Growing weeds to beat them by Bernie Reppel

Man examining plants

Would you believe scientists are actually planting weeds on a research farm?

The manager of a Queensland Wheat Research Institute trial farm just west of Toowoomba didn't like the idea much but was eventually convinced. This was one trial that needed weeds to be successful.

The weed planting, carried out by QWRI senior agronomist Steve Walker and technician Geoff Robinson, is part of a $ 1 million, integrated weed management program supported by growers through GRDC. This particular project is looking at ways to reduce reliance on herbicides in winter cereals.

The program aims for a 10 per cent reduction in weed control costs on northern region grain farms by the year 2010. It involves scientists from NSW Agriculture, the University of New England (UNE) and Queensland's Department of Primary Industries (QDPI).

Dr Walker says the project is building on earlier QDPI research into the effect of increased sowing rates and different row spacing on the competitiveness of wheat and barley against broadleafed weeds. The major finding was that barley is far more competitive than wheat.

"We are seeking to take that work further with two approaches, one short term, the other long," Dr Walker said. "We are looking at the interaction of sowing density and lower herbicide rates in barley and wheat, targeting wild oats in the first phase of the research last year and putting the emphasis on paradoxa grass — or wild canary — this coming winter.

"We will also try to find whether there are differences between the various wheat and barley cultivars approved for GRDC's northern region in their competitiveness with wild oats, paradoxa grass and possibly a couple of other broadleafed weeds."

The scientists are also looking at the effect of different levels of weed control on crop yield, and also the ongoing effects of different treatments, such as the reseeding in the following year of uncontrolled weeds.

Long-term trials

A longer-term approach centres on the development of four-year rotations, all using only wheat, barley and chickpea but bringing in the barley phase at different stages of the rotation. This would indicate how long barley's apparent ability to suppress weeds would be maintained.

"Already we have found that, as we increased sowing density, we could eliminate the use of herbicides for wild oat control without a disadvantage to barley yield," Dr Walker said.

Although some wild oats survived to reseed in following crops, Dr Walker said "we believe we may be able to achieve wild oat control with just a quarter of the normal rate of herbicide application."

Normal sowing density for winter cereals is around 75 plants per square metre, but the research team is trying rates as high as 150 plants and as low as 50. Earlier research had shown different row spacing had little effect.

Dr Walker said the long term rotation research would also include different approaches to weed control:

  • a more traditional, reactive one, applying herbicides as weeds were seen, and
  • a strategic approach based on increased sowing densities and bringing in a light herbicide application similar to spray-topping at times of high weed pressure.

Subprogram 1.3.06 Contact: Dr Steve Walker 076 39 8838

Region North