Poison Oak: Leaves of Three, Let Them Be

Jul 8, 2021

A red and orange shrub of poison oak growing in front of a building.

Pacific poison oak growing as a shrub. (Credit: J Sachs, poison-ivy.org)

Poison oak is a common native plant in California, growing everywhere from oak woodlands to urban parks. Chances are, you or someone you know has suffered from a rash due to poison oak at some point.

The best way to avoid exposure to poison oak is knowing how to identify it. While the classic adage “leaves of three, let them be” can help differentiate poison oak from true oaks, it's not always correct. Poison oak is also deciduous so detecting it in the winter or spring when there are no leaves can be tricky.

3 bright green poison oak leaflets on a stem with other leaves in the backgroun.

Poison oak showing 3 leaflets.
(Credit: J DiTomaso)

More information on about this plant can be found in the recently updated Pest Notes: Poison Oak. Authors Scott Oneto (UC Cooperative Extension Advisor in the Central Sierra region) and Joe DiTomaso (UC Cooperative Extension Weed Specialist Emeritus) added information on identification and biology and a new section on treating an allergic reaction from poison oak exposure. They also updated the chemical control section for managing the plant if it becomes a problem on your property.

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By Belinda J. Messenger-Sikes
Author - Urban IPM Writer Editor

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