Zimmerman Pine Moths
Zimmerman Pine Moths in recent years, the Zimmerman pine moth, Dioryctria zimmermani, has become very established among the region. 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 frass or pitch masses may reach golf-ball size and ultimately resemble clusters of small, pale grapes. The adults, rarely observed, are midsized moths, with gray wings blended with red-brown and marked with zigzag lines. Adults are difficult to distinguish from other members of this genus. Larvae are generally dirty white caterpillars, occasionally with some pink or green. They are found within the characteristic popcorn-like masses of sap on the trunks and branches. The Zimmerman pine moth has a one-year life cycle. It over-winters as a young caterpillar inside a small cocoon underneath bark scales. In mid- to late April and May, they again become active and tunnel into the tree. Tunneling may first occur around the branch tips, sometimes causing tip dieback. In late spring, they migrate to the base of branches, tunneling into the whorl area. There, masses of pitch form at the wound site. The larvae continue to feed into July. Once full-grown, they pupate within a chamber in the pitch mass. Zimmerman pine moths are most vulnerable to controls when larvae are active and exposed on the bark in spring and late summer. Control can be achieved by drenching trunk sprays that penetrate the bark scales, or systemically injecting an insecticide. Apply them around mid-April or in August to kill active, exposed larvae before they enter tree trunks.