All too familiar to most of us, army worms (tent caterpillars) seem to be everywhere. Although their defoliation to trees rarely kills, army worms are as much a nuisance as they are messy. The good news is that they will end visiting us in a few years as they have a cycle of 10 to 15 years. Ralph LaPlant Photo

It if isn’t the mosquitoes or deer flies, it’s the army worms. During the past few summers it appears we have been plagued with these creatures. They visit us every 10 to 15 years and it appears we are in the middle of the current visit, which will probably be peaking for a few more years.
Beginning in June, as a rule, army worms (also called tent caterpillars) start defoliating trees by chomping on the leaves of hardwoods. Thousands of acres can be preyed upon and aspen and birch trees in northern Minnesota and basswood and oaks in central southern Minnesota are main targets. They will feed on any broad-leaved tree except the red maple.
    The good news is that rarely does army worm defoliation cause the death of trees. If unaffected by drought and/or other complications, trees should rebound to a healthy status, as the caterpillars usually consume no more that 60% of a tree’s leaves.
These caterpillars can cause other problems. Back in 1952 it was reported that cars were sliding off of roads and plows were called out to remove the pests. A train was stuck attempting to climb a grade as it slipped. Again, the cause was army worms.
What can you do to “survive” an attack of army worms? The DNR suggests the following:
Brush the caterpillars off houses and lawn furniture with a stiff broom or a stream of water. It is important not to squish the caterpillars to prevent staining.
Cocoons are more difficult to remove than the caterpillars. Us a stiff broom to brush them off your house. Bag, burn, bury, or compost the cocoons to keep the caterpillars from coming back.
Beware of what chemicals you use to spray decks and lawn furniture. Some sprays can cause damage to paint or stain.
Use a biological insecticide with Bt (Bacillus thuringienses) in it. These chemicals are recommended by the DNR because of their safety and low toxicity to organisms other than forest tent caterpillars. Apply this to the leaves of trees and plants.
Watch fruit trees, raspberries, and garden plants closely. The effects of defoliation can be fatal.
Try duct-taping the trunks of your valued trees and apply Vaseline to the tape. This will make the trunk too slippery for the caterpillars. Remove the band after the caterpillars have built their cocoons.
The most helpful thing you can do for your trees is keep them well watered. This will keep the tree healthier and less susceptible to other diseases that are fatal during a forest tent caterpillar outbreak.
Be patient. They won’t be around forever, and if you help your plants through the outbreak, they will be back to normal in a year or two.