How to Identify & Treat Common Tree Diseases

Trees are essential for our environment, providing oxygen, shade, and habitats for wildlife. However, like all living organisms, they are susceptible to diseases that can weaken or even kill them if left untreated. Some tree diseases spread rapidly, affecting entire landscapes, while others develop slowly over time.

The Importance of Early Detection

Catching tree diseases early can prevent further damage, stop the spread to nearby trees, and save the affected tree from decline or being vulnerable to storm damage. Many diseases are treatable if addressed in the early stages.

Common Causes of Tree Diseases

• Fungi – The leading cause of tree diseases, often affecting leaves, bark, and roots.
• Bacteria & Viruses – Can enter trees through wounds or insect transmission.
• Environmental Stress – Drought, poor soil, pollution, or extreme temperatures weaken trees, making them more vulnerable.
• Insect Infestations – Some pests carry pathogens that infect trees.

Quick Fact: Over 90% of tree diseases are caused by fungal infections, but most can be managed with proper care and preventive measures.

Ash Dieback is only saved by removal of infected trees

Signs & Symptoms of Tree Diseases

General Warning Signs of Disease

• Leaf Discoloration – Yellowing, browning, or spotting on leaves.
• Wilting or Premature Leaf Drop – Leaves falling off before autumn.
• Cankers or Cracks in Bark – Sunken, dead patches on the trunk or branches.
• Fungal Growth – Mushrooms or white powdery coatings on bark and leaves.
• Branch Dieback – Upper branches lose leaves and stop producing new growth.
• Oozing or Sap Flow – Sticky or discoloured liquid seeping from wounds.

Tip: Compare a tree’s symptoms to seasonal changes—some leaf drop or colour shifts may be normal, but sudden or irregular changes are a red flag.

Common Tree Diseases, Symptoms & Treatments

Dutch Elm Disease (Ophiostoma novo-ulmi)

• Status in the UK: Widespread and highly destructive since the 1970s, wiping out millions of elm trees.
• Current Situation: While some resistant elm cultivars exist, Dutch Elm Disease remains a major issue, especially in England and Scotland.
• Symptoms: Leaves wilt and turn yellow, branches die back, brown streaking under bark.
• Cause: A fungal infection spread by elm bark beetles.

Treatment:

• Prune and destroy infected branches.
• Apply fungicidal injections in early stages.
• Remove severely infected trees to prevent spread.

Acute Oak Decline (AOD)

• Status in the UK: Major concerns for British trees
• Current Situation: Affects Oak Trees
• Symptoms: Dark fluid oozing from the bark, rapid branch dieback, tree death within 5-6 years.
• Cause: Bacterial infection, often associated with stress or climate change.
• Treatment: No cure—focus on prevention, maintaining tree health, and avoiding unnecessary injury.

Ash Dieback (Hymenoscyphus fraxineus)

• Status in the UK: Major concerns for British trees
• Current Situation: Affects Ash Trees
• Symptoms: Wilting, blackened leaves, dieback of branches, lesions on bark.
• Cause: A fungal pathogen devastating ash trees in the UK.
• Treatment: No cure, infected trees may need to be felled to prevent spread.

Powdery Mildew (Erysiphales fungi)

• Status in the UK: Common across the UK, affecting a wide range of trees, including oak, maple, sycamore, horse chestnut, and fruit trees.
• Current Situation: Particularly problematic in warm, humid summers, but rarely fatal.
• Symptoms: White powdery patches on leaves and stems.
• Cause: Fungal spores thrive in warm, humid conditions.

Treatment:

• Improve air circulation by thinning dense foliage.
• Apply sulphur-based fungicides as needed.
• Water trees at the base, not on the leaves, to prevent moisture build-up.

Honey Fungus (Armillaria mellea)

• Status in the UK: One of the most common and destructive tree diseases in Britain.
• Current Situation: Particularly affects beech, oak, fruit trees, and garden shrubs. It spreads underground and is difficult to control.
• Symptoms: White fungal growth under bark, honey-coloured mushrooms near tree base, and root rot.
  Cause: A highly aggressive fungus that spreads underground through roots.

Treatment:

• Remove infected trees and stumps to contain the spread.
• Improve soil drainage to reduce fungal growth.
• Use disease-resistant tree species when replanting.

Chestnut Blight (Cryphonectria parasitica)

• Status in the UK: Historically not common, but first confirmed in Britain in 2011 and now considered an emerging threat.
• Current Situation: Mainly affects sweet chestnuts, which are not as widespread in the UK as in mainland Europe, but could become a problem with climate change.
• Symptoms: Orange-brown cankers on bark, wilting leaves, dead branches.
• Cause: A fungal infection that enters through bark wounds.

Treatment:

• Prune and destroy infected branches immediately.
• Apply tree wound sealants to protect cuts.
• Support tree recovery using disease-resistant hybrids when replanting.

Prevention Strategies – Keeping Trees Healthy

Proper Tree Care & Maintenance

Regular Pruning: Remove dead or diseased branches to improve airflow and sunlight penetration.
Mulching: Retains soil moisture, suppresses weeds, and improves root health.
Soil Testing: Monitor and adjust pH and nutrients to maintain tree health.

Managing Environmental Stress

Avoid Overwatering: Excess moisture encourages fungal infections.
Plant Trees in Suitable Locations: Choose species that thrive in your region’s climate and soil.
Use Disease-Resistant Tree Varieties: Some species are naturally resistant to common diseases.

Tip: Keep an eye on trees seasonally for early signs of disease and act promptly.

When to Call a Tree Specialist

Knowing when to seek professional help can prevent further tree loss and protect surrounding vegetation. Call a certified arborist if:

• The disease symptoms persist despite treatment.
• The tree has large, dead branches or severe bark damage.
• Fungal growth is visible at the tree’s base.
• The tree is leaning dangerously or showing signs of structural weakness.

Tree specialists have the tools and expertise to diagnose diseases, apply effective treatments, and determine whether a tree can be saved.

Conclusion: Healthy Trees, Healthy Ecosystem

Early detection is crucial for managing tree diseases effectively. Proper tree care, pruning, and environmental management extend tree health and longevity. If unsure, consult a professional arborist for diagnosis and treatment.

Need help with tree disease diagnosis and treatment in Sussex? Contact Garnham Tree Surgery today for expert tree care services!