August 12, 2002

Resistance of annual ryegrass to glyphosate herbicides, widely-used in Australian agriculture, is growing.

According to Chris Preston, of the CRC for Australian Weed Management, there are now 11 confirmed ryegrass populations in Western Australia, Victoria, South Australia and Newe South Wales with resistance – most of these being in no-till grain or horticulture enterprises. He said resistance to glyphosate had so far only occurred where there had been intensive selection of resistance to glyphosate, little or no soil disturbance, and few other herbicides applied.

"All of the populations from no-till cropping are also resistant to other herbicides as well as glyphosate," Dr Preston said.

"To curb the development of resistance in weeds there is a need to keep weed numbers low, rotate herbicides with different modes of action, stop weeds from setting seeds and use different weed control methods – not herbicides exclusively."

Dr Preston, whose work is supported by the Grains Research and Development Corporation, can be contacted at +61 (0)8 8303 4455.