Using pasture to shock weeds out of crops

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AHRI’s Dr Yaseen Khalil oversaw the trial. Using diverse crop rotations is a key component in the WeedSmart Big 6 integrated weed management program. Photo by WeedSmartAU

Adding a pasture phase to a cropping rotation can take weeds by surprise and deplete their seed banks, research has found.

In 2019, WeedSmart began a three-year trial to see what pasture rotation rattled weeds the most.

The study found a one-in-three-year rotation in a wheat crop (using pasture legume serradella) reduced the rye-grass seed bank by more than 50 per cent.

The worst performing rotation was a none-in-three-year control, where wheat was sowed successively, even though best-practice herbicide and non-herbicide options were used.

Australian Herbicide Resistance Initiative (AHRI) research associate Yaseen Khalil said a single species pasture legume such as serradella provided multiple benefits and could put a large dent in the annual rye-grass seed bank.

“Pastures can be an effective tool to disrupt the evolution of herbicide resistance without compromising grain production,” Dr Khalil said.

“The pasture phase can build soil nitrogen stores, rapidly exhausting the weed seed bank and suppressing soil-borne crop pathogens.”

Alongside a team of researchers, Dr Khalil investigated the effects of seven different cropping rotations on high-weed-pressure fields in Bolgart and Brookton, in Western Australia.

The tests were done over the 2019, 2020 and 2021 winter growing seasons.

“At both sites, the more diverse rotations were as effective at reducing annual rye-grass seed production as three years of winter chemical fallow,” Dr Khalil said.

The study found early-season weed intervention during the pasture stage did little to suppress annual rye-grass on its own, but was effective on barley and brome grass.

Season-long ‘excellent control’ and ‘glyphosate-free’ treatment decimated grass weed seed production while allowing high pasture biomass and seed production.

Late season treatments done when the pasture is terminated were also effective in reducing the seed bank.

More information about the study can be found at WeedSmartAU.