There are a variety of tree-boring insects, from small adult beetles to the larval forms of moths and other beetle varieties. Damage can vary in severity, depending on the species of borer, with some pests causing only minor damage if controlled properly and others, like the emerald ash borer, typically proving fatal to the tree.
The first key to protecting trees is knowing what types of borer activity are most common in your area. The second key is recognizing the early symptoms of borer problems.
Holes and Frass
Borer holes are probably the most obvious sign that there's a problem. Unlike woodpecker holes, which are made in neat lines and patterns, borer holes tend to be more randomized over the bark. There may also be frass, or wood dust, around the hole or around the base of the tree, which is formed as the insect pushes the wood waste out of the hole as it bores.
Not any type of wood is consumed. Borers feed on the cambium layer, which is the thin nutrient-transporting layer just beneath the bark. As the cambium is consumed, fewer nutrients make it to the tips of the affected branch. Borer-caused branch die-off usually begins at the branch tip and progressively moves toward the trunk.
When the feeding occurs on the trunk, the destruction of the cambium layer causes the bark to loosen and eventually flake off. Once the bark falls off, you may even be able to see the squiggly tunnels where the borers were feeding.
Prevention and Solutions
Some species of borers can be destroyed, saving the tree. Others, like ash borers, are fatal once established but there are preventative measures you can take.
The type of pesticide applied depends on the tree variety and the local borer species. For fatal borers, preventative treatments on at-risk trees are best. For less fatal varieties, pesticides may be applied as a preventative or as a treatment for existing borer populations.
Sometimes an infestation can be stopped or at least slowed down by removing the worst affected branches. This requires careful pruning and proper disposal of infested wood. It may not be very effective if the borers have already gotten into the trunk.
Proper tree care is the best preventative. Trees that are kept trimmed, watered, and fertilized are less susceptible to borer infestation. Broken branches and bark damage should be cleaned up promptly by a tree professional so the wound doesn't attract pests.
Contact a tree service in your area if you suspect boring insects are causing trouble on your tree.