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Zimmerman Pine Moth

August 29, 2001

This is the time to be on the lookout for Zimmerman pine moth, Dioryctria zimmermani, larvae (caterpillars) actively crawling on the bark of trees. The larvae are highly exposed and susceptible to an insecticide spray, which provides an opportunity to kill the larvae before they enter the overwintering stage. Zimmer-man pine moth larvae feed on all pines, especially Scotch and Austrian. Larvae bore into trees and create masses of pitch at branch whorls on the trunk or on shoots near the terminal leader. These pitch masses may resemble galls. The larvae can kill terminal leaders; heavily infested terminals curve downward, resembling a fishhook. Repeated attacks by larvae can cause tops to break off, making the tree unsalable. Young trees are more susceptible to attack from the larvae, possibly due to the stress from transplanting.

Zimmerman pine moth adults are gray, with a 1- to 1-1/2-inch wingspan. The forewings are gray, mottled with a zigzag line pattern of red to dark gray, whereas the hindwings are pale yellow. The adults are active at night from mid-July to mid-August in most of Illinois and can live from 3 days to 2 weeks. Males and females are similar in size and color.

Female moths lay between 20 to 30 eggs underneath bark in the whorl region of trees. The eggs hatch in early August to early September into reddish brown larvae with dark brown heads. The young larvae, about 1/16 inch long, are very difficult to see with the naked eye when they first hatch. The body is covered with small black dots, each containing a sin-gle bristle. Larvae are about 3/4 inch long when fully grown. They are generally located at the base of ter-minal buds or under bark flakes. Young larvae are active on the outside of the tree in mid-August. From late summer to early fall, the newly emerged larvae feed on the bark and base of buds. The larvae overwinter in bark crevices in silken webs, forming what is referred to as a "hibernaculum." They emerge from these hibernacula in early April and crawl around on the bark before boring into the shoots and stem. The pupae--brown initially, turning to black--are found in shoots and pitch masses from mid-July to late August. There is one generation per year in Illinois.

Management of Zimmerman pine moth involves sanitation and the use of pest-control materials. On Christmas-tree plantations, scout regularly by visually inspecting a random sample of trees for the larvae and (later) for pitch masses on the main stem or terminal leader. Prune out damaged wood and injured shoots, or remove trees that are showing visible symptoms of Zimmerman pine moth damage. The pest-control materials chlorpyrifos (Dursban) or dimethoate (Cygon) can be used to control the larvae by spraying the bark and foliage in mid- to late August. Spray applications should be made again next year in April when the larvae leave the hibernacula and crawl across the bark before boring into the trunk or shoot. The best time to control Zimmerman pine moth is the caterpillar stage before it enters the bark. High-volume sprays should be used to drench the stem and bark, as a thick canopy of pine needles may prevent sprays from reaching the trunk.

Although Zimmerman pine moth larvae are susceptible to natural enemies, including parasites and pred-ators, their numbers are not sufficient to impact the population and prevent damage. 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 to minimize problems with this pest.

Author: Raymond A. Cloyd


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