Post date: Wednesday, 31st October 2012

Government "should have acted sooner" on ash dieback

 
Chalara Fraxinea

The public is being asked to look for the disease fruiting on fallen blackened twigs and leaf stalks of ash, from which its spores will begin the infection cycle anew next spring.

The strong prospect of Britain losing many of its ash trees to Chalara Fraxinea disease has prompted accusations that the government should have acted sooner.

Austin Brady of the Woodland Trust believes that the arrival of ash dieback disease (Chalara Fraxinea) on our shores is a real tragedy and has joined the appeal to the public to support a survey to discover how widespread the disease is, by reporting any cases they find.

In particular, they should look for it fruiting on fallen blackened twigs and leaf stalks of ash, from which its spores will begin the infection cycle anew next spring.

"The likelihood of major damage to our native and ancient woods, copses and hedgerows seems to be growing each day as we find out more about this disease, and the history of its impact on the continent," he says.

He notes that the disease was first picked up in the UK in February, in recently-planted trees imported from contaminated nurseries in Europe, where the disease has already devastated 90% of the species in Denmark.

But the Horticultural Trades Association (HTA) says it first expressed its concerns about the disease back in 2009. At the time, it says, plant health authorities responded that the disease was already established in the UK and no quarantine measures were appropriate.

Over this last summer, following discoveries in Norfolk and Suffolk of the disease on mature ash trees, some of which were not associated with any recent plantings, the Woodland Trust and others called for an immediate ban on ash plant imports and a ‘task force’ to be set up. The government has just announced that it is doing both.

Shadow environment secretary Mary Creagh has accused the government of being “asleep on the job” for not taking action to protect ash trees at an earlier stage.

“Ash dieback was found last February in a Buckinghamshire nursery,” she said. “Why did ministers sit back, cross their fingers and wait until the disease was found in the wild in June?”

The Task Force is headed by Professor Ian Boyd, and will include all of the key interests that are affected by the outbreak. Movement restrictions will also be imposed, so that trees from infected areas will not be able to be moved to other locations within the UK.

Announcing the ban on a visit to Cannock Chase, Staffordshire, Owen Paterson said: “This is a very serious disease that demands action to stop its spread. I have ordered both an import ban and movement restrictions on trees from infected areas. This comes into force immediately."

Steve Scott, area director for the Forestry Commission in the East of England, says that 100,000 trees have been destroyed so far, of which a “relatively small number” had been planted in Norfolk and Suffolk.

The HTA has issued a statement arguing that, "given that the sporelation period is now over, no further destruction notices should be served until the full extent of the outbreak has been determined".

It says that containment orders should be issued instead, to avoid unnecessary expenditure in the event that the survey finds that the disease is widespread.

How is it spread?

The disease is prevalent on the continent, where it can advance as much as 20km in a single year as its tiny fungal spores are dispersed by wind.

Environment minister David Heath said the cases in the wild in East Anglia were likely to have been as a result of spores carried on the wind from the continent.

Yet this remains uncertain, and is a key question for the Task Force to find out.

Local spread may be via rain splash or even transmission by insects. Over longer distances the risk of disease spread is most likely to be via the movement of diseased ash plants.

Biologist Hermann Falkner has gone so far as to suggest the disease may be exacerbated by climactic stress and microfungi.

The Woodland Trust believes that despite the fact that its policy has always been that sapling stock should be from seed collected from native trees, it has become apparent that some tree nurseries may have exported British seeds abroad to be grown on and re-imported for sale. Some of these may have unwittingly brought the disease back with them.

As all plants supplied to the Trust by nurseries came with paperwork to confirm that they were of UK provenance, which was, in effect, true, there was no reason to suspect they were imported.

At infected and suspected Chalara sites, including the Norfolk Wildlife Trust’s Lower Wood at Ashwellthorpe, visitors are being asked to clean footwear to avoid spreading the disease any further.

The HTA has signaled that "the industry will be seeking compensation from government for any financial losses it incurs" due to the disease. 

Symptoms

Ash dieback is a disease of ash trees caused by a fungus called Chalara Fraxinea. The disease causes leaf loss and crown dieback in affected trees and it may lead to tree death.

Common ash (Fraxinus excelsior) is the most frequently affected, species although Chalara Fraxinea and the ‘Pendula’ ornamental variety of common ash have also been reported as hosts.

Symptoms of Chalara Fraxinea can be visible on leaves, shoots and branches of affected trees. Trees with withered tops and shoots are very characteristic.

Heavily affected trees have extensive shoot, twig and branch dieback and often have prolific epicormic shoots.

Leaves can suffer from wilting and black-brownish discoloration at the leaf base and midrib. Dieback of shoots and twigs is also very characteristic. Small lens-shaped lesions or necrotic spots appear on the bark of stems and branches and enlarge to form perennial cankers.

These cause wilting and dieback of shoots and branches, particularly in the upper crown. Underneath the bark lesions, the wood has a brownish to grey discoloration which often extends longitudinally beyond the bark necrosis.

More information is at www.forestry.gov.uk/planthealth, and the University of East Anglia has launched an 'ashtag' iphone application to help identification and reporting. People without smartphones can upload images at the website: ddas.ah@forestry.gsi.gov.uk.

Story: David Thorpe, News Editor

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