Glyphosate resistance in mobile weeds across land uses: implications for area wide management of weeds

Weeds that have the ability to rapidly disperse across the landscape can create ongoing problems for individual land managers. Efforts by land managers to reduce the risk of a weed problem can be negated by such mobile weeds moving across boundaries. When mobile weeds are easy to control using current practices, there is little incentive for more coordinated action among land managers. However, for more difficult to control weeds (or resistant weeds) there may be a case for collective action through an area wide weed approach. This project examined the distribution of glyphosate resistant weeds at a local scale in the Sunraysia, the Riverina and the Darling Downs. Based on local land manager consultation, the study focused on the three most concerning mobile weeds: Conyza bonariensis (flaxleaf fleabane) in the Sunraysia, flaxleaf fleabane and Lolium rigidum (annual ryegrass) in the Riverina and Chloris virgata (feathertop Rhodes grass) in the Darling Downs. Geo-referenced weed seed samples, plants in the case of annual ryegrass, were collected from a variety of land uses in each district in 2019- 2020 and 2020-2021, including public land and roadsides, and the samples tested for resistance to glyphosate. Samples with survivors to glyphosate were considered to be resistant. High frequencies of glyphosate resistance were identified in all weeds and in all districts ranging from 5% of flaxleaf fleabane samples in the Sunraysia in 2021 to 81% of annual ryegrass samples in the Riverina in 2021. Spatial patterns of resistance status were analysed for each weed and region. Resistance occurred across the area sampled and was present on multiple land uses, including non-farm land. As land managers from multiple sectors already need to manage these resistant weeds, the incorporation by all land managers of practices that reduce seed production, and hence potential for spread of these weeds would be beneficial.

Preston, C., Dolman, F. C., Morgan, T., Quarisa, I., Kirby, R., & Ratcliff, C. (2022). Glyphosate resistance in mobile weeds across land uses: implications for area wide management of weeds. Proceedings of the 22nd Australasian Weeds Conference Adelaide September 2022, 194–197. https://caws.org.nz/wp-content/uploads/2024/08/22AWC_Proceedings_Rev_B_SEC_IDX-1-Edited-by-Melland-et-al-2022-1.pdf#0244-page1