“We have enjoyed the use of a product that is very nearly organic, with minimal residue effects, is highly effective and low cost. We want to extend its use for as long as is possible,” Parker said.
He doubted there was another silver bullet herbicide around the corner that could equal glyphosate on those strengths.
“I think if there was another chemical as good, it would have been developed. This is going to be about managing its use more carefully.”
He noted the resistance development echoed what had happened across the spectrum of agricultural treatments, including drenches and insecticides.
Chemical alternatives would probably involve adding a spray to treatments every few years with a different mode of action, possibly an “Escort” type metasulfuron spray, inevitably adding to the cost of weed control.
Australian farmers have dealt with glyphosate resistance for several years and estimates were alternative spray use had added about A$150 a hectare to control costs.
Parker said one alternative spray was Paraquat but acknowledged it would not be a preferred choice, requiring complete coverage of the plant and also having issues around resistance in some crops.
Sectors like winegrowing would also encounter problems using such sprays because of toxic residue issues and challenges they would bring to the industry’s Sustainability Policy, which aimed to include all winegrowers by last year.
Mechanical management of weeds through practices like mowing would be included in the project’s scope. But such apparently benign control brought problems of its own, aiding in the spread of resistant weed seed further afield.
The control along roadside corridors would be a key initial focus for the project and was an area Australian researchers initially neglected, focussing instead on pastures, Parker said.
He predicted farmers could face serious problems if resistance got into weeds like fleabane, which are dispersed easily on the wind.
The broadleaf weed has proven a headache for farmers in Canada and Australia. In Australia fleabane seedlings can withstand up to eight times recommended levels of glyphosate, can produce more than 100,000 seeds a plant and move easily on the wind.
In Australia the best approach has been a cocktail of herbicides, including 2-4-D and Paraquat.
Since the public confirmation of resistance in NZ late last year, there have been reports of resistant weeds from around the country.
However, scientists have not confirmed yet the location of other resistant species because testing to determine takes up to three months.
“It is not as simple as conducting a simple DNA test on one object, given different weeds have different responses to the spray,” Parker said.
One outcome hoped from the project is a quicker testing method, now in play through a PhD project, but it is doubtful this will be suitable for quick-analysis field use.
Developing best-management practices would also be essential to reduce the need for tillage to turn weeds into the ground, Parker said.
Soil conservation had been a major benefactor of glyphosate use, by reducing deep-cultivation requirements, he said.
