Wednesday, April 24, 2024

Herbicide resistance a growing issue

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Herbicide resistance is emerging as a serious and growing threat to New Zealand’s food production. Recent surveys have found that over half of arable farms and vineyards in some regions have weeds resistant to commonly used herbicides.
AgResearch senior scientist Dr Trevor James says with or without climate change, weeds have proven themselves to be highly adaptable when it comes to spreading beyond their usual habitats.
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AgResearch scientist Trevor James says the number of farmers affected by herbicide resistance is far greater than expected. Trevor checking out some herbicide-resistant ryegrass in a vineyard.

New research shows that dairy farms are being threatened by weeds resistant to herbicide.

Herbicide resistance is emerging as a serious and growing threat to New Zealand’s food production.

Recent surveys have found that over half of arable farms and vineyards in some regions have weeds resistant to commonly used herbicides.

AgResearch scientist Dr Trevor James says that when starting this research three years ago, they expected around 5% of farmers to be affected by herbicide resistance.

“The issue is that as this resistance grows, so does the costs and impacts on farmers and crop production in New Zealand,” James says.

“What we found was that the figure is actually closer to 50%. It was a surprising result and makes this a very present issue and not one we can push to the bottom of the list any longer.”

The common resistant weed species being identified include ryegrass, wild oats and chickweed, as well as first-time finds of resistant sow thistle (puha), summer grass, prairie grass and lesser canary grass. These new finds make the issue an emerging threat for dairy farmers as well.

“One of the new weeds we’ve found herbicide resistance to this year is summer grass and we found that in maize crops in the North Island. Any farmer that grows maize for silage knows that summer grass is a difficult weed to kill, so if it starts getting resistance to herbicides, it’s going to be an even larger problem,” he says.

“Similarly resistance in ryegrass is another problem for dairy farmers. While on the face of it you could view it as a good thing, being able to spray out a paddock without spraying out the ryegrass, but it’s quite likely that that resistance ryegrass won’t grow as well.”

Herbicide-resistant weeds were first detected in NZ in 1979, but until recently reporting of herbicide resistance has largely been ad hoc and left to growers and rural professionals to recognise and alert researchers. James stresses that farmers being open and talking about the issue will be crucial in efforts to fight this resistance issue.

“A big part of the issue that needs addressing is the social aspect. Historically and even today, herbicide resistance isn’t talked about among farmers enough,” he says.

“In tackling this we need farmers to be open and talk about it. Farmers are intelligent and have to make important decisions all the time, so a lot of our understanding of this issue from a wider perspective will come from farmers and the decisions they make and how that impacts herbicide resistance.”

He explained that herbicide resistance is an evolutionary process resulting from repeated exposure to the same or similar herbicide and thus is a slow process, which we can use to our advantage. But the solution won’t be as simple as finding the next best chemical, but more in finding a solution through genetics.

Understanding the mechanisms involved in resistance and how it’s passed through the generations of these plants is vital to figuring out strategies to address the issue.

There are 24 known mechanisms that herbicides use, but herbicide-resistant plants have a number of ways of stopping the herbicide working, or translocating it to another site. Figuring out the genetics of these specific mechanisms are difficult to work out and take time.

Work is being done to predict weeds likely to be the next resistant invaders and try to find any commonalities in the weeds that are already developing resistance, as well as to develop a rapid test that enables farmers to leave samples that can be analysed to determine if they are resistant or not.

“We’re also exploring alternatives to herbicides that could help stave off or avoid resistance developing, including tikanga Māori practices and new technology,” he says.

Stepping back from intensification and incorporating cover crops into rotations are also being investigated.

The survey, which is the first of its type for arable crops, is funded from the Ministry of Business Innovation and Employment Endeavour Fund.

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