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Forest Tent CaterpillarForest tent caterpillar (FTC) feeding on green ash was reported in northeastern North Dakota last week. These reports are not surprising since substantial defoliation of basswood, oak, and aspen by FTC has been reported in Canada, Minnesota, and/or southeastern North Dakota in recent years. 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 can often be found first near the egg masses. Unlike other tent caterpillars, FTCs do not produce large, unattractive webs. The caterpillars do congregate on stems and branches during the day. Forest tent caterpillars feed on ash, aspen, basswood, birch, cottonwood, elm, maple, oak, poplar, and other hardwoods. 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 which are attracted to lights, shutting off yard lights during late June and early to mid July may reduce the number of egg-laying adults attracted to areas where the larvae could become a nuisance the following year. Forest tent caterpillars did cause defoliation of aspen in parts of north-central and northeastern North Dakota several years ago and caused some defoliation of basswood and other hardwoods in southeastern North Dakota over the past three years. Most recent FTC reports in northern Minnesota and southeastern North Dakota have been of the defoliation of scattered clumps of trees. Most of the defoliated oaks and basswoods refoliated quickly, while aspen trees were slow to recover. Healthy green ash should refoliate by mid summer. Outbreaks may 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 treatments do become necessary, Bt can be effective when applied early. Bt works well to control young caterpillars, while permethrin, pyrethrins or other insecticides are needed for older larvae. Always follow pesticide labels. Review Previous
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