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Editorial - Fed up with caterpillars? Here's how to fight back

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Editorial - Fed up with caterpillars? Here's how to fight back
Alexandria Minnesota 225 7th Ave E
P.O. Box 549

It's hard to like forest tent caterpillars. They can be a messy nuisance. They feed on the leaves of trees, and in rare instances, can weaken them enough to kill them.


And their numbers are climbing. The Minnesota Department of Natural Resources expects their population could be building to a peak in 2014 or 2015.

The Echo Press ran a story about forest tent caterpillars last month. The story delved into the concerns some residents have about the biological insecticide, Foray 48B, that is used to kill the caterpillars. They're worried that the aerial spraying of 48B may pose unintentional health risks to humans and other animals.

Since then, we've received some helpful information from the DNR about simple steps homeowners can take to naturally control forest tent caterpillars:

• Remove egg masses. Remove and destroy overwintering egg masses from branches of small trees before eggs start to hatch in the spring.

• Brush off or spray with water. Caterpillars and cocoons can be brushed off houses, picnic tables, or decks with a stiff broom or brush or knocked down with a forceful spray of water. Be careful not to crush too many caterpillars; they can smear and leave marks on some paints.

• Turn off exterior lights. Moths of forest tent caterpillars are attracted to lights. When moths are abundant, turn off exterior lights. This may reduce the number of egg masses laid on nearby trees.

• Build barriers. If you can determine that there are no egg masses in a tree or if you have sprayed the tree, you may be able to prevent migrating caterpillars from climbing up the trunk by the use of barriers. Basically, you construct a barrier band around the trunk made of duct tape, tin foil or tar paper and coat it generously with grease (Tanglefoot or vaseline). Never apply grease directly to the tree bark. The barrier band should be in the shade or you run the risk of killing the bark and cambium under the band. Check the barrier band daily to see if more grease or Tanglefoot is necessary. Remove the band in early July after the caterpillars have formed cocoons.

• Enclose gardens. Although recommended by homeowners, this next method has not been scientifically proven. To protect an area (garden), build a 24-inch-tall enclosure of plastic sheeting and secure its lower edge to make sure that caterpillars can't crawl underneath it. Spray the sheeting with vegetable oil to prevent the caterpillars from climbing the wall. Repeat oil application daily, or more often as needed.

So what about using insecticides?

Experts with the DNR point out that forest tent caterpillars rarely cause severe damage to trees, and the forest does not normally need the protection of pesticides. However, for some landowners such as resort owners, aerial applications of an insecticide to control forest tent caterpillars may be an option to consider.

Several insecticides are registered for controlling forest tent caterpillars, including the biological insecticide, Bacillus thuringiensis var kurstaki (Btk), which makes up about 2 percent of the formula in Foray 48B.

The DNR strongly recommends the use of Btk because of its environmental safety. Btk is a naturally-occurring bacterium effective against caterpillars that eat treated leaves. Btk has virtually no effect on birds, people, aquatic arthropods, other animals, and most insects, according to the DNR.

The bottom line: If a private landowner decides to use an insecticide, they should use a low risk one like Foray 48B. If they're going to apply it aerially, they should consider their goals, the rights of their neighbors, any environmental concerns they have and their ability to pay for the treatment.

Lastly, don't forget about the natural strategies. They may require more time and elbow grease but will be a better approach for everyone.

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