Tree samples taken

Ministry of Agriculture and Forestry scientist Dr Wellcome Ho, of Auckland, and tree consultant...
Ministry of Agriculture and Forestry scientist Dr Wellcome Ho, of Auckland, and tree consultant Frank Buddingh, of Dunedin, examine one of the ailing plane trees in the Octagon yesterday. Photo by Gerard O'Brien.
An exotic vascular disease not seen before in New Zealand, and similar to the catastrophic Dutch elm disease, may be spreading through Dunedin's plane trees.

The fear was voiced yesterday by Dunedin tree consultant Frank Buddingh, as he and Ministry of Agriculture and Forestry scientist Dr Wellcome Ho, of Auckland, inspected ailing 119-year-old plane trees in the Octagon.

Dr Ho flew to Dunedin yesterday morning to spend the day examining the trees and taking samples to be analysed in a Maf laboratory in Auckland over the next few weeks.

Mr Buddingh told the Otago Daily Times one possibility was the trees were falling victim to a vascular disease new to New Zealand, known as Ceratocystis fimbriata.

The disease blocked the trees' vascular system, robbing them of nutrients and causing their near-dead appearance, he said.

Three plane trees at the Clutha District Council's offices in Balclutha had developed symptoms at the same time as the plane trees in the Octagon, in November last year, he said.

They were the only known occurrences of the suspected vascular disease, which was similar to Dutch elm disease, he said.

"If that is the case, it would be new in this country. That's what makes me uneasy.

"They are the only two places I know of that have got the symptoms," he said.

Dutch elm disease devastated elm trees in Europe and the United States last century and was found in Auckland in 1989.

Dunedin's plane trees had a history of anthracnose, a fungal disease considered the "common cold" of trees, which could cause new shoots to fail, but they usually recovered with pruning.

That had not happened this time, prompting concern among council staff.

Mr Buddingh said it appeared the disease attacking the Octagon trees was spreading slowly from one tree to the next.

By November, when the trees were due to take leaf again, more of the 16 trees could fail to come to life, he said.

"The trees have got roots connected with each other. If there's something going on in number one, it can go to number two," he said.

University of Otago plant pathologist Associate Prof Paul Guy, of Dunedin, said when contacted, specific strains of the Ceratocystis fimbriata disease targeted a wide range of host plants overseas, including plane trees in South America.

The disease could be spread by spores in the wind, beetles feeding on trees, and root systems that intertwined, particularly when rows of the same tree were planted together, he said.

The Maf database contained no records of the disease in New Zealand, but it was possible it had been here for some time and was only being noticed now as trees in public places showed symptoms, he said.

If confirmed by Maf tests, its arrival in New Zealand "could be quite devastating" to the country's plane trees, and possibly other species, he said.

"It could, just for example, become a pathogen of our eucalypt forests and other species," he said.

"Long term, if it's spread by the wind and insects, it's very, very hard to contain."

It was unlikely the Octagon plane trees could be saved if the disease was confirmed, he said.

A better strategy might be to destroy infected material by burning it, and replace the trees with a mixture of other tree types.

"But that's less attractive to the public. Unfortunately, it's a trade-off."

Dr Ho said the trees' symptoms were clearly evident, but it would take time for results to confirm what was attacking them.

Soil and branch samples taken yesterday would be tested in Auckland. Results from the branches were expected in two weeks and the soil in four or five weeks, he said.

chris.morris@odt.co.nz

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