By Julie Christensen
With their arresting tart flavor, limes are most often used for their juice, which flavors dishes from key lime pie to margaritas to guacamole. Like all citrus trees, limes are heat-loving plants that only grow outdoors in USDA plant hardiness zones 9 through 11. When it comes to varieties, you have several options. Persian limes (Citrus latifolia) are the type most often found commercially. They’re large and sweet, with a mild lime flavor. Key limes (Citrus aurantiifolia) are smaller, with intense lime flavor and a thin skin. Kaffir limes (Citrus hystrix) have a tart, acidic flavor and a bumpy rind.
Lime trees have the same cultural requirements as all citrus trees, and most disease problems can be prevented or minimized by good care. Plant them in full sun in light, well-draining soil. The trees don’t tolerate heavy clay soils or those high in salt. Plant them in early spring so they have time to become established before the heat of summer arrives. Plant them so the top of the rootball sits 1 inch above the soil. This planting strategy can help prevent some fungal diseases, such as gummosis.
Lime trees, and in particular, young lime trees, can suffer from sunburn or sunscald, which causes peeling, damaged bark. Paint the trees with a mixture of one part white flat latex paint and one part water or use a commercial tree wrap.
Water lime trees once or twice a week during the growing season so the soil stays moist to a depth of 6 inches beneath the surface. It’s better to water deeply less frequently. Signs of overwatering include cupped, drooping leaves. If this occurs, let the soil dry out before watering again.
In spite of the above precautions, lime trees occasionally suffer disease and insect pests. Below are the most common problems you’re likely to see and strategies for treatment.
Black Sooty Mold
Black sooty mold is a fungal growth that is caused by aphid infestations. The aphids excrete a sticky substance called honeydew as they feed on the leaves and stems of the lime tree. The aphids alone usually cause only minor damage. The black sooty mold feeds on the honeydew. It forms a black, powdery substance over the leaves and stems, which is not only unattractive, but can be destructive. In severe cases, it can stunt growth and kill the leaves. The mold sometimes grows on the fruit, as well. To control black sooty mold, you must control the aphids. Spray the tree with a heavy stream of water to dislodge the aphids and remove the mold. Or spray the tree with insecticidal soap or oil. Use a product labeled for citrus trees, and apply it on overcast days.
Brown fruit rot causes tan or brown spots to develop on fruit. The disease can spread after harvest when diseased limes are stored with healthy ones. Spray the trees with a copper-based fungicide before the rainy season. Store affected fruits separately and use them immediately.
Stylar end rot causes brown spots to develop on the blossom end of the fruit. Decay enters these spots, destroying the entire fruit. To avoid stylar end rot, pick limes in the afternoon in dry weather. Handle them gently.
Citrus canker is a bacterial infection that causes brown or yellow spots on leaves, which can also spread to the fruit. To prevent the disease, spray trees with a copper-based fungicide in the spring. Space lime trees so they get adequate air circulation. Use soaker hoses, instead of overhead sprinklers because wet leaves can spread the disease.
Citrus greening is a serious disease spread by the Asian citrus psyllid. It causes yellowed leaf veins. The leaves and stems may die back and the fruit turns bitter. There is no cure for this disease. Remove and destroy infected trees.
Trunk and Root Diseases
The most common problems you’ll encounter are those caused by the Phytophthora fungus. This pathogen causes root rots and trunk cankers. You might notice stunted growth, cracking bark or liquid oozing from the trunk. If cankers girdle the tree, it will die. To prevent root rots and cankers, plant trees in well-draining soil and avoid planting them too deeply. Avoid overwatering because soggy soils can contribute to the disease. Prune out infected branches and disinfect your tools between cuts with a solution of one part chlorine bleach to ten parts water.
For more information, visit the following link:
Citrus for the Home Garden from the University of California Extension
Citrus Diseases and Disorders from the University of California.
Julie Christensen learned about gardening on her grandfather’s farm and mother’s vegetable garden in southern Idaho. Today, she lives and gardens on the high plains of Colorado. When she’s not digging in the dirt, Julie writes about food, education, parenting and gardening.