Forest Tent Caterpillars

2022 Forest Tent Caterpillar Spraying Campaign

Around the beginning of June each year, lake residents start to notice a creepy-crawly phenomenon: worms. They seem to be everywhere! They cover your roof, the sides of your house, the lawn, your trees and bushes and even fall onto your plate as you’re enjoying lunch on the deck. No birds or animals eat the worms, so once they start multiplying there is no natural process that controls the worm population. Left unattended, these small creatures will happily defoliate every tree and bush in your yard by the end of summer. If this happens too many years in a row, eventually your vegetation will die.
Fortunately, there is a solution! You are probably aware that area lakes have been sprayed for these pests in the past… Those who choose to participate in the program pay a small fee of $35 and come spring, their property will be sprayed to prevent the otherwise inevitable nuisance.
Not only is it smart to take advantage of this program for yourself, it’s also a good idea to tell your neighbors about it as well. Your property and neighbors will not be sprayed if we do not receive enough money.
The eggs hatch in late May/early June, and approximately one week later, when the worms are about ¼ inch long, the sprayers come through. The database of paid participants of the worm-spraying program is downloaded into the aircraft’s GPS system, which keeps track of what properties to spray and what properties to skip. (Send e-mail to ‘’with property identification if you want to be skipped)
The Otter Tail Lakes Property Owner’s Association hires West Central Ag-Air out of Fergus Falls for the spraying. Residents taking advantage of the program are notified of the spraying schedule a couple of days before it begins. Once the spraying starts, the lakes receive two swipes of the spores and endotoxin of a soil born bacteria called Bacillus Thuringiensis, commonly abbreviated as Bt.
Bt affects nothing but the worms and has been in use for decades for caterpillar control throughout the United States and Canada. The commercial name of the product that is used is Foray 48B. Since the worms crawl to the top of the trees and eat their way down, aerial spraying is the most effective way of applying Bt. Spraying is most effective on a very windy, dry day. Because the Bt could wash off the trees before the worms ingest it, it’s important to spray when it won’t rain for at least two days.
Send in your $30 as soon as possible to protect the foliage around our favorite lakes!! Please make checks payable to OTLPOA Worm Fund and send to: POBox 21, Battle Lake, MN 56515-0021.   Also please add the name of your lake on the check.
For more information please visit the Otter Tail Lakes Property Owner’s Association website: or the DNR website at

Worm Spray Information

Worm Policy

University of Minnesota

Minnesota DNR