A five-year survey of the entire Australian cropping belt has revealed a sobering picture of growing herbicide resistance in key cropping weeds.

Dr John Broster from the Graham Centre for Agricultural Innovation heads up a joint herbicide resistance monitoring project between Charles Sturt University, Queensland Department of Agriculture and Fisheries and the Universities of Adelaide and Western Australia.

Dr Broster says if growers lose glyphosate, they’ll have to use more complex, more expensive methods of controlling weeds.

“If you use herbicides, you will get resistance,” Dr Broster said.

In a 5-year cycle the group visited 3000 randomly selected paddocks and took 2000 samples of the nation’s number one weed, ryegrass, which is followed by wild radish in WA, wild oats in Queensland and NSW, and sow thistle in fourth place

The most concerning discovery was the increasing resistance to the most important herbicide, glyphosate.

Across Australia glyphosate resistance is 5 per cent in the populations of ryegrass, but in a region like the Liverpool Plains in NSW it was in 29 per cent of the populations that were surveyed.

By using other methods to control plants that survive herbicide applications and prevent them from setting seed, then growers may be able to slow the development of resistance to enable the use of herbicides for longer.

Dr Broster says farmers generally are responsible in their management of weeds.

“Even though there are high levels of resistance in the ryegrass to selective herbicide groups, and even glyphosate, at harvest time when researchers collect the weed seeds, most populations are below one plant per square metre,” he said.

“So even though it’s more complicated, they’re managing populations quite well using alternative herbicides and other methods than herbicides to control the weed populations.”