Signs of Tree Disease: What to Look For

Trees rarely die suddenly. Most decline takes years, and the warning signs are visible to a careful eye long before the tree becomes a hazard. Here are the eight signs we watch for on every site.

1. Dead branches in the upper canopy

Dead branches at the top of the tree (crown dieback) are usually the first visible symptom of root or vascular system damage. A few dead branches scattered through the canopy are normal and usually pruned out as routine maintenance. Significant crown dieback — more than 20% of upper canopy — is a serious warning sign.

2. Mushrooms or conks at the base

Bracket fungi (Ganoderma, Phellinus, Armillaria) growing on the trunk or at the base of the tree indicate internal wood decay. The mushroom is the fruiting body — by the time it's visible, the decay inside the tree is well advanced.

3. Cracks or splits in the trunk

Vertical cracks down the trunk, especially at branch unions, indicate structural weakness. Some are old and stable; others are active and getting worse. An arborist can tell the difference.

4. Bark falling off in sheets

Some species (eucalypts, plane trees) shed bark as a normal seasonal process. Others (oaks, maples) don't — and bark falling off in sheets indicates the cambium underneath is dying.

5. Leaning where it didn't lean before

A tree that's developed a lean in the last twelve months is a serious concern. Either the root plate is failing, the soil has shifted, or the canopy weight has redistributed. A new lean after heavy rain especially deserves immediate inspection.

6. Sap or ooze running down the trunk

Bacterial wetwood, slime flux, or sap leakage from open wounds all indicate stress or active infection. Some species (mulberry, elm) ooze normally; others don't, and ongoing ooze is a sign something's wrong inside.

7. Premature leaf drop or off-season colour

Leaves dropping in summer, or autumn colour appearing in January, indicate the tree isn't able to maintain its canopy through stress. Often a sign of root damage from construction, drought, or compacted soil.

8. Hollow sound when you tap the trunk

A solid trunk has a solid thunk. A trunk that sounds hollow when tapped with a knuckle has internal decay. A drilling resistance test (resistograph) can confirm how much sound wood remains.

What to do if you see signs

Don't panic, don't ignore. Get a certified arborist to walk the tree and document the findings. Our tree management plans include annual structural inspections of significant trees — most major problems are caught and managed before they become removals.