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Chalara dieback of ash - Questions and Answers

How were diseased ash plants allowed to enter Britain? 
Hymenoscyphus fraxineus is not a “regulated” plant disease organism in European Union plant health law, which means that ash plants moved between Member States are not subject to inspection.

What regulatory protection measures were in place to stop it coming in?
EU legislation allows Member States to take national measures to prevent the entry and spread of pests and diseases not found on their territory, and the UK introduced such legislation for Great Britain on 29 October 2012. Northern Ireland and the Republic of Ireland have similar legislation.

Can we eradicate it?
No. The disease is now established in Great Britain and it will be impossible to eradicate.

Why is this organism not regulated at EU level?
The disease is already established in much of eastern and northern Europe, so action across the EU is not realistic. However, regions which remain free of the disease can be considered for “protected zone” status, which would introduce requirements for ash plants being moved into the region to come from a designated "pest-free area" for H. fraxineus. No such pest-free areas have yet been designated in any country.

Why can't we grow our own ash trees here instead of importing them?
We can and do grow our own trees, and people have the option to specify British-grown trees and plants if they wish. We strongly advise tree and plant buyers to be very careful to specify healthy stock from reputable suppliers, to practise good plant hygiene and biosecurity in their own gardens and woodlands etc to prevent accidental spread of plant diseases, and to report any notifiable plant diseases. Buyers should also be aware that seed gathered from British trees is sometimes sent to nurseries in continental Europe to be cultivated before being re-imported as seedlings.

I own or manage ash trees - how can I help?
There are several things you can do to help us get this disease under control.

a. Be vigilant – Chalara dieback could appear in ash trees anywhere in Britain. We encourage you to inspect frequently any ash trees in your care, and especially any which have been planted during the past seven or so years.  Make yourself familiar with the symptoms of Chalara dieback from the materials here. There are other causes of ash dieback, so it is important to distinguish them from Chalara dieback. However, if in doubt, report it.

b. Report it - if you think you have seen Chalara symptoms on ash trees in a new area of the country, please report them to us via our TreeAlert on-line form at See the map at to check whether Chalara dieback has already been confirmed in your area.

c. Buy with care – Be careful when buying plants to buy only from reputable suppliers, and specify disease-free stock. A list of countries where H. fraxineus is known to be present is at Question 7.

 d. Be diligent - Practise good plant hygiene and biosecurity in your own gardens and woodlands etc to prevent accidental spread of plant diseases. See our biosecurity advice for guidance on basic hygiene and biosecurity measures which you can take.

e. Keep up to date – Check our website regularly for updates on developments. ‘Follow’ our Tree Pest News account on Twitter at to receive rapid intelligence of new developments, delivered by text or email.

I have a grant or felling-licence agreement to plant ash trees this season. May I plant another species instead?
Now that movements of ash plants are prohibited, it is not possible to plant ash seedlings which are not already on the site. We are operating a flexible approach for those customers with existing grant or licence agreements which specify ash as a planting species, but it is essential that owners discuss the situation with their local Forestry Commission woodland officer before planting alternatives.

Further information about felling licences and how to obtain them is available on the following pages:




What species should I plant instead?
Species choice should be guided by management objectives and site conditions, and the decision tool Ecological Site Classification ESC3 is the key tool to help review options which are likely to be sustainable in the future climate. 

Detailed guidance on species choice in native broadleaved woodland can be found in Harmer, R., Kerr, G. and Thompson, R. 2010 Managing Native Broadleaved Woodland, from The Stationery Office, Edinburgh.  There is a wide range of alternatives species for sites with brown-earth soils, including aspen, beech, birch, field maple, hornbeam, oak, lime, rowan, sweet chestnut and sycamore. The species range is more restricted for calcareous soils, particularly shallow ones, and includes beech, birch, field maple, hawthorn, holly, lime, rowan, whitebeam and yew. Alder, aspen, willows and oaks are possible alternatives on moist to wet soils.

On sites where there are few restraints, non-native species can also be considered, and guidance can be found in the tree species information on the Forest Research website and links therein.

Some of the alternative species to ash, such as beech, sycamore and Norway maple, are particularly susceptible to bark stripping by grey squirrels.

There is a wider range of species to choose from for the urban environment, and the Right Tree for a Changing Climate website provides information on more than 300 species.

What advice do you have for the trade?
Be careful about the sourcing of, and the specification for, your plants. Keep good records of any imported stock, remain vigilant, inspect any recent plantings of ash, and report any suspicious signs.

What advice do you have for the public?
We welcome reports of ash with Chalara dieback symptoms. Please check with our symptoms guides and videos.

Please also follow the biosecurity advice on any signs at affected sites, to avoid accidentally spreading the disease on your boots, clothes, bicycle wheels etc.

What does a Plant Health Notice involve?
Owners of any recently planted ash plants which are found to be infected, or infected ash plants in nurseries or garden centres, can be served with statutory Plant Health Notices requiring them to destroy the plants, either by burning or deep burial on site, or to take steps to contain the disease on site.

Owners of infected ash plants plants in a new-planting site are advised to voluntarily remove and dispose of the plants to prevent the disease spreading regardless of whether they express symptoms of the disease. This is because experience with other plant diseases shows that we must presume that asymptomatic plants in close proximity to symptomatic plants are almost certainly infected, but are not yet showing symptoms.

In an established woodland or similar site, the Plant Health Notice will require movement restrictions and biosecurity measures to prevent the disease being spread from the site while we consider our disease control strategy.

Can the timber from infected ash trees still be used?
The timber in infected trees can still be usable for some purposes, although staining by the fungus might limit the range of end uses.

Last updated: 11th July 2017
Chalara dieback of ash - withering of young leaves caused by Chalara fraxinea fungus