Forest Tent Caterpillars Defoliating Oaks in Manitoba

Caterpillar Outbreak: Forest Tent Caterpillars, Not Tent Makers

The 1.5-inch gray-green caterpillars stripping your oaks near Lake Winnipeg are forest tent caterpillars—they don’t build tents. They have one generation per year, feed 2–4 weeks, then pupate. The “rain” is their frass (droppings).

Control in Canada

Canadian pesticide options are limited. In the U.S., products with permethrin, lambda-cyhalothrin, cyfluthrin, bifenthrin, carbaryl, acephate, or malathion work. Spraying the trunk kills caterpillars as they crawl down.

Good News

• They won’t kill the tree.
• Oaks will re-leaf this year if cold doesn’t come too early.
• Next spring, canopy returns normally.

Ride it out—nature usually balances these cycles.