HWSC effective for brome grass management

image of brome grass
Brome grass seed heads are often taller than the crop, and normally retain some seed at harvest. (Photo: C. Borger)

When it comes to controlling brome grass, new research supported by the Grains Research and Development Corporation (GRDC) indicates any amount of harvest weed seed control (HWSC) is better than none.

The ‘Emerging weeds’ GRDC investment, led by the University of Adelaide, included studies of brome grass in field trial sites at Wongan Hills, Western Australia, and Roseworthy in South Australia.

Western Australia Department of Primary Industries and Regional Development (DPIRD) research officer Catherine Borger, who led the Wongan Hills study, then used the findings to model HWSC outcomes for brome grass in the Weed Seed Wizard decision tool.

Her results confirmed that HWSC methods such as seed impact mills will help growers reduce the brome grass soil seedbank in their paddocks.

“The trials taught us a lot about how competitive brome grass can be in cereal crops and the quantity of seed it can produce under favourable conditions,” Dr Borger said.

“However, our modelling across six wheat and lentil rotations showed that even destroying 20 per cent of brome grass seed at each harvest could reduce the soil seedbank by half compared with no HWSC over the same period.”

Dr Borger says a key strategy for improving seed capture is to harvest early, as brome grass seed shedding is very unpredictable and may be triggered by genetic traits as well as environmental factors.

“If the harvest and weed seed capture can be completed before brome grass sheds most of its seed, the soil weed seed bank will be that much more diminished,” she said.

“Seed shedding can occur any time from October and can happen very rapidly, with plants going from 80 per cent seed retention to as little as 10 per cent in a matter of days.

“However, some populations may retain a portion of their seeds well into summer with no tendency to shed.”

Dr Borger said the modelling demonstrated the value of capturing any remaining seeds at harvest, even if the majority had already been shed.

“We were very encouraged to see that capturing just 20 per cent of brome grass seeds can have a powerful effect on reducing the soil seedbank,” she said.

“It shows any level of seed control is better than zero seed control at harvest, especially as part of a long-term integrated weed management strategy.”

The Weed Seed Wizard decision-making tool used for the modelling is freely available online and allows growers to set regional variables like rainfall and weed pressure.

It can be downloaded via the DPIRD website.

The field trial data Dr Borger and her team used for their modelling is currently being incorporated into the public version of Weed Seed Wizard.

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