Lawns, Gardens & Trees

Accessibility


Error
There was an error while rendering the portlet.
Error
There was an error while rendering the portlet.
| Share

Forest Tent Caterpillar Already Observed (May 18, 2011)

Tips on controlling the forest tent caterpillar from NDSU Extension Forester Joe Zeleznik

Last weekend I was looking at apple trees near Detroit Lakes, Minnesota.  On one tree I noticed tiny caterpillars swarming the tips of two branches (Figure 1).  I also found egg masses on those same branches.  The larvae are forest tent caterpillar (Malacosoma disstria).  The mature larvae of forest tent caterpillar are easy to distinguish by the white, keyhole-shaped markings along their top sides (Figure 2).  The young larvae in Figure 1 don’t show those markings yet, though three days later, they are beginning to develop.

 Young Forest Tent Caterpillar Larvae

Figure 1.  Very young larvae of forest tent caterpillar on the twig of an apple tree.  They lack the distinct keyhole-shaped markings on the top side as seen in mature larvae.  All photos by the author.

Mature Forest Tent Caterpillar Larvae

Figure 2.  Mature larva of forest tent caterpillar, Mandan, June 2007.  Notice the white, keyhole-shaped markings on the top of the larva.

Controlling the insect was incredibly easy in this case – I clipped the ends off of three branches, removing the larvae and the egg masses (Figure 3).  However, if the infestation had been heavy, chemical control may have become necessary.  In such situations, Bt works well to control young caterpillars, while permethrin or pyrethrins or other insecticides are needed for older larvae.  As always, when using pesticides, follow label instructions carefully.

Forest Tent Caterpillar Egg Mass

Figure 3. Egg mass of forest tent caterpillar

Creative Commons License
Feel free to use and share this content, but please do so under the conditions of our Creative Commons license and our Rules for Use. Thanks.