Southern region grain growers – in areas where ground cover is sufficient – are advised to control summer weeds at the earliest opportunity to optimise the potential for a multitude of agronomic and financial benefits.
Early summer weed management can boost water use efficiency, crop establishment and yields, herbicide efficacy, pest and disease control, nutrient availability and overall grower profitability.
Grains Research and Development Corporation (GRDC) research investments have shown that every dollar invested in summer weed control generates an average return of $5, with early action enhancing the prospective benefits of control.
The GRDC’s landmark National Water Use Efficiency (WUE) Initiative concluded that complete weed control, involving spraying 10 days after a significant rain event, resulted in the greatest subsequent winter crop yield across 300 to 700 millimetre annual rainfall areas when compared with late summer weed control and no control at all.
Summer weed control will be important for growers in those parts of the southern region where ground cover protecting topsoils is adequate. In areas where ground cover is scant following significant rainfall deficits and failed crops, growers will need to consider the risks of eliminating any existing vegetation too early, including weeds and volunteer crop plants, which can assist with erosion prevention.
If summer weed control is to be undertaken, agricultural scientist James Hunt, who was one of the key researchers leading the WUE Initiative, encourages growers to manage summer weeds at the three to five leaf stage using herbicides at registered label rates, as herbicide efficacy is generally highest when summer weeds are young and actively growing.
Dr Hunt, of La Trobe University (previously CSIRO), says summer weed control replicated experiments conducted during the WUE Initiative demonstrated average yield improvements in winter crop performance of 60 percent.
"This clearly shows the benefit of controlling summer weeds for improving yields of winter crops," Dr Hunt says.
"In seasons with high growing season rainfall, yield improvement was driven by nitrogen availability, in seasons with low growing season rainfall it was driven by water availability alone, and in average seasons it was driven by both nitrogen and water availability."
Dr Hunt says a further benefit of summer weed control is – where conditions are suitable – destruction of the green bridge (weeds and volunteer cereals) that can harbour pests and diseases between seasons, potentially reducing winter crop performance.
"Additionally, as we see rainfall patterns changing it is important to conserve any out-of-season rainfall and a major part of achieving this is through summer weed control," Dr Hunt says.
