In coming weeks biosecurity officials will be doubling down on efforts to identify if the fall army worm has established itself further in the upper North Island.
The highly invasive caterpillar moth was found in Tauranga in March and has since been identified in several Waikato maize sites and one at Pukekohe near Auckland.
A Tauranga Moana Biosecurity seminar updated industry on progress and options for controlling the moth this week.
Officials are hoping the colder winter months will kill off a moth that has become a major pest in Australia.
Native to Central America and common in tropical climates, the moth was first discovered in Australia in 2020, New Caledonia in 2021,and now New Zealand.
“It has been a very quick, consistent march across the globe and the damage it causes is pretty intense,” Ministry for Primary Industries’ response manager Kieran Patchell said.
The moth’s preferred diet is sorghum, maize/sweetcorn, and rice.
Patchell said it was at least fortunate that NZ only had one of those as a major food source.
“But they do still have quite a lot of host material when it runs out of primary feed. It will latch onto a wide range of host plants across 76 families. In NZ that includes potatoes, capsicums, aubergines, and some brassicas.”
The moth’s caterpillars have been detected on one brassica site.
Eighteen properties have been confirmed as detection sites to date.
Australia now has the pest established in Northern Territory, Western Australia and Queensland after initially trying to eliminate the caterpillar.
“And they are seeing re-invasion southward every year.”
The moth’s ability to travel 100km overnight has made it a particularly rapid spreader.
MPI officials are working to reduce reservoir populations of the pest and limit the chances it could persist into the warmer spring months when its preferred feed supplies will increase significantly.
“We are wanting to remove any host material, and modelling to better understand the spread risk, working collectively with all national bodies on this.”
An immediate challenge is getting a better handle on the full degree of the caterpillar’s spread.
“We suspect it does get cold enough in many areas to kill it off, but in Northland, maybe not and we need more surveillance there.”
Amelia Pascoe, the government-industry agreement relationship manager, said NZ has a strong history of managing lepidoptera (moth) incursions, including codling moth and painted apple moth.
“It has been a very quick, consistent march across the globe and the damage it causes is pretty intense.”Kieran Patchell
But she acknowledged the unpopularity of some controls, including the extensive painted apple moth aerial spray programme in 2002.
“We know from previous experience it can be hard to get community support across the line. Social media also now adds a layer of complication to that.”
Another technology that has proven successful is drone dispersal of sterile codling moth males, as done in Hawke’s Bay to control an outbreak there in 2018.
This is regarded as one of the most successful applications of the emerging technology to date.
Scion spray specialist Justin Nairn said unmanned remote vehicles were suitable for targeted spraying of tall trees and were more socially acceptable than conventional aerial applications.
However, they require early detection and strong surveillance to give a high degree of confidence the infected area was being well covered.