The two types of locust trees are black locust and honey locust. Both are fast-growing and bloom once a year. These trees are primarily for shade and are native to North America. They are generally adaptable to many climates and conditions, though the black locust is urban intolerant. Locust trees are beautiful,but are susceptible to a few diseases.
Verticillium wilt is a fungus that enters the plant through roots. Symptoms are not readily obvious but can include leaf curling and dying, abnormal red or yellow leaf coloring and wilting branches. Typically, the wilting may develop on one entire side of the tree. Verticillium wilt is uncontrollable once the tree is infected. Trees may die rather suddenly or could live for years with the disease. As of 2010, no fungicides have been helpful in fighting it.
A number of fungi or bacteria cause leaf spots. Leaf spot is easily identified -- leaves will suddenly appear with various sized and colored spots on the leaves of the tree. Most spots are brown, tan or black and concentric rings may also be present. Some spots may even be raised or drop out entirely from the leave.
In damp weather these spots will increase in size and number. Leaf spots are not usually life threatening to the locust tree. Tree caretakers can manually remove the infected leaves or may attempt to keep the tree's leaves drier. If a plant has a chronic condition and it is aesthetically bothersome, the best option may be to replace the plant entirely.
Several types of bacteria are associated with wetwood. When a locust tree contracts the disease, the wood will turn a yellow-brown color at the central core of the tree. This affected area will often look and feel wetter than surrounding wood and could ooze slime. Cracked wood can also occur during the wintertime if a tree has this disease. Wetwood seriously damages the wood's strength properties causing warping and splitting. There is no effective way to eliminate wetwood.
Cankers can also seriously affect both species of locust trees. They are dead sections of bark on the trucks and branches of trees which can be caused by various fungi and bacteria. Cankers kill bark in any affected areas, seriously threatening the tree's life. As cankers decay the wood, the tree becomes more and more vulnerable to high winds, heavy snows or ice.
The best method of avoiding cankers is prevention. Correct watering, suitable soil moisture and annual fertilization can help a tree fight off canker infections. Regular pruning in the early spring can reduce canker problems. Chronic canker problems may result in total plant replacement.