Two insects imported from Europe will this week be released to help tackle a highly invasive weed threatening some farms.
Tutsan has become a significant problem in parts of the central North Island, taking over large areas of agricultural and conservation land.
It reduces pasture production and is hard to kill, costing about $400 per hectare to control each year.
A moth and a beetle, imported from Georgia, will be released to help kill the weed.
The Environmental Protection Authority approved the release in May last year.
Landcare Research senior researcher Hugh Gourlay said testing had shown they did not threaten any native plant life.
The insects would be released near Taumarunui tomorrow.
"We'll be releasing 100 or 200 of the moths, and about 20 or 30 of the beetles.
"We don't have lots of the beetles at this stage as its proven quite difficult to rear them in large numbers."
Mr Gourlay said it would take some time to see results.
"Biological control is a long term process. It is one of the tools in the tool box for farmers to help them keep control of the pests that cause problems.
"Usually you would expect an absolute minimum of five years, but generally around 10 to maybe 20 years, before we would start seeing a significant impact on... whole plant populations from biological control insects."
There would be further releases, for at least another year.
"We will be continuing to rear these insects in large numbers and making releases of both of them around New Zealand for the rest of this summer and through the summers of 2017 and 2018."