As a deadly killer targets our trees, can we combat this threat to our landscape?

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The Government has called a summit to discuss a deadly disease that could devastate this country’s ash trees. Sheena Hastings reports.

SCIENTISTS, horticultural growers, the timber trade, conservation charities and owners of large tracts of prime British countryside are just some of the many interested parties who’ll gather for the first time in one room today to talk about a scourge that has so far been identified at 83 locations around the country, affecting one of our most beautiful native trees.

In the last six weeks, 100,000 ash trees have had to be destroyed due to the infection. Hundreds of staff members from government agencies are out checking sites across the UK for signs of the tree fungus Chalara ash dieback. The race against time is on, as autumnal leaf loss means tell-tale signs of the infection will fall away, making identification more difficult.

Over the last few days, plant health experts have been carrying out an urgent survey of a thousand sites which have had saplings from nurseries where Chalara has found to be present. They are also prioritising the examination of around 2,500 blocks of land, each 10 kilometres square, where mature ash trees are known to be present, seeking out traces of the disease in established woodland,

The current aim is to plot the disease’s distribution, and today’s summit in London will listen to ideas then attempt to formulate policy with regard to the management of the pest.

Ash trees suffering with the fungal infection have been found widely across Europe since trees now believed to have been infected with Chalara dieback were reported to be dying in large numbers in Poland in 1992. These have included forest trees, trees in urban areas such as parks and gardens, and also young trees in nurseries. In recent years, the disease has travelled across Europe, killing trees in a host of countries including France, the Netherlands, Sweden, Norway and Denmark.

In February this year, it was found in a consignment of infected trees sent from a nursery in the Netherlands to a nursery in Buckinghamshire. Since then, it has been identified in a number of locations in England and Scotland, including a college campus in South Yorkshire, a car park in Leicester, a Forestry Commission Scotland woodland west of Glasgow and a property in County Durham.

All these sites had received stocks of young ash plants from nurseries within the past five years. Further cases have also confirmed in the nursery trade.

Last month, scientists confirmed a small number of cases in East Anglia in ash trees which do not appear to have any association with recently supplied nursery stock.

The Department for the Environment, Food and 
Rural Affairs (Defra) says the infection is being treated as a quarantine pest under national emergency measures, and it is important that suspected cases of the disease are reported. Last week, Defra banned imports of ash saplings and movement of any trees.

Chalara dieback causes leaf loss and kills off the tree’s crown, often resulting in its death. It could potentially infect millions of trees in the UK, causing dramatic changes to the landscape in some places as well as seriously affecting the livelihoods of many in the horticultural and timber industries.

Whether you are a householder with one old ash tree in the garden, a private estate owner or the National Trust, with potentially tens of thousands of ash trees on its 15 properties in Yorkshire and the Humber alone, the Government is not currently offering compensation to anyone who may have to burn ash trees in situ and bury their leaves at least two metres underground, if Chalara tieback is identified. Defra says limited resources are better spent on research and surveillance.

For Thorpe Trees near York – one of the country’s largest tree nurseries – the season between November and March is the prime time for moving its saplings to the locations where they will spend the rest of their lives. Each year, the company sells 40,000-50,000 saplings, and the company stands to lose many tens of thousands of pounds.

“We have been inspected three times, and the our trees have tested negative for the disease,” says Richard Padgett of Thorpe Trees. “But we can’t sell anything until the Forestry Commission has declared a protected zone status to the nursery and a certain area around it.

“Already we’ve had one customer asking us to take ash trees out of their order and substitute it with something else. For now we just have to leave the trees in the ground.”

Over the last 10 years, tens of thousand of trees in Denmark have been killed by the disease, with young trees succumbing first. Spreading into the wood after the leaves, bark splits, tiny mushroom-like fungus grows on twigs and treetops die. About 90 per cent of the country’s ash trees are thought to have the deadly fungus, although (a possible cause for long-term hope) 10 per cent seem to be resistant to it. No treatment has so far b een found for infected trees, though.

Crowders, a large nursery in Lincolnshire that was forced to destroy 50,000 ash trees after 15 were found to be infected with ash dieback, is considering legal action against the government for failing to block imports of the tree sooner. The Horticultural Trade Association, representing 2,000 business including Crowders, has had talks with Defra about compensation and management of the disease, and is due to make a statement today.

The HTA says the government misdiagnosed the disease when the Association first alerted officials, who said the fungus was the same species as one already widespread in the UK which was not killing trees.

“It’s a really complicated fungus,” says Owen Redehan, of the Royal Horticultural Society, whose properties include Harrogate’s Harlow Carr Gardens. “There was already in the country an ash dieback fungus that didn’t kill. This one has been identified much more recently and is much more virulent. There was confusion about what the fungus was.”

As well as possibly being imported on young infected trees, it’s thought spores from the fungus have crossed the sea on air currents.

Ian Wright, plant health specialist for the National Trust, which owns 8,000 hectares of the Yorkshire Dales and Upper Wharfedale, says the long-term physical and financial ramifications of ash dieback are difficult to know because of the ‘slow burn’ nature of the disease.

“The Japanese larch and rhododendron disease phytophthora ramorum alone has cost the National Trust £1m since 2003, in payments for destruction of trees and shrubs and the loss of timber value. We have to look at ways to block the disease’s pathway and also at the resistant trees to find out why that is...But, looking at Denmark, the signs aren’t good.”