Outbreaks periodically kill large numbers of pines. Recent evidence indicates that mountain pine beetle populations are on the rise statewide. Mountain pine beetles only attack pines greater than seven to eight inches in diameter. The one-year life cycle of the beetle begins in August when adults exit dead trees and fly to attack nearby green trees. In early summer, about nine to ten months after being attacked, the needles of infested pines will turn reddish-brown.
Mountain pine beetles overwinter in the tunnel system as small white grubs with brown heads.
During outbreaks, infested trees produce enough mature beetles to kill one to three more trees. Prevention involves encouraging individual tree vigor, thinning dense, older pine forests, and application to live valuable trees of the insecticide carbaryl. For details about prevention or population reduction treatments contact your local office of Colorado State Forest Service or Colorado State Cooperative Extension, your county Pest Management of Open Space office, or a professional arborist. Permission is hereby given to duplicate this Plant talk Colorado TM script as is if credit is given to the sources.