Question
Jim,

I live in Houston on a property with many, many huge, mature pine and oak trees. I have a number of questions about treating for active infestation, preventative insecticidal treatment, and fertilization of trees to promote overall health and resistance to disease and insects.

I am mostly concerned with the health of three oak trees. These trees have holes in the trunks and brownish dust on the trunk and at the trunk's base. The holes generally range from tiny to probably a sixteenth-inch in diameter. Another tree has larger holes (quarter-inch), but I have seen woodpeckers on this tree, and the tree has died. Three tree companies (not arborists) have told me that wood borers are in these trees. The (apparently) infested trees that are still alive have thick, green foliage and look healthy, although I have been told that in at least one of them a portion of the trunk is hollow (basically, a "side" of the tree, about thirty percent). Will treating the infested trees save them? What insecticide should be used? What is the method of application (spraying, systemic, injection, or a combination of these--and if injection, do the holes in the trunk have to be sealed)? How often should application of insecticide be made?

One person has told me that application should be made routinely on an annual basis on the infested trees. Another person has told me that application should be made now and repeated next Spring on the infested trees because the insecticide lasts generally three to four months, depending on weather conditions. What do you think? Yet another person has told me to tree all hardwood trees (not pines), whether or not they show signs of active infestation, now and annually ever after. What is your opinion? Does it make sense to "preventatively treat" trees that do not show signs of borers?

I am convinced that I want to try to save the trees with borer infestation, so I am definitely going to have those trees treated. I just want to make certain that the proper insecticide and application procedure is followed. If repeat treatment is necessary on the infested trees, I want to make certain to do this. However, I do not want to unnecessarily treat trees that are not infested. I'm not thrilled about the chemicals, and the treatment is expensive!

The other issue of concern is a large water oak that shows signs of stress. This tree greens up nicely in the Spring, but by late Summer, thins out and defoliates early in the Fall. So the tree's cycle is thick green leaves, sparser leaves, then leaves turning a rusty color. This seems to happen regardless of drought or rainy conditions. I have been told that this tree is under stress and should be fertilized. I've been told that possibly the tree lacks iron. What do you think? In general, even for apparently healthy trees, do you think that annual tree fertilization is necessary? If so, would you recommend annual tree fertilization of hardwoods and pines, or just hardwoods?

I have received so much conflicting information that I am ready to consult an arborist, but the ones in Houston also are involved in spraying and fertilizing trees, and so it's difficult to feel convinced that there isn't a profit motive lurking beneath their advice. Please, please, please--I love my trees and would appreciate some advice. Thanks a million!  

Answer
This overall problem is too complicated to be able to answer without seeing the situation. I would suggest you contact the Texas Forest Service (state agency) and ask one of their Forester to come take a look--they also have a Pest management staff that can assist the Foresters in evaluating the situation. This needs someone on the ground that can give you advice without looking at dolllar signs the State foresters can and will do this.
Here is their contact web page for Houston county office.

http://txforestservice.tamu.edu/main/article.aspx?ctrl=3

Here is the Pest management staff web page if you want to contact them direct.
http://txforestservice.tamu.edu/main/article.aspx?id=1170