Phenoxy herbicides in Alberta rainfall: Potential effects on sensitive crops

Abstract

During 1999–2000, we detected phenoxy herbicides in Alberta rainfall at levels as high as 17 to 53 μg L -1 , or 60 to 149 μg m -2 . In this study, we conducted indoor bioassays to determine whether injury to sensitive crops could occur from such herbicides in Alberta rainfall. Spray conditions were chosen that maximized exposure of greenhouse-grown plants to simulated rain containing a mixture of 2,4-D, bromoxynil, MCPA and dicamba at 2.25 g ha -1 total rate. Bean and tomato plants showed permanent sub-lethal effects (P < 0.05), sunflowers showed enhanced effects (P < 0.05), while sugar beets showed only transient injury (P < 0.10). There were no effects (P > 0.05) on potatoes. Although caution is required when extrapolating from indoor bioassays, we conclude that injury to beans and tomatoes is possible in the field. Field experiments should be conducted to establish the likelihood of such injury. Key words: Phenoxy herbicides, atmospheric deposition, sub-lethal effects, non-target crops