No 'magic bullet' for weed control

20 Oct, 2014 11:00 PM
We just can’t afford to take any risks with glyphosate resistance

INNOVATIONS in herbicide usage for canola have been welcomed by the production sector and by weed management experts, but farmers have been warned not to rely on any one chemical to keep problem weeds at bay.

In recent weeks, Pacific Seeds has announced it will have the first dual stacked herbicide resistant canola variety on the market for commercial release next year, featuring both the genetically modified Roundup Ready (RR) trait and the conventionally bred triazine tolerant (TT) trait. It has dubbed the dual resistant varieties ‘RTs’.

Along with that, Nufarm has gained registration from the Australian Pesticides and Veterinary Medicines Authority (APVMA) for farmers to use a glyphosate product for a late season application in canola crops.

Previously the only product registered for late-season application on canola was a diquat-based product relatively inefficient in the control of ryegrass.

Chris Preston, herbicide resistance expert with the University of Adelaide, said the two advances would both be useful tools.

In terms of the ‘RT’ technology, Dr Preston said one of the biggest benefits would come in areas where farmers are struggling with resistance to the Group A chemical clethodim, often used under the trade name Select.

He said in Western Australia there was a different dynamic in play which meant growers were happier to use a straight RR variety, but in Victoria in particular, growers using RR varieties have missed the residual action of the atrazine used in a TT system.

“Once that second glyphosate application goes on with RR, you’re stuck and this can be a problem with late season germinations of weeds, in particular ryegrass.

“Traditionally, this is not as big a problem in Western Australia.”

However, Dr Preston said the technology needed to be used judiciously.

“We just can’t afford to take any risks with glyphosate resistance.

“There needs to be a strong overall herbicide rotation, including as many different modes of action as you can.”

He also advocated growers contemplate non-chemical weed seed controls, such as windrow burning.

Meanwhile, Grain Producers Australia (GPA) chairman Andrew Weidemann said the late season registration of glyphosate would be great for growers looking to control ryegrass that germinated towards the end of the growing season.

He said growers liked crop-topping as a means of controlling problem weeds, but were starved of options prior to this registration.

Mr Weidemann said GPA had worked hard in providing a submission to the APVMA as to why the product would be a boost to the production sector.

Dr Preston said the Nufarm glyphosate product would be a good option for the control of ryegrass.

“Current options aren’t as good at controlling ryegrass so it will be good for growers to have that option, but again, they cannot afford to rely too heavily on glyphosate.”

Mr Weidemann said growers were happy with requirements before growers used the Nufarm product.

“If requested, growers will have to declare the usage of glyphosate through a CVD (commodity Vendor Declaration) at delivery,” he said.

“All grain representative groups were engaged in developing the submission demonstrating necessary unity to achieve this significant advantage for producers.

“It is a great example of grains industry representation maturing and pulling together to get things done,” said Mr Weidemann.

Gregor Heard

Gregor Heard

is the national grains writer for Fairfax Agricultural Media


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