Soil-binding adjuvants can reduce herbicide loss via runoff

Concentrations of a range of pesticides exceed water-quality guidelines throughout the year in many fresh and estuarine water bodies of the Great Barrier Reef catchment. To mitigate its impact and maintain its productivity, the Australian sugar industry is looking at innovative options to reduce the movement of herbicides off site. Three oil-based adjuvants (Grounded (R) applied at 3 L/ha, Atpolan (R) soil Maxx applied at 0.4 L/ha and Ad-HereTM applied at 1L/ha according to their respective labels), a terpene-based adjuvant (Flextend (R) applied at 1.2 L/ha) and a polyol-based adjuvant (Watermaxx (R) 2 applied at 9.35 L/ha), were tested on bare soil and on a trash blanket for their potential to reduce runoff losses as well as improving the weed control efficacy of four registered pre-emergent herbicides applied at full label rate: imazapic (96 g/ha), hexazinone (975 g/ha), isoxaflutole (150 g/ha) and amicarbazone (700 g/ha). Herbicide-efficacy trials were implemented as randomised complete-blocks with three replicates and adjacent untreated controls. Losses of the tested pre-emergent herbicides in runoff were monitored using replicated rainfall simulations, delivering 80 mm of simulated rain, 48 h or 3 weeks after herbicide application. On green-cane trash-blanket, all oil-based adjuvants significantly increased the runoff of the tested herbicides, Flextend did not affect herbicide runoff and Watermaxx2 slightly reduced herbicide concentration in runoff by up to 25%. On bare soil, three of the tested adjuvants significantly reduced herbicide runoff losses. Grounded achieved the best outcomes by reducing herbicide concentration in runoff by about 35% when runoff occurred 48 h after application. Most of the tested products slightly increased herbicide efficacy on weeds in the efficacy trials, but the differences were not significant. If validated in other soil types and in bare soil ratoon cane, the use of Grounded (R)Psi could assist in improving the quality of runoff water leaving sugarcane paddocks and, therefore, reduce canegrowers impact on freshwater water and marine ecosystems.