Hypoxylon Canker in Oak Trees

Causal Agent

• Hypoxylon canker disease is caused by various Hypoxylon fungi, namely Hypoxylon atropunctatum. All oak trees are prone to the infection, with some varieties more severely affected than others. Other host trees of the fungus include hickory, elm, pecan, beech and maple. Hypoxlon canker is most widespread in the southern regions of the United States.

Symptoms

• An early symptom of the infection is a sudden thinning of the crown, accompanied by branch dieback. With disease progression, small sized patches of the infected bark start to separate and fall to the tree base, revealing red, tan or green powdery spore masses on the wood beneath. These exposed areas blacken and harden within a month or two. Foliage on infected branches starts to yellow and die. The disease is a wood-decaying disorder that rapidly rots the infected tree. The fungus often persists for extended periods in the bark of healthy trees without causing disease symptoms.

Favorable Conditions

• Hypoxylon canker-causing fungi are weak pathogens that rarely infect vigorous growing trees. The disease is frequently seen on drought-stressed trees. Trees that have high moisture content in their tissues resist the infection. The fungus grows in temperatures ranging between 50 to 100 degrees Fahrenheit, with an optimal temperature of 86 degrees. Oak trees suffering from oak wilt disease or those with excessive fill soil are also more prone to the disorder.

Control

• There is no cure for Hypoxylon canker once a tree is infected. Effective control strategies are targeted toward taking adequate preventative measures. This starts by ensuring that the tree stays in good health and is adequately irrigated to avoid drought-related stress. Minimize damage to bark and root areas, especially in trees that are located near construction sites, and do not use fill soil around the tree. Tree wounds are likely to become entry sites for the fungus.