Boa, CABI Insect bore hole in tomato. Maize shoot borer and its bore hole damage, with associated secondary rot and scattered frass. Julien Lamontagne-Godwin, CABI Mattthew Cock, CABI 108 Plantwise Diagnostic Field Guide


The plant material grows in an abnormal way, often as a GALLS/SWELLINGS swelling, for the benefit of the pest. Galls on roots, the roots are swollen and misshapen. Galls on woody twigs. These galls are growing in a disordered fashion and are not determinate. Eric Boa, CABI Phil Taylor, CABI Galls on the underside of tree leaves. Gall on buffalo gourd stem which has been cut open to reveal the insect larva inside. Phil Taylor, CABI Whitney Cranshaw, Colorado State University, Bugwood.org Insect galls on oak. Note that they are all precisely the same size. Spectacular galls on crack willow. Robert Reeder, CABI Robert Reeder, CABI Annexes 109


ROTS The tissue has to become soft and slimy (in addition to brown) to be considered a true rot. This sweet potato tuber has two areas of infection which are Fruit is especially prone to rotting as it is often sweet and soft. spreading through and across the tuber. These bananas are rotting from one end and it is spreading down the length of the banana. Charles Averre, North Carolina State University, Bugwood.org Scot Nelson, University of Hawaii The wheat roots on the left are blackened and rotten compared Classic rot on cacao; the rot is spreading up from the base of the with the healthy ones on the right. pod (surface growth is also visible on the outside of the fruit in the blackened area). William M. Brown Jr., Bugwood.org Phil Taylor, CABI 110 Plantwise Diagnostic Field Guide


This usually refers to streaks that are only visible once the stem has been split; make sure you compare it with a healthy stem. STAINING The insides of a tuber can be discoloured even though the material is not rotting. The discolouration on the outside of a fruit due to rotting or surface growth is not considered staining. Internal staining within a banana stem split lengthways. Internal staining within a banana stem cut crossways. Julien Lamontagne-Godwin, CABI Eric Boa, CABI The bark has been removed on this cinchona tree to reveal the Internal staining within a radish. Depending on whether the internal staining beneath. material had softened this could also be considered as rot. Julien Lamontagne-Godwin, CABI Eric Boa, CABI Brown flecks on the cut surface of a capsicum stem. Internal staining is a common symptom in field-grown tomatoes. Clemson University – USDA Cooperative Extension Slide Series, Phil Taylor, CABI Bugwood.org Annexes 111


DRYING Severe localised stress, often associated with dieback. On one small branch of this pear, the leaves have dried and Some branches on this coffee have dried. The whole plant is shrivelled. The remaining leaves appear unaffected. wilting but there are some areas where the material has dried. Phil Taylor, CABI Robert Reeder, CABI This eggplant has dried, the leaves have all shrivelled and turned This walnut fruit is drying. The condition is similar to rot but the brown, and the plant is dead or dying. material has not become soft and slimy but has remained hard and dry. Phil Taylor, CABI Andrej Kunca, National Forest Centre – Slovakia Complete drying of a coffee plant. Drying of isolated branches is a common symptom on mango. Robert Reeder, CABI Phil Taylor, CABI 112 Plantwise Diagnostic Field Guide


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Plantwise Diagnostic Field Guide A tool to diagnose crop problems and make recommendations for their management Compiled by Phil Taylor Every day, extension workers are bombarded by questions from farmers on how to overcome problems with their crops. The huge variety of crops grown and the numerous biotic and abiotic factors that can reduce crop quality and yield make it very difficult to diagnose all plant health problems and give good recommendations to farmers. The Plantwise Diagnostic Field Guide provides the essentials of diagnosing plant health problems, covering all the main problems that crops encounter (nine groups of pests and two abiotic conditions) to group level. It includes summary sheets that cross-reference symptoms with causes, line drawings of the major insect pest groups, and photos of the symptoms of the major microbial pest groups and symptoms associated with mineral deficiencies. This diagnostic field guide has a full colour glossary to allow for accurate symptom description. It also has a section that explains how to tell the difference between similar symptoms with different causes. Following a successful diagnosis, the farmer still requires advice on how to manage the problem. Basic principles of giving good recommendations are summarised in this book. Regarding pests (pathogens, animals and weeds), there is an emphasis on integrated pest management (IPM) with additional information on avoidance of the most toxic pesticides. CABI publishes high-quality books on all aspects of agriculture and applied life sciences for practitioners, researchers and students throughout the world. www.cabi.org/bookshop Space for bar code with ISBN included