Pines in Michigan are susceptible to a destructive, stem boring insect pest. The insect is Zimmerman Pine Moth which damages trees during its grub or larval stage. The trees become stunted and deformed after repeated attacks. Heavily attacked trees can eventually die.

HOSTS, DISTRIBUTION AND DAMAGE

The Zimmerman pine moth will attack many species of pine common to Michigan, including Austrian, Jack, and Scots pine. Stressed trees are most susceptible. The first sign of infestation by the Zimmerman Pine Moth is the appearance of small, reddish pitch masses. The pitch masses are usually found where branches join the main stem. The pitch mass is the result of a larva boring through the bark into the sapwood to feed. Additional pitch bleeds from the tree as larvae continue to tunnel and feed beneath the bark. The pitch masses eventually turn light yellow to off-white. Trees showing only this sign have probably been infested for only one or two years. Pitch masses may go unnoticed unless the trees are closely examined.

Older infestations are more easily recognized. Individual branches turn brown and die. Branches are often bent downward or broken off at the main trunk. Tops may be broken, dying, or dead. This may resemble damage caused by wind or heavy snows.

LIFE CYCLE

Adult moths emerge during mid summer. Moths are rarely observed, since they are most active during the late evening and night. They mate and lay eggs approximately one week after emergence. They often lay eggs under bark scales close to wounds or resin masses caused by previous attacks. The eggs hatch in about one week. The larvae may feed for a short time after emerging from the eggs, but soon seek a sheltered area. Here they spin a protective winter covering of silk-like material and spend the winter. The tiny larvae become active the following spring from April through mid May. The larvae are exposed to the outside environment for only this short interval. Treatment must be applied during this critical period. The larvae feed while tunneling under the bark. Their feeding activity lasts about 10 weeks, from early May through late July. Fully grown larvae are 3/4 to 1 inch long. They pupate in an enlarged tunnel or in a resin mass.

CONTROLLING ZIMMERMAN PINE MOTH

Control treatments are applied in the early spring and target the trunk and larger branches.

Deep root fertilizing helps trees maintain their health and vigor, thus lessoning the chances of infestation of a weak and stressed tree.

Photo: Whitney Cranshaw, Colorado State University, Bugwood.org

Photo: Steven Katovich, USDA Forest Service, Bugwood.org