How to Tell If Your Tree Is Sick

Trees are resilient, but they're not invincible. Disease, pests, and structural problems can take hold gradually — often going unnoticed until significant damage has been done. Catching problems early gives you the best chance of saving a tree and protecting the safety of your property.

Here are seven key warning signs every homeowner should know.

1. Unusual Leaf Discoloration or Drop

Leaves that turn yellow, brown, or spotted outside of normal seasonal patterns are often the first visible sign of trouble. Early leaf drop — especially in summer — can indicate fungal infection, root damage, or pest infestation. Look for patterns: discoloration affecting only one side of the tree may point to root or soil issues on that side.

2. Cankers and Sunken Bark Areas

Cankers are dead sections of bark that appear sunken, discolored, or cracked. They're often caused by fungal or bacterial infections and can girdle a branch or trunk, cutting off the flow of water and nutrients. If a canker encircles an entire branch, that branch is likely dying.

3. Fungal Growth at the Base or on the Trunk

Mushrooms, shelf fungi (also called bracket fungi), or other growths emerging from the bark or soil near the base of a tree are serious red flags. These fruiting bodies typically indicate internal wood rot — meaning decay may already be well advanced inside the trunk or roots by the time you see them.

4. Deadwood and Dead Branches

A few dead branches aren't always cause for alarm, but extensive deadwood — especially scattered throughout the canopy — suggests a systemic problem. Dead branches also pose a falling hazard, so they should be removed promptly regardless of the underlying cause.

5. Unusual Holes or Sawdust-Like Frass

Small round or D-shaped holes in the bark, often accompanied by fine powdery sawdust (called frass), are telltale signs of wood-boring beetles. Species like the Emerald Ash Borer and Asian Longhorned Beetle are highly destructive and can kill trees within a few years of infestation.

6. Wilting or Stunted Growth

If a tree consistently produces smaller-than-normal leaves, grows very slowly, or looks generally wilted despite adequate rainfall, it may be suffering from root rot, soil compaction, or a vascular disease like verticillium wilt or oak wilt.

7. Leaning or Shifting Trunk

A sudden lean — especially after a storm — can indicate root failure. Unlike trees that have grown at an angle over many years, a new lean is a structural emergency. Check around the base for heaving soil, exposed roots, or cracking, which all suggest the root system is compromised.

What to Do If You Notice These Signs

  1. Don't wait. Early intervention dramatically improves outcomes for diseased trees.
  2. Document the symptoms. Take clear photos of affected areas — close-ups of leaves, bark, and any fungi — to share with a professional.
  3. Contact a certified arborist. Many tree diseases require professional diagnosis and treatment. An ISA-certified arborist can assess the tree's overall health and recommend a course of action.
  4. Avoid DIY chemical treatments without diagnosis. Applying the wrong treatment can stress the tree further or mask symptoms without addressing the root cause.

Prevention Is Always Better Than Cure

Healthy trees are far more resistant to disease and pests. Proper watering, mulching, regular pruning, and avoiding soil compaction around the root zone all contribute to long-term tree vitality. Annual inspections by a qualified arborist can catch problems before they become serious — and before they become expensive.