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Unhealthy tree Ash dieback

Tree health and diseases

Our trees and woodlands are under regular threat, especially from pests and diseases, many of which have come from abroad. While these often cause little trouble in their native habitats, some of these organisms can be virulent, fast-spreading and unstable in new environments where the natural controls that would minimise their spread in their native habitats are not present.

The Authority works closely with the Forestry Commission with regard to tree health and diseases. We:

  • Keep up to date on the latest threats to trees in the National Park.
  • Report any sightings of pests and diseases to the Forestry Commission.
  • Assist the Forestry Commission with any remedial work or restrictions as necessary.
  • Promote best practice in biosecurity.

Landowners and homeowners can help by:

Who to contact

Forestry Commission

The Forestry Commission are ultimately responsible for advising, monitoring and taking action against tree pests and diseases. If you discover anything suspicious in the National Park you should report it to them. You may find the information on their website helpful. If you do identify anything that you would like to report, you can use this form or contact them using post, email or phone.

Yorkshire Dales National Park Authority

If you are unsure about a possible issue and would like reassurance before contacting the Forestry Commision, we can offer limited advice. It is most likely that we will refer you to the Forestry Commission. Please contact us to discuss further.

Current threats

Ash Dieback 

Ash dieback is a serious disease of ash trees which is caused by the fungal pathogen Hymenoscyphus fraxineus. The disease causes leaf loss and crown dieback in affected trees, and in most cases leads to tree death. Ash woodlands are a priority habitat in the Yorkshire Dales National Park and contain a number of tree species including ash, rowan, hazel, hawthorn and holly. We have been and will continue to monitor the progress of the disease and will endeavour to ensure that these habitats continue to be safeguarded. For more information please visit our page on Ash dieback

Bleeding canker of Horse Chestnut

The disease affects trees of all ages and is resulting in a significant loss of horse chestnut across the National Park. However, while it is often fatal, trees have been found to be able to tolerate the disease, have periods of remission and even recover.

Symptoms include bleeding lesions and dying bark, and in later stages die back of the canopy causing the trees to become more susceptible to secondary illnesses such as armillaria. Horse chestnut is not a native tree but it nevertheless makes a significant contribution to the landscape of the area.

Phytophthora ramorum

P. ramorum (also known as or ramorum blight and sudden larch death), is a highly destructive water mould which affects a wide range of plants. In recent years it has led to the felling of thousands of hectares of larch woodland in the UK and it is present within the Dales. A notifiable disease, it infects bark and foliage causing wilt, blackened needles and needle drop.

Phytophthora austrocedri

P. austrocedri is an aggressive pathogen causing foliage discolouration and die back of juniper. Juniper is one of our rarest native trees and unfortunately the disease is affecting the small number of populations we have in the Dales.

You can find the most up to date information of tree pests and diseases in the UK on the Forest Research website