New tree health forum established
UK experts report on latest developments...
A new panel of experts from across the sector has been convened by Defra and The Tree Council. The Tree Health Operations Forum will meet three times a year to assess the ongoing challenges facing tree health and establishment, and the effectiveness of interventions to combat them. Read on to find out more about the issues highlighted after a challenging summer for our treescapes.
Autumn/ Winter 2025 snapshot
The first panel of experts from government, research bodies, local authorities and charities met at the end of 2025. Reflecting on Summer 2025, The Tree Council team highlighted the role of UK weather as context for changing conditions relating to tree health, pests and diseases. Notably:
Summer 2025 was the warmest on record in terms of mean temperature, and sunshine hours were above average for all three summer months.
The UK received 62% of its average rainfall for the month in August.
2025, 2023, 2022 and 2018 all rank among UK’s top 10 warmest summers since records began in 1884.
Forest Research highlighted the potential threat of Ceratocystis platani (canker stain of plane) to London plane trees, particularly in urban environments. Canker stain of plane is an aggressive fungal pathogen found in mainland Europe that kills plane trees within 2-10 years. It can spread through human activity (contaminated machinery and tools), through roots and through waterways. It is not currently present in the UK but is established in France and some other European countries. With no known biological or chemical controls, Forest Research emphasised that if introduced to the UK it is likely to spread and have a significant impact on populations of London plane. Importantly, the main mitigation is robust biosecurity: preventing contamination through tools and human activity, and through restriction on movements of plane trees from areas where canker stain is present.
The Plan Tree team from Kent County Council (KCC) then presented its tree establishment and monitoring programme, which aims to plant 1.5 million trees by 2050, with over 375,000 trees planted since 2020. Their monitoring of recently planted trees suggests current planting practices are not well-suited to increasingly extreme climate conditions. Removal of tall vegetation and long grass around newly planted trees may reduce resilience to hot, dry spells and presence of tree guards can exacerbate heat stress. The experiences of this summer reflect a need for updated evidence-based guidance that is tailored to local climate, soil type and condition and planting densities. Further trials are needed on the impact of guard types, grass length, mulching and watering regimes.
The Tree Council then shared its early findings from monitoring a wide range of newly-planted trees across the UK. Instead of using a simple “alive or dead” assessment of condition, The Tree Council introduced a four-tier system: excellent, good, poor, and dead. While preliminary headline figures show a promising 78% survival rate, a large percentage of trees are alive but in poor condition which could mean they may not survive in following years. Establishment success in areas seemed to be driven by higher rainfall, low browsing and the combination of high rainfall plus mulching. They also found that bracken and tall vegetation promoted shelter during high-heat and stress periods, but these are all early findings and more data is needed to be confident in the results
In the context of warmer summers, The Royal Parks then discussed the dramatic impact of warmer summers on mature urban trees with drought, heat, and soil degradation intensifying tree stress, increasing susceptibility to pests, diseases, and structural failure. The Royal Parks highlighted Massaria as a disease of particular concern for plane trees, leading to branch drop. Plane trees are increasingly susceptible to Massaria during times of environmental stress such as droughts. The team also noted ongoing concerns in other species: oak processionary moth (OPM); bleeding canker of horse chestnut; sweet chestnut blight; and sooty bark disease on sycamore. Norway maple, lime, and birch are also experiencing stem bleeds linked to Phytophthora and drought stress. Adaptive, species-specific management is needed as climate-driven stressors accelerate, and planting of non-native species was raised as a possibility for urban areas where heat stress is high.
Our Autumn 2025 forum then concluded with a final presentation by Defra, noting that continued findings of Ips typographus (eight-toothed European spruce bark beetle) in 2025/26 season have triggered a 3-year risk-based eradication strategy across southeast England and East Anglia. A demarcated area (DMA) in the South East and East Anglia now restricts felling, movement, and planting of Spruce over 3m in height and encourages proactive removal of Spruce and replanting other species. Updates on Phytophthora pluvialis included a longer-term review of policy underway, including a review of the appropriateness of maintaining demarcated areas. A consultation on an update to the Pest Risk Analysis and future management of P. pluvialis is open until the 26th January. You can share your views here: Pest risk analyses - UK Plant Health Information Portal.
What tree health symptoms to look for in your area following hot, dry summers
Summer 2025 was the warmest on record in the UK in terms of mean temperature and received just 62% of its average rainfall for the month of August. High temperatures and drought can stress trees, making them more vulnerable to pest and disease infection. Forum members discussed some key areas of concern for specific tree species. Note that this is not an exhaustive list but reflects those that were highlighted in the forum.
