After five years of research in more than 30 focus paddocks, the Department of Agriculture stands behind integrated weed management (IWM) as a practical working solution to control ryegrass.

Department researcher Peter Newman said the extensive project, funded by the Grains Research and Development Corporation, would be discussed at the Department’s Agribusiness Crop Updates next week and later at the Liebe, Mingenew and Geraldton Regional Updates.

Mr Newman said growers using a combination of herbicide and integrated weed management (IWM) techniques were achieving improved reygrass control despite high levels of herbicide resistance.

He said grower groups worked with the Departrment over the 2001 to 2005 seasons to evaluate IWM strategies, including pasture phase, crop topping, windrow burning and herbicide application.

”Growers helped monitor 33 focus paddocks for ryegrass numbers and farming practices, and were surveyed in 2001 and 2005 to measure changes in their farming systems and IWM,” Mr Newman said.

“Ryegrass numbers were generally reduced for the majority of paddocks. Results showed ryegrass numbers decreased in 67 per cent of focus paddocks, increased in one paddock (3 per cent) and stayed the same in the remaining 30 per cent.”

Mr Newman said one of the biggest issues of weed management was the over-use of herbicide. Widespread resistance to trifluralin would occur if growers relied entirely on this method of weed control.

“Growers who added IWM techniques such as pasture phase, crop topping and windrow burning generally managed to erode a ryegrass seed bank. This reduced weed competition with the crop and reduced the pressure to use herbicides,’ he said.

“Crop topping of lupins to reduce seed set of annual ryegrass was rated by growers as one of the most important IWM techniques. 

“Many growers said that crop topping was beneficial to the rotation even where they felt that they did not crop top at the ideal time.” 

Mr Newman said rotating paddocks from cropping to pasture and/or livestock was generally not popular with growers who had herbicide resistance problems as they made the majority of their income from cropping. 

“However, many of the case studies showed that even one year of pasture would benefit the farming system,” he said.

“Several growers experienced improved crop yields where they included pasture in the farming system due to nutrition and disease implications as well as improved weed control.” 

Mr Newman said the harvest management of weeds had also been adopted in large areas of Western Australia over the past five years. 

“A survey relating to the 2004 harvest indicated that 50 per cent of growers were burning windrows to destroy weed seeds. This number is likely to be higher now,” he said.

“This result shows that many growers are now looking to target weed seeds at harvest, which represents a new window of opportunity that has been overlooked until now.” 

For more information on dates and venues for Regional Crop Updates visit www.agric.wa.gov.au/cropupdates