Auckland Council biosecurity experts want 23km of tracks in the Waitakere Regional Park closed in an attempt to stop the spread of the deadly disease sweeping through the kauri population.
Kauri dieback in the Waitakere Ranges began causing concern about five years ago and after a recent census of each kauri in the park, it's believed nearly 1000, or 8 per cent, are visibly infected, with another 3 per cent "doubtful".
Councillors at tomorrow's meeting of the Parks Recreation and Heritage Forum, will be asked to take a "precautionary approach" and quarantine areas of kauri that appear to be healthy until the experts can come up with a possible cure or treatment. A similar approach is being foreshadowed for stands of kauri in the Hunua Ranges regional parks, which appear to have so far escaped the ravages of the killer phytophthora taxon Agathis (PTA).
Jack Craw, AC biosecurity manager says "I call it the HIV for kauri, and where we were three years ago was where they were with HIV 30 years ago. They knew they had something that was killing, but they didn't know what it was or how it spread."
He says the organism and how it is spread, have been pinned down, and while they still don't know how to kill it, "we know how to stop it spreading by appropriate behaviours".
In research work over the past three years, not only has the disease been identified as a foreign (almost certain) import that has been lurking around, possibly since the 1950s or longer. It has also been ascertained that its spores hitch a ride on damp soil, or clay - of which the Waitakeres have plenty.
Wild pigs rooting around the base of trees have been targeted in a big culling exercise, but the main vector is believed to be the boots of passing trampers.
Mr Craw says every affected tree has been plotted on to a map of the ranges and 68 per cent are either on the edge of a walking track, or within 50m of one.
Despite the establishment of more than 100 shoe-disinfecting stations within the track network, the disease has continued to spread along the track network since the survey began in 2008. Monitoring of these "phytosanitary stations" showed that around half of park users ignored the signs asking for their co-operation, with compliance at some as low as 28 per cent. The main offenders were casual hikers.
The sensible solution then, is to quarantine the remaining healthy stands of kauri until more progress is made on how to handle the disease. In the end, it might not be enough to save the kauri. But as the experts are arguing, it's better than standing aside and letting people with dirty boots continue to infect healthy specimens.
Like it's ubiquitous cousin, phytophthora cinnamomi, which causes dieback in many species worldwide, the PTA spore can be killed with the fungicide phosphite. Local avocado orchards are annually treated to ward off P. cinnamomi. But what dosage does a kauri need and how would you apply it?
The scientists don't even know what has triggered the deadly Waitakere epidemic, especially as the potential killer appears to have migrated into our kauri forests more than half a century ago.
PTA was first discovered on Great Barrier Island in 1972 in a kauri plantation, planted in the 1950s from seedlings supplied from the Forest Service Nursery in Waipoua Forest, Northland. Sent to Kew Gardens, London, it was misidentified as an existing member of the phytophthora family.
It's only now, with the help of modern techniques, that the linkage has been made and the fact that it's something "new." Investigations back in Waipoua, home of forest giant Tane Mahuta, revealed that PTA is rife there and in nearby Trounson Kauri Park, which suggests the Waitakere outbreak, might have come, via Great Barrier, from the North. But if so, why has it only now become so prominent, and virulent.
The more immediate question is what can we do about it. The proposal before tomorrow's meeting is do our best to delay, or halt, its spread. Scarily, it might already be incubating within the healthy trees.
Either way, we have to do what we can. And if closing a few tracks might help then let's get on with it.By Brian Rudman Email Brian