Biosecurity New Zealand has lifted all timber movement controls in the Whirinaki area north of Napier after a successful eradication of the red imported fire ant there.
A surveillance programme involving almost a million ant baits has been running since a nest of 30,000 ants was discovered at the Pan Pac timber mill in mid 2006.
Fire ants originate from South America. They have a wasp-like sting and are one of the world's most invasive species.
The ants could threaten the health of people, native plants and animals if allowed to gain a foothold in New Zealand.
While the ants did not pose any risk to its forests, Pan Pac managing director Doug Ducker says the company did not want the pest getting into its plant.
Biosecurity New Zealand says the eradication programme succeeded because the fire ant nest was found when it was only two years old.