In recent years, the Zimmerman pine moth, Dioryctria zimmermani, has become established along the Front Range. Austrian pines have been most commonly infested. Scotch and ponderosa pines are also reported as hosts.

Branches typically break at the crotch area where they join the trunk. Dead and dying branches, most often in the upper half of the tree, commonly indicate infestations. The first external symptoms of injury are popcorn-like pitch masses at wound sites. The pitch masses may reach golf-ball size and ultimately resemble clusters of small, pale grapes.