Using cereal varieties which compete strongly with weeds could cut by 50 per cent the rate at which weeds develop herbicide resistance.
A simulation model developed in the USA produced this early result by evaluating the effect of more competitive cereals against wild oats.
Nearer home, a University of Adelaide project aims to provide growers with wheat cultivars that are significantly more competitive with common weed species.
Experiments with varieties already commercially available showed they vary considerably in ability to compete with annual ryegrass. The main factors appear to be differences in early shoot and root growth and crop ground cover. The project has already shown that the use of competitive varieties, in conjunction with other weed management strategies, will reduce the rate of resistance development. With moderate weed infestations, growers can use more competitive varieties to reduce their reliance on herbicides without sacrificing profitability.
Wheat varieties Halberd, Excalibur, Molineux, Frame and Buckley consistently performed better in weedy situations. On the other hand, Janz, Ouyen and Rosella turned out to be poorly competitive against weeds. Krichauff, a relatively new variety, performed well against weeds at moderate infestations. However, at high weed burden, large yield losses can occur which could be related to its high yield potential. Growers should remember that varietal performance can be affected by both climatic and soil conditions. They should check crop improvement and weed competitiveness trials in their district.
The Adelaide researchers believe competitive crops will become a valuable component of integrated weed management and have provided information on evaluated commercial varieties on their weed research web page at Roseworthy campus (http://www.roseworthy.adelaide.edu.au/AFS).
Competition studies in the west
In Western Australia an AGWEST project also investigated how cereals compete with weeds and measured their success not in terms of crop yield but by calculating how many weeds they eliminated.
The researchers reported that the differences between varieties were not associated solely with plant height or early vigour. Choosing a competitive variety was most likely to be useful when combined with other techniques such as increased crop density and delayed sowing to reduce early weed competition.
The take-home message is that farmers should consider a variety's weed suppressive ability as one part of an integrated weed management system.
Programs 3.3.2 (SA), 3.3.3 (WA)
Contact: Dr Gurjeet Gill 08 8303 7744 (SA), Dr Wal Anderson 08 9690 2192 (WA)
At a glance: Competitive crops — how they scored...
- triticale and rye competed well
- barley generally did better than wheat
- amongst wheats, Halberd and Excalibur did best in the South Australian trials, and in the West, Gutha and Eradu were the most effective
- at Roseworthy, field peas were poor but better than chickpeas and lentils
- canola was an 'intermediate' competitor.
Some of the wheat varieties listed are older and have been superseded by new varieties. However, the message for researchers and farmers is to take note of the particular attributes that compete well with weeds—Ed.