Kauri trees taking medicine

A new treatment technique is being tested in two of New Plymouth's kauri plantations after confirmation of at least one tree-killing disease.

At least 13 trees in Pukekura Park's kauri grove, and five in the Fred Cowling Plantation in Barrett Domain, have been infected with Armillaria sp, or honey fungus, a wood decay fungus causing trees to weep sap from their trunk.

These symptoms, which were caught early, are also similar to the extremely serious Phytophthora taxon Agathis (PTA), a microscopic fungus-like pathogen found in Waitakere kauri in April last year.

New Plymouth District Council took immediate action by testing for PTA, or kauri rot, and treating for both PTA and honey fungus with a new phosphorus-based pill, recommended by a bio-deterioration consultant.

Arborist Conrad Pattison has been drilling three or four holes in the infected kauri and then dropping in about eight of the pills per tree.

It was the same principle as giving a human an aspirin, he said.

"Phosphorus is a real common chemical used in fertiliser," Mr Pattison said.

"The tree breaks it [down] because it's got a coating on it.

"It's just like a pill that you swallow.

"The coating will break down and then the chemical will get distributed through the vascular system, that's the transport system for all the nutrients."

Mr Pattison said the thickness of kauri sap often made using other treatments ineffective and such diseases were often caught too late.

It will take time to extract the fungus from the New Plymouth samples to test for PTA, while there is no known study on stopping honey fungus.

"I've done other conifers before and used chemicals in liquid form – an injector – the gum just blocks them up real quick so you don't know how much chemicals are actually getting in there, so this is a real good way to do it."

After inserting the pills the holes are plugged to stop insects and pathogens getting in.

Mr Pattison said it would take up to six months to see the results and more pill doses would be administered every three years to remove all traces of the disease.

"This is all new, apparently they use it a lot in the kiwifruit industry, and they want to use it in the avocado industry because they get a lot of PTA diseases."

Signs were placed in both plantations advising the public to keep themselves and dogs to the walking tracks, and to wash shoes thoroughly before visiting other forest areas.

- © Fairfax NZ News