GROWERS concerned about barley grass should check crops before harvest and ‘rank’ paddocks according to levels of the weed to help guide management and seeding strategies for the next cropping season.
Addressing a Western Australian WeedSmart Week forum in Perth, University of Adelaide research officer, Ben Fleet, said barley grass had become a major weed in lower rainfall areas of South Australia, including the northern Eyre Peninsula, where it was causing high control costs and yield losses.
He said it was also regarded as an ‘emerging weed’ in WA cropping systems.
Mr Fleet said now was a good time for farmers to inspect paddocks for barley grass following final post-emergent herbicide applications and before harvest.
“Ideally, where barley grass is found to be prevalent, two consecutive seasons of high control is recommended to help deplete seedbank numbers,” he said.
Mr Fleet said many South Australian barley grass populations had developed high levels of ‘dormancy’ due to selection pressure from reliance on pre-sowing weed management practices such as knockdown herbicide use, and germination was being triggered later in the season by wet, cold conditions.
Dormancy is when viable seed does not germinate under ideal germination conditions.
Mr Fleet said there could be limited control measures available to manage barley grass populations emerging in cereals.
“However, time of sowing can be manipulated to help manage dormant barley grass,” he said.
“When there are very early breaking rains, growers can sow their ‘dirtiest’ paddocks early to allow the crop to get established before the barley grass germinates, resulting in a higher competitive advantage for the crop against dormant weeds.
“Alternatively, if there is a late start to the cropping season, growers can delay sowing these weediest paddocks so they have the best chance of achieving an effective control with a knockdown herbicide.
“Crop competition can also be improved by using narrow row spacings and increased seeding rates.
Multiple control tactics
Mr Fleet said growers could help preserve the effectiveness of post-emergent Group A and B herbicides by using multiple weed control tactics.
Western Australian Department of Agriculture and Food (DAFWA) researcher Abul Hashem said WA research was showing that barley grass was emerging later than it had in the past and that it was now tending to emerge in-crop and one to two weeks later than brome grass.
“This suggests that barley grass populations may be developing dormancy in WA and that application of effective in-crop herbicides and adjusted seeding strategies may also be necessary in this State to control late emergence of this weed,” he said.
Dr Hashem said recently completed GRDC-funded research by DAFWA, in collaboration with the Australian Herbicide Resistance Initiative, had shown that applying two to three tonnes per hectare of lime sand to WA acid soil significantly reduced barley grass density in three to four years.
Other emerging weeds of WA being investigated in the ‘Seedbank biology of emerging weeds’ project include Afghan melon, brome grass, button grass, caltrop, doublegee, roly-poly, sowthistle, windmill grass and wireweed.
Dr Hashem and his team are collecting seed of the weeds and studying seed dormancy, seed dispersal, seed bank persistence, seed production potential, and competitiveness with crops.
More information about barley grass management is available by searching ‘barley grass’ on the DAFWA website www.agric.wa.gov.au