Monthly Update April 2018
Industry must look to new pest control options
New Zealand’s hothouse tomato industry must look for more biocontrol methods to manage pests, says Tomatoes NZ chair Alasdair MacLeod.
That was the main message Mr MacLeod took from an afternoon the Tomatoes NZ board spent with scientists from the Bio-Protection Research Centre (BPRC), Future Farming Centre (FFC), and Plant & Food Research (PFR), at Lincoln University last month.
“Our industry is currently worth about $120 million, and our target is to get to $200 million,” Mr MacLeod said.
“The reality is that the only way we can ever grow that value is through exporting a premium product. The people who pay for a premium product are incredibly discerning – they demand organic, GMO-free, and spray-free.
“We don’t have a choice, this is the way we have to go.”
Dr Charles ‘Merf’ Merfield of the FFC told Tomatoes NZ four methods were available to control horticultural pests – chemical, ecological, biological, and physical. New Zealand’s industry had relied for too long on chemical control alone.
“Chemicals are becoming less effective because of over-use and increased pest resistance, and there are very few new chemical controls coming through,” Dr Merfield said. “Over the past 70 years horticulture has almost exhausted the chemical options for pest control. The future of pest management lies in physical, ecological, and biological control.”
The FFC was already working on two promising avenues for controlling the tomato potato psyllid (TPP), using UV light and mesh.
Dr Merfield showed board members an experiment involving two sticky traps placed in a hothouse containing TPP – one under a UV light, and one not under UV light. The trap under UV light was covered in TPP, while the other had caught very few of the insect pests.
Another method, tested on potatoes, was to use mesh crop covers, which not only kept TPP out, but also deprived any that did get through of the UV light they needed. Potatoes grown under mesh also produced a much higher yield. The next step would be to try growing tomatoes under mesh to see what happened.
Dr Steve Wratten, principal investigator with the BPRC and Professor of Ecology at Lincoln University, said many people believed New Zealand needed to import biocontrol agents. But many biocontrol agents were already here and had worked well in hothouses before spraying became the norm.
For example, Encarsia formosa was a well-known parasite of hothouse whitefly, but pesticides knocked it out.
Hearing this was a “real ah-ha moment” for most of the board, said Mr MacLeod. “If there wasn’t any biocontrol of whitefly, for example, there would be whitefly everywhere. So something out there is eating it!”
However, as a relatively small industry, Tomatoes NZ struggled to fund research into new methods of control.
“We need to find ways of working with other industries,” he said. “But we don’t need to go looking for a solution that’s solely applicable to hothouse tomatoes – we have to start looking at who else we can work with to get a good outcome.” A proposed Primary Growth Partnership for the horticulture industry offers one avenue for collaboration.
Growers could also encourage the natural enemies of plant pests, so they worked more effectively, for longer, said Prof Wratten.
In vineyards, planting buckwheat between the rows of vines created a beneficial environment for predatory insects by providing them with shelter, nectar, alternative food, and pollen (often called SNAP).
“A parasitic wasp that lives for just three days on water alone lives for 42 to 43 days when it has access to buckwheat flowers,” Prof Wratten said. Testing showed that other parasitic wasps, including the TPP parasite Tamarixia, also thrived on buckwheat, so planting it with crops would help to naturally control many horticultural pests.
During the afternoon, BPRC Director Travis Glare told the board there were precedents for an industry going chemical-free.
Increasing pesticide resistance, and pressure from governments and consumers meant much of Europe had moved to more integrated pest management (IPM) strategies, using biological and management approaches, rather than synthetic chemicals. “There are tools available, if growers can commit to an IPM approach,” he said.
Tomatoes NZ general manager Helen Barnes said the board was rethinking its strategy after the presentations. “There was really a lot of excitement from our board members about what we had seen and heard.
“We weren’t aware of the depth and range of research the scientists were doing. I know we will be coming back and having another talk about where we might go next.”