justnorth posted on May 31, 2007 10:28 :: 1352 Views
Two species of moth caterpillars are causing heavy defoliation on many acres of hardwood trees and woody shrubs in Cass County just south of Gull Lake between highway 210 west of Baxter and north along highway 18. Light defoliation was spotted along highway 77 (Pine Beach Road) from highway 18 to highway 371 and 3 miles north of this junction. There are additional reports of these defoliators in hardwood trees in and around Nisswa and Backus.
The heavily defoliated trees will start to refoliate in late June if they have sufficient reserve energy. If they were stressed by last year’s drought and do not have enough energy reserves, branch dieback on heavily defoliated trees and death of defoliated seedlings could occur.
One of the caterpillars is the linden looper (Erannis tiliaria). It is full grown at about 1 ½ inches long, has a rusty-brown head, and a bright yellow body with ten thin and wavy black lines on its back. The second caterpillar species is the fall cankerworm (Alsophila pometaria). It is full-grown at 1 inch long, varies from light green to dark brownish green, has a pale green to almost black head, and a median black wide stripe along the center of its back. When there are fewer numbers, these caterpillars tend to be light green and have longitudinal white lines along their backs.
These caterpillars will be done feeding by mid-June and the trees will grow replacement leaves by mid-July. In view of last year’s drought and its lasting effects on trees, it would be wise to maintain the vigor of affected hardwood trees and shrubs. Water them each week if rainfall is less than 1 inch per week. Some people might be interested in using insecticides and they could use Bt-containing products to minimize defoliation. These defoliators are usually controlled by parasitic insects so, the use of chemical insecticides and insecticidal soaps would not be recommended in order to preserve their natural enemies.
Another control strategy is to trap them in sticky bands this fall in order to lower their population next year. Since these insects pupate in the soil and the females can’t fly, the females will need to climb up the trees to lay eggs in the upper branches. The eggs will hatch next year. So, in early September, individual hardwood trees can be wrapped with sticky bands to trap the egg-laden females as they climb the trees. To create a sticky band, use a tanglefoot product on cloth bands or aluminum foil. Do not use any petroleum products because they can kill trees.
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