Weed resistance to herbicides has become endemic in New Zealand, with researchers finding at least half the country’s arable farms and vineyards have species resistant to common treatments.
Longtime AgResearch scientist Dr Trevor James says the instance of resistance was 10 times greater than his and his colleagues’ best estimates. That number was confirmed through a national survey of farms in Southland, Waikato, Bay of Plenty and vineyards in Marlborough and North Canterbury.
“We estimated there would be about 5% of properties with resistant weeds. But our survey found 54 out of 87 properties had herbicide resistance in weeds. It was a very surprising result and makes weed resistance in NZ a very present danger, not a distant one,” James said.
James’ career has spanned the history of weed resistance in NZ. He witnessed the discovery in 1979 of the first documented case of resistance, which was fathen weed to the active atrazine in Waikato maize crops.
The common resistant weed species being identified by scientists include ryegrass, wild oats, chickweed and first-time finds of summer grass, puha, prairie grass and lesser canary grass.
The survey was the first of its type for arable crops, funded from the Ministry of Business Innovation and Employment Endeavour Fund.
To fully understand the scope and mechanisms of resistance, James and colleagues are embarking on a research programme that involves getting inside farmers’ heads, as much as the weeds’ behaviour.
“I have been in this game for a long time, talking to farmers about weed resistance and approaches to help reduce it occurring. But we have engaged an AgResearch sociologist to help us better understand how decisions are made that will impact weed resistance,” he said.
“It may even find that perhaps the influencer is the bank manager when they realise their farmer client’s crops will not be as productive as a result of weed resistance. We want to find out these sorts of things.”
Analysis of meta-data on weed infestation from around the globe by Lincoln University professor Philip Hulme will help better predict weeds likely to be the next resistant invaders and try to find any commonalities in the weeds that are already developing resistance.
“It may be that some species are more predisposed to resistance than others,” he said.
Massey researchers are also trying to develop a rapid test that enables farmers to leave samples that can be analysed to determine if they are resistant or not.
Finally, researchers are exploring alternatives to herbicides that may help stave off or avoid resistance developing, including tikanga Māori practices and new technology.
“This also includes stepping back from intensification, which I think we know deep down has backfired somewhat in this area,” he said.
Work includes incorporating cover crops into rotations.
For maize, using a cover crop over winter of oats, fava beans or lupins has been found to significantly reduce weed infestation and the need to spray.
James also hinted at some cutting-edge technology researchers have developed, which is being accessed for its ability to be upscaled and will be revealed in a year’s time.
Project to pull biocontrol levers
As resistance grows among the New Zealand weed species population, a project to try and deal with some of the country’s most invasive weed pests is reaching for bio-control as a solution.
The Ministry for Primary Industries (MPI) and Manaaki Whenua – Landcare Research are leading a study into biocontrol methods that may provide an ongoing means to control weeds. It comes as conventional synthetic herbicides face the threat of tougher residue levels or even outright bans from trading partners.
Chair of the governing group Phil McKenzie says golden wattle, Chilean needle grass, old man’s beard, woolly nightshade, Chilean flame creeper and yellow flag iris were the six weeds to be targeted by the work.
Chilean needle grass has the potential to spread through 15 million hectares of New Zealand, but presently infests about 3700ha of land, largely in Hawke’s Bay, and is a major health issue for stock when its needle-like seeds penetrate skin, muscle and eyes.
Woolly nightshade is found in Bay of Plenty, has a distinctive kerosene smell and spreads easily. The plant has fine hairs that are irritable to skin and cause trouble breathing when inhaled.
Biocontrol methods use one living organism to control another and current biocontrols include broom leaf beetle for broom and the Californian thistle gall fly for Californian thistle. Typically, biocontrol requires importing and releasing organisms from the plant’s native habitat.
The project is aiming to secure Environmental Protection Authority approval for the release of new biocontrol agents for at least three of the six weeds.
McKenzie says there are 15 regional councils co-investing in the project. The Department of Conservation is also engaging in the work.
MPI director of investment programmes Steve Penno says by adopting what has worked in previous biocontrol programmes, progress would be accelerated considerably.
