Zimmerman pine moth is a common trunk and scaffold branch borer in Scotch, Austrian, and red pine in Illinois. It is a shoot tip borer in Eastern white pine. Although it is difficult to control once inside the tree, its life cycle makes it relatively easy to control while on the outside of the tree.
Trunk damage appears as white, crusted areas of pitch an inch or two wide at branch whorls. Sometimes this also appears as whitish cones of pitch about one inch in length along with oozing pitch at the branch whorl. The caterpillars are located in the trunk underneath this pitch. They tunnel under the bark as well as deeper into the trunk and base of branches.
Commonly, associated branches will die. The death and flagging of these branches allows easy identification of attacked trees, even at highway speeds. Closer inspection for masses of pitch determines whether the damage is due to Zimmerman pine moth or other cause. Tunneling into the trunk for several years weakens the trunk to where it snaps off at that location, causing the loss of the upper part of the tree. The tree survives this loss as lateral buds will break and produce new trunks. However, without pruning, the tree usually becomes multi-trunked from that point upward. This changes the overall appearance of the tree from that of a tall, telephone pole shape into a squatty candelabra shape.
The location of pitch at the branch whorl is important. Pine pitch moth can cause similar damage, but the pitch is located just under the branch whorl rather than between the branches. Yellow-bellied sapsucker feeding also results in large exudation of pitch, but occurs on the trunk between branch whorls. These woodpeckers require an open stretch of trunk to perch, resulting in their attack between the whorls.
Tip damage to Eastern white pine causes two or more inches of dieback. The needles turn brown and the tip usually bends downwards. Slicing open the shoot longitudinally during the summer reveals the feeding larva. The loss of the shoot results in lateral bud break and subsequent bushier foliage but not as much longitudinal growth. Generally, lateral shoots are attacked. Attack of the apical shoot on the tree causes a multiple-trunked tree if pruning and shoot training does not occur.
Full grown caterpillars are about one inch long and whitish to tan or greenish with dark brown spots. They pupate in or below the exuded pitch, emerging as one-half inch long light to dark gray moths. Emergence of the moths varies from mid-July in southern Illinois to mid-August in northern Illinois. Mating and egg-laying occurs soon after emergence. With egg hatch occuring a couple of weeks after moth emergence, this ranges from early to late August from southern to northern Illinois, respectively.
The young caterpillars on trunk-attacked trees feed on bark and crawl around on the bark for several weeks in the late summer before forming a hibernaculum under a piece of bark to spend the winter. A hibernaculum is a cocoon of silk that the larva spins around itself. After spending the winter in the hibernaculum, it emerges in the spring and roams across the bark for several days before tunneling under it. This behavior provides time periods in the late summer into early fall and early spring when the caterpillar is susceptible to exterior insecticide application.
On Eastern white pine and other shoot-attacked trees, the caterpillars feed on terminal buds scales and form their hibernacula under the bud scales. Roaming activity and exposure to insecticide application occurs at the same time as trunk-attacking caterpillars.
This is the time of year to spray Scotch, Austrian, and red pine trunks and major branches with bifenthrin (Onyx), cyfluthrin (Tempo), permethrin (Astro), or other labeled insecticide to control Zimmerman pine moth. Spraying can be confined to the lower ten to twelve feet of pines under eight inches in diameter as this moth rarely attacks higher in the tree. It also is not a trunk problem on larger trees, although scaffold branches can be attacked. Spray the ends of the branches on Eastern white pine. (Phil Nixon)