The Ministry for Primary industries says the crop-killing fall armyworm has now been confirmed at 26 properties nationwide.

Biosecurity New Zealand put the call out to growers to check their crops back in March, when an egg mass of the moth was detected in Tauranga.

The "hitchhiker" pest can chew through crops and other horticulture species and can travel vast distances.

MPI's director of readiness and response services John Walsh says some confirmed infestations of fall armyworm date back to last summer.

"So far, we've found fall armyworms in six regions across the country.

"The first one was in Tauranga, we have a number in the Waikato, a couple in Auckland, in Waitara in Taranaki, in Gisborne and in Northland.

"We've also had fall armyworm reported to us in corn bought in a supermarket in Taranaki, and that corn was grown in Christchurch, so we're also considering Christchurch to have had one infestation as well."

Walsh says eradicating the pest is very unlikely, but early research shows our cold winters can reduce its numbers and give it less time to do damage.

"If it does survive the winter here, we face the risk of continued invasion from Australia, because it's likely to have arrived here from a wind event from Australia, so we continue to have that problem.

"But because we are generally a more temperate climate, even if it does survive the winter, it's highly unlikely to have the number of life cycles that it has in warmer climates, which cause the major problems from fall armyworm in warmer parts of the world, where it could have 10 or 11 life cycles in a season."

Walsh says the colder weather means the worm will have less time to establish itself here and successive generations won't have a chance to wreak havoc on crops.

"In New Zealand, three or four life cycles is probably the maximum we're going to get."

Federated Farmers arable industry chairperson Colin Hurst says the infestations are a concern and they are keeping a close eye on the pest.

He says there's a lot to learn about how fall armyworm impacted crops and other horticulture species in New Zealand.

"The thing about fall armyworm, is that its favored host is maize crops, but it will live and survive on other other plants and species, so we don't even know what might do to native plants, our taonga species, so we need to understand that, too."

Hurst says growers are happy with how MPI is responding to the infestations.

-RNZ.