Lime, Citrus aurantifolia
, is a small perennial evergreen tree in the family Rutaceae grown for its sour fruit. The lime tree is irregularly branched and possesses sharp spines. The leaves of the tree are elliptical with small rounded teeth around the edge. The leaves can grow 4–8 cm (1.6–3.2 in) in length. The tree produces small, cupped white flowers and yellowish-green fruit which is round or egg-like in shape. Lime trees can reach 5 m (16 ft) in height and can produce fruit for many years. Lime may also be referred to as sour lime, key lime, Mexican lime, acid lime or West Indian lime and originated in southeast Asia.
Lime fruits on the tree
Lime fruit growing on the tree
Lime fruit close-up
Limes sliced open
Lime fruit is commonly used to make juices and cordials or for extraction of citric acid. It may be used as a flavoring in cooking. Lime oil can be extracted from the peel of the fruit.
Lime is a tropical plant and the trees grow best in regions with hot summers and warm winters where temperatures are typically between 25 and 30°C (77–86°F). Limes are more sensitive to cold than lemons and trees are killed by freezing conditions without protection. Lime trees are the most drought tolerant of all citrus trees conditions and will grow best when planted in a well-draining sandy loam with a pH between 6.0 and 7.5. Soil must be deep enough to permit adequate root development. Lime trees will grow best when positioned in full sunlight.
Unlike many other fruit bearing trees, limes are commonly propagated from seed as the will produce offspring that is true to the parent plant. In some cases, trees are propagated by removing offshoots from the main trunk (called suckers) and replanting although, if the tree is grafted, it should be noted that the suckers will be the same variety of the rootstock.
The best time to plant citrus trees is in Spring after all danger of frost has passed in your area. Trees should be planted at or higher than the level of the nursery pot. Once the tree is positioned in the planting hole, backfill the soil by about half and water to allow the soil to settle around the lower roots before filling in the hole. The newly planted tree should be watered every few days.
Newly planted trees require proper irrigation to ensure they become established. During the first year, water should be applied at the base of the trunk so that the root ball is kept moist to allow the roots to establish in the soil. Newly planted trees should be provided with water every 3–7 days. The soil should be moist, but not wet. Trees planted in sandy soils will require water more frequently. Young trees will also require a light application of fertilizer every month in the first year. Lime trees will need protected from cold temperatures to prevent damage. Soil can be mounded up around the trunk during the winter and removed in the Spring. Trees can also be protected by stringing christmas lights in the branches and covering the leaves with tarps. In areas with cold winters, lime trees are best grown in containers which allows them to be moved indoors during the winter months.
CABI Crop Protection Compendium. (2014). Citrus aurantiifolia (lime) datasheet. Available at: http://www.cabi.org/cpc/datasheet/13438. [Accessed 10 February 15]. Paid subscription required
Gilman, E. F. & Watson, D. G. (1993). Citrus. University of Florida. Available at: http://hort.ufl.edu/database/documents/pdf/tree_fact_sheets/citsppa.pdf. [Accessed 10 February 15]. Free to access
Morton, J. (1987). Mexican lime. In Fruits of warm climates. Creative Resource Systems, Inc. Available at: http://www.hort.purdue.edu/newcrop/morton/mexican_lime.html. [Accessed 10 February 15]. Free to access
Timmer, L. W., Garnsey, S. M. & Graham, J. H. (2000). Compendium of Citrus Diseases. American Phytopathological Society Press. Available at: http://www.apsnet.org/apsstore/shopapspress/Pages/42481.aspx. Available for purchase from APS Press
Common Pests and Diseases
Category : Fungal
Anthracnose (Colletotrichum acutatum) on Citrus latifolia.
Leaves dropping prematurely; leaves covered in dark fungal spores; red to green or black streaks on the mature fruits.
If disease is damaging then appropriate fungicides should be applied to whole tree.
Armillaria root rot (Mushroom root rot)
Armillaria spp. often produce abundant quantities of white spores.
Armillaria mycelial mat
Armillaria root rot (Armillaria solidipes) fruiting bodies
Trees may wilt suddenly and collapse or decline slowly; leaves become chlorotic and drop from tree; if large parts of root are destroyed then whole canopy is affected; trunk may have area of rotting bark at the base; lesions on the trunk resemble Phytophthora gummosis; clusters of mushrooms may be present at the bottom of the tree and fan shaped mycelial mats are often present between the bark and the wood.
Disease is difficult to control once it becomes established in an orchard; affected trees showing signs of decline should be removed along with as much of the roots system as possible; area where infected tree was should not be replanted with health citrus for a period of at least one year; fumigating soil can help to reduce soil inoculum but is not always completely effective.
Black root rot
Small brown-black lesions on roots which may coalesce and turn entire root black; root cortex may slough off to reveal the vascular tissue below; leaves of plant may be chlorotic.
Keep glasshouses well lit and warm during winter to encourage vigorous root growth; use good quality potting soil which provides goo aeration.
Water-soaked or black lesions on leaf petioles;which rapidly expand along the leif midrib; cankers on twigs and branches; twigs may be girdles and die; leaves turning black and dying; black lesions may be present on fruit.
In areas where disease is severe, copper fungicides should be applied in Fall and WInter prior to the first rains.
Symptoms of Diaporthe citri on citrus twig. The pycnidial conidiomata are visible.
