Wayne Thompson

Wayne Thompson is a NZ Herald reporter.

Deadly bug returns to threaten trees in NZ

Biosecurity effort begins after whole valley infected with Dutch elm disease.

The scolytid beetle carries disease spores from tree to tree. Photo / Supplied
The scolytid beetle carries disease spores from tree to tree. Photo / Supplied

A fatal and fast-spreading disease has claimed 50 trees in South Auckland despite millions of dollars being spent in an attempt to stop it.

About 50 elm trees have been removed from private property in Whitford, after they were infected with Dutch elm disease.

It is the greatest number of diseased elms seen at one site in New Zealand since the disease was first found in Myers Park, central Auckland, in 1989 and prompted a major biosecurity control effort.

Auckland Council arboriculture and landscape adviser Simon Cook yesterday urged people to call the council if they saw signs of wilting, curling or yellowing leaves and dying branches.

The fungal disease - spread by bark beetles - could kill all of the 17,000 elms in Auckland as well as those throughout the country.

Control measures have been imposed, including a ban on moving elm vegetation in and out of the area between the Bombay Hills and Albany, as well as storing elm for firewood.

Mr Cook said that after the disease was identified on a couple of trees at Whitford, a search was made in the surrounding area and the whole valley of trees was found to be infected.

The trees were removed by helicopter and chipped on site and drenched with insecticide.

He said the Whitford case was a timely reminder that although the disease had faded from the headlines, if it spread it was a killer.

No country had eradicated the disease. Overseas, it wiped out 100 million elms throughout Britain, Europe and parts of North America.

The 1989 discovery of the disease in Myers Park prompted the immediate inspection and removal of hundreds of infected trees from parks and private gardens.

Controls were enforced on moving elm vegetation and wood within Auckland, with severe penalties under the Biosecurity Act.

A decade later, after a survey of all elms in Auckland and spending by the Government and local authorities of $3 million on eradication, it was thought the disease was contained.

In 2007, MAF Biosecurity deemed the disease was no longer a priority and stopped funding the national management programme.

Responsibility was given to Auckland City Council.

"Since then, we have continued a vigorous campaign, which has included monitoring, running a beetle-trapping system and conducting ongoing elm surveys around Auckland," said Mr Cook.

One in 10 Auckland properties has elms, which are admired for their large serrated leaves.

Traps baited with pheromone caught 150 infected beetles during the 2010-11 summer compared with 10 the previous season and nine trees were affected, with removal costs shared between home owners and the council.

Dutch elm disease

What is it?
A virulent disease of elm and zelkova trees caused by the fungus Ophiostoma novo-ulmi.

How is it spread?
The scolytid bark beetle carries fungal spores from tree to tree in summer but it can also be spread through roots grafting between neighbouring trees.

How quickly does it kill a tree?
From two weeks to a few months.

What are the signs?
Wilting, curling or yellowing leaves and dying branches.

How do I report it?
Contact Auckland Council 09 301 1010.

- NZ Herald

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