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Auckland Council has confirmed that more than 50 elm trees in Whitford have been found to have Dutch elm disease, a destructive and fast spreading disease that was prominent in the early 1990s.
The trees were on private land. It is the greatest number of diseased elms seen at one site in New Zealand since the disease was first found in Auckland’s Myers Park in 1989.
Auckland Council acted quickly, having the trees removed by helicopter and then processed on the site, including using insecticide to kill the beetle that spreads the disease.
Auckland Council Arboriculture and Landscape Advisor, Simon Cook, says the discovery is a timely reminder that although the disease has faded from the headlines, it remains a risk to all estimated 17,000 elm trees in Auckland and those throughout New Zealand.
Dutch elm disease is a virulent disease of Elm and Zelkova caused by the fungus Ophiostoma novo-ulmi. It is spread by the bark beetle (Scolytus multistriatus) carrying fungal spores from tree to tree, but can also spread directly through root grafting between neighbouring trees. The beetle flies during the summer months, once temperatures reach 21 degrees.
The programme is considered a national programme although the disease is still only found in Auckland. The Government transitioned the programme, which had been run by the former Ministry of Agriculture and Forestry, to the then Auckland City Council in 2007.
“Since then, we have continued a vigorous campaign, which has included monitoring, running a beetle trapping system and conducting ongoing elm surveys around Auckland,” says Mr Cook.
Mr Cook said great success has been made in controlling the disease since the outbreak in the early 1990s, but no country in the world has managed to eradicate the disease completely. The disease has been blamed for the death of the majority of elms in the United States and Europe.
Elms are a very common urban and agrarian tree throughout New Zealand. In many parts of Auckland, one in 10 properties has elms. Elm trees are easily distinguished by their large leaves, which feature serrated edges, symmetrical veins, and an asymmetrical base.
“Identifying infected trees is critical so owners of elm trees should watch for signs of wilting, curling, or yellowing leaves or dying or dead branches and trees,” says Mr Cook.
After a positive identification was made of the disease on a couple of the trees at Whitford, an extensive search was made in the surrounding area and the whole valley of infected trees was discovered.
Mr Cook said that if the disease spread, it would kill all elms in Auckland, which is why the council was acting quickly to deal with the problem.
“The disease is nearly always fatal. It often kills trees it infects in just a few months and can sometimes kill in as little as two weeks. Infected trees always have to be removed to prevent the disease spreading further and to prevent dying trees becoming a hazard.”
Anyone who thinks they have found an infected tree, is advised to contact Auckland Council on 09 301 0101.
Movement controls prohibit the movement of elm material in and out of the Auckland area between the Bombays and Albany. Storage of elm wood is also prohibited under the Biosecurity Act 1993.