Locust Tree Has Cankers and Dead Limbs

Disease Identification

• All varieties of honeylocust trees are prone to thyronectria canker disease caused by the Thyronectria austro-Americana fungus. The fungus also affects oriental honeylocusts and certain hardwood trees such as willow, bur oak, American elm and white ash. The disease is more common in trees growing in warmer, humid climates and is rarely a problem in the northern states like Wisconsin or Minnesota.

Symptoms

• The disease starts with the appearance of reddish yellow, sunken or flat areas with callus-like ridges on the outer margins on stem's thinner bark. The cankers on the thicker bark on the trunk are not discolored, but its sapwood is yellow or red under the infected areas. Leaves start to yellow and fall, and affected branches eventually die. Foliage of the infected tree changes color earlier in fall with earlier leaf drop. Cankers appearing at the base of the tree are fatal to the tree.

Favorable Conditions

• Stressed and weak trees are more prone to canker infections. Disease is also more frequently seen in honeylocusts used as windbreaks. Infection attacks trees both in rural and urban settings. Careless pruning cuts and sunburned bark on the southwest sides of the tree are more prone to infection. Inadequately watered trees suffering from drought stress, especially during early spring and summer are more likely to get infected.

Management

• The best management practice for avoiding possible infection of thyronectria canker is to take preventative measures to ensure infection does not occur. There are no curative treatments for the fungi once a tree is infected. Plant trees in an open site that does not restrict root growth. Keep trees well irrigated to avoid drought-related stress. Do not overwater, as wet soil invites a number of soil-borne fungi. Prune and remove infected branches and scratch out smaller cankers to reduce chances of disease spreading to other areas.