Hypoxylon canker is a devastating disease of hardwood trees in the southern U.S. I had never seen this disease before until last Friday. I visited a pecan orchard where several trees were dead and others were in the last throes of life. The bark was falling off the trees, but the real tell-tale sign (at least to me) was on the dead trees — they had hard, black, tar-like sections under the bark. I asked the orchard caretaker if he applied tar to wounds on the tree. He said no. It was then I was sure of the problem. So, what to do about it?
Unfortunately, there is not a lot to do. Tree removal is the best option. Hypoxylon canker strikes trees that have been stressed. These pecan trees had been severely stressed during Hurricane Katrina, but also to drought conditions in recent years. The Hypoxylon fungus does not infect healthy trees, so keeping trees watered and fertilized will help avoid this disease. Once established, it can be spread by spores from tree to trees, therefore it is imperative to get the infected trees out of the orchard.
The symptoms can vary depending on the tree species, but the first sign is usually thinning out of the canopy (fewer leaves, dying branches, etc.). This publication has some great photos of the symptoms:
Below are the black tar-like symptoms: