Comparative efficacy and environmental profile of the newly registered herbicide Palmero®TX

Promoting weed control strategies that help reduce the movement of herbicides off site has been a priority for the sugar industry for the last decade. Pre-emergent herbicides are a very useful farming tool as they prevent weeds from germinating for weeks, but this long-desired persistence has a drawback as active ingredients can be transported by runoff into water bodies of the Great Barrier Reef catchment. A new pre-emergent herbicide Palmero®TX (isoxaflutole 150 g/ha, terbuthylazine 1500 g/ha), recently registered for use in sugarcane in Australia, was compared to Bobcat®i-MAXX SG (imazapic 94.5 g/ha, hexazinone 472.5 g/ha), AmiTron® (amicarbazone 700g/ha) plus Balance® ((isoxaflutole 150 g/ha), and Valor® (flumioxazin 350 g/ha), in trash blanketed ratoons, monitored in 2020 in far-northern Queensland. This paper reports on the herbicide efficacies in preventing weed germination and on comparative runoff loss of the herbicidal actives and their associated aquatic risk. Efficacy trials were implemented with three replicates and adjacent untreated controls. Losses in runoff were monitored using replicated rainfall simulations. Weed control varied at each site depending on the environmental conditions and the weed species. Palmero®TX performance was either equivalent to other tested alternative products, or inferior, although the nature of its limitations needs further investigation. Runoff data highlighted relatively high runoff losses of terbuthylazine in line with its higher application rate. However, when runoff occurred 3 weeks after spraying, terbuthylazine losses in runoff were lower than expected. With an estimated protective concentration that will protect 95% of the freshwater species of 1.2 ?g/kg for terbuthylazine and 0.46 ?g/kg for isoxaflutole, Palmero®TX had a slightly lower impact on aquatic freshwater species compared to Bobcat®i-MAXX SG, although slightly higher than AmiTron®+ Balance® when runoff occurred 3 weeks after spraying. The faster reduction in terbuthylazine runoff loss over time makes Palmero®TX a suitable pre-emergent herbicide alternative on trash blankets.