Most Common Tree Diseases & Pests in the UK: Identification and Endangered Trees

Introduced, pest-related, or viral diseases are damaging to native trees here in the UK, some of which have been standing for hundreds of years.

Good biosecurity practice is becoming a growing priority and the UK government have labelled the “damage to our trees, woods and forests from insect pests and organisms” as “significant.” More importantly, this interest is now shared by both the public and corporations alike, who are actively taking responsibility for nurturing the environment through initiatives like planting native trees.

Since the 2000’s, the demand for rare and exotic hardwoods, the increasing use of timbers in transport, and an interest in unique plants has resulted in a harmful growth of imported pests and bacteria from abroad. Many developments, including natural pests and disease, have created an urgency to better understand our trees and the challenges they face.

Trees are constantly under pressure all the time from a variety of diseases and pests, which can have dire consequences for their health. From leaf damage to wilting, these can be identified by common symptoms. Many businesses want trees to thrive rather than simply survive.

Which trees are most at-risk?

We’ve analysed data from the International Union for Conservation of Nature (IUCN) to identify some of the most at-risk trees in the UK, particularly those threatened by pests and landscape changes. This information is crucial for understanding how tree diseases and pests affect our native tree populations and the overall health of our woodlands.

Here are the key findings regarding the most vulnerable tree species:

Critically Endangered Trees in the UK

Several tree species in the UK are critically endangered due to various threats, including pests and diseases. The most at-risk trees include:

1. Catacol Whitebeam
2. Arran Service Tree
3. Cheddar Whitebeam
4. Ship Rock Whitebeam
5. Green’s Whitebeam
6. Sorbus Spectans (A type of Whitebeam)
   

Another noticeable tree classified as ‘vulnerable’ is the horse chestnut, which is nostalgic for many living in the British countryside. Known for bearing conkers, these trees have been celebrated by children and are associated with autumn.

Common Tree Pests Threatening Native Trees in the UK

While there are numerous blights that affect our native trees, the Woodland Trust has identified some major ones that negaNumerous pests threaten our native trees, with some causing significant damage to woodlands across the UK.

The Woodland Trust has identified several key pests that pose a serious risk to our forest ecosystems. Understanding these threats is crucial for protecting our trees and preserving biodiversity.

Asian and Citrus Longhorn Beetles

The Asian and Citrus Longhorn Beetle is a significant threat to a variety of broadleaf trees in the UK. This pest is often inadvertently imported on wooden crates and infected plants, particularly bonsai trees from China. Its capacity for widespread damage makes it crucial to monitor and manage this pest effectively.

Endangered Trees:

• Alder
• Birch
• Whitebeam
• Oak
• Willow

Bronze Birch Borer

The Bronze Birch Borer poses a considerable risk to both European and UK birch trees. As strong fliers, these beetles can spread rapidly, leading to potential infestations that threaten tree health. To mitigate this risk, the importation of birch trees from the US or Canada is strictly prohibited.

Endangered Trees:

• Silver Birch
• Betula Pendula
• Downy Birch
• Sweet Birch

Eight-Toothed Spruce Bark Beetle

The Eight-Toothed Spruce Bark Beetle is responsible for significant dieback in spruce trees and carries a pathogenic fungus that can exacerbate tree health issues. Last found in the UK in 2018 after accidental importation, its potential impact on Scotland’s rare and protected pine forests raises considerable concern.

Endangered Trees:

• Norway Spruce
• Sitka Spruce
• Scots Pine
• Larch

Elm Zig-Zag Sawfly

Since its arrival in the UK in 2017, the Elm Zig-Zag Sawfly has caused notable damage to Elm populations, particularly in the Southeast and East Midlands. The larvae of this pest can severely damage leaves, making the trees vulnerable to further harm and drought conditions.

Endangered Trees:

• English Elm
• Wych Elm
• Smooth-Leaved Elm

Oak Lace Bug

Although the UK has some native lace bug species, the Oak Lace Bug is particularly harmful, with no current populations present. However, the risk of it spreading locally remains high, which could severely affect the process of photosynthesis for oak trees and their surrounding ecosystems.

