Biological control agents must be used to stem the spread of wild ginger, according to Northland Regional Council.
Biosecurity manager Don McKenzie is dwarfed by wild ginger at Helena Bay near Whangarei. Photo: Supplied / Northland Regional Council
It said this species - originally native to Nepal - loved Northland's warm and wet climate and had already spread through at least 5000 hectares of the region.
The council's biosecurity manager, Don McKenzie, said wild ginger took over the forest floor and prevented native species from regenerating.
"We have seen it for at least the past 50 years working its way from the road edges to our best forests," he said.
"We see it in our waterways and in our production forests, we are losing this war."
Mr McKenzie said herbicides were only partly successful and could affect other plants.
Instead, New Zealand needed to invest in smarter technologies, especially biological control agents, he said.
"These little agents are natural predators of this plant," he said.
"In its home range, wild ginger does not grow in colonies at all. In fact in Nepal and Northern India it is very hard to find and that is because it has some natural predators - little insects that keep control of the plant.
"We think some of these insects could to the same in New Zealand."
Mr McKenzie said this idea was in its very early stages and he realised there would be a lot of work needed to get approval for new organisms.
But a website set up to combat wild ginger mentions five possible insect species and two main ones: the stem-mining fly and the ginger weevil.
