Tree pests and diseases

A guide to 18 conditions that can affect UK trees.

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

Watch: forest biosecurity

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

Click on an image below to learn how to identify some of the pests and diseases that can affect Oak, Ash and Horse Chestnut trees, and get tips on how to spot our six Most Unwanted.

Oak leaf Ash leaves
Horse Chestnut leaf Emerald Ash Borer


Report a pest or disease sighting

Have you spotted one of our 18 pests and diseases? Your information could be vital in helping protect our trees. Please submit details and include pictures if you can.

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?