Common Diseases of Lemon Trees

By Julie Christensen
If you’re lucky enough to live in USDA plant hardiness zones 8 through 11, you should add lemon trees (Citron limon) to your list of landscaping plants. These trees are valued not only for their tart, flavorful fruit, but their shrub-like form and large glossy leaves. ‘Lisbon’ is the most commonly grown traditional lemon. It reliably produces heavy yields of large, tart fruit. ‘Lisbon’ tolerates adverse conditions, such as heat, drought and frost, better than most true lemon varieties.

‘Meyer’ lemon is believed to be a cross between a lemon and an orange. ‘Meyer’ lemon trees are smaller than most lemon trees and their fruit is sweet, flavorful and thin-skinned. The original ‘Meyer’ lemons carried the tresteza virus. They were banned for many years in most citrus-growing states. New improved varieties don’t harbor the virus and are safe to grow anywhere. ‘Meyer’ lemons are the most cold hardy of the lemon varieties, and have growing requirements similar to oranges.

Lemons need full sun and well-draining soil. Plant them in an area protected from hot, dry winds or frost pockets, such as on the south side of the house. Water them once or twice each week during the growing season. Proper cultural care can prevent most diseases and pests, but watch out for the following problems:

Tristeza

Tristeza is a fungal disease that causes a variety of symptoms, ranging from leaf yellowing or dropping, stunted growth to poor fruit production. The tree quickly declines and often dies due to root rot. Symptoms are most obvious during the summer because the weakened root system can’t take up water. Tristeza is spread by aphids feeding on the leaves. To control the disease, spray trees infested with aphids with insecticidal oil or soap, coating both the tops and undersides of the leaves. Buy certified disease-free trees from a reputable nursery, rather than home stores.

Botrytis

Botrytis is more common in lemons than other citrus fruits, especially in locations with cool, moist weather. The disease causes brown or gray, velvety growths on twigs and blossoms. As the disease progresses, the twigs may die back and fruit may be affected. Trees sometimes lose leaves and fruit drops prematurely. To prevent botrytis, plant lemon trees in full sun. Space the trees so air circulates freely and prune them to open up the canopy to light. Prune out infected branches and discard them.

Lemon Tree Root Rots and Trunk Cankers

The Phytophthora fungus causes several problems, including gummosis and root rots. Early symptoms include poor growth, lesions and oozing from the trunk. As the disease progresses, it can girdle the tree, killing it. The disease advances most rapidly during moist, cool weather. To control fungal diseases, plant lemon trees in well-draining, light or sandy soil. Make sure the top of the root ball is planted 1 inch above the soil surface. If you have heavy soil, consider planting lemon trees in raised beds to improve drainage. Spray the trees with a copper-based fungicide before the rainy season arrives and prune out infected branches. Treat your pruning tools with a solution of one part chlorine bleach to ten parts water between cuts.

Lemon Fruit Problems

Lemons are subject to several problems of the fruit. Brown rot causes tan to brown spots near the top of the fruit. As the disease progresses, the spots become enlarged and the fruit rots. To prevent this problem, harvest lemons in the afternoon during dry, warm weather. Septoria spot causes brown to reddish brown lesions on the fruit. Control Septoria spot by spraying trees with a copper-based fungicide. Use soaker hoses instead of overhead sprinklers and avoid handling trees when the leaves are wet.

Want to learn more about lemon trees?

For more information, visit the following links:

How to Manage Citrus Pests from the University of California IPM Online.

Citrus Disease Management from Texas A & M University.

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.