Zimmerman Pine Moth – What looks like a tree disease, but is a tree pest
Zimmerman Pine Moth – Why your Austrian Pine trunk looks like an old candle stick.
A pest that attacks Austrian, Ponderosa and Scotch pine. It prefers Austrian pine and is quite common along the Front Range. Considered a nuisance more than a damaging insect. This is arguable as repeated attacks often end up with branch failures because of the extensive tunneling the larvae do around branch unions on the trees.
The best way to detect these pests is to look for the physical signs of their presence In the tree. It appears as a mass of “pitch“ ( a mixture of frass and sap) on the trunk bark near branch unions. Sometimes referred to as “popcorn“ it is a combination of the larvae tunneling into the cambium and the tree attempting to push the pest out with copious amounts of sap.
Zimmerman pine moth caterpillars tunnel under the bark from late April into May. Usually by the end of June the popcorn can be seen around the branch unions where they have begun to rally and feast. The larvae reach full size in July and pupate inside the pitch mass (popcorn). The Adults come out in August and lay eggs near old pitch tubes. The eggs hatch and the larvae seek shelter under the bark scales where they overwinter (hibernate).
Damage is to trees is from the physical tunneling of the caterpillars under the bark and in the whorly wood where branches attach to trunks. This leads to branch dieback and branch failure when the tunneling is extensive.
The best management with this pest is to keep the trees healthy through proper watering and regular soil treatments. If trees are attacked they can be protected from further damaging generations by applying a trunk spray in April and again in late July or early August. This should be done for several growing seasons and then can be stopped and the trees monitored for new infestations annually thereafter.