Herbicide resistant "superweeds" have been discovered in New Zealand for the first time.
The Foundation for Arable Research (FAR) said the first case of glyphosate resistance in weeds has been found in annual ryegrass on a vineyard in Marlborough.
Glyphosate, the active ingredient in weedkillers such as Roundup, is the most frequently-used herbicide in New Zealand agriculture.
FAR chief executive Nick Pyke said testing by AgResearch confirmed the result but he the industry does not yet know if, or how far, resistant weeds have spread.
He says Roundup resistance can cause big headaches for farmers and they need to start assessing their spray programmes.
"Elsewhere in the world, glyphosate resistance is a fairly significant problem to some farming systems," Mr Pyke said.
"In Australia, for instance, annual ryegrass that is resistant to glyphosate is causing fairly significant problems".
"There are a number of strategies for managing and controlling it. The major one that farmers need to be thinking about is alternating their herbicide groups so that they are not reliant on just one herbicide".
Farmers could also use cultural controls, such as grazing or mowing weeds or some other methods of stopping the weeds dispersing seed.
Overseas, as weeds have evolved to become resistant to the herbicide, they have become known as super-weeds.
Australia was the first country to develop superweeds and Mr Pyke said it has a big impact there on yields, such as when annual ryegrass gets into arable crops or hay paddocks.
Mr Pyke said if farmers notice weeds surviving Roundup spraying, they need to contact their chemical suppliers and ensure the weeds are sent for testing.
He said a testing programme is underway which will survey other high risk sites - such as along roadsides, where local authorities use Roundup regularly.
