RHS and Defra call on the public to become citizen scientists and help monitor tree health

The Royal Horticultural Society (RHS), Defra, APHA and Forest Research are asking the public to help monitor sweet chestnut trees for known problems and diseases to help map the spread of organisms new to the UK, launching during this year’s National Plant Health Week.

Sweet chestnut trees (Castanea sativa) are some of our most iconic street trees, also found in parks and woods across the country, providing food and a habitat for a diverse range of wildlife.
Unfortunately, the health of these trees is facing a growing threat from two devastating problems: the oriental chestnut gall wasp (OCGW) and a fungus, chestnut blight. To tackle this issue, the organisations are asking the public to become citizen scientists and check a sweet chestnut tree where they live, reporting any signs of disease or where the trees are healthy. 
Getting involved in the project is easy and doesn’t require any specialist knowledge.  
To get involved with the project just a few simple steps are needed: 
  1. Make sure you know how to identify a sweet chestnut tree 
  1. When you see a sweet chestnut, look for signs of sweet chestnut blight or oriental chestnut gall wasp 
  1. Take photos of the tree and any symptoms of OCGW or chestnut blight 
  1. Go to Tree Alert, the official government reporting tool for tree health, and fill in a report  
Signs to look out for include distorted leaves or buds with swellings (galls), a sparse crown and sunken, cracking or discoloured bark. Please visit the RHS website for full details.
The public are encouraged to report healthy trees, showing no signs or symptoms of OCGW or chestnut blight. Together with reports of OCGW and chestnut blight, this will inform Forest Research scientists of where affected trees are, as well as the proportion being affected. The data will be used to create a national map of the health of sweet chestnut trees across Britain, which will be invaluable for targeting future surveillance efforts and showing where current efforts protect trees are working. The process will also support efforts to monitor new or emerging threats to all tree health.  
The threats posed by chestnut gall wasp and chestnut blight are significant. The OCGW lays its eggs inside the tree’s buds, causing abnormal growths, known as galls, which can stunt the tree’s growth and reduce its ability to produce nuts. Chestnut blight is a fungal disease that causes cankers on the tree’s bark and can eventually kill the tree. Both diseases are spreading across Europe and pose a major threat to the health of sweet chestnut trees. 
Nicola Spence, UK Chief Plant Health Officer, said: “Sweet chestnut trees – like many other plant and tree species – are increasingly vulnerable to pests and diseases.
“Encouraging the public to be good plant health citizens and report disease sightings is absolutely crucial if we are to minimise the risk to our cherished treescapes.”
Dr Jassy Drakulic, RHS Plant Pathologist, added: “The Check a Sweet Chestnut project is a vital tool in the fight to protect tree health and provides a great opportunity for members of the public to get involved in conservation efforts. By working together to record and monitor these trees we are helping safeguard Britain’s sweet chestnut trees for future generations to enjoy.” 
The Check a Sweet Chestnut project previously ran in 2021 with partners including the RHS and Universities from across Europe, acting as a successful case study on tree health reporting by the public. Records from citizen scientists mapped 350 sweet chestnut trees in Britain and helped show that OCGW had reached Berkshire, South Cambridgeshire and Norfolk, where no records previously existed.  
The organisations are launching the project to coincide with National Plant Health Week (NPHW), 8-14 May 2023. NPHW is a collaborative effort by over 30 organisations to raise awareness of plant health and actions that everyone can take to keep plants and trees healthy.   
Further actions you can take to improve plant heath are: 
  • ‘Don’t risk it!’ - Don’t bring plant material (plants, trees, fruit and seeds) into the UK from trips abroad. These might be carrying harmful pests and diseases 
  • Buy your plants and trees responsibly - Source plants from reputable nurseries and suppliers 
  • Keep it clean - Clean boots, bikes and buggies before visiting woodlands and parks, to avoid spreading harmful organisms like fungi, bacteria and insects 
The information collected by the public on sweet chestnut tree health will be published during National Tree Week in November 2023. 
For more information on the project please visit  

Notes to editors

For more information contact Claire Thorpe: [email protected]  
About the RHS 
The Royal Horticultural Society (RHS) was founded in 1804 and is the UK’s largest gardening charity. 

The RHS vision is to enrich everyone’s life through plants, and make the UK a greener and more beautiful place via its inspirational gardens and shows, science research and advisory, extensive library collections and far-reaching education and community programmes. With over 600,000 members the RHS also shares its horticultural knowledge and expertise with millions of people every year through its website and publications. 

In 2021, the RHS launched its Sustainability Strategy, committing to be net positive for nature and people by 2030. The supporting RHS Planet-Friendly Gardening Campaign will continue to harness the power of the UK’s 30 million gardeners to help tackle the climate and biodiversity crisis. 

We are solely funded by our members, visitors and supporters. 

For more information visit 

RHS Registered Charity No. 222879/SC038262 
About Forest Research
Forest Research is Great Britain’s principal organisation for forestry and tree-related research and is internationally renowned for the provision of evidence and scientific services in support of sustainable forestry. @Forest_Research

Forest Research Tree Health Diagnostic and Advisory Service:

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The Royal Horticultural Society is the UK’s leading gardening charity. We aim to enrich everyone’s life through plants, and make the UK a greener and more beautiful place.