Pressure on for weed control

Herbicide resistance sparks quest for new weed control methods

Cropping
Good advice: Paul McIntosh, Australian Herbicide Resistance Initiative (AHRI), is urging growers to consider alternative weed control methods to minimise further development of resistance among pest weeds.

Good advice: Paul McIntosh, Australian Herbicide Resistance Initiative (AHRI), is urging growers to consider alternative weed control methods to minimise further development of resistance among pest weeds.

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With herbicide resistance making weed control an everyday struggle for Queensland farmers, agronomists and researchers are suggesting alternative methods for higher success rates.

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These days it seems Queensland farmers are not only waking in the morning hoping for rain but wondering how to control species of difficult weeds when rain does fall.

According to Paul McIntosh from the Australian Herbicide Resistance Initiative (AHRI), Australia is growing a reputation for having plenty of herbicide resistant weeds in its paddocks.  

“We need to diversify with other weed control measures and most importantly stop seed set in order to reduce resistance,” he said. 

“This diversification drive is not only directed at our cropping rotations and alternating our current herbicide modes of action, we should also examine the different methods of harvest weed seed control (HWSC).” 

Mr McIntosh said he believed HWSC practices would become part of Queensland farmers’ weed control doctrine as they had in Western Australian paddocks.

Contrary to popular belief, Mr McIntosh said Leslie Research Centre studies concluded grass plants such as Feathertop Rhodes retained 60 per cent or more of their seeds at harvest time.

“If we can collect these weed seeds from the header and put in chaff and weed seed pin trash windrows for burning, can you imagine the huge reduction in your weed seed bank in the soil?”  

Mr McIntosh said another option was to use strategic cultivation techniques to bury weed seeds, where Feathertop Rhodes seeds became unviable at depths of more than 50 millimetres. 

“One Feathertop Rhodes plant can yield between 100,000 and 200,000 seeds so we need to diversify our control methods,” he said.

“The viability of this Feathertop Rhodes seed can be between four and 40 per cent, so minimum seeds and germination percentages can still result in 4000 seedlings- our herbicides are not going to continuously handle these huge numbers sustainably.” 

Tony Bender, Hopelands, said milk thistle was now of great concern to farmers.

“Milk thistle used to be a winter weed but it’s adapting to our climate and you see it all year round now so we’ve got to change our methodology,” Mr Bender said.

With Glyphosate failing in many paddocks and likely resistance to Paraquat and Group A products also developing, Mr McIntosh encouraged farmers to strongly consider HWSC methods of weed control.

“Control of our serial pest weeds like barnyard grass, feathertop, fleabane and milk thistle can’t be taken lightly, however I concede it may be some time before HWSC methods are fully adopted in Queensland,” he said.

“We’re not at the tipping point where the different modes of herbicides are under complete failure yet, but at the same time we all assumed nothing could become resistant to Paraquat yet it's starting to occur in horticultural pursuits- it’s important we consider other weed control options in our broadacre scene.”

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