Melanose (Diaporthe citri) infected fruit
Small brown sunken spots which become raised and surrounded by a yellow halo; lesions eventually turn corky in texture; severe infections can cause newly emerging leaves to be crinkled and distorted; if infection of fruit occurs soon after petal fall, the pathogen causes large lesions on the fruit surface which may coalesce to produce large patches; late infection of fruit causes discrete pustules on the fruit.
If young trees become infected, it is possible to control the disease by pruning but this is not usually feasible for older trees; fungicides must be applied frequently in order to control the disease.
Category : Bacterial
Twig symptoms of citrus canker (Xanthomonas citri)
Leaves symptom of citrus canker (Xanthomonas citri)
Raised lesions on leaves, often at leaf margin or tip; lesions may also be present on twigs and fruits; young lesions are usually surrounded by yellow halo; depressed brown craters formed from collapse of lesions.
If the disease is introduced to an area, all infected trees should be removed and destroyed; in areas where disease is endemic, windbreaks can help to reduce disease severity; cultural control of the disease should focus on controlling leaf miner populations, utilizing wind breaks and applications of copper sprays.
Category : Other
Huanglongbing (Citrus greening, Yellow dragon disease)
Candidatus Liberibacter asiativus
Candidatus Liberibacter africanus
Candidatus Liberibacter americanus
Citrus greening (Candidatus Liberibacter asiaticus)
Citrus greening (Candidatus Liberibacter asiaticus) infected leaves
Citrus greening (Candidatus Liberibacter asiaticus) infected leaves
Symptoms of citrus greening (Candidatus Liberibacter asiaticus)
Yellowing of one limb or one area of canopy; yellowing of leaf veins; blotchy mottling on leaf blades; twig and limb dieback; fruits dropping prematurely; small upwardly pointing leaves; small, misshapen fruit; fruit very bitter
(i) Cultural control
Once a tree becomes infected with HLB, it cannot be cured. Control is therefore reliant on preventing the disease occurring in the first place and this is achieved through strict quarantining to prevent the introduction of citrus psyllids to areas which are currently free of the pest. Areas which are subject to quarantine have restrictions placed on the movement of citrus plants, fruit, equipment and items made from citrus.
Infected trees should be removed as quickly as possible from plantations and destroyed. Identification of infected trees should be achieved through several surveys to ensure that infected trees which are not yet showing symptoms are identified. In Florida, the recommendation is to scout groves at least 4 times a year for disease symptoms.
(ii) Control of citrus psyllids
Citrus psyllid populations can be controlled through the application of chemical sprays. Insecticides have proved very effective at controlling T. eryreae in South Africa where systemic insecticides are applied to the tree at the base of the trunk. In areas of the USA, Citrus health management areas (CHMAs) have been created to encourage neighbouring growers to work together to prevent the disease. Control strategies which have been implemented by the program include scouting, mapping and large-scale spraying to control citrus psyllids.
Category : Viral
Citrus tristeza virus (CTV)
Symptoms of tristeza virus on lime leaf
Pitting on lime stems caused by infection with tristeza virus
Light green foliage; poor new growth; leaves may be dropping from tree; young trees blooming early; severely infected trees are stunted and bushy in appearance with chlorotic leaves and brittle twigs; some strains of the virus cause elongated pits in the trunk and branches which give the wood a rope-like appearance
Quarantine procedures are used to control tristeza and prevent the pathogen from entering areas which are currently free of the disease
Category : Insects
Aphids (Black citrus aphid and Brown citrus aphid)
Brown citrus aphid (Toxoptera citricida)
Brown citrus aphid (Toxoptera citricida) infestation
Leaves curling; leaves and twigs covered in sticky substance which may be growing sooty mold; trees may show symptoms of tristeza (see entry); insects are small and soft bodied and are black in color.
Aphid numbers tend to naturally decline as leaves harden off but can be a problem on young trees or varieties which continually produce flushes of new growth; pesticides are not generally recommended due to resistance and trees can withstand a high degree of leaf curling.
Citrus leaf miner
Adult citrus leafminer moth
Citrus leafminer larvae
Citrus leafminer damaged leaves
Citrus leafminer infected leaves
Thin, winding trails on leaves; heavy infestation can result in curled and distorted leaves; adult leafminer is a tiny moth which lays its eggs in the leaf; larvae hatch and feed on leaf interior.
Insecticide application are rarely warranted in mature orchards as yields are unaffected; young trees should be treated with appropriate insecticides to prevent retarded growth; cultural control methods include removal of water sprouts from trees and refraining from pruning live branches more than once a year to encourage uniform growth flushes which are short in duration.
Soft scales (Black scale, Brown soft scale , Citricolla scale)
Florida red scale (Chrysomphalus aonidum)
Pyriform scale (Protopulvinaria pyriformis)
Citricola scale (Coccus pseudomagnoliarum)
Soft scale (Coccus capparidis)
Citricola scale (Coccus pseudomagnoliarum) infestation
Leaves covered in sticky substance and may have growth of sooty mold; reduced tree vigor; leaves and/or fruit dropping from plants; presence of black, brown or gray flattened scales on leaves, twigs and/or branches.
Organically acceptable methods of control include the application of horticultural oils and preservation of natural enemies.
South African citrus thrips (Scirtothrips aurantii) damage
California citrus thrips (Scirtothrips citri)
Insect feeds under sepals of young fruit and causes a ring of scarred tissue as the rind expands; adult thrips are orange-yellow in color.
Insecticide application is rarely required as healthy trees can withstand heavy feeding damage; insecticides can actually promote thrips populations by stimulating reproduction.