Resistant Weeds – “Immunize” Your Farm, Says Australian Weed Specialist

WeedSeeker - Optically-based spot-spraying of weeds.

WeedSeeker - Optically-based spot-spraying of weeds.

In the fight against herbicide-resistant weeds, Tony Cook calls on his growers to immunize their farms against the threat.

Tony Cook, Weed Specialist, Department of Primary Industries, New South Wales, Australia
Tony Cook, Weed Specialist, Department of Primary Industries, New South Wales, Australia

That’s a different way to think about prevention, although the approach includes key methods advocated by weed scientists far and wide. For Cook, it means taking steps that prevent widescale problems.

Cook, an Australian weed specialist with the Department of Primary Industries in New South Wales, notes that the spread of herbicide-resistant weeds is quite predictable. Once a few materialize, it’s a given that the problem will spread and intensify if that first batch goes unattended.

“If growers concentrate on minimising or preventing weed seed set, they can win against herbicide resistance,” Cook noted in a web article on the Australian site, weedsmart.com. “The trick is to use a variety of means to keep weed numbers low and to keep pressure on seed set. If resistant plants are prevented from setting seed, then the problem is contained.”

To gain a fuller understanding of what’s working in terms of preventing resistant populations, Cook interviewed four farmers in Australia’s northern region who had steadily beaten back patches of 4 glyphosate-resistant weed species. The weed list included a couple of species familiar to U.S. farmers – barnyardgrass and annual ryegrass.

The growers drove down seed numbers in the soil by preventing weed seed set for at least 5 years, Cook found.

“The costs associated with treating the patches is an additional expense but this pales in significance against the cost of doing nothing and allowing the patches to spread across paddocks (fields) and beyond,” he says.

“Some growers have been successful in completely eradicating herbicide resistant plants from patches of one hectare (2.47 acres) or less through very focused efforts to prevent seed set,” he specifies.

Cook says that a wide array of methods – both mechanical and chemical – went into the farmers’ strategies.

“A shift in cropping rotation and well-timed use of paraquat in place of glyphosate is another useful strategy to drive down weed numbers for these key species,” he adds. “While spot spraying can be a good option, it is easy to miss the outlier plants in a small patch.”

Optical sprayers also might better target stray weeds, as would followup treatments with different modes of action.

And avoiding continuous use of a given herbicide will prolong its life, Cook says.

“We know that routine use of glyphosate every year in the fallow will cause glyphosate resistance in the weed population within 15 years if no follow-up action is taken to remove survivors,” he adds. “It may then take another 5 or 6 years for the glyphosate resistant weeds to dominate in a paddock, again if no follow-up action is taken.”

More details about Cook’s findings can be found in a webinar conducted by Cook and Peter Newman with the Australian Herbicide Resistance Initiative.