Grains Research and Development

Date: 01.06.1999

How to outnumber weeds

Integrated weed management means using a mixed bag of techniques against weeds rather than using only the same or related herbicides and thus inviting herbicide resistance. Farmers and researchers are trialing various alternative strategies.

Below are the results of trials conducted by the Birchip Cropping Group in 1997 and 1998 looking at competition from crops as a method to keep weed levels low. The trials look at the control of grass weeds in wheat.

Increasing crop cover may be an effective control option for grass weeds, and it will be cheaper than using grass herbicides.

Trial results from two dry seasons, 1997 and 1998 (with 1998 complicated by frost), showed high sowing rates (120 kg/ha) and narrow row spacings (17 cm or 7 inches) had the highest yield in all wheat varieties tested.

Method

Three different wheat varieties were sown at two sites (Birchip and the Resistant Ryegrass site) at three sowing rates (60, 90 and 120 kg/ha) and three row spacings (17, 22 and 34 cm, or 7, 9 and 14 inches). All treatments were replicated and measurements included crop establishment, weed cover and yield.

Results

At both sites yields increased significantly with the higher sowing rates and narrow row spacings.

The higher-yield trend with higher sowing rates and narrower row spacings was the same at the Resistant Ryegrass site as at Birchip. At the Resistant Ryegrass site the varieties sown were Frame, Goldmark and Rosella. The frost in October reduced yields by at least 50 per cent. At this site Rosella was by far the best performer in yield.

Grain screenings also improved with narrower spacings and higher sowing rates. As the sowing rate increased and row spacings became narrower, the screenings decreased. Frame had lower screenings than Goldmark and Silverstar.

Protein

However, protein contents were highest for the lowest sowing rates (e.g. for Goldmark sown at 60 kg/ha, protein was 10.5 per cent; sown at 90 kg/ha, protein was 10.4 per cent; and sown at 120 kg/ha, protein was 10.0 per cent). As an average of all sowing rates and row spacings, Frame had the highest protein content (10.5 per cent), followed by Goldmark (10.3 per cent), followed by Silverstar (9.8 per cent).

Grass weed numbers were much lower when wheat was sown at high rates and narrow row spacings. The trends were the same at the Resistant Ryegrass site although at this site the ryegrass numbers were still unacceptably high at the narrowest row spacings and highest sowing rate.

There were no significant differences between the three varieties in their ability to compete with weeds. The strongest competitive response was from row width, followed by sowing rate.

Program 3.5.2

Contact: Ms Caroline Peters 03 5492 2787

Wheat yield (t/ha) at Birchip (three varieties, three row spacings and three sowing rates)
 FrameGoldmarkSilverstar
row width cm - sow rate kg/ha172234172234172234
602.562.411.892.402.301.712.432.211.55
902.642.482.112.422.411.882.572.631.74
1202.712.592.082.652.631.942.632.381.97
Wheat yield (t/ha) at Resistant Ryegrass Site (three varieties, three row spacings and three sowing rates)
 FrameGoldmarkSilverstar
row width cm - sow rate kg/ha172234172234172234
600.490.510.430.510.450.471.481.671.18
900.750.700.530.880.720.631.581.571.30
1200.930.870.720.940.930.761.841.701.43
Screenings (%) in wheat at Birchip (three varieties, three row spacings and three sowing rates)
 FrameGoldmarkSilverstar
row width cm - sow rate kg/ha172234172234172234
603.74.15.06.66.212.76.37.48.7
903.33.94.26.35.99.16.56.37.5
1202.83.24.86.06.48.35.86.77.9
Ryegrass (stalks/m2) at Birchip (three varieties, three row spacings and three sowing rates)
 FrameGoldmarkSilverstar
row width cm - sow rate kg/ha172234172234172234
606521225918915924694154301
9012415424511116619058157265
120601162811321461873660203