Is Your Tree Sick? How to Spot Diseases and Pests

Trees usually warn you before they fail

A tree that drops a limb on your roof or has to be taken down in a hurry rarely got that way overnight. Most decline slowly, and the early signs show up in the leaves, bark, and branches long before the tree becomes a hazard. Learning to read those signs helps you act while the tree can still be saved, or at least plan a removal on your own schedule instead of during a storm.

Here is what to look for, and when the problem is bigger than a homeowner should handle alone.

Start with the canopy

The leaves tell you a lot about what is happening below. On a healthy tree, the canopy is full and evenly colored for the season. Warning signs include:

• Leaves that turn brown, yellow, or red well before fall
• Bare patches where the canopy looks thin or see-through
• Spots, blotches, or a powdery coating on the foliage
• Wilting or curling during weather that should not stress the tree
• Buds that never open in spring on part of the tree

One sparse branch might mean nothing. A pattern that spreads across the canopy from one year to the next is worth a closer look.

Check the trunk and bark

Move your eyes down to the trunk. Bark should be reasonably intact for the species, without large wounds or soft areas. Things that should get your attention:

• Cracks that run deep or vertically up the trunk
• Sunken, discolored patches called cankers, sometimes oozing sap or a dark liquid
• Loose or peeling bark on a tree that is not a natural shedder like a sycamore
• Mushrooms or shelf-like fungus growing on the trunk or at the base

That last one matters more than people expect. Fungus at the root flare often signals decay inside the wood, where you cannot see it. A tree can look fine up top and still be rotting at the core.

Look at the branches and roots

Look up for deadwood: branches with no leaves in summer, brittle twigs that snap cleanly with no green inside, or large limbs that have lost their bark. A few dead twigs are normal. Several big dead limbs, especially high in the tree, raise the risk of something heavy coming down.

At ground level, watch for heaving soil, exposed roots that feel soft or look blackened, and any lean that seems new. A tree that has always leaned is usually fine. A tree that starts leaning after a storm may have root damage.

Know the usual suspects

You do not need to name the exact disease, but it helps to know the categories.

Fungal diseases are the most common. Anthracnose blotches and curls leaves in wet springs. Oak wilt and Dutch elm disease move through a tree's water system and can kill it fast. Root and butt rot works out of sight, weakening the base.

Insects do their own damage. The emerald ash borer has wiped out ash trees across much of the country, leaving D-shaped exit holes and thinning crowns. Bark beetles target stressed conifers. Aphids and scale weaken a tree slowly and coat everything below in sticky residue.

Environmental stress sets the stage for both. Drought, compacted soil, mower and string-trimmer wounds, and dirt piled over the roots during construction all wear down a tree's defenses and invite disease and pests in.

What you can handle yourself

A lot of tree health comes down to not making things worse:

• Water deeply during dry stretches, especially for young trees, and let the soil dry between soakings
• Spread mulch in a wide ring, kept a few inches back from the trunk, never mounded against it
• Keep mowers and trimmers away from the bark
• Prune out small dead or broken branches you can safely reach from the ground
• Clean up fallen leaves from a tree you suspect is diseased, so spores do not overwinter and start the cycle again

These steps will not cure a serious infection, but they keep a healthy tree healthy and give a struggling one a better chance.

When to bring in a pro

Some situations are past the point of a garden hose and hand pruners. Call a tree service or certified arborist when:

• A disease is spreading through the canopy year over year
• You see fungus at the base or a large cavity in the trunk
• Big dead limbs hang over the house, driveway, or a play area
• The tree has developed a new lean, or the soil around it is lifting
• You want a straight answer on whether a valuable tree can be treated or should come down

A good arborist can often save a tree that looks doomed, and will tell you honestly when it cannot. Either way, a trained eye catches trouble inside the wood that you cannot see from the lawn.

The bottom line

Walk your property a couple of times a year and actually look at your trees: the full canopy in summer, the bare structure in winter. Catching a problem while it is still one branch or one soft patch of bark gives you options. Wait until a limb is already on the ground, and the only option left is cleanup.