Endangered Trees:

• English Oak
• Sessile Oak
• Turkey Oak

Oak Processionary Moth

The Oak Processionary Moth is notorious for its damaging effects on both trees and humans. Its caterpillars have irritating spines that can cause skin rashes and itching. Initially confined to Greater London after its accidental introduction in 2006, this moth has since spread, stripping oak trees of their leaves and creating nests that complicate their natural shedding process.

Endangered Trees:

• English Oak
• Pedunculate Oak
• Red Oak

Red-Necked Longhorn Beetle

The Red-Necked Longhorn Beetle typically infects cherry trees, hiding in the trunk where signs of infestation are not apparent until significant damage has occurred. The beetles burrow and remain concealed in the trunk during colder weather, emerging only when temperatures rise, making early detection challenging.

Endangered Trees:

• Cherry
• Plum
• Apricot

Diseases Affecting UK Native Trees

Dutch Elm disease has already claimed the lives of 60 million trees, highlighting the severity of the threats facing native tree populations. Currently, the UK is grappling with six epidemic-level pests and diseases. 

As climate change continues to impact our environment, the prevalence of tree diseases is expected to rise, with warmer and wetter conditions fostering the growth of harmful bacteria and pathogens.

Several dangerous diseases pose significant risks to native trees, including:

Ash Dieback

Predicted to affect 80% of Ash trees fatally, Ash dieback has the potential to kill, damage or harm numerous EAsh dieback is predicted to affect 80% of ash trees fatally, potentially killing, damaging, or harming numerous European species of ash. While it does not impact the native hosts where it originated in Japan, it has devastated European trees for over 30 years.

This disease has cost taxpayers up to £15 billion in efforts to combat its spread, making it one of the biggest threats to native trees in the UK today.

Acute Oak Decline

Acute Oak Decline is a phenomenon observed for the past two decades, particularly affecting older oak trees that may die within five years. This decline typically results from a combination of environmental stress and other contributing factors.

Phytophthora Ramorum

Phytophthora ramorum is a water mould that causes Sudden Oak Death, impacting several tree species, including oak, larch, and rhododendron. This disease can lead to significant tree mortality and has been a growing concern in UK woodlands.

Horse Chestnut Bleeding Canker

This bacterial disease affects horse chestnut trees, leading to the characteristic bleeding of sap from infected areas. While it may not always be fatal, it significantly weakens trees, making them more susceptible to other pests and diseases.

Chalara Ash Dieback

Similar to Ash dieback, Chalara is another fungal disease that specifically targets ash trees. Its rapid spread and potential to devastate ash populations pose a severe threat to the biodiversity of UK woodlands.

Tree Diseases, Pests and the Law

Since Brexit, there is now different ‘plant passports’ that are required to import trees, plants, soil matter and more, into England, Scotland and Wales. To bring certain high risk plants and plant products into Great Britain you must now have a Phytosanitary Certificate (PC).

For moving plants around Great Britain, specifically in commercial settings, you will need a UK Plant Passport. This details information about the plant, it’s origin and more.

The UK Law on imported plants is strict, as we are easily able to control what pests, diseases and alien species are brought in with strict restrictions

Prevention of Tree Diseases and Pests

Preventing the spread of tree diseases and pests involves a multifaceted approach. In addition to implementing strict regulations on plant passports and sourcing practices, there are several proactive measures that can be taken to safeguard our native trees. 

Grounds Care Group is committed to adhering to all biosecurity regulations, ensuring that our tree surgeons are well-informed about any legal changes, especially in light of post-Brexit adjustments.

How Tree Surgery Can Battle Pests and Diseases

Tree surgeons and arborists possess the expertise to identify pests and diseases much earlier than the untrained eye. Regular visits from skilled tree surgeons are essential for maintaining the health and longevity of your trees.

At Grounds Care Group, we offer specialised tree surveys that help detect signs of pests and diseases early on, allowing for timely intervention and treatment. For more information on how we can help protect your trees from potential threats, contact us today!