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University of California Cooperative Extension Ventura County
669 County Square Drive, Suite 100
Ventura, CA 93003
Phone: 805.645.1451
Fax: 805.645.1474
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The office will be closed for the following holidays:
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Poison Oak
Poison oak is native to most areas of California. It is an especially common inhabitant in the oak woodlands on the Central Coast. As people move into these areas, they can expect to encounter poison oak in their landscape and the surrounding vegetation. The plant is usually a woody shrub but may also have a vine form (climb on other plants). In full sunlight it may develop a dense shrub canopy one to six feet high and be a single plant or a clump several feet in diameter. Poison oak is deciduous (loses its leaves in winter).
The plant usually produces leaves consisting of three leaflets. But vigorous plants may have leaves with five, seven or nine leaflets. The leaflets have smooth, lobed margins. The surface of the leaflets is glossy or dull. In spring, poison oak produces clusters of small, white-green flowers, which emerge from where leaves attach to the stem. In late summer/early fall whitish green, round fruit (berries) are produced (no acorns). In spring/summer the leaves are green or sometimes light red. In late summer/fall the plant develops pretty fall colors of orange, yellow and red.
All parts of the plant are toxic to those persons who are sensitive to the urushiol present in oil-resin in the sap of the plant. Interestingly, goats, sheep, deer, and horses can graze poison oak without ill effect. In fact, goats are sometimes used to control it. Be careful with animals that have been in poison oak. Sap from their fur can give you dermatitis. Poison oak pollen can cause severe respiratory problems if inhaled. And contact with smoke from burning poison oak can also cause skin and respiratory problems. Contact with sap, pollen or smoke may cause a severe dermatitis characterized by large blisters and swelling for several days. Severe gastric distress and even death may result from the ingestion of leaves or fruit.
The danger of poisoning is greatest in spring and summer when plants are full of sap and bleed easily when bruised or cut. Sap, dried sap or pollen on clothing can remain toxic for years. Persons vary in their sensitivity to poison oak with some having no reaction at all to the opposite extreme of severe dermatitis and respiratory distress when exposed to the plant.
If you are one of the latter persons, you probably should not get involved in any control operations. Elimination of poison oak can be done manually by digging it out. This is best done in winter when the plant is fully dormant. Most persons can handle poison oak with leather gloves and a long-sleeved shirt. However, you should probably plan to discard both when the job is completed. Herbicides can also be used with good effect. The poison oak should be sprayed when in full leaf and growing vigorously. The poison oak should be completely wetted with the spray. To eradicate a patch of poison oak, more than one application may be needed. So, spray once, then wait until the plant produces some regrowth to apply a second application. The same procedure should be used if a third, fourth, etc., application is needed. Never burn poison oak. Uprooted plants and brush should be placed in an out-of-the-way location to decay or take to a disposal site.