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Garlic (Allium Sativum)

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See questions about Garlic (Allium Sativum)

Description

Garlic is one of the most used crops among the cultivated Allium species. It is a perennial flowering plant that grows from a bulb that contains outer layers of thin, whitish sheaths or skin that enclose various lobes known as cloves. One garlic bulb may contain 10 to 20 edible cloves that are asymmetrical in shape, except for the small ones, which are close to the center. Cloves, which are also covered by protective whitish skin, have a distinctive smell.

Garlic, either in fresh or powdered form, is mainly used as a seasoning or condiment for flavoring food. It also has nutritional value, as raw garlic contains protein, starch, small amounts of fat and sugar, and high levels of potassium and vitamin C. Furthermore, garlic is widely valued for its medicinal importance as it contains bioactive constituents that are believed to help the body fight viral, fungal, and bacterial infections, among other health benefits such as lowering blood sugar and cholesterol levels, among others.

In addition, garlic extracts have pesticide properties that play a vital role in protecting plants from some pests and diseases like African armyworm, downy mildew, and rice bugs, among others. While it is beneficial in organic farming, its use as a pesticide should be moderated as it can kill beneficial soil bacteria and insects due to its broad-spectrum effects.

Garlic is believed to have originated in Central Asia (China). It then spread to the Mediterranean region in ancient times and was already known in Egypt by 3000 BC. Today, garlic is cultivated across the globe at latitudes ranging from 5 to 50 in both the northern and southern hemispheres.

Crop Details 

Scientific Name: Allium Sativum

Common Name: Kitungu saumu (Swahili




Uses & Benefits

Garlic is primarily used for flavoring food and can be dried, ground or powdered for this purpose.




Varieties

It is difficult to identify the wild primogenitor of common garlic due to the presence of numerous cultivars (clones). This makes it difficult to classify the clones. Despite this, there are two well-known garlic varieties, namely, cv. group Ophioscorodon, also known as hard-necked garlic, and cv. group Common Garlic, commonly referred to as soft-necked garlic (CABI, 2019).

While the cv. group Common Garlic has a straight stalk, the cv. group Ophioscorodon, on the other hand, has a curvy scape. In addition, hard-necked garlic is best suited for the northern climate, while soft-necked garlic flourishes in southern climates. The two varieties do well in Kenya, although the soft-necked is more commonly planted.




Propagation

Basic Requirements

Temperature, and length of day are important factors in bulbing and bolting. Garlic is grown in a temperature-limited range of 9–28 °C. It is required that the propagules be exposed to 10–15 °C for 2 months to allow proper bulbing. Moreover, lower temperatures ranging from -2 to 6 °C are necessary for vernalization. Day length (>12 hours), on the other hand, stimulates clove formation. Garlic growth is easily adapted to all latitudes due to its wide genetic variation in response to temperature and day length. For instance, it is grown in the highlands around the equator to increase its growth. Also, garlic growth is recommended during the prevailing long-day season and at high altitudes in the tropics. In areas that experience long seasons of sub-freezing temperatures, mulching is advised to protect the plants from the cold. Mulching also conserves moisture and control weed growth.  

Garlic requires fertile, well-drained, non-crusting mineral soil, in organic matter to increase yields. It should also be planted in raised beds to allow good soil drainage, which is essential.

Garlic plants perform well in areas with low rainfall since excess rain and humidity are bad for their growth. Regular irrigation during dry seasons is advised, where moisture in the top 30 cm of the soil should be maintained during the entire growth period to attain maximum yields. However, in some areas, stopping irrigation three weeks before harvest is recommended to prevent rotting and skin color loss.

Growing from Seed

Prepare the soil a few weeks before planting for aeration; remove rocks and loosen the soil. While garlic can grow in soil with high organic matter, it can also grow in a variety of soil conditions and pH levels. A basal dressing of 200 kg/ha of triple superphosphate is recommended during soil tillage.

Garlic is usually grown as an annual crop. It is normally cultivated using cloves as seeds. To have quality and maximum yields, a farmer needs to plant healthy cloves. During seed selection, it is recommended that cloves planted should be of about equal weight (depending on cultivar) for uniformity purposes. The quantity of planting material is dependent on the size of the clove and the density of the plants.  

