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Boring Pine Moths

August 19, 1998
Two species of moth are likely to bore into the trunks of pine, causing masses of pitch to accumulate. Repeated attacks may cause the death of major branches or the trunk to snap off. If the trunk snaps off, the tree typically develops multiple leaders, drastically changing its final shape.

Now is the time to treat for Zimmerman pine moth. The adults are gray with a mottled forewing of red and gray. Eggs probably have been laid near the edges of wounds on branches through the first half of August. The eggs hatch in about two weeks, so hatch can occur from mid-August to the end of August. Young larvae wander over the tree before finding a sheltered place under the bark to spend the winter. In spring, they feed on the bark and then enter the tree where the bark is thin and tunnel into the cambium. The larvae will become 3/4 inch long and are pink to green or grayish with black spots. The larvae tend to feed under the bark of branches and trunk where the branches join the trunk. Masses of pitch accumulate on the bark over feeding areas. Scotch pine is the preferred host, but other species of pine are also readily attacked. Sprays of chlorpyrifos (Dursban) or dimethoate (Cygon) will be effective now but will be even more effective next spring when Magnolia x soulangiana is in pink bud to early bloom.

The pitch mass borer prefers white pine, but will also attack Austrian, Scotch, and jack pines as well as white, Norway, and Colorado blue spruce. The adult is a black moth with an orange spot in the middle of the body and orangish markings on the underside. This moth has bluish-black wings and is wasplike in appearance. Eggs are laid in late June and July around old and new wounds and on the trunk under branches. The hatching larvae feed under the bark in the cambium, causing large amounts of pitch to accumulate on the bark. Larvae will be up to one inch long and are creamy white. Dursban or Cygon will be effective in mid-July.

Prying off masses of pitch in early June and digging larvae out of the trunk will enable you to tell which borer you have. If you check for larvae now, you may find pitch moth larvae, but you will not know whether you have Zimmerman pine moth unless you find the one-inch-long, brown pupal skins of recently emerged moths sticking out of the burrows.

Author: Phil Nixon Cliff Sadof, Purdue University


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