Recently, the Kondinin Group conducted a survey of 200 farmers and found that the overwhelming majority were practising herbicide rotation in their cropping systems.
Peter Newman, Communication Leader with the Australian Herbicide Resistance Initiative says this confirms that most growers are implementing practices aimed at reducing the risk of herbicide resistance on their farms. “Rotating herbicide chemistry is essential,” he says. “But it is not enough on its own. A diverse weed management program must include more tactics to help protect the chemistry that we have available to us for weed control.”
“Glyphosate is by far the world’s best herbicide,” he says. “It is highly effective in so many situations and its widespread use is justified. What we need to start implementing are tactics that will protect the usefulness of glyphosate, and other herbicides, well into the future.”
“We know that rotating chemical modes of action is useful as a broad tactic but when it comes to particular chemicals, like glyphosate, that are so widely used it is important that seeds from any weeds that survive a spray application do not enter the seed bank.”
“So a trusted herbicide can be used, and used often, provided there is a strategy in place to remove all survivors, including any seeds,” says Mr Newman. “If possible this strategy should include non-chemical tactics to provide the double-knock effect.”
Can I rely on herbicide rotation to avoid herbicide resistance?
Short answer: No.
Longer answer: There are documented cases of herbicide resistance occurring on farms where herbicide rotation was conscientiously implemented. We even have cases where ryegrass has developed resistance to glyphosate and paraquat, despite rotation between these two herbicides.
Is it true that weeds can be resistant to herbicides I haven’t ever used?
Short answer: Yes.
Longer answer: Metabolic resistance is an alarming phenomenon that we are gaining a greater understanding of . In a laboratory experiment annual ryegrass plants were treated with low doses of Sakura® to see if they would become resistant to this herbicide. They did, and they also became resistant to Avadex® and Boxer Gold®, which had not been applied during the experiment. This meant that some individual plants had the ability to stop the action of, or metabolise, these herbicides with different modes of action, before they reached the various target sites.
Do non-herbicide weed controls really help avoid herbicide resistance?
Short answer: Yes.
Longer answer: Managing herbicide resistant weeds is all about managing the weed seed bank. Farms where non-herbicide tactics are part of the system have less weeds and lower levels of herbicide resistance. The ideal second knock to follow a herbicide is a mechanical, non-herbicide option such as haymaking, cultivation or grazing. Effective weed management requires the implementation of as many tactics from the WeedSmart 10 Point Plan as possible. Using one or two of these tactics is not enough.
How to ask a WeedSmart question
Ask your questions about the spread of herbicide resistance, or any herbicide resistance management strategy, using this blog or using Twitter @WeedSmartAU.