Correlation of Chemical Analysis of Residual Levels of Aminocyclopyrachlor in Soil to Biological Responses of Alfalfa, Cotton, Soybean, and Sunflower

Abstract Researchers, product registration personnel, and growers desire the ability to chemically detect residual amounts of herbicides in soil at concentrations below those necessary to cause phytotoxicity to sensitive nontarget or rotational crop plants. Alfalfa, cotton, soybean, and sunflower, crops sensitive to low concentrations of aminocyclopyrachlor in soil, were planted at field test sites approximately 1 yr after aminocyclopyrachlor methyl was applied. Soil samples were collected when rotational crops were planted and were analyzed for aminocyclopyrachlor by a method based on high performance liquid chromatography tandem mass spectrometry (HPLC/MS/MS), with a limit of detection (LOD) of 0.1 part per billion (ppb) (soil oven-dry weight basis). Loglogistic dose–response analysis correlated visual phytotoxic plant responses to residual concentrations of aminocyclopyrachlor in the soil. Concentrations of aminocyclopyrachlor estimated to cause 25% phytotoxicity to alfalfa, cotton, soybean, and sunflo...