Zimmerman Pine Moth
Zimmerman pine moth has long been a pest of pines in the Midwest but has become increasingly noticeable in the past few years. The larva of this moth species is a borer that attacks pine tree trunks and lateral branches. Trees rarely are killed by this insect but they are disfigured as branches die. Borer damage can weaken trees and cause trunks or branches to break off during heavy ice, snow or wind.
ZPM causes the greatest damage to Scots, Austrian and red pines, though other species may be attacked. Infestation is determined by the presence of resin or pitch masses on the tree trunks where the larvae are feeding beneath the bark. Pitch masses may be 2 to 4 inches in diameter and are usually located at branch whorls where the branches join the main trunk. Fresh pitch masses where the larvae are active will be white, soft, and shiny. Pitch masses from earlier generations will be hard, gray, and dull. These may go unnoticed until the tree trunk is examined closely.
The small, gray ZPM adults are most abundant from late July to mid-August. The females lay their eggs on tree trunks, usually near wounds such as old borer damage and yellowbellied sapsucker feeding holes. The larvae emerge from the eggs by late August and crawl under loose bark scales or into wounds to spend the winter.
In spring, the larvae burrow into the bark and begin to feed. Full-grown larvae are present by late July. These are about 3/4 inch long and pink to greenish in color. They have a brown head and numerous tiny dark spots on the body. The larvae pupate at the end of the larval tunnel and two weeks later the moths emerge to start the cycle over. There is only one generation per year.
ZPM tends to develop in abundance on one or a few trees within a planting. Removing these “brood trees” may be a practical option. If there is a limited infestation on one or a few trees, remove pitch masses in mid summer and dig out the larvae with a knife and discard.
Heavy infestations may require a combination of sanitation and insecticide spraying. Larvae must be on the outside the bark at the time of insecticide spraying for treatment to be effective. Suggested times are mid-August before hibernation or mid-April before larvae tunnel into the trunk. Indicator plants that coincide with the appearance of these vulnerable stages include Hydrangea “Grandiflora” in pink bloom and Canada goldenrod in bloom in August, and Magnolia in pink bud and sugar maple beginning to bloom in April. The entire tree, but especially the trunk must be thoroughly sprayed with the insecticide solution to achieve control.