Have you ever seen a dead oak tree that looked like someone painted black, brown, silver or gray blotches all over it? If so you were probably looking at a tree that had died from hypoxylon canker disease. Hypoxylon canker (Hypoxylon atropunctatum) is a fungal disease that has been around for a number of years affecting mostly oak trees in both forest and landscape settings. This disease is more prevalent in the red oak family (red, pin, and black oaks) but it can be observed in white and chestnut oak as well. Research has shown that hypoxylon canker normally affects oak trees that have been weakened due to drought, root damage, physical injury, gypsy moth defoliation etc. The fungus attacks a tree from an open wound and may lay dormant for a long time until the tree is weakened enough to prevent it from repelling the disease. When this occurs the fungus will spread throughout the tree, usually causing the tips of branches turn yellow, wilt, and then die back. As the disease spreads the tree will slowly die over the course of 2-3 years. The bark of the infected tree will begin to slough off exposing the fungal fruiting bodies called stroma. This dense, hard crusty matt of fungal cells can change colors depending on whether they are active or not, so the colors can range from black, brown, or silver to gray. The fungus may be limited to a certain section of the tree or it may extend the entire length of the trunk. The hypoxylon fungus sends out numerous spores that blow through the wind and can infect other trees (oaks, etc). It is very difficult to prevent spores from affecting other trees due to their mobility. In a landscape setting some arborists recommend cutting down the infected tree and removing all parts from the site.
Hypoxylon is usually classified as a “secondary” pest of oaks meaning that it impacts weak trees unlike primary pests like gypsy moth, bacterial leaf scorch, and oak wilt that will attack both healthy and weak trees. Hypoxylon canker along with two- lined chestnut borer and shoestring root rot are the main causes of a gradual decline and death of stressed oak trees known as oak decline. The best way to prevent hypoxylon canker and oak decline in general is to keep your oaks healthy by preventing damage, watering in times of drought, avoiding early season defoliation, limiting disturbances around the tree etc.
Article by FCFCDB
Nature Notes for 4/21/2013