Looking beyond Glyphosate for Site-Specific Fallow Weed Control in Australian Grain Production

Summer annual weed species in northern Australian summer fallows are frequently present at low densities and, increasingly, are glyphosate-resistant, creating the need for alternative herbicides for site-specific weed control. Alternative non-selective herbicide treatments are effective on problematic summer fallow weeds; however, many are yet to be evaluated as site-specific (spot spraying) treatments. This study aimed to identify herbicides that could be used in place of glyphosate to control larger/mature Chloris virgata and Sonchus oleraceus plants. The response of these weed species to 12 herbicide treatments was evaluated in pot experiments conducted over summer/autumn 2022. Despite herbicide treatments not being consistently effective across both species, there were instances where control was achieved by some herbicide treatments. S. oleraceus was controlled (i.e., & LE;10% plant survival) by glufosinate-ammonium, paraquat and also with protoporphyrinogen-oxidase (PPO)-inhibiting herbicides saflufenacil, tiafenacil and trifludimoxazin. However, these results were not consistent in repeated studies or for C. virgata. Glyphosate was the only herbicide that controlled C. virgata. A glyphosate replacement as a spot-spraying treatment was not identified, and until further studies are more successful, alternative approaches are needed to preserve the ongoing effectiveness of this herbicide.

Automated summary

Summer annual weed species in northern Australian summer fallows are frequently present at low densities and are increasingly glyphosate-resistant. This study aimed to identify herbicides that could be used as alternatives to control Chloris virgata and Sonchus oleraceus plants. While some herbicide treatments showed control of S. oleraceus, consistent control or replacement for C. virgata was not achieved. Glyphosate was the only effective herbicide for C. virgata, highlighting the need for alternative approaches to preserve the effectiveness of glyphosate.