There are many kinds of wood borers that can affect oak trees. Longhorn beetles are just one general group. Treatments for borers are time-critical. The spray treatments must be made at specific times for best effect. The adult insect emerges from the tree, mates and then lays eggs. The eggs hatch and the larvae then tunnel through the bark to the wood. To be effective, the insecticides must be on the bark just prior to the egg laying. The tiny larvae then have to chew through the insecticide, and never make it inside the tree. Once they get inside the bark, there is little that can be done to control them. Injections are expensive, and only partially effective. Ask for a positive identification of the insect and reference on what the proper timing of the treatments should be. If the answers aren’t forthcoming, you may have the wrong arborist.
Hypoxylon canker is a fungus disease of the bark, and is somewhat common on oaks. It is usually considered to be a secondary infection, meaning it infects trees that are weakened by some other factor. (The borers are also usually secondary pests.) Drought, heat or other climatic conditions are often the factors that start the process. To have an effective program, you need to know all of the things that are affecting the tree, so you can plan the best approach to managing the trees.
There are no chemical treatments for hypoxylon or other bark diseases. Spraying will have no effect. Heavy infections on specific branchs can be pruned out to limit spread, but that can also disfigure the tree. Although not highly aggressive, the disease can kill limbs and branches, and even whole trees if it gets bad enough.
What you really need is a full management program. That does not mean it has to be excessively expensive, though. You just need to know what the problems are, not just the symptoms. Watering or basic soil treatments may do more for the health of the trees than spraying a lot of chemicals around. In any event, 40 acres is a lot of spraying.
You should be able to get some help locally by contacting your Cooperative Extension office. Look in the county or state listing in the phone book. At least they should be able to help with identification of the borers, and give you information on treatments materials and timing. They may also know of any other types of problems that might be affecting your trees.
Russ Carlson, RCA, BCMA
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