Developing Economic Injury Levels for Thrips (Frankliniella occidentalis) in Idaho Alfalfa Under Controlled Pest Populations

Thrips are a new pest of alfalfa in Eastern Idaho. University of Idaho Extension Educators studied the yield losses associated with this pest in a controlled greenhouse experiment. This data has been used to calculate the economic injury level (EIL) of thrips in alfalfa. The EIL represents the level of insect infestation at which control measures will begin to be economically viable. We calculate that for the 2021 growing season conditions the EIL was approximately 20 thrips per six stems. We also calculated EIL curves that growers and consultants can use as spray costs and hay values change.