Pussy Willow Blister Gall: Identification and Management

Those Yellow Bumps Are Willow Blister Galls

The small yellow bumps coating your pussy willow (Salix discolor) leaves are willow blister galls—caused by a tiny gall midge (Rabdophaga spp.), not a disease.

What They Are

• Midge lays eggs on developing leaves.
• Larval feeding triggers plant to form hollow, blister-like galls.
• Larvae develop inside, protected from predators.
• Galls turn brown, larvae exit, cycle repeats.

Impact Assessment

Primarily cosmetic. Galls rarely cause significant harm to established willows. They're unsightly but the tree tolerates them well. Severe infestations on young plants may reduce photosynthetic capacity slightly.

Management Options

1. Do nothing (recommended for mature plants). Natural enemies (parasitic wasps) often suppress populations.
2. Prune and destroy heavily galled leaves/branches in early spring before adults emerge.
3. Rake and remove fallen leaves to reduce overwintering population.
4. Insecticides are rarely warranted and difficult to time (target adults during brief emergence).

Resources for Confirmation

• Colorado State: Willow Blister Gall
• Ohio State: Galls on Trees and Shrubs

Your pussy willow will outgrow this—willows are remarkably resilient!