For maximum management with insecticides, this is one of the times of year to treat for Zimmerman pine moth, Dioryctria zimmermani (Grote). Zimmerman pine moth larvae (caterpillars) feed on all pines, especially Scotch and Austrian. Larvae bore into trees and create masses of pitch resembling galls at branch whorls on the main stem or on shoots near the terminal leader. Larvae can kill terminal leaders. Heavily infested terminals curve downward, resembling a fishhook. Repeated attacks by larvae in the trunk can cause tops to break off, which makes the tree unsalable.
Adults are gray with a 1- to 1-1/2-inch wingspan. Forewings are gray and mottled with a zigzag line pattern of red and gray. Adults are active at night from mid-July to mid-August. They can live from three days to two weeks. Female moths can lay between 20 to 30 eggs underneath bark in the whorl region of trees. From late July to early September, eggs hatch into pinkish green larvae with a brown head.The body is covered with small black dots. These young larvae feed at the base of terminal buds and on the bark of the trunk in late summer and fall.
Larvae overwinter in bark crevices in silken webs (hibernacula). In the spring, they leave the hibernacula and crawl across the bark before tunneling into the trunk or shoot. They then bore into the shoots and stem where they form a characteristic pitch mass at the entrance site to the tunnel where they feed. Older, fully grown larvae are approximately 3/4 inch long. The brown pupae are found in shoots and pitch masses from mid-July to late August.
Management of Zimmerman pine moth involves sanitation and the use of chemical insecticides. On Christmas tree plantations, scout regularly by visually inspecting trees for pitch masses on the main stem or terminal leader. Prune out damaged wood and injured shoots or remove trees that show visible symptoms of Zimmerman pine moth damage.
The larvae are active on the outside of the tree in early April and from late summer to fall, making them susceptible to insecticides. The insecticide chlorpyri-fos (Dursban) or dimethoate (Cygon) can be used to control the larvae by spraying the bark and foliage in April or from mid- to late August. The best time to control this insect is in the caterpillar stage before it enters the bark. Use high volume sprays to drench the stem and bark because a thick canopy of pine needles may prevent sprays from reaching the trunk. Planting resistant varieties of Scotch pine such as the short-needled varieties from Greece, Turkey, and west and south Eurasia may be a long-term alternative option to minimize problems with Zimmerman pine moth.