Organophosphate insecticides are frequently found in California’s waterways and have been a concern of water quality regulators for years. The presence of these insecticides is associated with irrigation and storm water runoff from both urban and agricultural sources. Choosing an insecticide with minimal potential to move offsite can protect surface water quality. Our research showed that organophosphate insecticides used for Egyptian alfalfa weevil control in alfalfa moved offsite in irrigation tail-water at concentrations toxic to the water flea, Ceriodaphnia dubia. Tail-water samples from pyrethroid treated fields did not induce toxicity to the water flea, nor did we find any chemical traces of pyrethroids in these tailwater samples at a detection limit of 50 ppt. Although pyrethroids can move offsite attached to soil particles, higher levels of sediments were often found in the source than tailwater samples from alfalfa fields. The pyrethroids gave significantly better control of the Egyptian alfalfa weevil than the organophosphate treatments.
Species 1: Coleoptera Curculionidae Hypera brunneipennis (Egyptian alfalfa weevil)
Keywords: insecticides, water quality
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