[ASC-media] Media release: local impact on herbicides

JCA Media jca.media at starclass.com.au
Wed Sep 27 15:06:36 CEST 2006

Cooperative Research Centre for Australian Weed Management

Media Release 

September 28, 2006


Local conditions can drastically alter the effectiveness of herbicides - a factor costing farmers around $30m a year.

On each farm every year there are days when spraying herbicides at the recommended rate may fail to achieve proper weed kill - especially when the weeds are stressed, says Mr John Moore of the Weeds CRC.

Using rates recommended by the agrichemical industry and a series of experiments on farms in Western Australia, NSW and Victoria, Mr Moore explains that Dr Andrew Todd and Dr Dick Medd of the Weeds CRC developed a prototype decision support system to improve the effectiveness of herbicide use.

"When checked against the weather at York in the WA wheatbelt, we noted eight days out of sixty when spraying at the recommended rate would have provided less than 90% control of wild oats," says Mr Moore. "During the same period, just 150km away at Merredin, there were just three days when the farmer should have left his sprayer in the shed."

The research has concentrated on wild oats (Avena), one of the most prevalent weeds in Australia's grain growing areas.

 "We have shown that using the technique, Australia's grain growers could save up to $30m a year in herbicide applications," he says.
In an example of this approach, research presented this week at the 15th Australian Weeds Conference in Adelaide showed how large data sets available on the use of the herbicide clodinafop has allowed the construction of a model to guide the use of that chemical by farmers.

Scientist Dr Todd Andrews said that the model allows a user to predict how effective the herbicide would be under certain temperature and moisture conditions, and at particular dose rates, before applying it. If the prediction were not satisfactory, the spraying could be put off until conditions were more suitable.

Mr Moore says that farmers naturally want the best results for minimal cost. The researchers point out that each herbicide has a recommended rate of application which is supplied by the manufacturer, but say this is for average conditions and higher or lower rates may be appropriate at other times.

"Out on the farm, there are many factors which can change the best rate of application," says Mr Moore, "including the fact that herbicides are expensive. A farmer may be able to achieve good results with lower rates under optimal conditions."

"Reduced rates of herbicide usually lead to reduced reliability, so the decision to reduce the rate has to be based on good data and accurate interpretation," he says.

Herbicide effectiveness can be seriously lessened by the condition of the plants being sprayed, says Mr Moore. Plants which are stressed are able to survive being sprayed, but their level of stress may not be apparent.

A plant which is stressed is less likely to absorb herbicide at any rate of application.

"A weed which is wilting is obviously stressed, but there are levels of stress which are much harder to detect and which can have a pronounced effect on herbicide survival," he says. "This can depend on rainfall, temperature, soil condition, and competition for water and nitrogen from other plants."

"All of these need to be factored into the equation when making a decision about when to spray and what rate of herbicide to use."

Mr Moore says that farmers with a relatively small area of crops are able to pick and choose when to spray, and can avoid periods when high rates would be required. Large broadacre properties often do not have this flexibility, and the farmer or manager needs to adjust rates of herbicide to suit the conditions on the day.

Soil moisture and temperature are the major variables, and high air temperatures may require a farmer to use more water per hectare.

Mr Moore says that the decision support system is being used now by government and industry researchers to assess herbicide performance, and to advise farmers on herbicide use. A public version is expected to be ready in 2008.

More information and photographs from:
Mr John Moore, Weeds CRC and Department of Agriculture and Food WA,  0429 669 950
Dr Todd Andrews, NSW Department of Primary Industries 0429 987 405
Both researchers are attending the 15th Australian Weeds Conference in Adelaide 24-28 Sept, and can also be contacted there via the conference media room -  Peter Martin, 0429 830 366, or Rita Reitano 0419 184 153.

For more stories from the conference see http://www.plevin.com.au/15AWC2006/ 
For more information and stories from the Weeds CRC, see www.weeds.crc.org.au

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