Large Red Damselfly

Tree pests and diseases

What is the difference between Ash decline and Ash dieback? How do you spot the signs of Horse Chestnut Leaf-miner?

Learn how to identify some of the pests and diseases that can affect Oak, Ash and Horse Chestnut trees, as well as our six Most Unwanted.


OPAL logoA good biosecurity routine can reduce the risk of spreading diseases and invasive species.

Watch this video to find out more about forest biosecurity measures

Report a pest or disease sighting

Have you spotted one of our 18 pests and diseases? Your information could be vital in helping scientists protect our trees. Enter the details of your sighting and include pictures if you can.


Oak leaf Ash leaves
Horse Chestnut leaf Emerald Ash Borer


Concerned about a tree?

Are you worried about the health of a tree you've surveyed? Do you want to know how your data could be helping scientists?