What Is Wrong With My Black Locust?

Are there any discolored, sunken cankers on twigs, stems, and trunks; orange fruiting bodies may be present?

Are there any mushrooms or fungus conks on the tree?

Are the leaves covered with white powder?

Are there any visible entrance holes in the trunk with frass, or excrement, coming out of them?

Are there any tiny entry holes accompanied by frass in the bark of the tree?

Do the leaves have holes?

Do the twigs have clublike galls on them?

Is there a white, sticky froth covering the insect eggs on twigs?

Are the leaves discolored, foliage may be webbed?

Does the trunk or the branches have small holes, limbs die, or break off?

Nectria canker on trees is a fungal infection. The pathogen known as nectria invades fresh wounds and damaged areas of bark and wood. Orange fruiting bodies appear during spring and summer. Nectria rarely kills older, established trees. There is no cure for nectria canker. Prevent it by avoiding pruning during wet conditions, and by protecting your trees from winter injury.

Heart rot is a fungal disease that may cause problems for black locust trees. This fungal disease enters trees that have been injured by a storm or improper pruning. Once the fungus enters the tree, it slowly rots the wood, weakening and eventually killing the tree. To prevent heart rot, prune the tree regularly to remove branches damaged by ice or wind.

White, powdery patches on the leaves are caused by a fungal disease Powdery mildew. Powdery mildew usually appears in damp places. Encourage good air circulation around the affected plants by thining them and any surrounding plants. Water plants from below to keep foliage dry. Any affected leaves should be cut off and removed. Any commercial fungicidal spray will protect your plant from further infections.

Sensitive plant may be infested by carpenter worms, which are wood-boring caterpillars that can cause significant damage. Their hairy bodies are typically greenish-white, with a brown head. Adult carpenter worms are large moths, with mottled black and gray wings. To control carpenter worms, commercially available beneficial nematodes can be effective.

Bark beetles bore under the bark to create shallow galleries in which they lay eggs. The beetle is considered a minor pest and tends to attack trees that have already been weakened by drought or are otherwise stressed. Control is usually unnecessary for the beetle.

Several species of leaf-feeding caterpillars will feed on the black locust leaves. They may also feed on stems, flowers, and fruit. Handpick and destroy caterpillars, or spray plants with BTK if caterpillars are feeding. Many foliage-feeding caterpillar populations are controlled by general predators, parasites, or naturally occurring viruses.

Gall midges are insects whose orange larvae tunnel into young shoots. One-inch-long swellings form around the developing larvae on the twig. Leaves on the branch may wilt or turn brown. Prune off and destroy galls as soon as you see them.

Treehoppers lay eggs under the bark of twigs. The insect itself is not seen but the white, sticky froth covering the eggs is quite noticeable. The insect is seldom serious. Use Horticultural Oil in a dormant spray dosage to control treehoppers. The Horticultural Oil should be applied when the temperatures are between 35 and 85 degrees Fahrenheit.

Spider mites are known to cause problems for black locust trees. You can control spider mites by spraying plants thoroughly with water 2-3 times a day for several days. For severe infestations, spray plants with insecticidal soap or pyrethrin.

Longhorn borers attack trees, mining the inner bark and wood of branches and trunk. Prune off borer-infested branches. If you see borer holes in your trees, probe into them with a flexible wire or inject a solution of parasitic nematodes. After treatment, seal holes with putty.

Mineral deficiencies can cause tip chlorosis or necrosis or cause foliage to discolor, fade, distort, or become spotted, sometimes in a characteristic pattern that can be recognized to identify the cause. When nutrient deficiencies occur, nitrogen and iron are the most commonly seen deficiencies. Apply only the mineral found to be deficient. Excess nutrients, on the other hand, causes symptoms like leaf tip dieback, marginal leaf chlorosis, necrosis (or burn), branch dieback, and pest problems. In this case, you should provide good drainage, and use good practices during fertilization and irrigation.