Waikato growers urged to watch out for fall armyworm caterpillars

Further infestations of a crop-killing moth could cost New Zealand farmers tens of millions of dollars if populations survive the winter.


The fall armyworm Spodoptera frugiperda is the name of the larvae of the pest.

Eggs were found in suburban Tauranga in monitoring traps last month and caterpillars have now been found at two farms in Tamahere, just south of Hamilton.

The army worm has destroyed maize and sweet corn plants in Africa, the United States and Australia.

New Zealand scientists suspect the species crossed the gap to Aotearoa, but the butterflies prefer tropical climates and damage is seasonal, so infestations may die out here in winter.

AgResearch scientist Dr Craig Phillips of the Better Border Security research collaboration said it was a “worrying sign” that the first eggs had been found in the surveillance trap in the town of Tauranga.

“And then the incursion that was detected in Waikato more recently, the population development there is reasonably well advanced, and you would think it’s been there most of the summer. That suggests that the army worm Autumn has a reasonably wide distribution in Waikato and possibly Bay of Plenty already.”

If eradication failed, he expected significant costs to farmers over the next five to ten years.

“It’s another pest that eats away at what our livestock would otherwise eat or our corn farmers would otherwise produce for humans, and it’s easy for those costs to quickly run into the tens of millions.”

The butterflies arrived in Australia in early 2020 and, in the worst case scenario, the larvae destroyed entire enclosures.

Stuart Kearns of Plant Health Australia saw the incursion spread from the Torres Strait across the states, as moths traveled huge distances “over 300, 400 kilometers overnight with the right winds during the phase transport”.

But the damage was caused by the caterpillars feeding on the leaves of the plants.

“There were isolated paddocks where the maize or maize was in the right stage of growth for them to enter early, and the harvest was probably not monitored properly, as often as it should have been. So there was some devastation.”

He said other paddocks “had high numbers and a lot of damage, but they actually grew through that”.

“They [larvae] were detected, they were sprayed, of course, and then the corn grew, grew because of this damage. So corn is a pretty amazing plant.”

Waikato Federated Farmers Arable President Keith Holmes said it was very concerning.

“We’ll have to look at spraying and once a crop gets to a certain stage, that will mean helicopter spraying which costs about $1,600 an hour plus other materials, so it’s extremely expensive,” a- he declared.

Holmes hoped the government would subsidize the cost of destroying infected crops.

“And with the post-Covid situation and the war in Ukraine, we know that corn is going to be very expensive for growth next year.

“We also know that there will likely be at least a 30% increase in the price dairy farmers will have to pay, as well as a significant increase in the need to spray for FAW.

“It’s just another cost and it ends up affecting your bottom line or your confidence.”

Holmes said New Zealand’s border security was too lax, but Biosecurity New Zealand said it was only a matter of time before the moths flew overhead, making the pests very difficult to ward off .

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Deputy chief executive Stuart Anderson said a risk analysis was carried out last year predicting a possible wind incursion from Australia within five years.

He was optimistic that the coming winter would “dramatically reduce survivability…which gives us the opportunity to get this under control and hopefully minimize any potential spread”.

It was unclear whether the populations of Tauranga and Waikato were related, he said.

The Foundation for Arable Research is urging sweetcorn and maize growers to keep a close eye on the pest, which can chew through 350 species of plants but prefers grasses and cereals.

Growers are urged to check their crops and report any signs of the pest.

The larvae feed on more than 350 plant species, but Fall Armyworms are difficult to tell apart from other species of moths already present on our coasts.

Larvae have white inverted “Y” markings on the head between the eyes and body colors can vary from pink to dark brown.

Photos should be reported to Biosecurity New Zealand for identification via MPI and sightings should be reported to the hotline 0800 9966.

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