Poison Oak (Toxicodendron diversilobum)

Poison Oak
Copyright © Lawrence M Kelly

Poison oak is the bane of many landowners and outdoor enthusiasts. It is a native plant in the Pacific Northwest and is widespread throughout the region. Many forested woodlands in Oregon have patches of poison oak, so it is important that you know how to recognize it. Even though you may not be allergic to it, your family and friends may be, so you will need to know how to avoid it or treat it. It has been said that there are two kinds of people: "those who get poison oak, and those who are going to get poison oak." Identifying it is relatively easy; dealing with it is often not. Contact can cause mild to severe rashes, swelling and discomfort.

Identification of Poison Oak

It can be found along fencerows, in open forests and pastures, near streambanks and climbing up trees as a vine. In sunny areas, poison oak can grow as a shrub, usually from 1 to 6 feet high (although sometimes larger). In shady areas, it can be seen as a vine, winding its way up the trunks of trees and larger shrubs. The vine cultivates rootlets on the stems, enabling them to affix to tree trunks and other surfaces.

The plant can usually be identified by the unique three-leaf structure. Leaves are usually 1 to 4 inches long, with lobed or toothed edges. In the spring, the leaves of young plants are shiny red, turning shiny green as they mature. In the fall, the foliage changes from green to orange and red (giving a nice "fall color" effect).

In the spring, the plants have small clusters of greenish-white flowers. By late summer, green and white fruits, resembling berries, are formed.

Poison Oak Effects

Urushiol is a poisonous, oily substance contained in all parts of the poison oak plant, including roots, stalks, stems, leaves, berries and flowers, during all times of year. Dead poison oak plants can have active urushiol oil on them for up to 5 years. Poison oak rash, which can be be mild in some people and extreme in others, is cause by contact with urushiol.

Transfer of urushiol to the skin can be direct (by actually touching the plant) or indirect (by touching a contaminated object such as pets, tools, gloves, firewood or clothing). Burning poison oak plants can result in particulates that carry urushiol into the air; coming in contact with, or inhaling, the smoke can cause severe cases of poisioning. Do not burn poison oak!

If You've Been Around Poison Oak

If you have been in or around poison oak, it may help to wash thoroughly with cool running water and soap as soon as possible. If you're in the woods, rinsing in a running stream can be effective. Even if you avoided touching the plants, immediately change your clothes and wash potentially contaiminated clothing before wearing it again. Clean gloves or tools carefully. If your pets have been in the brush and may have been contaminated, avoid touching them until they have been washed as any urushiol oil on their coats could be transferred to you.

The rash, if it appears, can be in the mild form of itchy red bumps, or in the more severe form of red, itchy, blisters, either of which can last from days to weeks. There are over-the-counter treatments for poison oak rash that may have some effect. For extreme cases, a visit to the doctor may be in order. If you think you might have inhaled any smoke from buring poison oak plants, contact a doctor immediately.

Management of Poison Oak

The main ways for managing poison oak are mechanical removal by hand pulling or treament with herbicides. Maintaining a healthy cover of desirable vegetation will reduce potential invasion. Grazing by sheep and goats can be effective in small areas.

Mechanical Removal

Plants can be physically removed through hand pulling or mechanical grubbing using a shovel or pick. It is essential to remove the entire plant, including its roots; leaving the rootstock will allow them to vigorously resprout. Mowing has little effect unless it's done at least four times during the growing season.

Mechanical removal is not recommended if you are sensitive to the poison oak!

Chemical Control

There are several herbicides that can be effective against poison oak when correctly applied. The Pacific Northwest Weed Management Handbook has a section on treatment of poison oak and the University of California also publishes information on herbicide use in theirinformatino on poison oak.

Burning

Never burn poison oak plants, alive or dead!