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
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.
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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