During planting, place selected cloves 8–10 cm apart within the rows and 15-20 cm between rows to leave enough space for bulbs to grow and mature well. The cloves should be planted with the pointed side up and the base down. Garlic plants are best grown as sole crops on raised beds alternated with furrows. Protect the garlic cloves through mulching.

General Care and Maintenance

Planting, watering, weeding, and harvesting are all done by hand.

Avoid under-watering or over-watering the plants to allow optimal bulb formation. In cases where there is no rain, light watering (one inch deep) is enough. Dripline irrigation is recommended during the dry season.

Remove weeds that might hinder the crops from accessing maximum light, water, and nutrients. This can be done by mulching, hand hoeing, or spraying herbicides.

80 kg/ha of ammonium sulphate is mixed with 50 kg/ha of potassium chloride and 80 kg/ha of urea and then applied as side dressings at 15, 30, and 45 days after planting.

Harvesting 

Garlic grows about 60 cm (2 feet) tall. The duration of subsequent growth and development phases strongly depends on the prevailing conditions. The total growing period varies depending on the area, where harvesting takes place 3–4 months after planting (in the tropics) to about 9 months (for winter garlic in temperate regions). Harvesting is done once the leaves start turning yellow and begin to dry up. Once ready, the farmer pulls the bulbs out of the soil using their hands. They are then tied in bunches for drying and later stored in a dry place with good ventilation to inhibit growth or decay.




References

Cabi Digital Library. (2019). Allium sativum (garlic). Retrieved on 2023-01-09 https://www.cabidigitallibrary.org/doi/abs/10.1079/cabicompendium.4250. 

FatSecret. (Feb 4, 2008). Food database and calorie counter: Garlic. FatSecret Website. Retrieved Jan 11, 2023,   https://www.fatsecret.com/calories-nutrition/usda/garlic?portionid=59114&portionamount=100.000

Infonet Biovision: Plant Extract: Garlic. Infonet Biovision Website. Retrieved Jan 11, 2023 https://infonet-biovision.org/PlantHealth/Plant-extract-Garlic

Mishra, R. K., Jaiswal, R. K., Kumar, D., Saabale, P. R., & Singh, A. (2014). Management of major diseases and insect pests of onion and garlic: A comprehensive review. Journal of Plant Breeding and Crop Science, 6(11), 160-170.

Welbaum, G. E. (2015). Family Amaryllidaceae, subfamily Allioideae. Vegetable production and practices, 267-288.

 




Common Pests and Diseases

Diseases

Category : Fungal

Downy mildew Peronospora destructor

Symptoms
Pale spots or elongated patches on leaves; gray-purple fuzzy growth on leaf surface; leaves turning pale then yellow; leaf tips collapsing
Cause
Fungus
Comments
Disease emergence favored by cool temperatures and leaf wetness
Management
Avoid planting infected sets; rotate crops to non-allium species for 3-4 years; plant in well-draining areas and do not overcrowd plants; destroy all infected crop debris; apply appropriate foliar fungicides taking care to apply thoroughly to waxy leaves

Purple blotch Alternaria porri

Symptoms
Small water-soaked lesions lesions on leaves or stalk with white centers; which enlarge to become zonate and brown to purple in color with red or purple margin surrounded by yellow zone; large lesions may coalesce and girdle leaf, killing any tissue between the lesions and the leaf tip; severely infected foliage may die
Cause
Fungi
Comments
Disease emergence favored by wet foliage, with sporulation occuring during the night during periods of high humidity
Management
Cultural controls include long rotations with non-hosts and the reduction of leaf wetness by planting in well-draining soil and timing irrigation to allow plants to dry adequately during the day; some fungicides are effective at controlling the disease but should be rotated for optimal control

Rust Puccinia porri

Symptoms
Small white flecks on leaves and stems which develop into circular or elongated orange pustules; severe infestations can cause leaves to yellow and die
Cause
Fungus
Comments
Favors high humidity but low rainfall; spores can be transported over long distances by wind
Management
No resistance known; use only disease-free seed and plant in well-draining soil; control weeds around crop; apply appropriate protective fungicide

White rot Sclerotium cepivorum

Symptoms
Older leaves yellowing; stunted growth; death of all leaves; fluffy white growth on base of bulb which spreads up bulb to storage leaves
Cause
Fungus
Comments
Once disease is established the field is unusable for garlic production; fungus can survive in soil for 20 years and is one of the most damaging diseases of Allium crops worldwide, causing major crop losses
Management
Fungicide treatment may not be effective at controlling white rot under conditions which are favorable to the fungi's development and control may have to rely on cultural methods: avoid transferring soil or plant material between sites; treat seeds with hot water prior to planting; use a long term rotation with non-allium crops; apply appropriate fungicides if available

