Red Bumps on One Maple Only: Insect Galls, Not Disease

Red Bumps on One Maple Only: Insect Galls, Not Disease

Raised red bumps on the undersides of leaves on a single maple, while a nearby oak and another maple are unaffected, are almost certainly insect galls (e.g., maple bladder gall mites). Galls are species-specific and often appear on individual trees due to microclimate or genetic variation.

What to Do

• Collect a few leaves and visit your county Extension office for confirmation.
• Photograph the bumps close-up and email to a plant diagnostic clinic.
• If galls, no treatment is needed—they are cosmetic and do not harm the tree.

The oak between them is irrelevant; gall mites are host-specific to maples.