Exotic invasive pests may be more newsworthy, but native pests can also be the cause of damage

With so much focus on exotic pests when they move into our forest resources, there is a tendency to overlook damage from native species, such as the sugar maple borer.

Exposed borer damage | Photo by Mike Schira, MSU Extension
Exposed borer damage | Photo by Mike Schira, MSU Extension

Many of the high profile forest pests in the news today are relatively newly introduced exotic species. The more lethal or devastating the pest, the more attention it is likely to be getting. For example emerald ash borer (Agrilus planipennis), which is eliminating wide swaths of ash trees across the eastern United States, is in the news on a regular basis.

Native pest species, particularly those that don’t kill tree, tend to get overlooked. A good example is sugar maple borer (Glycobius speciosus) a relatively obscure pest that can have devastating impact on the value of sugar maple trees.

The adult sugar maple borer, an attractive looking long horn beetle, isn’t the stage of life that does the damage. As with many insect species it is the larval stage, which feeds by boring along the inner bark of the tree that causes the damage.

Adult borers lay eggs in midsummer in rough bark pockets along the main stem of sugar maple trees. Larva hatch from the eggs shortly after they are laid, penetrate the bark and begin mining, leaving deep groves in the sapwood. The larva overwinter two years while continuing feeding in the warmer growing months, pupate the second spring with adults emerging in June or July to restart the cycle.

Although the larva seldom kill the host tree, the feeding kills the living bark adjacent to the areas being mined causing gaping dead spots or wounds in the trees. As this damage is usually on the main stem of the trees it eliminates any chance for the tree to be used for veneer or even lumber in most cases. This damage severely reduces any potential monetary value for this valuable species and relegates its potential to firewood or, at best, pulpwood.

Sometimes, in faster growing trees, the damage will grow over but the damage to value will last throughout the life of the tree. More often, ugly open wounds will persist with the tree walling off the damaged area, eventually the dead wood will weaken and the tree will snap off at the site of the infestation.

Stressed, slower growing trees seem to be more likely to be host to the sugar maple borers so one control solution suggested is to manage you northern hardwood stands to promote the best desirable growth of the stand. The randomness of attack from this native pest doesn’t lend itself to effective control through the use of pesticides.

Michigan State University Extension bulletin Northern Hardwood Forest Management (E2769) provides some valuable suggestions for management of the timber type/s where sugar maple is the predominate species. Active management of these stands should make them less desirable to the sugar maple borer and help maintain the growth, health and monetary value of your maple forest stands.

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