Advancing environmental values in cotton catchments using risk assessment

Abstract

This project provided valuable review of environmental impact and development of risk assessment strategies within the Australian Cotton Industry. It was found that GM technologies can reduce potential environmental impact by reducing or changing pesticide use practice. Although the benefits of Bt cotton varieties and reduced endosulfan use are well documented, a strong correlation between pesticide use (per ha) and average rainfall was observed. This indicates that climatic conditions offer a potential predictor of environmental impact. These results are based on the assumption that insect pressure is greater during wetter periods, thus requiring more insecticide use. We would therefore expect to observe an increase in pesticide use and environmental impact when growing conditions improve, commensurate to the use of Bollgard cotton within the industry. Analysis of environmental impact of herbicide use did not show a significant reduction associated with the introduction of Roundup Ready (RR) cotton. These results indicate that improvements in herbicide use scenarios could potentially have been made by reduced use of "high impact" residual herbicides with introduction of RR cotton but this did not occur. However, the use of RR Flex and Liberty Link cotton may improve the potential environmental impact of herbicide use if such reductions in use of residuals is achieved. We also identified a slight negative trend (r2=0.3) between herbicide application and precipitation. This indicates that if the climates become drier then an increase in herbicide use (g/ha) will be observed. We expect this was either a response of growers, aiming for a higher level of crop protection for improved yields or reducing the risk of crop failure, or a more virulent response by weeds during dry periods. The results of the analyses conducted within this project were used to direct industry goals with respect to environmental custodianship. An experiment conducted within this project showed that pesticide residues dissipate faster in actively composted cotton gin trash (GT) than in passively composted GT. This experiment evolved from a previous study concerning potential environmental exposure and the regulation of GT wastes. Whilst composting of GT is recommended to reduce the concentration of pesticide residues, the resources required may be too large for an effective BMP. Further studies, with respect to reuse of GT, are more likely to identify a more suitable industry-wide management practices.