Insecticide choice for alfalfa may protect water quality
Rachael Freeman Long, UC Cooperative Extension (UCCE) Farm Advisor, Yolo County
Mary Nett, Water Quality Consulting
Daniel H. Putnam, UCCE Specialist in Alfalfa and Forages, UC Davis
Guomin Shan, Research Scientist Dow Agroscicnces, Indianapolis (formerly Dept. of Entomology, UC Davis)
Jerry L. Schmierer, Farm Advisor, Colusa County
Barbara A. Reed, Glenn County
California Agriculture 56(5):163-169. DOI: 10.3733/ca.v056n05p163.
Some insecticides used for controlling Egyptian alfalfa weevil have been detected in California's surface waters and are of concern, due to their impact on water quality and toxicity to some aquatic life. To assess the impact of insecticide choice on water quality, we collected tail-water samples from on-farm alfalfa sites in the northern Sacramento Valley over a 3-year period. Samples were collected during irrigation after organophosphate and pyrethroid sprays were applied. We found significant differences between insecticide classes in the mortality of Ceriodaphnia dubia (water flea), a test organism used to detect pesticides in water. Nearly all sites where organophosphate insecticides were used resulted in 100% water flea mortality in a 24-hour test of tail-water samples; pyrethroid-treated sections of the same fields exhibited insignificant flea mortality. The pyrethroids we used provided significantly better control of Egyptian alfalfa weevil than the organophosphates, with no significant differences in beneficial insect counts. Although water runoff does not always occur in alfalfa fields, insecticide choice may be an important tool for protecting water quality. In addition, consideration should be given to the fact that pyrethroids, while they proved advantageous in these experiments, can affect beneficial species and do have high toxicity to fish at extremely low concentrations.
R. Freeman Long is UC Cooperative Extension (UCCE) Farm Advisor, Yolo County; M. Nett is owner, Water Quality Consulting, Colorado Springs, Colo. (formerly Walnut Creek, Calif.);; D.H. Putnam is UCCE Specialist in Alfalfa and Forages, UC Davis; G. Shan is Research Scientist Dow Agroscicnces, Indianapolis (formerly Dept. of Entomology, UC Davis); J. Schmierer is Farm Advisor, Colusa County; B. Reed is Farm Advisor, Glenn County;
Thanks to the California State Water Resources Control Board for providing funds for this work; Corin Pease, Irene Wibawa and Dave Brown for assistance with the fieldwork; and the UC Davis Aquatic Toxicology Lab.