A large infestation of feathertop Rhodes grass in southern WA, where it is spreading with summer rains.
Four populations of the increasingly widespread annual sub-tropical grass feathertop Rhodes grass (Chloris virgata) have been confirmed resistant to glyphosate.
Feathertop Rhodes grass (FTR) is yet another species that has increased its abundance during the past 10 years, largely due to the widespread adoption of no-till cropping and the shift to glyphosate-based weed control on road verges.
Dr Chris Preston, chair of the Australian Glyphosate Sustainability Working Group, says two populations from cropping in New South Wales and Queensland and two from roadsides in South Australia have not been able to be controlled with glyphosate at the seedling stage and have therefore been classified as resistant.
“Glyphosate is normally effective on actively growing seedlings; however, once FTR begins to tiller it is tolerant of very high rates.”
While the weed is not listed on any glyphosate herbicide labels, glyphosate has been widely used in Queensland and northern NSW to control seedlings.
FTR has been found across Australia for decades as a weed of roadsides, fencelines and unmanaged land, especially in summer rainfall areas and irrigated agriculture.
During the past 15 years it has become a major cropping weed in Queensland and northern NSW, as well as horticultural plantings such as vineyards.
The success of FTR is due to its rapid production of large numbers of seeds that are easily shed from the heads. Seeds germinate if left on the soil surface with sufficient moisture and temperatures above 25°C. Seedbanks appear to be short-lived (about 12 months) and burial of seed at any depth prevents germination.
Management strategies need to involve a range of tactics aimed at stopping the production of any fertile seed.
“This poses challenges on roadsides where most road managers have opted for glyphosate as the main strategy,” Dr Preston says.
“A shift to grass-selective Group A herbicides without a robust second ‘knock’ will lead to the rapid development of Group A resistance in this species.”
Australian Glyphosate Sustainability Working Group;
Dr Chris Preston, University of Adelaide,
08 8313 7237,
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