Alert: Are the Weeds Winning?

Cartoon of farmer with weed sprayer attacked by large weed while scientist looks on, commenting: "That's odd - it gave excellent results back at the lab!"

Call for more integrated strategy

Are the weeds winning? It's becoming a more common question with news of growing herbicide resistance in cropping weeds. Agronomists, such as John Holmes of Agriculture WA, remain optimistic about the war against weeds, but believe there has to be a massive and immediate change in battle strategies by farmers and their advisers. "Basically people are reacting (to herbicide resistance), not planning," Mr Holmes told Ground Cover

"One example is the huge increase in the use of trifluralin by graingrowers. In WA alone it has gone from about 90,000 litres used in 1990, to 1.5-2 million litres today. This seems to be a straightforward reaction by farmers to resistance to other herbicides."

Single herbicide use suicidal

Rather than relying on a single herbicide to control weeds, Mr Holmes and his colleagues are imploring farmers to adopt a spectrum of weed control measures including the use of multi-group herbicide mixes, delayed sowing, hay making and green manuring, spray topping pastures, crop topping lupins and peas and other control measures such as weed seed catching at harvest and burning and swathing crop residues.

Ross Britton of Primary Industries SA, one of six extension officers on a GRDC-supported resistance awareness program, says that most farmers are aware of herbicide resistance and its cause. "However, the majority have yet to adopt integrated weed management (IWM) as part of their farm operations," he said. "As an industry we need to recognise that weed flora change, depending on what control and management methods are used.

"For example, heavy reliance on group A or group B products will lead to resistant weed populations. Another example — as you increase soil fertility, so will you get more capeweed, ryegrass and barley grass."

Getting on top of ryegrass

Stephen Powles and John Matthews, of the Cooperative Research Centre for Weed Management Systems, forcefully advocate integrated weed management (IWM) strategies (see an introduction to the CRC, p10). They warned at the recent GRDC-sponsored Australian Weeds Conference that successful long-term management of multiple herbicide resistance in ryegrass could not be achieved by simply changing herbicides.

"Research on IWM strategies has shown that delayed crop seeding, increased crop density and competitive crops, as well as non-crop periods can reduce the ryegrass populations to below the crop damage threshold in many instances," they said.

"The most far-reaching change required for successful management (of herbicide resistance) involves a change in attitude by growers and those who advise them."