[ASC-media] Media release: nature outsmarts science

JCA Media jca.media at starclass.com.au
Tue Aug 22 03:18:24 CEST 2006

Cooperative Research Centre for Australian Weed Management 

Media Release 06/06

August 22, 2006


In the war between plants and human ingenuity, the weeds appear to be gaining the upper hand.

Thirty-three different species of weeds are now reported to have developed resistance to herbicides commonly used in Australian farming systems, says Dr Chris Preston, programme leader for the Weeds CRC. 

The worst offenders are annual ryegrass, wild radish and wild oats.

And of the thirteen 'families' of chemicals used to control weeds, resistance to ten has now been found in various agricultural weeds, Dr Preston says.

"Those ten groups of herbicides, as you'd expect, are the ones that are most commonly used in our cropping systems," he adds.

In a few areas of Australia the herbicide resistance problem has become so acute that there are no longer any herbicides available to control particular weeds - such as annual ryegrass - in some crops.

"It means that we've got to be a lot smarter in how we manage the weed problem," Dr Preston says.  "But the good news is that there are plenty of farmers who are showing that it can be done."

The key to future success in weed control lies in 'breaking the bank' - taking measures which lead to less weed seed being deposited in the soil to create a problem in future years.

Dr Preston says that many farmers are tackling the weed problem through smarter rotations - controlling problem weeds in break crops rather than in the main cereal crop.

"We're seeing more producers doing their economic analysis over several years, instead of year by year.  That might mean spending a bit more on weed control in the year you grow a less important crop, in order to make a greater profit when you grow the main crop, which is generally wheat."

Several new herbicides are also under development but, he says, these will have to be used judiciously to delay as long as possible the development of resistance.

And more producers are turning to mechanical methods of weed control, such as the use of chaff carts behind harvesters, which gather up paddock residues including weed seeds for burning, so reducing the amount weed seed in the soil for the following year.

Precision farmers are experimenting with techniques such as inter-row tilling to keep down weeds - though this requires very precise and consistent navigation to avoid damage to the crop.

"Almost all successful farmers are now taking serious steps to get on top of the weed seed bank," Dr Preston says. "The dilemma we face is that as one succeeds in controlling one weed, another is usually there to take its place."

On mixed farms the rotation of pasture with crop offers far greater potential to control problem weeds: a high quality pasture is excellent for suppressing weeds and the art lies in watching out for 'bald spots' where weed invasions usually start.

Among the new technologies becoming available are better ways to identify and predict the onset of weed invasions, so they can be dealt with before becoming a problem.

Researchers are also working on biological methods for sterilising weeds or preventing seed-set.

"It's fair to say that the options for weed control are shrinking, as more weeds develop resistance to the most common herbicides, but with good management this process can be stretched out considerably - and meanwhile new methods are under development," Dr Preston concludes.

More information:
Dr Chris Preston, Weeds CRC and Adelaide University, 
Ph 08 8303 7237 or 0438 892 362
Peter Martin, Weeds CRC, ph 08 8303 6693 or 0429 830 366

More information about the ASC-media mailing list