London plane
Canker stain of plane (Ceratocystis platani)
Not currently in the UK but present in Europe, as far north as Paris. Highly aggressive; causes tree mortality within 2–10 years, with no known chemical or biological controls or resistance.
Symptoms: Dieback of canopy, canopy wilt, yellow lesions under the bark.
Level of concern: Very high due to high potential impact and rapid spread.
Massaria disease of plane (Splanchnonema platani)
Strong link to drought stress, weakens upper surfaces of limbs which can cause sudden branch failure.
Symptoms: Cankers on upper branch surfaces, rapid decay of branches, branch cracking.
Level of concern: High for urban areas, especially where plane trees overhang footpaths or roads.
Plane lace bug (Corythucha ciliata)
Currently uncommon, localised outbreaks, but likely to increase with warming climate.
Symptoms: Leaf stippling of small yellow dots, discolouration, early leaf drop.
Level of concern: Low priority - emerging pest.
Spruce
Larger eight-toothed European spruce bark beetle (Ips typographus)
Invasive pest with ongoing outbreaks in southeast England and East Anglia. Prefers stressed, weakened or dead trees, but can infect live trees where numbers are high enough. Continued findings of Ips typographus in 2025/26 season have triggered a 3-year risk-based eradication strategy across southeast England and East Anglia. Demarcated area (DMA) in the southeast and East Anglia restricts felling, movement, and planting of spruce over 3m in height.
Symptoms: Individual or groups of dead spruce trees, linear gallery system visible on bark and wood underneath.
Level of concern: High.
Oak
Oak processionary moth (Thaumetopoea processionea)
Large cluster of caterpillars defoliates trees which can increase vulnerability to secondary pests and disease. Irritating hairs on caterpillars can pose public health risk.
Symptoms: Nest clusters, silk trails, reduced foliage.
Level of concern: High in Buffer Zone and Pest Free Area. Low to medium in Established Area. Designated areas can be viewed here.
Sycamore
Sooty bark disease (Cryptostroma corticale)
Windborne fungal pathogen causing rapid mortality in drought-stressed trees.
Symptoms: Black sooty spores under bark, bark flaking, sudden dieback.
Level of concern: High, especially in the year or two following hot summers causing tree stress.
Horse chestnut
Bleeding canker (Pseudomonas syringae pathovar aescul)
Bacterial pathogen causing decline of horse chestnut. Impact varies, some trees can withstand years of infection, others can die within a few years.
Symptoms: Oozing lesions on trunk, crown decline, bark necrosis.
Level of concern: High in urban areas where trees are stressed.
Sweet chestnut
Sweet chestnut blight (Cryphonectria parasitica)
A destructive fungus under official controls in a few sites in central and southern England which causes progressive decline and usually results in tree mortality.
Symptoms: Orange spores on discoloured bark, canopy wilt and browning, cankers.
Level of concern: Moderate/ high depending on regional abundance of sweet chestnut trees.
Looking forward
Disease and pest management
The group discussed the importance of ongoing monitoring and reporting of pests and diseases across the country. Advice for land managers remains to:
Report any pest or diseases spotted in your area through Forest Research’s Tree Alert portal.
Ensure appropriate biosecurity protocols are in place and follow best practice for tree procurement, planting and maintenance. Be aware of specific transmission pathways for emerging pests and diseases.
UK policy review for Phytophthora pluvialis
A longer-term review of the Phytophthora pluvialis policy is underway including a review of the appropriateness of maintaining demarcated areas. A consultation of an update to the Pest Risk Analysis and future management of P. pluvialis is open until the 26 January. You can share your views by following this link Pest risk analyses - UK Plant Health Information Portal
Monitoring tree establishment
There is currently limited evidence and no consistent, standardised approach to measuring tree establishment success, resulting in scarce and fragmented data. To address this gap, The Tree Council is working in partnership with Defra, Forest Research and Fera Science to develop and test improved approaches to assessing and supporting tree establishment. It is recommended that land managers:
Monitor newly planted trees to better understand the impact of local climate, soil type and condition, especially in the context of warmer weather.
Plant tree species carefully selected for their resilience to drought and stress.
Explore alternative tree establishment methods e.g., promote natural regeneration to reduce financial burden on tree management programmes.
Ask an expert
Get in touch with any questions or topics you’d like discussed in the next Tree Health Operations Forum by email to scienceandresearch@treecouncil.org.uk.
For guidance around tree establishment, monitoring and survival, as well as pests and diseases, and seasonal advice, please visit The Tree Council’s Guidance Hub.
Find out more about The Tree Council at treecouncil.org.uk. Sign up to our monthly newsletter The Leaflet, and follow our social accounts: Instagram, TikTok, Facebook, LinkedIn, X/Twitter, YouTube.
*This post was edited on January 22 2026