Common Tree Diseases and Treatments

Trees are among the most valuable assets in any garden or landscape. They provide beauty, shade, oxygen, and a home for wildlife. A mature tree can take decades to establish, yet in just a few short years it may become weakened by disease if not cared for properly. In the UK, several well-known tree diseases threaten our native species, and many homeowners do not realise there is a problem until it has progressed too far. This is why professional tree services play such an important role in identifying issues early and ensuring trees remain healthy and safe.

Being able to identify common tree diseases and knowing the options for treatment will help you make informed decisions about the health of your garden. This is where the advice of a professional such as a Plymouth tree surgeon becomes invaluable. They can diagnose conditions accurately, suggest management strategies, and carry out any work safely.

Why Tree Diseases Occur

Tree diseases usually arise from fungi, bacteria, or viruses, but the underlying cause often comes down to stress. A tree under pressure from drought, compacted soil, poor nutrition, or root damage is more vulnerable to infection.

Some of the most common reasons include:

• Environmental stress: Long dry spells or waterlogging weaken roots.
  
• Soil compaction: Common in urban areas where vehicles or foot traffic press down the ground, making it harder for roots to absorb oxygen.
  
• Injuries: Cuts from strimmers, poor pruning techniques, or storm damage can open the way for pathogens.
  
• Spread from other plants: Spores, insects, and animals can carry diseases from tree to tree.

Because of these factors, prevention is just as important as treatment. Healthy, well-maintained trees are much more resistant to disease.

The Most Common Tree Diseases in the UK

Below is an in-depth look at the most widespread tree diseases you might encounter, how to spot them, and what treatments or actions may be needed.

1. Ash Dieback (Chalara fraxinea)

Ash dieback is currently one of the most destructive tree diseases in Europe, threatening to wipe out much of the UK’s ash population.

• Symptoms:
  
  • Blackened, shrivelled leaves in spring and summer.
    
  • Diamond-shaped lesions where branches join stems.
    
  • Dieback starting at the crown and working downwards.
    
  • Young saplings dying quickly, older trees declining gradually.
    
• Treatment:
  There is no cure. Infected trees should be monitored and made safe, as falling branches can be hazardous. In some cases, trees showing tolerance are left to encourage resistant strains. If removal is necessary, a Plymouth tree surgeon can safely fell the tree and advise on suitable replacement planting.

2. Dutch Elm Disease

Dutch elm disease devastated elm populations in the 1960s and 1970s, and while fewer elms remain today, the disease is still active.

• Symptoms:
  
  • Yellowing and curling leaves that turn brown in midsummer.
    
  • Twigs and branches dying from the top down.
    
  • Brown streaks in the sapwood visible when bark is peeled back.
    
• Treatment:
  Infected elms rarely recover. Small outbreaks may be managed by removing diseased branches, but in most cases the tree needs to be removed and burned to stop the fungus spreading via elm bark beetles. Disease-resistant cultivars are slowly being reintroduced in some areas.

3. Honey Fungus (Armillaria)

Honey fungus is a group of fungi that spreads underground through black bootlace-like rhizomorphs, attacking the roots of trees and shrubs.

• Symptoms:
  
  • Clumps of honey-coloured mushrooms at the base of the tree in autumn.
    
  • White, fan-like fungal sheets under the bark.
    
  • Strong mushroom smell around roots.
    
  • Dieback, leaf yellowing, and sudden death in severe cases.
    
• Treatment:
  No chemical cure exists. Management involves removing stumps and infected roots, improving soil drainage, and planting resistant species such as beech or yew. Where removal is required, a Plymouth tree surgeon can safely extract affected trees and advise on replanting strategies.

4. Oak Decline

Oak decline refers to a combination of factors (fungal infections, pests, and environmental stress) that weaken oak trees.

• Symptoms:
  
  • Sparse or discoloured foliage.
    
  • Small, stunted leaves.
    
  • Cracks and lesions in bark.
    
  • Dead branches high in the crown.
    
• Treatment:
  While there is no single cure, good tree care is key. This includes mulching around the base, avoiding soil compaction, watering during droughts, and removing deadwood. In severe cases, a Plymouth tree surgeon may recommend reduction pruning to ease the stress load on the tree.

5. Powdery Mildew

Powdery mildew is common on sycamore, oak, and horse chestnut trees, but it can affect many species.

• Symptoms:
  
  • A white, talc-like coating on leaves and shoots.
    
  • Curling or distorted leaves.
    
  • Premature leaf fall.
    
• Treatment:
  Often not life-threatening but can reduce growth. Pruning for better airflow, removing infected leaves, and applying fungicides (where appropriate) may help. Keeping the tree vigorous through good watering and feeding reduces susceptibility.

6. Bleeding Canker of Horse Chestnut

This bacterial infection has become increasingly widespread in recent years.

• Symptoms:
  
  • Rusty-red or black fluid oozing from bark cracks.
    
  • Lesions that kill sections of bark.
    
  • Yellowing leaves and thinning crowns.
    
  • Premature leaf drop.
    
• Treatment:
  No cure is available, but pruning affected areas and improving conditions may prolong tree life. Severely infected trees can become unstable and may need safe removal.

7. Sooty Bark Disease of Sycamore

This fungal disease particularly affects stressed sycamores, especially after hot summers.

• Symptoms:
  
  • Leaves wilting suddenly in summer.
    
  • Blackened, peeling bark resembling soot.
    
  • Rapid decline, often resulting in death.
    
• Treatment:
  Infected trees cannot usually be saved and should be removed promptly for safety reasons. A Plymouth tree surgeon can handle this safely and recommend alternative species for replanting.

8. Phytophthora Root Rot

Phytophthora affects a wide range of trees, including alder, beech, and oak.

• Symptoms:
  
  • Crown dieback.
    
  • Discoloured or yellowing foliage.
    
  • Bleeding cankers on the trunk.
    
  • Root decay and poor anchorage.
    
• Treatment:
  Managing soil drainage is crucial. Removal of infected trees is often necessary, and replanting should be done with resistant species.

How to Prevent Tree Diseases

While not every disease can be avoided, you can significantly reduce risk by:

• Regular inspections – Check trees each season for signs of discolouration, dieback, or fungal growth.
  
• Professional pruning – Correct pruning reduces the chance of infection by minimising wounds.
  
• Soil care – Mulching, watering in dry spells, and avoiding compaction helps roots remain strong.
  
• Right tree, right place – Plant species suited to local soil and climate to reduce stress.
  
• Sanitation – Remove fallen leaves and infected material to prevent the spread of spores.

Why Call a Tree Surgeon?

Tree diseases are complex and often misdiagnosed. Attempting DIY treatment without proper knowledge can worsen the problem or make the tree unsafe. A professional Plymouth tree surgeon can:

• Correctly identify the disease.
  
• Recommend effective treatments or management plans.
  
• Prune or remove infected wood safely.
  
• Advise on replanting with disease-resistant species.
  
• Ensure work complies with UK tree preservation and safety laws.

Final Thoughts

Trees are long-term investments in your garden, but they are not invincible. From devastating diseases like ash dieback to more manageable issues such as powdery mildew, early action makes the biggest difference.

Caring for trees properly, preventing stress, and seeking expert advice when something looks wrong will keep your garden safe and flourishing. If you suspect a tree on your property may be diseased, contacting a qualified Plymouth tree surgeon is the best step you can take to protect both your trees and your outdoor space.