Auckand Council is expanding trials of a treatment for kauri dieback in the Waitakere Ranges but sceptics say it won't stop the devastating tree disease.
Kauri dieback is spreading rapidly in the ranges.
The council has begun a six-week programme to inject phosphite into trees on the Maungaroa Ridge - a badly infected area.
Scientist and kauri dieback expert Nick Waipara said the treatment was promising, but protected individual trees rather than stopping the disease.
Dr Waipara said if the council or government really wanted to stop kauri dieback there were better ways.
"Stopping the spread in and out of the areas through track closure or better cleaning stations or rāhui - those tools to actually be proactive and preventative should be the number one investment."