There are several woody plants that can be attacked by insects that bore or tunnel into trunks, stems, shoots and roots. Borers can kill branches and eventually kill the entire plant. Bores are usually the worm stage of a beetle or moth. The symptoms of a borer problem can be dieback or thinning of a tree. Sawdust, sticky sap and holes in the bark are signs that a bore has invaded.
A plant that is stressed is more likely to have a borer problem. Stress may be from poor growing conditions caused by drought, poor planting site, construction, mower damage etc. Healthy trees attract fewer insects and can withstand some borer activity. Maintaining a healthy plant by watering and properly fertilizing will help prevent borer injury.
After borers have tunneled into the plant, you can prune off the infected parts to help control. Or you can try crushing them with a flexible wire or knife inserted into the hole or by injecting an insecticide into the hole. Insecticide sprays can be used as a way to prevent borer infestation. Timing of the preventative sprays is critical. Applied too early or too late you will waste your time and money. The best defense against borers is to maintain healthy plants, select plants that are not a susceptible to borer damage and prune out infested branches as the appear. Contact your county Extension office, Master Gardener hotline or local nursery for more information.
Reference: MU Guide G7190 Insect Borers of Fruit Trees