Sunday, July 3, 2022

Glyphosate resistance confirmed in NZ

The first New Zealand case of glyphosate resistance has been confirmed in annual ryegrass on a Marlborough vineyard.

The discovery was made as part of a project led by the Foundation of Arable Research (FAR) and funded by the Ministry for Primary Industries’ Sustainable Farming Fund (SFF).

At present it is an isolated case, but FAR chief executive Nick Pyke said it was a warning to users of glyphosate that they needed to be aware of the danger of resistance developing and be careful how they used it.

“Environmental repercussions would include the increased use of, and dependence on, less environmentally friendly herbicide options, greater dependence on more intensive cultivation, leading to greater degradation of soil structure and soil health, and the risk of some weeds spreading as the cost of controlling them would increase,” he said.

“On-farm the impacts would include reduced income, due to increased chemical costs and reduced crop yields. Removing glyphosate from the suite of available chemicals would also increase the resistance pressure on other herbicides.”

Mike Parker, the Avoiding Glyphosate Resistance team project manager, said glyphosate was the most frequently used herbicide in New Zealand agriculture and although there had been some anecdotal reports of resistance, this was the first confirmed occurrence.

Glyphosate is one of the most environmentally friendly herbicides on the market and the repercussions of losing the use of it would be serious.

Dr Trevor James, from AgResearch, who leads the Avoiding Glyphosate Resistance project with Dr Kerry Harrington of Massey University, said the case in Marlborough was identified following a report from a chemical company.

“In the autumn of 2011 we received a call from a chemical company representative stating that glyphosate was not killing all the weeds, specifically some grasses, on a vineyard in Marlborough,” James said.

“We obtained some of the surviving plants and grew them in the glasshouse until some of them set seed in autumn 2012. The seed we collected was then grown in the spring of 2012, and these plants treated with various rates of glyphosate.

“We found that nearly half the tested plants showed symptoms of glyphosate resistance.”

James said the best way to avoid glyphosate resistance was to ensure it was not the only chemical used on the same paddock year after year.

Instead, he recommended mixing it with a herbicide from a different mode-of-action group every three or four years. This would kill any weeds that might be building up resistance.

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