How to Identify a Diseased Tree & When to Call an Arborist

Dutch Elm Disease

Introduction

Trees are essential to our environment, providing oxygen, shade, and beauty. However, like any living organism, trees can suffer from diseases that weaken their structure and, if left untreated, can lead to tree death and property damage. Identifying a diseased tree early can help prevent its deterioration and the spread of infection to nearby trees. But how do you know when your tree is sick, and when should you call a professional arborist?

In this guide, we’ll explore the most common signs of tree disease, how to identify various infections, and when to seek expert help from an ISA-certified arborist.

Why It’s Important to Identify Tree Disease Early

✅ Prevents Spread – Some tree diseases are highly contagious and can spread to surrounding trees if not addressed promptly.

✅ Ensures Safety – Diseased trees become structurally weak, increasing the risk of falling branches and tree failure, which can cause property damage or injury.

✅ Protects Property Value – Healthy trees enhance curb appeal and property value, while diseased trees can become an eyesore and liability.

✅ Saves Money – Early treatment is often more cost-effective than emergency removal and extensive property repairs.

Common Signs of a Diseased Tree

Not all tree diseases are obvious at first glance. However, several key warning signs can indicate a problem.

1. Unusual Leaf Discoloration & Defoliation 🍂

• Leaves turning yellow, brown, or developing dark spots outside of normal seasonal changes.

• Premature leaf drop in spring or summer.

• Leaves curling or appearing scorched.

• Possible Causes: Anthracnose, bacterial leaf scorch, Dutch Elm Disease.

2. Fungal Growth & Mushrooms 🍄

• Mushrooms or fungal growth on the trunk or base of the tree.

• White, black, or powdery mildew on leaves.

• Cankers or decayed areas with fungal spores.

• Possible Causes: Root rot, heartwood decay, butt rot.

3. Bark Abnormalities & Cracks 🌳

• Bark splitting, cracking, or peeling away.

• Sunken or raised patches on the trunk.

• Sap oozing from wounds or spots with black, tar-like residue.

• Possible Causes: Canker diseases, frost damage, bacterial infections.

4. Weak or Dead Branches 🌿

• Brittle, breaking, or hollow branches.

• No buds forming in spring.

• Falling branches in calm weather.

• Possible Causes: Blight, pest infestations, advanced disease decay.

5. Sudden Limb Drop ⚠

• Large limbs falling unexpectedly, even on a calm day.

• Signs of internal decay on fallen branches.

• Possible Causes: Summer limb drop (common in oaks), dehydration stress, fungal infections.

6. Pests & Insect Infestation 🐛

• Holes in bark or leaves.

• Sawdust-like material (frass) at the base of the tree.

• Visible pests like Emerald Ash Borer, Asian Longhorn Beetle, or tent caterpillars.

• Possible Causes: Insect infestation leading to secondary disease.

Common Tree Diseases in Ontario

Different tree species are susceptible to specific diseases. Here are a few of the most common ones in Ontario:

🔹 Dutch Elm Disease (DED) – A fungal infection spread by elm bark beetles, leading to leaf wilting and branch death.

🔹 Oak Wilt – A lethal disease causing leaf discoloration and rapid tree decline.

🔹 Anthracnose – Affects maples, sycamores, and dogwoods, causing leaf blight and premature defoliation.

🔹 Fire Blight – A bacterial disease that affects fruit trees, causing branches to appear burned or scorched.

🔹 Root Rot – Affects trees growing in poorly drained soil, leading to slow decline and instability.

When Should You Call an Arborist?

While minor issues like a few dead branches can sometimes be handled with DIY pruning, some situations require professional intervention.

📌 Call an arborist if you notice:

• Disease symptoms spreading quickly.

• Multiple infected branches or neighboring trees showing similar issues.

• Large, dead limbs that pose a fall risk.

• Mushrooms or fungal growth at the base of the trunk.

• Unstable leaning trees with root damage.

Emergency Situations 🚨

Some tree diseases weaken the structure so much that they become an immediate hazard. Call an arborist immediately if:

• A tree is leaning significantly after a storm.

• Large branches have fallen near structures or power lines.

• You suspect a tree is at risk of sudden failure.

Preventative Tree Care Tips

Regular tree maintenance can help prevent diseases and extend the lifespan of your trees. Here are some proactive measures you can take:

✅ Prune Properly – Remove dead or diseased branches to improve airflow and tree health. ✅ Mulch Smartly – Apply mulch around the base of trees to retain moisture, but avoid piling it against the trunk. ✅ Water Wisely – Deep, infrequent watering encourages strong root growth, while overwatering can lead to fungal infections. ✅ Inspect Regularly – Look for early signs of disease and address them before they worsen. ✅ Hire an Arborist for Annual Inspections – Certified professionals can detect potential problems before they become severe.

Frequently Asked Questions About Tree Disease

1. Can a diseased tree be saved?

It depends on the severity and type of disease. Some fungal infections can be treated with proper pruning and antifungal treatments, while bacterial infections may require tree removal to prevent spread.

2. How much does it cost to treat a diseased tree?

Treatment costs vary based on tree size, disease severity, and required interventions. Basic disease management may cost $150–$500, while advanced treatments or removals can be higher.

3. What happens if I leave a diseased tree untreated?

Untreated tree diseases can weaken structural integrity, making the tree a safety hazard. Additionally, infections can spread to other trees, leading to widespread damage.

4. Do tree diseases affect property value?

Yes. Diseased or dying trees can decrease curb appeal and property value. Well-maintained trees, on the other hand, enhance aesthetics and add value.

Conclusion

Early detection is key to managing tree diseases effectively. If you notice any of the signs mentioned above, don’t wait—call a professional arborist for an evaluation. Taking action early can save your tree, protect your property, and maintain a safe outdoor environment.

📞 Concerned about a diseased tree? Zen Tree Care provides expert diagnosis, treatment, and tree health management services in the GTA and Simcoe County. Contact us today!