Category : Viral

Mosaic Garlic mosaic virus (GarMV)

Symptoms
Mosaic patterns on leaves; chlorotic mottling or streaks on leaves; stunted plant growth and reduced bulb size
Cause
Virus
Comments
Transmitted by aphids; infections can be latent and produce no symptoms; infection in garlic are often found alongside other viruses such as onion yellow dwarf
Management
Plant virus-free cloves that were produced from meristem tip culture in virus-free conditions

Pests

Category : Mites

Bulb mites Rhizoglyphus spp.
Tyrophagus spp.

Symptoms
Stunted plant growth; reduced stand; bulbs rotting in ground or in storage; pest is a cream-white, bulbous mite <1 mm in length, which resembles a pearl with legs
Cause
Arachnid
Comments
Damage to plants by bulb mites allows secondary invasion by other pathogens and can cause bulb rots
Management
Do not plant successive crops of onion or garlic in same location; allow field to fallow to ensure that any residual organic matter decomposes completely - crop residues can harbor mite populations; treating garlic seed cloves with hot water prior to planting may help reduce mite populations

Category : Insects

Leafminers Lyriomyza spp.

Symptoms
Thin, white, winding trails on leaves; heavy mining can result in white blotches on leaves and leaves dropping from the plant prematurely; early infestation can cause yield to be reduced; adult leafminer is a small black and yellow fly which lays its eggs in the leaf; larvae hatch and feed on leaf interior
Cause
Insects
Comments
Mature larvae drop from leaves into soil to pupate; entire lifecycle can take as little as 2 weeks in warm weather; insect may go through 7 to 10 generations per year
Management
Check transplants for signs of leafminer damage prior to planting; remove plants from soil immediately after harvest; only use insecticides when leafminer damage has been identified as unnecessary spraying will also reduce populations of their natural enemies

Onion maggot Delia antiqua

Symptoms
Stunted or wilting seedlings; plant will commonly break at soil line if an attempt is made to pull it up; if infestation occurs when plants are bulbing, bulbs will be deformed and susceptable to storage rots after harvest; adult insect is a greyish fly which lays white, elongate eggs around the base of the plant; the larvae that emerge from the eggs are tiny and white and bore into the plant; mature larvae are about 1 cm (0.4 in) long with feeding hooks
Cause
Insect
Comments
Females can lay several hundred eggs during their 2-4 week lifespan; insect overwinters as pupae in the soil
Management
Management of onion maggots is heavily reliant on good snaitation; all onion bulbs should be removed at the end of the season as maggots will die without a food source; commercial onion growers must often rely on the application of appropriate granular insecticides and, in some cases, insecticide sprays are also required; home gardeners should try to remove any volunteer wild onion and chive plants as these can act as an infection source; floating row covers may help to protect plants and prevent females from laying eggs around plants

Thrips (Onion thrips, Western flower thrips) Thrips tabaci
Frankliniella occidentalis

Symptoms
Discolored, distorted tissue; scarring of leaves; severly infected plants may have a silvery appearance; insect is small (1.5 mm) and slender and best viewed using a hand lens; adult thrips are pale yellow to light brown and the nymphs are smaller and lighter in color
Cause
Insect
Comments
Onion thrips and western flower thrips have an extensive host range and can be introduced to garlic from other plants
Management
Natural enemies include some species of predatory mite, pirate bugs and lacewings; avoid planting onion in close proximity to grain fields as thrips populations build up on these plant in the spring; overhead irrigation of plants may help reduce thrips numbers; apply appropriate insecticides at first sign of thrips damage

Category : Nematodes

Lesion nematode Pratylenchus penetrans

Symptoms
Stunted plants; root system lacks fine roots; round or irregular lesions on roots
Cause
Nematode
Comments
Lesion nematode has one of the widest host ranges of any nematode; nematode enters the plant through the root epidermis and consumes cell contents
Management
Hot water dips can be used to control nematodes in bulbs; crop rotation is not usually very effective at controlling lesion nematodes due to its extensive host range
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