Managing Hershey Kiss Galls on Oak Trees

What Are Hershey Kiss Galls?

These are leaf galls caused by tiny gall wasps (family Cynipidae). The adult wasp lays eggs on the leaf surface and secretes a chemical that forces the leaf tissue to form a protective, gall structure around the developing larvae. The galls resemble Hershey's Kisses—hence the name.

Why Sprays Don't Work Well

Contact insecticides target adult wasps, which are present only briefly during egg-laying. Once larvae are inside the gall, they are shielded from sprays. Timing is extremely difficult.

Effective Systemic Treatment

Apply a systemic insecticide (e.g., Bayer Advanced Tree & Shrub Insect Control, active ingredient imidacloprid) as a soil drench in early spring as leaves bud out. The tree transports the chemical to the leaves; when larvae feed, they ingest it and die. This won't prevent galls in the current year but significantly reduces next year's population.

Application Tips

• Follow label rates based on trunk diameter.
• Water thoroughly after application to move product into the root zone.
• Avoid spraying blooming plants to protect pollinators.

Long-Term Outlook

Gall wasps rarely threaten tree health. Heavy infestations may cause early leaf drop, but oaks generally tolerate them well. Systemic treatment every few years keeps populations manageable without broad-spectrum spraying.