The first fall armyworms for the 2023/24 growing season have been confirmed in Northland.
Biosecurity officer at the Foundation for Arable Research (FAR) Ash Mills said the find means the pest has successfully overwintered.
Mills said until now it was unknown if it would survive the weather conditions that had prevailed since July.
Fall armyworm has the most detrimental impact on crops planted late, he said.
With most crops planted early there is no “immediate panic”, he said.
“There don’t seem to be too many late crops going in, which is where fall armyworm potentially could have significant economic damage,” Mills said.
It is not expected that the pest’s population distribution will be much different to last season, he said.
Ash said FAR’s main concern is to collect data and to get growers involved with collections.
An area like Northland needs a full day’s worth of frost to kill off significant numbers of the pest, and the short hours of frost the region experienced were not sufficient, he said.
Mills said researchers want to find out if the worm managed to survive in “a little thermal blanket” of rye grass or kikuyu.
It possibly also survived flooding events by pupating in free-draining sandy soils and not drowning, he said.
Mills said finds of the pest have to be kept on ice, and then transferred to ethanol, so that the foundation can do DNA studies and figure out where the pest overwintered.
“As soon as your maize is in, get out there as often as you can, identify any damage and then identify your pest. There’s a lot of other species that have similar characteristics or markings. Take a sample, put it in the freezer, put it on ethanol, take really good photos and then contact me,” he said.
Three other moth captures need to be analysed to see if they are fall armyworm, he said.
Mills said when used according to guidelines, the approved chemical Sparta is efficient.