Weedkiller resistance 'serious issue'

Industry response to last year's announcement glyphosate-resistant weeds had been identified in New Zealand for the first time has been positive and supportive, according to the leader of a project working on avoiding glyphosate resistance.

Mike Parker from the Foundation for Arable Research (FAR), who leads the avoiding glyphosate resistance project, said representatives from primary sectors as well as regional councils and roading authorities were working together to identify and deal with existing cases, and to develop strategies to minimise the number of new cases.

''Last year's announcement has really been a timely reminder, and it is great to see all of these groups working together to find solutions to what is, potentially, a very serious issue.

''Glyphosate is environmentally benign and cost effective, and as such has become the most frequently used herbicide in New Zealand. If we were to lose it from the list of available products, farmers, councils and roadside managers would be looking at substantial environmental and financial impacts,'' Mr Parker said.

Since the initial discovery of glyphosate-resistant annual ryegrass on a vineyard in Marlborough, four more cases, also on Marlborough vineyards, have been confirmed by weed experts Kerry Harrington, of Massey University, and Trevor James, of AgResearch.

Dr James said the four latest cases were investigated last year, but since December's announcement more reports of weeds surviving glyphosate treatment had been coming in from all around New Zealand.

''All of these cases need to be investigated, although it is likely that many will be the result of application misses or errors, rather than resistance. When glyphosate is applied in the wrong conditions, or when spray penetration is insufficient to reach below canopy plants, this is counted as `glyphosate failure'.

''A key part of our research project is the development of clear, sector-specific recommendations for the use of glyphosate. We hope that these best management practices will reduce the number of glyphosate failures and also the number of cases of resistance, which is generally linked to overuse of the chemical.''

Dr James said testing for resistance was taking around three months, as individual plants had to be transported to a quarantine laboratory, split into tillers, grown out, and then treated with varying rates of glyphosate.