Question
Hi Jim, my mother has three 40 foot Water Oaks in her back yard. She lives in Lake Charles, Louisiana. Recently, in the last 4-6 months one tree has developed a black spot in the fork of the lowest major branch. It's black with a rusty border, maybe a foot and a half long and 8 inches wide. My mother also says it's becoming more obvious as time goes by, which I gather means it's growing. I might also add that this has happened in the wake of Hurricane Rita when there was a tremendous amount of water in the yard for approximately two weeks and mud and debris for another 4 months.

Might you have any advice on what it might be or who we might contact to save this lovely tree? Any advice would be greatly appreciated.

Thank you,

Jan and Gantt

Answer
These are HYPOXYLON CANKERS. Hypoxylon canker causes a dark brown discoloration of the sapwood. With age the infected wood is lighter in color and has black zones or patterns in the wood when observed in cross section.

Hypoxylon canker occurs primarily on trees which are or have been in stressed conditions. Trees which have been damaged by excessive fill soil are often attacked by this organism. In your case the flooding.

No known control of Hypoxylon canker exists.Prevention is the best way to avoid the canker. In landscape, water and fertilize trees properly (especially during droughts) and keep them free from soil compaction and wounds. Homeowners should be aware that the fungus remains active on deadwood. Therefore, if the wood is to be used as fuel, it should be burned as soon as possible to prevent further spore produc-tion and subsequent spread of disease.  The best thing to do is fertilize the trees. Apply the fertilizer in the spring around the tree from about tow feet from the trunk out to where the limbs hang. Use a all around fertilizer like 13-13-13.