Spray and walk away? Not for much longer
Pesticide resistance is often compared with antibiotic resistance in humans. The more heavily a product is relied upon, the greater the chance the pest, weed or disease it is designed to control will adapt and become harder to kill.
For New Zealand growers, that is no longer a distant or theoretical risk.
A Lighter Touch programme director Livia Esterhazy said some horticulture, viticulture and arable crops already had a very limited number of effective crop-protection tools available.
“If you’ve got a limited number of tools, you’ll use those tools more, and that only increases the risk of resistance,” she said.
“Ultimately, we do not want to reach the point where growers have no tools left in the toolbox.”
A new national campaign, Keep What Works, Working, is encouraging growers to talk with their agronomists and advisers before spray programmes are locked in for the season.
The campaign is led by A Lighter Touch, a government and industry programme focused on moving crop protection towards more integrated biological, ecological and chemical approaches.
Its message is simple: protecting the products growers rely on now will require thousands of practical decisions across farms, orchards and vineyards.
Esterhazy said one of the biggest challenges was that resistance could develop slowly and be difficult to detect.
By the time growers noticed their current chemicals were losing efficacy, resistance could already be well established in the crop.
Growers needed to monitor how well their existing crop-protection programmes were working, but the aim was to act before a product began to fail.
Good resistance management could include biodiverse planting, biological controls, beneficial insects and new technologies that reduced growers’ reliance on agrichemicals.
In one A Lighter Touch brassica trial targeting diamondback moth, the use of chemistry was reduced by two-thirds while still producing a commercially harvestable crop.
In another trial, a tiny biological-control wasp was introduced into tomato greenhouses to help manage tomato potato psyllid.
By the second year of the trial, no chemistry was used.
“There is no silver bullet, but there are ways of supporting the use of agrichemicals so that when growers do need them, they are effective,” Esterhazy said.
The scale of pesticide resistance in New Zealand is still not fully understood.
Until recently, surveillance and testing had largely been carried out separately by individual sectors and organisations, making it difficult to build a clear national picture.
A Lighter Touch has now completed work identifying who is monitoring resistance and where, but further work is needed to establish which crops are most at risk and how widespread the problem has become.
Some within the industry regard resistance as one of the biggest challenges the current generation of growers will face.
Economic modelling commissioned by A Lighter Touch estimated that reduced resistance management could cost New Zealand’s horticulture, viticulture and arable sectors between $74 million and more than $1.26 billion over 10 years, depending on how severe and widespread the problem became.
The figures are scenario-based estimates rather than predictions, but they highlight the potential consequences of lower yields, declining crop quality, higher input costs and market-access risks.
Esterhazy said growers understood resistance, but immediate financial and production pressures could make it easy to defer action.
“Sometimes the priority is simply getting the required yield this season, and resistance becomes something to deal with next year.
“The further you kick the can down the road, the bigger the problem will be when it hits.”
The campaign was not asking growers to change their entire production systems overnight.
Instead, it encouraged them to start with a conversation, review their current programmes and consider adding new tools that could reduce their reliance on chemistry.
Esterhazy said resistance was not just a New Zealand issue. It was a major global problem with implications for food production and food security.
She said large-scale monoculture systems overseas could increase pressure on crops, with the same plants grown in the same fields and the same chemicals used year after year.
Esterhazy pointed to Brazil, where resistance problems in soy became so serious that the crop came close to collapse and the government moved to speed up the registration of biological products.
“It sounds dramatic that a whole crop in a country could collapse through resistance, but it has happened.”
New Zealand had an advantage because its industries were relatively small and growers, researchers and advisers were often willing to share information.
That collaboration needed to continue, she said, particularly with A Lighter Touch due to finish at the end of its seven-year funding term in March 2027.
Horticulture New Zealand and other industry partners were working with the programme to ensure its resources, resistance-management strategies and collaborative networks were not lost.
Esterhazy said the work needed to evolve rather than simply end when the funding stopped.
Ultimately, the campaign came back to protecting the crop-protection products growers already had.
“We cannot just keep spraying and hope the problem will go away, because these pests and diseases know how to adapt.
“At the end of the day, all we want growers to do is have a conversation.”
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