Both the trunk and large branches should be sprayed. Attacking beetles die as they attempted to chew through the bark. This treatment can be effective when trees are weakened or threatened by a localized beetle outbreak and should not be used indiscriminately, Celaya said. Primitive bark sprays are not recommended for trees already attacked or affected by serious problems or severe injuries. Pesticides used improperly can kill beneficial insects and can be harmful to people, animals and plants, cautions the Arizona State Land Department.
Prevention is the best way to reduce losses due to bark beetles.
Healthy trees are usually not infested. Properly thinning trees to relieve overcrowding in late fall or early winter can reduce future losses. It is also useful for reducing and suppressing forest fires. Homeowners should consider slow, deep and infrequent watering of stressed or damaged trees nearest the house, with a properly installed and maintained drip system or a soaker hose located around the dripline of the tree.