Weeds fight back against pesticide

Ryegrass resistant to glyphosate herbicides, including Roundup, has shown up in New Zealand for the first time, on a Marlborough vineyard.

Foundation for Arable Research chief executive Nick Pyke said a chemical company representative alerted the organisation to the possible glyphosate resistance in autumn last year.

The foundation grew plants taken from the vineyard and from their seed then treated them with glyphosate, discovering that nearly half showed resistance.

Mr Pyke said repercussions would include a growing dependence on less environmentally-friendly herbicides, the need for increased cultivation resulting in damage to soil structure and health and weeds spreading because of the cost of control.

Seddon farmer and grapegrower Andrew Jones said the discovery "scares the hell out of me". Everyone reached for glyphosate brands, including Roundup, because it was cheap, but would now need to alternate with more expensive options.

On his cropping country, Mr Jones applied herbicide once, or twice if needed, in spring to kill a cover crop or pasture before directly drilling replacement species. This minimum tillage technique conserved soil structure and retained moisture by avoiding cultivation.

The paddock would not be sprayed again for six months to five or more years, depending on whether a short rotation crop was planted or a permanent pasture such as lucerne.

In his 50 ha vineyard, Mr Jones had cut glyphosate applications from up to three times a year to once or twice, opting to live with an at times untidy vineyard to reduce costs.

However, weeds must be controlled because they competed with vines for nutrients and moisture, he said.

"Roundup works well and is cheap," he said.

"The thing that disappoints me is that direct drilling works with nature but she is fighting back by making weeds hard to kill."

While bad news, this was not the end of the world, Mr Jones said. Farmers and growers would learn to use the precise amount of glyphosate needed for weed control, to rotate with alternative chemicals and employ mechanical control methods.

Marlborough Winegrowers chairman Dominic Pecchenino said grapegrowers had learned to tolerate more weeds in their vineyards and increasingly employing non-chemical control such as undervine tilling, mowing, and grazing sheep.

Fruitfed sales manager Richard Rutherford of Blenheim said it was a matter of time until the glyphosate-resistant ryegrass found in Australia and the United States showed up in Marlborough.

"The main implication will be having to use other and more expensive herbicides," he said.

Buster, for example, was four times the price of glyphosate and applied at a higher rate.

However, his company already sold thousands of litres of Buster because unlike glyphosate, it would not damage or kill vines.

Green Party list MP Steffan Browning, who lives in Marlborough, said the discovery of Roundup-resistant ryegrass showed the need for organic systems. "The solution is clear; chemical use must be reduced ," said Mr Browning.

The Ministry for Primary Industries is supporting the foundation to highlight then research the problem and find solutions, through its Sustainable Farming Fund. The project runs until July 2015.

The Marlborough Express