Infested branch broken off at crotch (21977 bytes)

Zimmerman Pine Moth

By Carl Wilson, Horticulturist, Denver Cooperative Extension

Dead and dying branches in the upper half of pine trees are a sign of Zimmerman pine moth infestation. Austrian pines are most commonly infested, although Scots and ponderosa pines are also damaged. This insect has become established along the Front Range in recent years.

Infested branches typically break at the crotch where they join the trunk (see above).

 The first external sign of injury is the production of popcorn- like pitch masses at wound sites. The size of golf balls, masses resemble clusters of small, pale colored grapes.

Zimmerman pine moth overwinter as young caterpillars in cocoons under bark scales. They tunnel into trees in late-April and early May. By late spring, they move down to tunnel at the base of branches created the pitch masses.

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Pitch masses

By July, larvae reach full size and pupate within the pitch masses. Adults emerge from cocoons in late July and August. Eggs are laid that hatch into the caterpillars that overwinter under the bark.

The moth is most vulnerable during late summer and again in spring when they are exposed and active on the bark. A drenching trunk spray applied in August and/or mid-April should kill larvae before they enter trunks. Astro has provided a high degree of control in Colorado State University tests.

Photographs courtesy of University of Nebraska Cooperative Extension.

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Date last revised: 01/05/2010