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Big savings in reducing insecticide use

Published on 02/08/2023

He said he could give examples in his home country of hundreds of growers who had adopted IPM practices. Not only had they done that, but had taken it further, reducing sprays for potato moth from ten to seven.
“That’s not far-fetched – it’s ba
sic biology,” he said. “If you’re prepared to put in the effort, you can do the same, I’m absolutely certain.”
One grower of 20 years stand
ing through adopting IPM was now using less chemical over his whole growing operation than he had previously used on just one crop. “It works,” Horne said.

Based in Victoria, most of the
work of his company, IPM Technologies, is in reducing insecticide use by showing growers and their advisers the impact of chemicals on beneficial species. He and colleague Jessica Page who have worked on IPM strategies and training for over 25 years across a range of crops in Australia, are now developing an IPM strategy for tomato potato psyllid (TPP) both there and in this country.

For many crops there were only
three control agents - pesticides, management practices and bio-logical control.

“There’s nothing else,” he said.
“That’s what you’ve got to look at.”
An IPM system was never static
and would change over time. Growers could try to add on as many options as they could to build into their strategy.

“People ring us when there’s
a crisis, when pesticides don’t work,” he said.
Brassica crops were going
through this scenario in Australia at present after some pesticides were withdrawn and export restrictions were enacted because of growers spraying the wrong chemical.

Pests were similar in NZ with
the main problems for potatoes being potato tuber moth (PTM), which could cause significant damage where there was no cool storage on or offshore.

Beneficial insects could be used
such as parasitic wasps and damsel bugs, which were more important across the Tasman. Damsel bugs and brown lace-wing could be used on TPP as well as aphids, thrips and caterpillars.

There were predatory thrips as
well as pest thrips and a parasitic wasp which stung PTM had been introduced over 50 years ago. Three of these wasps are now established in Australia, compared with just one in NZ.
Horne said big advantage was
that PTM caterpillars could be pulled apart in the field to find the wasp maggots, instead of needing to be bred up in a laboratory ‘and then telling the grower they should have sprayed three weeks ago’.

Another parasitic wasp of lepi
doptera which wasn’t present in this country, copidosma, was polyembryonic, meaning it could divide and produce 50 wasps.
Cultural controls were equally
or possibly more important, he said. Soil management, rolling, variety selection and irrigation all helped maintain soil structure.
As the crop died down moths laid
their eggs on the soil and caterpillars could go down the small soil cracks to find potato tubers.

“So your soil cover needs to be
good, because it doesn’t take much soil to stop them going down,” he said.

Controlling weeds such as fat
hen could get rid of thrips and self-sown potatoes could be a big problem.

“Use chemicals only as a sup
porting tool,” Horne said. Growers should consider the impact spraying could have on beneficials, choosing them on the basis of the insects they wanted to look after.

“You might choose a soft chemi
cal, rather than blasting everything away. And if you choose the wrong product, you can make things worse.”

In one case he was involved in
an Australian grower who used few pesticides but sprayed fungicides every few weeks mistakenly applied Axe, a broad-spectrum insecticide instead of the fungicide, Miravis Ace.

“Early on he smelt it but by the
time he called application off half the paddock had been sprayed,” he said.
When Horne later monitored
the paddock every leaf he turned over had aphids present, an exponential increase.

The incorrect spray application
had killed off the ladybirds and lacewings which would usually take out the aphid population.

“Fortunately there was no virus
present but if there had been it would have been rampant.”

Many pesticides were safe with
biologicals which meant a strategy had now been built up with many control options.

For more detail visit potatoesnz.

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