Vegetable growers are working with the Department of Conservation and other agencies to eradicate a voracious new pest that is a threat to brassica crops.
The great white butterfly was first seen in the Nelson city area in 2010 and is starting to spread outside the city boundaries.
Vegetables New Zealand director Mark O'Connor has a market garden on Nelson's Waimea Plain and says the butterfly has to potential to cause far more damage than the smaller common white butterfly if allowed to escape.
The butterfly can fly long distances, is able to lay up to 300 eggs and the caterpillars are huge, at up to 4cm long.
Mr O'Connor says the butterfly emerges in autumn and if efforts are made now to control it there is a good chance it will be possible to eradicate the pest.
He says the great white butterfly is also a threat to native cress species, and the dairy industry with its heavy reliance on brassica forage crops should also be concerned.
People wanting to report sightings of the pest and its caterpillars and eggs can phone 0800 80 99 66.