Managing Wood-boring Insects

To keep your trees healthy, one will want to watch out for what is called wood-boring insects. These insects are considered secondary invaders, which means if your tree is already unhealthy, infestation of these insects will only damage them more. So what can you do to avoid these wood-boring creatures? According to the local extension agency, here are a few good horticultural practices:

•    Select well-adapted species of trees and shrubs that are not commonly attacked by woodborers in your area. Arizona ash, birch, cottonwood, locust, soft maple, flowering stone fruits (such as peaches and plums), slash pines (in west Texas), willow and poplar are especially prone to borer attack.
•    Choose and prepare a good planting site to avoid plant stress, freeze damage, sunscald and windburn.
•    Minimize plant stress and use proper watering and fertilization practices.
•    Avoid injury to tree trunks from lawn mowers, weed trimmers or construction. 
•    Promptly care for wounded or broken plant parts using pruning or wound paint during all but the coldest months of the year.
•    Properly thin and prune during colder months.
•    Remove and destroy infested, dying or dead plants or plant parts, including fallen limbs.
•    Wrap tree trunks and limbs with quarter-inch hardware cloth spaced about 1 1/2 inches from the tree’s surface where woodpecker damage is likely. Sometimes wrapping trunks to prevent borer attack is ineffective and may, under certain conditions, increase the rate of infestation. Using plastic trunk protectors to help prevent injury from lawn mowers and weed trimmers is a good idea.

So what about the use of pesticides, you may ask?  Once trees and shrubs are infested, non-chemical options for borer control are limited. One option is to remove and destroy heavily infested or injured plants. Damage sites also can be inspected closely to determine if the larvae stages can be extracted from the plant with a pocketknife, wire or other suitable tool.   Again, it is important to remember that stressed, unhealthy trees can be attacked repeatedly and will need repeated applications of insecticide indefinitely. In most cases this is neither economical nor environmentally justified. When chemical treatments are used, efforts always should be made to improve overall tree health.

Insecticide products registered for borer control are applied as sprays to the trunks and branches, and are non-systemic, residual insecticides (e.g., bendiocarb, carbaryl, chlorpyrifos, endosulfan, es-fenvalerate, f luvalinate, lin-dane, methoxychlor, sumithion). While these products do not kill larvae that have already penetrated the sapwood or heartwood, they will kill adult and larval stages tunneling through the treated bark layer. These are primarily a preventive treatment. Some products (those containing paradichlorobenzene and ethylene dichloride) act as fumigants to repel egg-laying adults or kill accessible larvae.  

Trunk injection products (containing acephate, dicrotophos and oxydemeton-methyl) are registered for treatment of some borers. These products are supposed to work by delivering insecticides into the cambium and phloem tissues where borers feed. These injections are most effective against sap feeding insects and rarely affect woodborer larvae. Research has shown that damage caused by inserting the injection devices into trunks can be significant.

One way to protect your trees is to consider where these wood boring insects are coming from. Most adult woodborers emerge from firewood stored indoors. While most of these insects are not considered harmful, old house borer and powderpost beetles will attack seasoned, dry wood inside the home. Treating firewood with insecticide is both ineffective and potentially dangerous to the homeowner. Wood should be stored outdoors away from the house until just before use. If firewood is infested with borers it can be treated by wrapping it in a tarp and allowing sunlight to heat it. Stacking wood layers in alternate directions will help it dry and reduce areas that can harbor insects.

By practicing these few things, you could save yourself a lot of time and money in protecting your trees.