Weeds scientists are going to work a whole lot harder convince graingrowers in northern New South Wales and Queensland of the benefits of Integrated Weed Management (IWM).

With a major national campaign promoting the benefits of IWM about to begin, it’s timely to look at the results of a GRDC supported resistance project that wound up on June 30.

(And don’t worry, a new GRDC project – also a collaborative effort between the NSW and Queensland Departments of Primary Industries – is on the way, building on the knowledge of research to date.) 

Of course IWM is not new.  Farmers have been combining tillage, grazing animals, crop rotations and a range of herbicides to manage weeds for many years. 

But the reasons for using a broader range of weed control techniques are getting stronger everyday as the supply of novel herbicide chemistry dwindles and the resistance to the traditional products increases.

The project entitled “the risk and preventative IWM strategies for herbicide resistance in the diverse farming systems of the northern region” identified that while there is some commonality of problem of weed species, there are many regional differences too. 

Grass herbicides, for instance, are used more in northern NSW than in southern Queensland, while virtually none are used in Central Queensland, reflecting the difference in winter grass weed populations across the region.

The project finding pertinent to IWM was that, right across the northern region, weed management relies heavily on herbicides. High crop seeding rates are not common.

That indicates most growers are not looking to crop competition as another tool to manage weeds, and that’s one thing they are going to be asked to do under IWM.

The project identified the main weeds for summer and winter fallows, sorghum, wheat and chickpea crops for each of the zones – Central Queensland, southern Queensland and northern NSW.

A “very diverse” total of 105 weed species was identified, just 23 of them common to all three cropping zones 

The major common weeds were two broadleaves – sowthistle and wild turnip – and two summer grasses, barnyard and liverseed.

While glyphosate, and mixes with glyphosate, were very common across the region, the importance of the glyphosate mix partner differed between the cropping zones.

Use and importance of pre-emergence herbicides in crop varied considerable between the zones.

Atrazine was the major herbicide used in sorghum, with metolachlor also there, but predominantly in northern NSW.

The project team concluded that while a diversity of management practices was recorded, herbicide resistance had been, and continues to be, an issue for the region.