Cankers on Locust Trees

Disease Identification

• Locusts are susceptible to damage from the nectria canker. The disease is also referred to as the honeylocust canker and is caused by the fungus Nectria cinnabarina. Other possible hosts of the pathogen include a number of hardwoods including elm, maple and honeylocust.

Symptoms

• The infection is characterized by the appearance of oval to elongated, red- to brown-shaded, sunken areas of tree bark. The wood under the affected patches is dark and dead. The discoloration and depth of the canker increases as infection progresses. Cankers are more noticeable on younger branches. Cracks appear on the margins of healthy and diseased areas.

Damage

• Cankers on branches slowly start to kill the entire branch above as they encircle and girdle the area. Foliage starts to yellow and die since the fungus disrupts the flow of water and nutrients by damaging the inner cambial layer. Woody decay fungi start to enter the tree through affected areas. These include Polyporus spp. or Schizophyllum commune fungi. Trees that are extensively damaged by cankers cannot be saved, according to the University of Wisconsin Extension.

Control

• Minimize wounds and damage to the tree as these are the main sites of infection. Nectria fungus can enter fresh tree wounds within a week of the cut. Do not prune trees that are drought or heat stressed, and prune only when required. Avoid pruning during wet weather as fungal spores are easily spread with wet pruning tools. Cover all cut areas with wound dressing. There is no control for the disease once the tree is infected. In some cases the tree may also heal naturally by growing a callus around the infected site.