What is ZPM?

Written by: Kyle Babicky, Certified Arborist WI-0889A

Posted: 2018 | Insect Control | Winter

Pitch masses on tree trunk cause by Zimmerman pine moths.

ZPM is short for Zimmerman Pine Moth, which is a serious pest of many species of pine trees. Austrian and Scots pines are the most commonly affected species in our area. The damage caused by these insects can go largely unnoticed unless a trained eye detects the issue before it becomes a major problem.

A key indicator that Zimmerman Pine Moth has been feeding on your pine tree is the formation of “pitch masses” (shown in the attached photo). These are usually found along the trunk or large branches. Pitch masses form as the pine tree pushes out sap in an attempt to defend itself against the attack. These pitch masses can often look like yellowish-tan colored gum stuck to the bark of the tree.
The larval stage of Zimmerman Pine Moth is the life stage that does the main damage on pines. Larvae feed on the cambium tissue within the pine tree just beneath the bark. This causes a disruption in nutrient and water transport. The damage from larval feeding can also have a girdling effect on the tree, causing the main trunk or large branches to be prone to breakage. Since larvae are feeding underneath the bark where they are protected, they can be a difficult pest to control.

The best method for managing Zimmerman Pine Moth is an insecticide application when the insect is exposed on the outside of the tree. The time frames in which Zimmerman Pine Moths are vulnerable happen twice each year. The first opportunity is in early spring when larvae emerge from overwintering and begin chewing into the inner bark. The second opportunity is during late summer when the adult insects search for a new spot to lay their eggs. The eggs hatch in about a week and new larvae begin to feed for a very brief time before overwintering again. A well-timed application works both on contact of Zimmerman Pine Moths, as well as gives the bark a protective coating just before the larvae begin chewing into it.

Application timing is critical for effectiveness of Zimmerman Pine Moth treatments. Timing isn’t as simple as spraying the tree by a certain date, because nature does not follow our typical calendar. Insects’ bodies respond naturally to an accumulation of sunlight and temperature throughout each year. This is referred to as Growing Degree Days. Tracking this “warmth calendar” is a science all in itself. Our Certified Arborists at Wachtel Tree Science track Growing Degree Days and seasonal milestones or “phenological indicators” for proper timing of our applications to ensure maximum effectiveness.

If you are concerned about the health of your pine tree, please give us a call. One of our Certified Arborists would be happy to inspect your trees and provide any necessary recommendations for keeping them healthy and beautiful!