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 (