A sighting of fall armyworm has been confirmed in a fodder beet paddock in Central Otago last week.
The Foundation for Arable Research (Far) said that the discovery showed the pest could be found on leaves of different crops and live in the South as temperatures warm.
The pest had been found on about 100 properties across New Zealand since September last year.
A dozen of the finds were on the West Coast.
All South Island maize and sweet corn crops should be scouted, the foundation said.