FOREST TENT CATERPILLARS

I continue to receive calls regarding forest tent caterpillars in some of our ornamental trees. Forest tent caterpillars 
overwinter as fully developed larvae in egg cases which are laid in masses encircling small twigs. The tiny caterpillars emerge in early spring and are often found near the egg masses. Unlike other tent caterpillars the forest tent caterpillar does not form large unattractive webs. The caterpillars do congregate on stems and branches during the day and feed at night. As the larvae enlarge, keyhole shaped spots along their backs and broad bluish lateral bands become evident. These markings make identification relatively simple. Since the adults are moths attracted to lights, if you can shut off outdoor lights during late June to mid-July will reduce the number of egg laying adults attracted to areas where larvae could be a nuisance next year.

Outbreaks last one to four years in North Dakota. It is difficult to determine how much damage the forest tent caterpillars will cause this year and during the next few years in the state. If treatment is necessary, Bt can be effective if applied early. Other insecticides permethrin, the pyrethrins or such things as Sevin are needed to control the older larvae. Trees that have suffered leaf feeding should not suffer permanent damage and will leaf out again this year.

Dale L. Siebert
Extension Agent/Cropping Systems
Richland County Extension
418 2nd Avenue N.
Wahpeton, ND 58075
701-642-7793
dsiebert@ndsuext.nodak.edu

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