Herbicidal effects on nontarget vegetation: investigating the limitations of current pesticide registration guidelines.

The impact of herbicide exposure on nontarget vegetation within agroecosystems has sparked extensive research that revealed that current pesticide registration guidelines may be inadequate at predicting the effects of herbicides on wild plants and habitats. This study extends the current interest by presenting three experiments highlighting some of the limitations to current phytotoxicity testing guidelines. Several crops and wild plant species were grown under greenhouse conditions following standard protocol for phytotoxicity testing. Plants were sprayed with five different herbicides at the four- to six-leaf stage, and biomass was recorded at 28 d after spray. Results showed that current regulatory protocol will likely underestimate herbicide phytotoxicity if testing does not include data for the complete tank-mix formulation. The present study also showed that the range in herbicide sensitivity among cultivars of the same crop can be quite extensive and that, depending on the cultivar included in a risk assessment, conclusions regarding the phytotoxicity of any given herbicide may differ. Although no significant differences in sensitivity were found between crops and related wild species, results revealed that current guidelines are too rigid in terms of species selection. Considering the variability among crop cultivars, coupled with the ecological importance and the ease of germination of many noncrop plant species, pesticide regulatory guidelines would be improved if wild species were included in testing. Findings of the present study indicate that current pesticide regulatory guidelines require modifications to ensure a more accurate assessment of herbicide effects on nontarget plant species.