Keeping our chemicals in their place – In the field

Abstract

This project specifically examined whether off-site movement of pesticides could be managed through the use of a range of tools and techniques including adjuvants, product formulations, product placement and application methodology. Specifically, imidacloprid applied as controlled release (suSCon) proved to reduce imidacloprid losses via runoff and leachates when compared to imidacloprid liquid (Confidor Guard) applied yearly. To reduce imidacloprid runoff loss when imidacloprid liquid is applied in ratoon cane with coulters, a consistent depth of application of 100 mm across the field was essential, as shallow or surface applications proved to dramatically increase imidacloprid losses. Closing the application slot did not assist in reducing runoff losses of imidacloprid. Different types of soil binding adjuvants added to the spray tank were tested for their role in minimising herbicide runoff losses. The oil-based adjuvant Grounded® proved to significantly reduce herbicide losses via runoff in a freshly tilled plant cane scenario, yet not in bare soil or trash blanketed ratoons. The polyol-based adjuvant Watermaxx®2 slightly reduced runoff losses in plant cane and trash blanketed ratoons. All tested adjuvants generally tended to slightly improve herbicide efficacy (non-significantly). Controlled released formulations of imazapic, hexazinone and isoxaflutole were sourced from an overseas supplier for testing. Difficulties in applying the microbeads using standard spray application equipment prevented homogeneous application and jeopardised the experiments. In preliminary trials, mill by-products (mud and ash) incorporated in plant cane or banded in ratoon generally resulted in an increase in residual herbicide concentrations and loads and a reduction in their efficacy to control weeds. These conclusions need validating in paddock-scale experiments. A proof-of-concept experiment using sorbents based on biochar proved effective in removing PS II herbicides from the runoff water. This technology could be used in an end-of-row capture device to reduce pesticide loads in drainage water leaving sugarcane fields.