TALKIN WITH DOKKEN: What can be done to control tent caterpillars?

Q. I've heard reports that this is going to be a bad year for forest tent caterpillars. Where is the risk of an outbreak the highest and what can be done to control the pests?...

Q. I've heard reports that this is going to be a bad year for forest tent caterpillars. Where is the risk of an outbreak the highest and what can be done to control the pests?

A. You're right -- it's definitely looking to be a bad year for the leaf-munching caterpillars in parts of Minnesota and, to a lesser extent, North Dakota.

Forest tent caterpillars tend to peak every 10 to 15 years. They're gross and squishy and occur in huge gobs, crawling up walls and trees and just about anything else that can be scaled. But fortunately, they don't cause a health risk to humans and don't result in long-term damage to trees and other plants, except in rare cases.

According to the Department of Natural Resources, the potential for moderate to heavy defoliation is greatest in portions of north-central and east-central Minnesota. Far northwest Minnesota, including Kittson County and the western half of Marshall County, isn't expected to have any defoliation, although a trace to light problems are forecast for eastern Marshall and adjacent parts of western Beltrami counties.

The forecast predicts trace defoliation in Roseau and Lake of the Woods counties.


The peak of the infestation generally occurs the first three weeks of June, so it won't be long before we know the extent of the outbreak. Cross your fingers it's not like 2001, when every tree from Grand Forks to Lake of the Woods and points beyond seemed to be stripped bare.

As for managing the pests, the DNR says caterpillars and cocoons can be brushed off walls, picnic tables or decks with a stiff broom or knocked down with a pressure washer. Just don't use too much pressure because the caterpillars can smear and leave marks on some painted surfaces.

Insecticides such as Tempo or a microbial treatment called Btk (marketed as DiPel or Thuricide), also can keep the caterpillars at bay, though spraying won't lessen the risk of caterpillars next year. I've also heard of homeowners erecting small fences and smearing them with Vaseline to prevent the caterpillars from crawling into specific areas.

Unfortunately, there's no cure-all for dealing with these pests. Outbreaks usually run their course by late June, and severe outbreaks eventually result in the population reaching a "tipping point" and crashing.

You'll find more information about forest tent caterpillars and controlling them by going to the DNR website at and typing "forest tent caterpillar" in the search window on the upper right corner of the page.

If you have a question for Talkin' with Dokken, call (701) 780-1148 or send an email to .

Brad Dokken joined the Herald company in November 1985 as a copy editor for Agweek magazine and has been the Grand Forks Herald's outdoors editor since 1998.

Besides his role as an outdoors writer, Dokken has an extensive background in northwest Minnesota and Canadian border issues and provides occasional coverage on those topics.

Reach him at, by phone at (701) 780-1148 or on Twitter at @gfhoutdoor.
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