Colorado Potato Beetles plentiful in Red River Valley

It’s shaping up to be a Colorado Potato Beetle (CPB) year in the Red River Valley. Seems even if an at-plant insecticide was applied, CPB are plentiful in some fields. There are a few possible reasons this is happening.

The past winter was a good one, not only for us, but for the overwintering CPB. The milder temps probably resulted in lower winter mortality.

Over the past few years, I’ve been monitoring insecticide resistance in Minnesota and North Dakota CPB populations. We’ve started to see decreased sensitivity to neonicotinoid insecticides (by far the most common at-plant being used) in the central Red River Valley.

We’ve had some very wet conditions in some locations after planting. The at-plant insecticides are all water soluble, that’s what allows them to become systemic in the plants. The wetter the soils, the greater the potential for leaching, decreasing the amount of insecticide available to be taken up by the plant lowering efficacy.

Finally, we’re about 40-50 days post planting in many of these fields. The at-plant insecticides provide enough concentration to control CPB for 45-60 days post application. Given the current conditions, even fields that received an at-plant insecticide are probably susceptible to CPB by now.

Regardless of why, the issue is now management. Given how quickly this insect develops resistance, we want to make certain we’re rotating the modes of action of our insecticides; cheap controls today could mean much more expensive tactics will be needed later.

So, if you had a neonicotinoid insecticide applied at-plant, you’ll want to change up the mode of action for foliar applications. Click here for insecticide information.

If you do suspect you are dealing with a resistant population of CPB, call Ian MacRae at 218-281-8611 (office) or 218-280-9887 (cell) to arrange a test of the population.

— Ian MacRae, University of Minnesota

Source: University of Minnestoa Extension