Stacking the odds for wild radish control

Photo of northern wheatbelt agronomist Grant Thompson

Northern wheatbelt agronomist Grant Thompson, of Crop Circle Consulting, is coordinating wild radish herbicide sequencing trials.

Spraying wild radish early as part of a two-spray strategy at the start of the growing season, proved to be the best control tactic in 2013 trials.

Key points

  • Wild radish is an escalating problem in the northern wheatbelt
  • There is widespread wild radish resistance to herbicides such as SUs, diflufenican, MCPA and 2,4-D amine
  • Newer registered chemicals, such as pyrasulfotole and pyraflufen-ethyl, are highly effective at controlling radish, which has led to their rapid and widespread adoption in recent years
  • Ideally wild radish should be sprayed when it is small, about the size of the top of a beer can
 

The trials were carried out through an initiative of the GRDC’s Regional Cropping Solutions Network (RCSN) Geraldton Port Zone to find the most effective integrated management practices to control wild radish in cereal crops.

The aim is to develop herbicide solutions to:

  • avoid using the same product twice in a single growing season;
  • get timing and application rates right; and
  • delay the onset of wild radish resistance and prolong the efficacy of new actives pyrasulfotole (for example, Velocity® and Precept®) and pyraflufen-ethyl (for example, Ecopar®).

Australian Herbicide Resistance Initiative (AHRI) communications leader Peter Newman says that while it might be tempting for growers to use two applications of one of these new, effective herbicides in a single year, this would rapidly lead to the evolution of resistance to the new products.

In 2012, the first year of the RCSN-funded trials, it was shown that older herbicide groups could still be effective against wild radish, but the key to success was targeting small weeds and using a two-spray strategy.

To further evaluate these options, trials were set up in 2013 at Northampton, Casuarinas and Chapman Valley.

These were coordinated by local agronomist Grant Thompson, of Crop Circle Consulting, and focused on stacked (or multiple) herbicide-resistant radish.

He says some of the wild radish populations in the trials were resistant to up to four herbicide modes of action, including SUs, IMIs, diflufenican, MCPA and 2,4-D amine.

“Across the northern wheatbelt this is a common problem and it is increasing grower reliance on pyrasulfotole and pyraflufen-ethyl,” he says.

Mr Thompson says the 2013 wild radish trials backed up findings from the previous year’s research that an early first spray and timely second spray were the best knockdown tactics for wild radish early in the growing season.

He stresses these control measures are best used as part of year-round, integrated weed-control programs that include non-herbicide measures.

Early application is crucial

The Northampton and Casuarinas 2013 trials achieved almost 100 per cent weed control when the first spray occurred at the 1.5 to 2-leaf stage (or as early as the label allowed) and was followed four weeks later with a second spray to control subsequent germinations and ‘mop up’ any survivors.

Photo of wild radish

Wild radish is the scourge on the northern WA wheatbelt.

PHOTOS: Melissa Williams

 

Mr Thompson says early sprays using Jaguar® (Groups C and F) at a rate of one litre per hectare and Velocity® at 670 millilitres per hectare were the most effective, regardless of the chemistry of the second spray.

This was a similar result to the 2012 trials, where two spray strategies that used Velocity® first were generally more robust and achieved 90 to 100 per cent wild radish control.

Bromicide 200 used in 2013 trials as the first spray at a rate of 1.5L/ha also achieved good wild radish control. But it was marginally less effective than Jaguar® or Velocity®, regardless of the herbicide applied four weeks later.

Mr Thompson says the trials showed there are many alternatives for a second spray to 2,4-D amine, which is now ineffective in many areas of the northern wheatbelt.

Delaying does not pay

Radish populations sprayed later – at the five leaf stage – in 2013 trials often achieved unacceptable results, with wild radish control ranging from zero to 90 per cent.

Mr Thompson emphasises that the Chapman Valley trial showed holding off for a single late herbicide application produced the worst wild radish control results across all trial sites.

In 2012 trials, a one-spray strategy – whether applied early or late – was far less effective in controlling radish than a two-spray strategy and achieved only 45 to 85 per cent successful wild radish control.

Grain quality

Mr Thompson is now analysing harvest results from the 2013 northern wheatbelt trials. He will compare the effects of herbicide sequences, timing and application on grain yield, quality and returns.

More information:

Grant Thompson, Crop Circle Consulting,
0427 652 521,
grant@cropcircleconsulting.com.au;

Cameron Weeks, RCSN Geraldton Port Zone,
0427 006 944,
cameron@planfarm.com.au

WeedSmart:

www.weedsmart.org.au

RCSN groups:
www.grdc.com.au/rcsn

 

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