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Seed clumps on ash trees not signs of disease, says Forestry Commission

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ASH KEYS (Fraxinus excelsior)

The Forestry Commission is reassuring the public that unusually large quantities of clumps of seeds hanging on ash trees this autumn do not mean the trees have Chalara ash dieback disease.

Dr John Morgan, Head of the Commission’s Plant Health Service, said the disease can be difficult to recognise in the autumn, when ash leaves are changing colour anyway. He explained,

“What some people are mistaking for symptoms of disease are actually a sign of the exceptionally productive fruiting season, or ‘mast year’, we’ve had. The clumps of seeds, known as keys, can sometimes look like the blackened and shrivelled leaves which are a symptom of the disease, so it is easy to see how the mistake can be made.

“The best way to recognise Chalara in the autumn is by the elongated, diamond-shaped lesions, or discolouring, which it causes in the bark of stems and branches around the points where leaves, twigs and branches are attached. This discoloured bark often has splits in it.”

The disease is caused by the Chalara fraxinea fungus, and Forestry Commission monitoring has indicated that there has been little apparent spread of the disease in 2013. Most observed spread has been over short distances in local areas which have higher levels of the fungus in ‘wider-environment’ situations such as mature woodland. This means that new cases are more likely to appear in counties such as Norfolk, Suffolk, Essex, Kent and a small number of other areas.

Dr Morgan added,

“We welcome reports of suspected cases, especially in new areas. However, we do encourage people to check first that the tree really is an ash tree and the symptoms are Chalara symptoms, and we have published identification guides on our website at”

Suspected cases can be reported with the Forestry Commission’s Tree Alert smartphone app or on-line form, which are available from the above web page.

Dr Morgan reminded park managers and garden owners in affected areas that they can help to slow the spread of the disease locally by burning (where permitted), burying or composting fallen ash leaves to break the fungus’s lifecycle.

  • Chalara fraxinea will be one of about 650 plant pests and pathogens categorised for a risk register which the Forestry Commission, Defra and other stakeholders are developing. This register will help to strengthen biosecurity and reduce risks to tree and plant health at the border and within the UK. Other measures under way to tackle the disease are outlined below.


  1. The Forestry Commission welcomes reports of suspected new cases of Chalara dieback to help it monitor the disease. However, only cases in new areas are likely to be followed up, and priority is given to reports with good-quality photographs of the symptoms.
  2. A regularly updated map of sites where infected ash trees have been confirmed is published at Sites are indicated by orange dots for infections in recently planted young trees, many of which have since been destroyed; and red dots for infections in the wider environment, such as older trees in woods and hedgerows. Most wider-environment sites are in East Anglia and South-East England, supporting evidence that the disease has entered Great Britain as wind-blown spores from continental Europe as well as in imports of infected ash plants for planting.
  3. Owners of infected trees are not required to take any particular action unless they are served with a Plant Health Notice by a plant health authority requiring action, such as destroying the infected trees. Where they are used, notices are usually applied to infected plants in nurseries or recently planted ash trees to prevent the disease spreading into the surrounding area. However, owners should monitor infected trees, and fell or prune them if they pose a risk of falling and causing injury or damage as they weaken.
  4. In close consultation with key stakeholders, Defra and the Scottish and Welsh Governments are implementing country management plans which aim to identify ash trees which are resistant to Chalara, slow the spread of the disease, and support affected woodland owners to re-plant with other species.
  5. Potential chemical treatments for Chalara are undergoing field trials under Fera* supervision. Fera expects to have some indication by the end of 2013 of what products - from the 14 shortlisted - might be most effective, but these would still need to be subject to more wide-scale testing on mature trees. Fera will publish updates on its website as each element of the chemical trials is completed. (* Food & Environment Research Agency)
  6. Large-scale field planting trials are under way in east and south- England to try to identify ash plants with resistance to Chalara dieback. The sites will be maintained for five years, after which any resistant individual plants will be identified and used for breeding work.
  7. A Defra-BBSRC* co-funded Nornex project into genomic testing has begun. The research aims to provide robust molecular markers for accelerated selection of resistant ash and to advance understanding of the nature of the fungus. (* Biotechnology & Biological Sciences Research Council)
  8. Further information about the unusually fruitful year for British trees is available in the news area of the Forestry Commission website.


  • England and GB overall - Charlton Clark, 0131 314 6500;
  • Scotland – Steve Williams 0131 314 6508 or Paul Munro 0131 314 6507;
  • Wales – Clive Davies (Natural Resources Wales) 0300 068 0061.