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Efficient herbicide use pays off

Tristram Herstlet has been growing cotton on Reardon Farms at Talwood for 7 years. Speaking to his CottonInfo Regional Extension Officer, Tristram outlined how he is managing the threat of resistant weeds.

He is faced with a series of weeds each season, including barnyard grass, fleabane, milk thistle, red pig weed, peachvine, feathertop Rhodes grass, bathurst burr, black oats, phalaris and turnip weed. Resistance has been confirmed in barnyard grass (resistant to Group M herbicides – glyphosate) and black oats (resistant to Group A).


Tristram Herstlet, Reardon Farms and Michael Brosnan B&W Rural

Tristram expects to have additional problems with resistance in the future, particularly with feathertop Rhodes grass and glyphosate.

To manage the existing and potential future resistance threats, Tristram has implemented an integrated approach to weed management, in collaboration with consultant Michael Brosnan of B&W Rural at Mungindi.

“We regularly discuss our weeds management program with our agronomist. By the time we plant cotton, we have a program in place and know what we want to do,” Tristram said.

“Our strategy is threefold: to minimise future resistance, prolong the use life of each herbicide, and avoid the problem of weed shifts.

“We do this by having different tactics, such as rotating our chemical groups, cultivation, crop rotation and farm hygiene. We are well aware of the dire consequences of having multiple grass and broadleaf weeds resistant to glyphosate – and we are currently managing two cases of resistance, in barnyard grass and black oats,” Tristram said.

Tristram takes a holistic approach to integrated weed management.

“We use control methods at a whole farm level, at a management unit level, down to an individual field basis. And we apply as many options as possible to try and control the weeds that are resistant, and prevent further resistance developing,” Tristram said.

“We use a Group L treatment instead of glyphosate (Group M) to give the field a break. More recently, we are using a Group K as a post-plant, pre-emergent in cotton. We intend to follow this with cultivation. We haven’t felt that we’ve needed a layby (a residual herbicide used to control weeds in-crop) as the other control methods are currently working.

“We also have a range of other tactics. All of our contractors are required to have clean gear when they come on farm. We practice ‘Come Clean Go Clean’ primarily for disease protection, but an added benefit is weed management.

“We also use chippers, predominately in non-crop areas, but also in-crop if necessary, such as if fleabane has become an issue. We try to keep everything spotless, as the fewer the weeds, the fewer the seeds for next year.”

Tristram believes the future of weed management lies in robotics and microwave technology.

“On our dryland areas we use a camera spray system, which we purchased in 2016. The driver behind the purchase was the ability to spray the dryland fallow area when cotton is in, and the ability to put on higher rates of chemical to kill fleabane without using a hormone,” Tristram said.

“The system was a serious investment – a total of $640,000, including a tractor, sprayer and boom – but we’re spraying at the moment and it costs only $5 per hectare with this new system, versus $11.60 per hectare with a full boom.

“Based on this, we’re saving around $2,000 per day in chemical with the new system. Most importantly, we’re really happy with the results: the cameras work on the chlorophyll in the plants, and the results are fantastic: we’re getting a good weed kill,” he said.

Source: CottonInfo Weed Control case studies

Further information: CottonInfo weed management page

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