Maple Leaf Blister: Cosmetic Concern, Not a Health Threat

Symptoms

An October Glory maple shows grayish-brown, raised spots clustering along leaf veins—resembling a watermelon rind—with some leaf curling and browning at edges.

Diagnosis: Taphrina Leaf Blister

The culprit is a fungus (Taphrina spp.) that overwinters in bud scales and infects emerging leaves in wet springs. The spots are blister-like but cause no lasting harm.

Prognosis

• Infected leaves may drop early but are typically replaced within weeks.
• Tree health is unaffected; no repeated infection cycles occur in summer.
• Outbreaks correlate with unusually wet springs (like 2009) and are rare in normal years.

Management

No action required. The tree will outgrow the damage. For prized specimens where cosmetic perfection is desired, apply a single preventive fungicide spray (chlorothalonil, lime sulfur, Bordeaux mixture, or fixed copper) just before bud break next spring.