Poison Oak Resource Updated

Pests in the Urban Landscape

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UCANR: Promoting healthy people and communities

Poison Oak Resource Updated

Author: Belinda J. Messenger-Sikes

Published on: July 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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Public Value: UCANR: Promoting healthy people and communities

Focus Area Tags: Natural Resources, Pest Management, Yard & Garden

Tags: control (64), DiTomaso (7), Oneto (5), pest (177), pest management (136), Pest Notes (118), poison oak (6), UC IPM (373), weed (17)

Comments: 1

Comments:

by Allen Buchinski

on July 9, 2021 at 2:02 PM

"Leaves of three" is a nice mnemonic device, but the UC Poison Oak Pest Note says "Although uncommon, leaves can occasionally have five or seven leaflets, and in rare cases nine". It goes on to say "The diversity in leaf size and shape accounts for the Latin term diversilobum in the species name."

The Santa Clara Master Gardener Help Desk had a five-lobed photo submitted for ID last year,. Unfortunately, it was initially misidentified due to that mnemonic. I'd attach the photo if this form would let me. :-)