Australia
October 22, 2014

With winter crop harvest fast approaching, growers are being urged to take weed seed samples to help map out an effective weed management strategy for the upcoming season.

An accurate picture of weeds’ resistance status across individual paddocks and farms is critical if growers are to manage hard-to-kill weeds and avoid costly, ineffective control tactics according to Grain Orana Alliance (GOA) chief executive officer Maurie Street (pictured).

“Growers need to know their enemy. Taking seed samples from survivor weeds at harvest and sending them off for testing will allow growers to assess their control options for next year,” Mr Street said.

“Herbicide resistance costs the northern grains industry tens of millions of dollars each year and unless growers understand the resistance status of the weeds on their farm, they can’t have full confidence that their normal control measures will continue to work in the future.”

GOA, a Grains Research and Development Corporation (GRDC) funded grower solution group, recently coordinated a survey of weeds present at harvest last year which showed an alarming level of herbicide resistance across the central western New South Wales cropping belt.

The testing found that an unprecedented 87% of ryegrass samples were resistant to two or more mode of action (MOA) groups and half of these were resistant to four or more MOAs.

“These results suggest that single resistance is rare and also confirmed a number of cases of ryegrass populations resistant to herbicides that had never been applied on the paddocks where they were collected,” Mr Street said.

“This highlights that hygiene is extremely important to prevent introducing resistant weeds by accident and that resistance to an MOA can occur as a result of resistance developed to an alternate MOA.

“While the results certainly give significant cause for concern, they aren’t entirely surprising in that the survey wasn’t random. The samples were from weeds present at last year’s harvest so were therefore most likely to have survived herbicide application and have some herbicide resistance – it really defines the worst case scenario.”

With at least half of the herbicide options lost to growers, Mr Street was particularly concerned over the number of samples that tested resistant to glyphosate.

He said that although the percentage of samples resistant to Group M products was very low, about 6%, these products were an essential component of zero till farming and losing them would have far-reaching consequences.

“What this survey proves is that we have to employ new tactics to control our weeds. The first step is for growers to determine the extent and nature of herbicide resistance in weeds on their properties and once that is clear, an effective control program incorporating chemical and non-chemical control options can be developed,” he said.

“There has been strong interest in harvest weed seed control measures, like narrow windrow burning, to start the campaign against resistant weeds and I expect wide adoption of non-herbicide tactics over the next few years.”

For more information on weed seed control and integrated weed management strategies, visit www.weedsmart.org.au/wp-content/uploads/2013/01/WeedSmart_SustainabilityGuide_V14-Northern_LR.pdf