KEY POINTS:
Holiday makers exploring forests this summer could spread an illness that is killing New Zealand's kauri trees.
In a move reminiscent of the South Island's didymo algae spread, Government agencies will next week put up signs asking visitors to wash their shoes before walking in kauri forests.
The scare is over a mysterious illness called Phytophthora taxon Agthis (PTA), which weakens, yellows and bleeds kauri but does not hurt other trees.
PTA makes no distinction between young and old trees, and arborists say it could devastate kauri forests many hundreds of years old.
Nobody knows how far it has spread. But of the four regions where kauri grow naturally in New Zealand - Auckland, Northland, Waikato and the Bay of Plenty - only Waikato has no signs of PTA.
Government agencies fear that, as summer warms up, visitors will unwittingly infect healthy forests such as those in the Coromandel.
Fiona Bancroft, manager of a joint effort by MAF biosecurity, the Department of Conservation and four regional councils to fight PTA, said visitors should wash their shoes before and after walking in forests, stick to marked paths, keep dogs on leads and avoid walking on kauri roots.
One of the forests known to be infected - Northland's Trounson Park - is not far from the Waipoua forest, home to the country's biggest known kauri, 1500-year-old Tane Mahuta.
Research begins next month to find out which forests are affected. Since PTA was found near Piha in 2006, it has been seen in the forests in the Waitakere ranges, Great Barrier Island and Northland. It is thought people, dogs and trucks spread it with soil.
Spores of PTA were found on Great Barrier in the 1970s but scientists did not know what they were. Its menace was not appreciated because it looked similar to another common and less harmful tree disease.
Alarm bells sounded years later when DNA testing revealed a new disease, genetically similar to the more common one but deadly only to kauri.
Scientists had the original spores tested in a British laboratory, where they had been cryogenically frozen since the 1970s, and found they were the same as the new disease.
By that time, PTA had found its way to forests on the mainland. Now New Zealand arborists plan to look at the Queensland and Fijian versions of kauri to see if they have a similar disease. Even quite close relatives of kauri such as Norfolk Pine and Monkey Puzzle trees are not affected.
Government agencies hope to know more in three or four months.
