One of the most interesting things with my job is watching the odd and unusual cycles in nature.
For instance during the Spring of 2009, I received five phone calls over three days about “giant” ants. I had received only one other call about the ants in 1990 and I have not received another since 2009.
The ants are the winged breeding stage of the leaf cutter ant, they are almost 4-inches long.
Now I have a new one! All of a sudden we are seeing an outbreak of HypoxylonCanker on our oak trees. In my 30 years, I have not had single call about this problem and now this week alone I have had four calls.
The callers are reporting that the bark is falling off their oak trees. The bark is piling up like small pieces of mulch round the base of the tree. Where the bark has fallen off, the tree is covered with a fine talcum powder substance that is either light tan of gray in color. As the powdery spores develop under the bark, the pressure pops the bark off.
Homeowners also have seen squirrels pulling the bark off. This disease is not rare, it is in and around ours tree all the time, but due to the droughts and heat stress from last summer and our mild winter the disease is flourishing.
The following is a description of hypoxylon canker taken from the Texas Plant Disease Handbook:
"Hypoxylon Canker (fungus - Hypoxylon atropunctatum and other Hypoxylon spp.): The disease is first evident as a dieback of one or more branches. The foliage of the diseased limbs turns yellow and dries. This dieback continues from branch to branch through the stem until eventually the tree dies. This may require one or more years depending upon the environment and amount of stress experienced by the tree. Near death or shortly after tree death the outer bark sloughs off and exposes large masses of brown, dusty one-celled spores (conidia). These spores are gone within a few weeks and a grayish surface is visible. This is covered with numerous black fruiting structures. Mature fruiting structures (perithecia) can forcibly discharge sexual spores (ascospores) for distances of 60 mm. They are then blown to surrounding trees where infection occurs again. Entry appears to be through injured surfaces on limbs or trunk. The fungus grows best at 86 degrees F but can grow at 50 and 100 degrees F.”
Once you have the symptoms, there is no chemical treatments, because the fungus is located within the tree. The only prevention is to give trees a healthy environment. Hypoxyloncanker occurs primarily on trees that have been in stressed conditions. Trees which have been damaged by excessive fill soil (construction damage) are also prime candidates. Avoid injury to the trunk and limbs and never apply fill soil around the trees.
My only step last summer was watering my trees. I stopped watering my St. Augustine grass and concentrated only on my trees. Every two weeks, I would turn my sprinklers on long enough to allow the moisture to soak in 10 to 12 inches.
Keep in mind, a trees feeder roots can go twice as far as the leaf edge of the tree. It was not cheap, but remember I said about every two weeks. I lost part of my St. Augustine, which I can replace, but I cannot replace my mature trees in my yard.
Here is also a good write-up on this disease from the Texas Forest Service website:
“There is no known control for Hypoxylon canker once symptoms begin to appear. Because the disease is internal and kills the sapwood of the tree, fungicide sprays are completely ineffective. Valued trees in home landscapes should receive additional care during drought periods. Watering should begin before injury occurs. Apply one to two inches of water per week during the summer. Fertilization in the fall or winter at the rate of two pounds of 13-13-13 per inch of trunk diameter should improve the vigor of drought stressed trees and make them less susceptible to disease attack. The fertilizer should be spread on the soil surface beneath and 20 percent beyond the drip line of the crown of the tree. If the tree cannot be watered, fertilization should not be used.”
Good sanitation practices should be followed with severely infected or dead trees removed as soon as possible. The wood from the tree can be used for firewood with little concern for further spread of the disease. If the tree is allowed to stand after it dies, the fungus destroys so much of the sapwood that the wood is of little value as firewood.
Sorry for more bad news. We are going to see the effects of last year’s heat and drought for years to come!