During the 2021 season, we conducted an insecticide trial evaluating a new insecticide being developed for a range of crops. It could be a very good fit for alfalfa weevil given the efficacy we saw as well as the critical need for novel modes of action for alfalfa weevil management. The need for more modes of action comes from the growing issue with pyrethroid resistance in alfalfa weevils. Across the US (an in California), there are now populations of pyrethroid-resistant alfalfa weevils. We are addressing this in a separate project, focusing primarily on resistance to lambda-cyhalothrin. New modes of action could allow for rotation, something that is very difficult given that currently, effective options are mainly limited to...
- Author: Thomas Getts
- Author: Rachael Long
Picture 1: Adult alfalfa weevil
Alfalfa weevils, key pests of alfalfa hay, have been showing pyrethroid insecticide resistance within the Intermountain region, specifically in the Scott Valley area west of Mount Shasta. In some alfalfa fields, weevil counts have been off the charts with 100 weevils per sweep, FIVE times the economic threshold level. These same fields showed little efficacy on weevil control by pyrethroids. In a 2016 test only 3-15% of weevils collected from conventional fields died from exposure to pyrethroids. Weevils collected from organic alfalfa fields that had no exposure to pyrethroids showed a 92% mortality (