Chestnut Blight Fungus on Oak Trees

Causal Agent

• Chestnut blight is a fungus disease caused by Endothia parasitica. The post oak tree is most susceptible to the infections although certain other oaks are also affected. The American chestnut tree is the primary host of the disease. Besides post oak and chestnut trees, chestnut blight is also a minor disease of hickory, sumac and maple trees.

Symptoms

• The disease is characterized by the appearance of numerous cankers on stems and branches. The foliage on infected branches starts to yellow and wilt. The bark starts to split and dies in patches in the affected areas as the plant cells gradually die. The cambium layer under the bark also starts to brown. Reddish-orange masses of fungal spores are visible on the bark near the cankers. These spores are spread rapidly by animals and splashing rain to other healthy trees.

Damage

• Chestnut blight commonly affects the larger, more established trees. The disease is lethal to the American chestnut; it can kill saplings rapidly. The fungus enters trees through wounds and through the furrows and cracks of mature bark. The cankers kill the affected stems and branches and eventually the entire tree. Secondary tree pests start to infest the tree under the cracked, disease infested bark. The cankers continue to infest and spread even after the tree is dead.

Control

• There is no cure for the chestnut blight disease and research is still being conducted to find an effective control strategy at publication time. Research is also being conducted on isolating resistant varieties and developing hypovirulent fungal strains. Hypovirulent strains work by attacking the causal agent of the infection and also promote healing in infected tree tissues when applied to the cankers.