A few years ago, a bioassay of alfalfa weevil larvae collected in a central Kentucky alfalfa field showed low levels of control by a pyrethroid compared to other insecticide modes of action. In this particular instance, pyrethroids were used exclusively for alfalfa weevil control for well over a dozen years. For alfalfa weevil, there are only 4 different modes of action registered. When pyrethroids lose their effectiveness, only three modes of action are left to select from for this pest. So, growers must be careful to not overuse one mode of action such that the pest population in an area becomes tolerant to that insecticide, or even resistant. Once a population becomes resistant to an insecticide or a group of insecticides, the population may stay resistant for a long period of time, even if the insecticide is not used. Read the full article in KY Pest News here.