According to the University of Minnesota Extension SpudBug newsletter, 2016 is shaping up to be a Colorado potato beetle year in the Red River Valley. It seems that even if an at-plant insecticide was applied, Colorado potato beetles are plentiful in some potato fields.
Ian MacRae of the University of Minnesota Department of Entomology—the writer of the SpudBug newsletter—provides a number of possible reasons for this happening:
- Last winter was a good one for overwintering Colorado potato beetles in the Red River Valley. The milder temperatures probably resulted in lower winter mortality.
- Over the past few years, MacRae has been monitoring insecticide resistance in Colorado Potato Beetle populations in North Dakota and Minnesota. He has started to see decreased sensitivity to neonicotinoid in the central Red River Valley.
- Some very wet conditions after planting existed in many parts of the Red River Valley. 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.
- The Red River Valley is 40 to 50 days past planting in many of these fields. At-plant insecticides provide enough concentration to control Colorado potato beetle for 45 to 60 days post-application. Given current conditions, even fields that received an at-plant insecticide are probably susceptible to Colorado potato beetle by now.
Here are MacRae’s remarks regarding management and the attention growers need to pay to the development of resistance:
“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.”
Source: PotatoPro