Research into kauri die-back is now at the point where decisions can be made about treating sick kauri in state forests, the scientist leading the research says.
Dr Ian Horner heads the team that has successfully treated diseased kauri with phosphite in a five-year trial; injecting the trees with the horticultural chemical used to combat fungal infections in avocado and other crops.
He is now supervising the treatment of kauri by private landowners in the Auckland region as part of the community project Kauri Rescue.
But the disease, phytophthora agathadicidis, is also invading publicly- owned forests such as Trounson and Waipoua in Northland, where some of the largest kauri are located.
So far famous trees including Tane Mahuta are unaffected, but many others are dying.
At the launch of the Kauri Rescue project for private landowners in Northland this week, some asked why dying kauri in public forests such as Trounson and Waipoua were not being treated.
One man from nearby Waimamaku said he saw dead and dying trees all the time as he drove through the area.
Dr Horner said that was the challenge now facing the authorities in charge of those forests.
"We're at the stage now where we can start making some hard decisions about whether phosphite, for example, could be rolled out and used potentially to treat at least some areas of those public forests," he said.
Dr Horner said there was now a big discussion to be had by DOC, MPI, iwi and regional councils over the coming months.
He said recovery rates for trees treated with phosphite were encouraging.
Some trees injected with the chemical just once in the trials had shed their lesions and remained healthy five years on, giving some hope that treating larger kauri forests could be a viable proposition, Dr Horner said.