Mesh cheaper than chemicals in stopping potato disease

Charles Merfield with mesh which is more successful in warding off pests than chemicals.

Charles Merfield with mesh which is more successful in warding off pests than chemicals.

Scientist Dr Charles Merfield believes he has the answer to solving the problem of the potato psyllid, which costs growers about $10 million a year.

Trials using mesh to cover the crops have shown an "astonishing" reduction in numbers of the insect, which delivers a damaging bacterium to the plant and tubers, causing major production losses.

Not only does the mesh ward off the insects, it is about $1000 per hectare cheaper than chemicals, and increases yields by 12 per cent, so that gross margin profit rose between 27 to 75 per cent.

Comparative yield of moonlight potatoes grown under mesh, left, and without mesh. They were the harvest from a test of ...

Comparative yield of moonlight potatoes grown under mesh, left, and without mesh. They were the harvest from a test of very fine mesh (0.15 x 0.35mm).

"The economics are just amazing.  If this is not a stunning win for the New Zealand potato industry I don't know what is," Merfield, who is based at the Future Farming Centre at Lincoln University, said.

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"The result is utterly stunning, it is effectively complete control of potato psyllid. In comparison achieving complete control of any insect pest on crops with agrichemicals is nigh on impossible.  That this can be achieved with a non-chemical approach is even more heartening as it also addresses the spectre of insecticide resistance."

The psyllid arrived in New Zealand just over a decade ago and since then most growers have used a variety of chemicals to cope with the pest.

Merfield has been conducting field trials with the mesh for four years, and is enthusiastic about the results of this year's tests which he said could be scaled up from small fields to large ones.

The mesh - made up of tough plastic, like woven fishing lines - has been used in Europe for at least two decades and was a response to the fact the EU had run out of chemicals it could use on crops such as turnips and swedes.

Merfield compared two systems of potato growing: one using the "full monty" chemical regime versus three meshes with different hole sizes (0.7, 0.4 and 0.3 mm).

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The potato crop that was sprayed had 1614 psyllids, compared with just four, five and three for the crop under the different size mesh.

He said he was pleasantly surprised that the smallest sized mesh was the most successful, especially in relation to humidity, because he expected humidity levels to be higher under the 0.3mm mesh.

The mesh did not manage to stop aphids from damaging crops. Merfield puts this down to the fact that the aphids lay their tiny eggs on top of the mesh, and they manage to penetrate through.

His solution is to introduce a range of biological agents, including parasitic wasps, lacewings, ladybirds, otherwise the aphids go "ballistic".  

While there was an upfront capital cost, the mesh lasted about 10 years. In Europe, after they have finished with it, large scale growers sell some of the viable sections of mesh to small growers.

Potatoes NZ chief executive Chris Claridge said the mesh was just one of the options growers were looking at.

"Dr Merfield has done some positive work, but there's now a need to scale that up."

Plant & Food Research crop protection specialist Dr Jessica Dohmen-Vereijssen said before the psyllid arrived potato growers did not have to spray their crops.

She backed the use of the mesh but said more work was needed to see if it would work in large fields. Besides the problem of aphids being able to penetrate the mesh, it also made it harder to check for pathogens.  

 Merfield will present his results to next week's Potatoes NZ Conference in Pukekohe.

 - Stuff

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