Control of brome grass is becoming increasingly difficult throughout south-eastern Australia’s cropping zone due to high herbicide resistance, increasing seed dormancy and spread of the weed from its traditional low rainfall area to new regions.
Brome grass growing in wheat at a University of Adelaide trial at Balaklava
GRDC-funded research by the University of Adelaide is investigating methods to effectively manage brome grass without heavy reliance on herbicides.
Research officer Sam Kleemann says that the key to managing brome is to take a long-term approach.
“Growers in the past often had the belief that one year was adequate to control brome but we’ve debunked that premise. Our work has shown that brome seeds have very high persistence in the soil, with 20-30 percent of seeds carrying over from one year to the next. This means you need an absolute minimum of two years to get control over a brome problem,” he said.
Dr Kleemann recommends a strategy addressing weed seed-set and rotations to reduce the reliance on pre-emergent and post-emergent herbicides.
“There has been a shift in the seed biology, particularly in great brome (B. diandrus), which means the seed dormancy has been increasing and the weeds are not germinating until at or after sowing. This means that pre-sowing control is less effective and puts much greater reliance onto pre-emergent and group B selective herbicides,” Dr Kleemann said.
Surveys by the university in a previous GRDC-funded project showed high levels of resistance to group B herbicides, with 40-50 percent resistance to Atlantis® and CrusaderTM in the South Australian Mallee and 40 percent resistance to Atlantis® in Victoria.
“This rise in resistance means there may be a time soon when we will have no post-emergent herbicides that can be used in cereals on brome grass, and while we’ve been working hard to identify new chemistries, so far there are no good results – we don’t have anything up our sleeves,” he said.
Pre-emergent control options are no more promising because most common options are ineffective. The most common practice in wheat is use of trifluralin but our trials have shown trifluralin may only provide about 50 percent control in wheat. The combination of Sakura® and Avadex® has been shown to be more effective but the high cost means it is often uneconomical.
With herbicide control providing no easy solutions, an integrated weed management strategy is needed to control the problem weed.
“Where there are severe brome patches in cereals, in the range of >50 plants per square metre, I would recommend growers patch out the area with a knockdown herbicide such as glyphosate before it can set seed. Where the soil type permits, narrow windrow burning can be a good control method, or else options such as chaff carts can help reduce the seedbank,” Dr Kleemann said.
“However the most effective control will be to use rotations. For a severe infestation, use a pulse or break crop with a grass selective herbicide and crop-topping, followed by a Clearfield variety using imi chemistry. If there is still some weeds after two years, go to barley with trifluralin and metribuzin for a third-step control.”
Full results from the trials are expected 2017.
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Read the GRDC Brome grass fact sheet
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article on Narrow windrow burning
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