Wednesday, July 6, 2022

Organic solution to TPP

If you’re prepared to “swallow the aggro”, a pokey little plot at Lincoln University hints at world-leading relief for tomato and potato growers ravaged by combinations of psyllid, blight and aphid.

Dr Charles Merfield runs the 14-month-old Future Farming Centre, an outfit funded by a charitable trust that has a practical, organic-centred approach to agriculture.

When it comes to the tomato and potato pest known widely as TPP, Merfield has a bright, white example of how the organic method can pay for itself.

Many growers have spent heavily on agri-chemicals since TPP was discovered in Auckland in 2006, having arrived from the United States.

In the North Island it is wiping out crops and has caused a huge increase in pesticide use, Merfield says.

He says large organic growers have been tied in knots by the pest and life hasn’t been much brighter for the “conventional guys”, who are dealing with chemical resistance.

That is why Merfield is excited about plastic insect-mesh crop covers laid out in the north-west corner of Lincoln’s campus.

Last year he did a “very quick and dirty trial” using glasshouse quarantine mesh, throwing some of it over a field of potatoes.

It kept the psyllid numbers down dramatically, even if the most determined still managed to slip under the material.

“But we also got a dramatic reduction in potato blight, which was the real eye-opener. You’d kind of expect the covers to work – it’s pretty straightforward stuff – but the big concern was that if you have high humidity underneath you’ll have lots of potato blight. We got completely the opposite.”

This result encouraged Merfield and a small band of helpers to apply a purpose-built mesh cover from Europe.

It is a form of mono-filament, polypropylene plastic, which Merfield likens to thin, woven fishing line.

“If we have a similar result this year we should have very low numbers of psyllid underneath the potatoes and hopefully we’ll see the same result in the blight,” he said.

Sticky traps will record the insect invasion, spore traps will register blight and data loggers will measure temperature.

“If this pans out, we could have not only a non-chemical solution for psyllid on field crops but if we’re also getting a significant blight result this could be quite important globally,” he said.

For example, he said, in India and wider parts of Asia there are major problems with potato tuber moth. If the Lincoln trials could be replicated around New Zealand and then overseas the mesh covers could be a perfect non-chemical control for the month – and deal to blight as well.

“So there could be the start of a whole new way of managing blight, by actually putting covers over crops and looking at what the causal effect is.”

It might be light at play, Merfield said, but he admitted he had no idea. The next step would be repeating the trial at up to eight sites around NZ.

In terms of cost, he knows the mesh lasts about 10 years and you could probably spend about $10,000/ha on it.

“So that’s about $1000/year. Some of the conventional growers are spending more than that on the insecticides.”

All said it was not cheap and in some senses would be a “pain in the butt” to set up and maintain, he conceded.

But he hopes that even the most blighted growers will try the mesh treatment, especially seed potato specialists, who are also worried about aphid-vector viruses.

His believes the mesh can stop aphids, psyllid and possibly blight in form of a three-in-one insurance policy. Ideally it would be a case of “put this on, you walk away and shut the gate.”

“You just swallow the aggro. You say ‘I’m going to make another $300/ha by using sheet rather than chemicals and I’m not going to have resistance problems – my market’s going to be happier’. You go, just get the gear, get the labour organised and get on with it.

“You can just imagine there’s stakes here and some poor sod has got to go round and pull it. If you’re doing it on a field you’d have a sheet 100 metres long, just going over the entire field and you’d mechanise it with bits and pieces. So it’s not an easy solution but if it’s your only solution and it’s cheaper than a chemical solution…I’ve found very few growers and farmers who don’t understand ‘cheaper’.”

Merfield suspects organic potato farmers who have previously had to walk away from the game because of the psyllid might now be able to plant again on their own terms, giving retailers an adjusted price that compensates for mesh over the crop.

“It would be a rather rosy, warm feeling to ring up the supermarket and tell them what the price is going to be,” he says.

Related story: Insect nets may be useful in NZ

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