Mexican Lime Leaf Problems

Bacterial and Algal Diseases

• Mexican lime trees grown in home gardens are highly susceptible to citrus canker. The bacterial pathogens (Xanthomonas campestris pv. citri) first cause tiny spots to develop on leaves. These small sores enlarge into large brown lesions that often have yellow halos. The stems and lime fruit rinds occasionally develop canker sores as well. Severe canker infections lead to leaf drop and consequently weaken lime trees.

  Red alga organisms (Cephaleuros virescens) cause raised, grayish-green lesions on leaves. The sores eventually take on a reddish-brown color as the alga produces microscopic spores. The red alga organisms sometimes spread to the limbs, girdling and killing branches and causing the leaves growing above the infection site to drop from the tree.

Fungal Diseases

• Mexican limes may suffer from fungal diseases during long stretches of humid or wet weather. Citrus scab fungus (Elsinoe fawcetti) causes raised, light-colored, corky growths to form on young leaves. The developing leaves often look distorted or misshapen.

  Lime anthracnose disease (Colletotrichum gloeosporioides) causes brown, necrotic lesions to form on leaves. The dead leaf tissue eventually falls out, giving the foliage a shot-hole appearance. Infected trees typically suffer from premature leaf drop. The fungal pathogens also infect buds, blossoms and developing shoots, which results in twig dieback, misshapen limes and premature fruit drop.

  Greasy spot fungus (Mycosphaerella citri) initially causes yellow spots on the top surfaces of leaves. Brown, greasy-looking blisters develop on the undersides of leaves just beneath those spots. Greasy spot can cause leaf drop and make your Mexican lime tree lose vigor.

Preventing Fungal Diseases

• Prevent fungal diseases on your Mexican lime's leaves by planting the tree in a fully sunny spot. Promote air circulation by planting lime trees at least 12 feet away from other trees, buildings and structures. Avoid getting the leaves wet when watering because fungi spread easily through splashing water droplets. Water Mexican lime trees every other week only during prolonged dry spells, penetrating the soil to a depth of 18 to 36 inches each watering session.

Treating Leaf Diseases

• Copper-based fungicides can treat various bacterial and fungal infections. Following the directions and safety precautions on the product's label, mix 1/2 to 2 fluid ounces of copper-based product with 1 gallon of water, or according to dilution rates on the label. Put the solution in a garden sprayer and thoroughly cover the tops and undersides of leaves. For optimal control, start treating your lime tree whenever the weather forecast predicts prolonged stretches of damp or humid weather for your area. Otherwise, start treatment when disease symptoms first appear. Repeat applications every 14 days until the disease clears up.