Zimmerman Pine Moth

Zimmerman Pine Moth

Zimmerman Pine Moth (Dioryctria zimmermani) is a non-native moth that attacks pine trees. It is established throughout the eastern United States, though mostly found in the Great Lakes Region. Primarily known for attacking Austrian Pine and Scotch Pine, Zimmerman Pine Moth is also known to attach Eastern White, Red, and Mugo Pines. Beyond landscape trees, it’s also known to cause a lot of damage to Christmas tree plantations.

How does it damage trees?

Caterpillars may first infect a tree by entering through new branch tips, causing die back. The caterpillars overwinter on shallow holes in the bark. When they emerge in spring, they feed for a while and then bore into the tree bark at the base of branches, creating large, irregular wounds where resin collects. These wounds can weaken branch attachments and lead to branch death and/or failure. Left untreated, the tree can lose numerous branches or its top, leaving the tree weakened and permanently disfigured.

What should I look for?

The first thing you may notice to clue you into a Zimmerman Pine Moth infestation is browning and dropping of new growth. This can also occur on the top of the tree. Often the biggest clues are large masses of pitch that resemble popcorn at the base of branches. Fresh, shiny masses are a clue that there is an active infestation. In the Summer, you may see white crumbs of caterpillar excrement collected around the wound sites. It’s common for damage to be concentrated near the top of the tree, but can be found in the lower canopy as well.

The caterpillars are about 1 inch in length and are dirty white or gray, sometimes displaying green or pink. You may be able to find caterpillars hiding under the pitch masses when they are active in spring. Caterpillars then retreat into the bark for a few months. Adults are mid-sized moths that emerge in late July or August. Their wings are gray and mottled red-brown that sometimes show a zig-zag pattern. Moths are active for a short period of time until they lay eggs in late Summer. The eggs hatch after one week. New caterpillars are then present on the bark’s surface until they again retreat into holes in the bark and prepare for winter.

What should I do if I find Zimmerman Pine Moth on my trees?

Zimmerman Pine moth can be controlled with an insecticide spray. Sprays should be applied in Spring when the caterpillars emerge and are active. A second spray in late Summer when the eggs hatch can increase effectiveness. Sprays should be concentrated on the entire trunk and bases of branches. There is no need to spray the foliage. Homeowners can use permethrin, which is available at nurseries and hardware stores. Always read all precautionary statements and follow instructions. You can also contact your Tree Health Management certified arborist to perform sprays. Remember that timing of the sprays is important for treatments to be effective. It may take several years of treatment to fully remove the moths from the landscape. Heavily infested trees can also be removed and destroyed to prevent spreading to surrounding trees.

The best way to avoid infestations is keep your pines healthy. Avoid unnecessary injury, which can give caterpillars an entry point Mulch your trees with an organic mulch (or even better, leave the needles). Make sure to keep your trees watered during times of drought and through heat waves. Healthy trees are better at fighting off infestations.