Austrailians Confirm Roundup-Resistant Brome Grass

Australian weed scientists have confirmed a population of Roundup-resistant great brome grass in the state of South Australia.

"This is the first time that this highly competitive annual grass weed of crops and pastures has evolved resistance to glyphosate and is the third Australian weed species confirmed as resistant to glyphosate in the past 12 months," according to an announcement from the country's Grains Research and Development Corporation. "

The resistant brome grass was found surviving in a pasture where an old fence had been removed and cropped over and a pre-sowing application of glyphosate had been applied. The fence line had previously been sprayed with glyphosate for many years with no other weed control tactics used."

Brome grass test samples in 
Australia after Roundup applications. 
Photo Australian Grain Research 
and Development Corporation.

"This is a huge concern to Australian grain growers because this highly competitive weed has been becoming a major problem in reduced-tillage farming," said Associate Professor Chris Preston, chair of the Australian Glyphosate Sustainability Working Group and leader of the University of Adelaide team which confirmed the result. "Currently, the number of glyphosate-resistant ryegrass populations evolving along fence lines is exploding. That and this new discovery are a real 'wake-up call’ and show that any weed might develop glyphosate resistance and growers need to be vigilant."

Brome grass is a major weed of crop and pasture on lighter textured soils across the southern and western Australian cereal belts. In wheat, there are few effective in-crop herbicide options for this species, and it can reduce yields by 30 to 40%. It also emerges after crop establishment enabling it to compete strongly with the crop and produce large amounts of seed.

Brome grass is also a host to a range of cereal crop diseases including take-all and barley net-blotch, while the mature seeds can injure stock. Populations of brome grass are already resistant to grass selective Group A and Group B herbicides in Victoria and Group B and Group C herbicides in Western Australia.

Preston knows that managing brome grass and other weeds along fence lines requires a diverse approach. Herbicides with different modes-of-action to glyphosate need to be included. On erosion-prone sites ground cover needs to be maintained so control along fences and firebreaks should take place late winter to early spring. The older tactic of sowing crops to the fence line then baling and spraying an area along the edge of the crop for a firebreak is a valuable way of stopping weeds moving into the crop while protecting the soil.