An intensive campaign has begun in the Nelson-Tasman area to get rid of a new pest that could cost farmers millions of dollars.
The Department of Conservation is leading the charge against the great white butterfly during its spring breeding season.
The great white butterfly was first found in New Zealand in a Nelson city garden in 2010.
It targets brassica vegetables such as broccoli, cabbage and cauliflower as well as garden plants such as nasturtiums .
Dairy farmers use brassicas as stock feed and DoC says any spread of the butterfly on such large-scale crops would force farmers to use sprays to eradicate it at a cost of millions of dollars a year.
In the Nelson Tasman region - the only area in which the pest is currently found - DoC has assigned 25 staff to scour gardens for its caterpillars and eggs and destroy them.