Pine moth larvae

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.

Damage caused by Zimmerman pine moths

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.