Pest

Galls

Odd bumps, balls or pouches on leaves and twigs, made by tiny insects or mites; usually harmless.

What you'll see

• Round balls, bumps, cones, blisters or fuzzy patches on leaves, twigs or buds.
• Common on oaks, maples, witch hazel, spruce and many other trees and shrubs, often in large numbers.
• The plant otherwise grows normally, though heavily galled leaves may drop early.

Why it happens

Gall wasps, mites, midges, aphids and other tiny creatures lay eggs or feed in the plant, and their chemicals make it grow a swelling around them. A few galls come from fungi or bacteria.

How to fix it

1. Most galls need no treatment; they look odd but rarely harm the plant.
2. Pick off galled leaves, or prune out twig galls while they are green, before the insects emerge.
3. Rake up and bin fallen galled leaves in autumn.
4. Sprays don't work once galls have formed.
5. For galls that return badly, spray horticultural oil at the dormant rate before bud break, as the label says, keeping kids and pets away.

Keep it from coming back

• If a galled plant looks weak, look for another cause such as drought or root problems.
• Watch oaks for twig galls, which can kill branches in large numbers, and prune them out early.
• Avoid broad-spectrum sprays, so birds and parasitic wasps can keep gall makers in check.

Sources

• University of Maryland Extension: Tree and shrub galls
• Clemson HGIC: Galls and outgrowths

General guidance, not a diagnosis. For valuable, edible or outdoor crops, check with a local extension service or plant expert. Use any product exactly as its label says, and keep children and pets away while it dries.