Farmers across the Wimmera are being encouraged to tackle the spread of brome grass in the region.
A campaign to raise awareness and to support farmers to address the problem was launched in March with a series of workshops organised by Agriculture Victoria and supported by Wimmera Catchment Management Authority and Wimmera Farming Network.
Speaking at the workshops, South Australian weeds research scientist Dr Sam Kleemann said a concerted three-year effort on brome grass is needed to overcome this serious weed occurring on grain farms.
"Only 20 years ago, brome grass was not classed as a weed of significance in the region.
"Now it causes $20 million in lost cereal yield each year across south-eastern Australia, of which $4.5 million is in the Wimmera alone. This does not include the costs of controlling the weed," he said.
The highly competitive weed can reduce wheat yields by 30 to 50 per cent with only 100 plants per square metre.
Brome grass has proliferated with the adoption of no-till farming, early sowing and dry sowing. The weed can produce multiple germinations each year.
Dr Kleemann said brome grass has evolved in modern farming systems with higher levels of seed dormancy, making management more difficult.
"You don't need a lot of plants to inflict a lot of pain," he said. "It is a competitive weed and can severely reduce yields with the presence of only low weed numbers.
"Brome grass populations have evolved to withstand modern farming practices by becoming more dormant and germinating later making them harder to control. For example, brome grass populations in crops can germinate an average 20 days later than when found along fence lines."
In any one season approximately 25 per cent of the seedbank does not germinate but instead persists and can carry over into the next year, making longer-term management important. Fortunately most seed only survives up to three years.
Dr Kleemann said that even after the first year of applying brome grass controls, there is still enough viable seed to kickstart the population.
"If you take your foot off the brake, then even in a dry year brome grass can produce more than 8000 seeds per square metre and about a quarter of the seeds will carry over into the next season without germinating. So, with significant brome patches where seedbanks are large you need a minimum of three years of control to make an impact."
Growers are advised to use a range of tactics to drive weed numbers down. In addition to herbicides, non-chemical control methods should be employed, including harvest weed seed control.
While resistance to selective herbicides is still low in brome grass, growers should identify whether any apparent herbicide failure was application-related, resistance or both. Growers are also encouraged to test for herbicide resistance when herbicides did not work.
Dr Kleemann said pulse crops or vetch were good options in the first year of brome grass control, enabling growers to use a grass-selective herbicide and crop-top.
"Hay cutting and chemical fallow tactics are also very helpful, reducing brome grass numbers by 95 per cent.
"In the Mallee, some growers opted to spray out patches of brome grass in crops before it set seed," he said.
A Clearfield™ cereal (using an 'imi' herbicide) can be highly effective in the second year, followed by a barley variety with good crop competition.
The Agriculture Victoria workshops were supported by the Wimmera Catchment Management Authority and Wimmera Farming Network.
