Recognizing a sick or dying tree before it becomes a hazard is one of the most valuable things a Lehigh Valley homeowner can do. Trees rarely fail without warning — the warning signs are just easy to miss if you do not know what to look for.
Stone Ridge Landscaping has been identifying diseased, declining, and hazardous trees across Lehigh and Northampton Counties for 25 years. Here is a comprehensive guide to reading the signs.
Crown and Canopy Warning Signs
Dieback from the Top Down
When a tree starts dying from the tips of its upper branches inward and downward — called dieback or flagging — something is wrong at the root or vascular level. Top-down dieback is one of the primary signs of emerald ash borer in ash trees, and it progresses faster than most homeowners expect. A tree with 30 percent crown dieback this year may have 60 percent next year.
Sparse or Off-Season Leaf Drop
A tree dropping leaves heavily in summer (outside of normal fall timing) is under severe stress. In the Lehigh Valley, this is commonly caused by drought stress, oak wilt, root damage from construction activity, or vascular disease. A sudden mid-summer leaf drop across the full canopy is a red flag requiring prompt attention.
Premature Fall Color
Leaves turning color weeks before surrounding trees of the same species — particularly just on one side or one branch system — can signal vascular disease, root damage, or girdling roots cutting off water transport to part of the crown.
Dead Branches in the Upper Crown
One or two dead branches in an otherwise healthy canopy is normal. But multiple dead branches concentrated in the upper crown, or an increasing proportion of dead wood year over year, signals progressive decline. Lionstailiing — where the interior branches die and leaves are only present at branch tips — is a particular warning sign.
Trunk and Bark Warning Signs
Shelf or Conk Fungi
Bracket fungi growing from the trunk or major roots are one of the most reliable indicators of significant internal decay. The fungal fruiting body is only visible externally when internal decay is already extensive — by the time you see conks on a tree, the structural integrity of the affected wood is severely compromised. This is almost always a removal indicator.
Vertical Cracks in the Bark
Vertical cracks running along the trunk, especially those that appear to extend through the wood rather than just the bark surface, indicate severe mechanical stress. Cracks that open and close seasonally are a sign of internal stress that warrants professional evaluation.
Seeping Wounds or Wet Wood
Bacterial wetwood (slime flux) causes trees to ooze foul-smelling, discolored liquid from wounds or branch attachments. While often manageable and not immediately lethal, it signals internal bacteria and decay in the affected wood column.
Woodpecker Activity
Heavy, systematic woodpecker feeding — particularly excavated patches where pileated woodpeckers are going after carpenter ants — indicates something is living inside the wood. Carpenter ants in a tree almost always mean decayed wood; they do not colonize sound wood.
D-Shaped Exit Holes
Small, D-shaped holes (about 1/8 inch across) in the bark of an ash tree are the exit holes of emerald ash borer adults. By the time these are visible, the infestation has been active for at least one to two years. Look also for S-shaped serpentine galleries visible under loosened bark, and the blonding pattern where woodpeckers have stripped sections of bark looking for EAB larvae.
Root Zone Warning Signs
Soil Heaving or Cracking at the Base
If you notice the soil cracking or heaving on the windward side of a tree (the side opposite a lean), the root plate is beginning to lift. This is a structural emergency — not a wait-and-see situation. A tree with an actively lifting root plate can fail completely without further warning, especially in the next wind event.
Mushrooms at the Base
Mushrooms growing from the root flare or from the soil in the root zone indicate root decay fungi. Armillaria (honey fungus), Ganoderma, and Inonotus are common root rot pathogens in the Lehigh Valley. Root decay is particularly serious because it undermines the tree foundation — a tree with extensive root rot can look perfectly healthy above ground right until it tips over.
Girdling Roots
A girdling root is a root that circles the trunk and gradually strangles the vascular system. Trees with girdling roots often show gradual decline over many years — thinning canopy, reduced growth, partial dieback — without an obvious cause. Look for roots that run horizontally across the trunk base rather than flaring outward normally.
Pest and Disease Identification by Species
Ash Trees — Emerald Ash Borer
Signs: top-down crown dieback, D-shaped exit holes (1/8 inch), S-shaped galleries under bark, woodpecker flecking, epicormic sprouting from the trunk base (a stress response). Nearly all untreated ash in Lehigh and Northampton Counties are affected. Treatment is only viable with less than 30 percent canopy dieback; beyond that, removal is the only realistic option.
Oak Trees — Oak Wilt
Signs: rapid browning and dropping of leaves beginning in May or June (red oak group), brown discoloration in the sapwood visible when a small branch is cut. Red, black, pin, and scarlet oaks can die within weeks of infection. The most important prevention measure: never prune oaks between April and October in the Lehigh Valley.
Beech Trees — Beech Leaf Disease
Signs: dark banding or striping between leaf veins, leaves that are thickened, leathery, or shriveled, progressive canopy thinning, bud failure. No cure exists. The nematode responsible is now confirmed in all 67 Pennsylvania counties.
Hemlock — Hemlock Woolly Adelgid
Signs: white woolly tufts at the base of needles (most visible in late winter), needle drop beginning at branch tips, progressive crown thinning. Eastern hemlock — Pennsylvania state tree — can die within 4 to 10 years of untreated infestation. Treatment with imidacloprid or trunk injection of emamectin benzoate is highly effective if started early.
Sycamore and Dogwood — Anthracnose
Signs: brown, scorched-looking blotches on leaves, shoot dieback, leaf drop in spring during cool wet conditions. Anthracnose is a consistent issue in Lehigh Valley springs but is rarely fatal to established mature trees. It is more of a cosmetic concern than a structural one.
What to Do When You Spot a Warning Sign
- Do not wait for symptoms to worsen. Early-stage disease is treatable; late-stage disease usually means removal is the only option.
- Get a professional assessment. Many symptoms overlap between diseases, pests, and abiotic stress. Accurate diagnosis matters for choosing the right response.
- Document what you see. Photos of bark, canopy, root zone, and any fungi help any arborist assess the situation faster.
- Address the hazard appropriately. A dying tree over a structure is not a watch-and-wait situation — the structural risk increases as decline progresses.