Controlling poison oak and ivy

Last Updated: 
July 12, 2006

CORVALLIS - Poison oak and poison ivy are each a different species, but they are similar in appearance, and have the same effect on humans. They both can spoil a walk in the woods.

They also respond similarly to efforts of control, according to Susan Aldrich-Markham, field crops agent with the Oregon State University Extension Service.

Poison oak is common to western Oregon and Washington; poison ivy is found in eastern Oregon and Washington. Both these native perennial weeds are spread by birds, who feed on the seeds in the winter, inadvertently dispersing the plants all around the countryside.

Poison oak sometimes grows as a vine; poison ivy never climbs. But they both can be found along fencerows, open woodlands, stream banks and rocky canyons.

Both poison oak and poison ivy are identified by their leaves, which are usually divided into three leaflets. Shiny when young, the leaflets range from half an inch to two inches long, although poison oak leaves may be larger. Flowers are greenish white, about a quarter-inch across, borne in clusters. The fruits are white, berrylike, glossy and dry when ripe. The leaves of both species turn brilliant red in the fall. All parts of poison oak and ivy except the pollen are poisonous year-round.

These plants contain an oily substance, urushiol, which may cause a painful irritation and blistering of the skin, according to Aldrich-Markham. Human reactions vary from extreme susceptibility to near immunity. People may become allergic later in life after repeated exposure.

To control poison oak or poison ivy on your property, Aldrich-Markham suggests three possible strategies - dig out individual plants, graze goats in larger infested areas or use an herbicide. Do not burn the area, because inhaled smoke can result in irritation in the lungs.

To hand-pull individual plants, wear protective clothing and gloves. Pull plants when the soil is wet and loose. Cut all vines growing up trees and pull as much of the vine away from the trunk as possible. Mowing and grazing have little effect unless repeated frequently.

After working with poison oak or ivy, wash exposed skin as soon as possible with soap and cold water. Follow with rubbing alcohol or a solution of alcohol and water in equal proportions to dissolve the unabsorbed poisons. Do not wash contaminated clothing with other clothing.

If you choose to use herbicides, spray either in the late spring or early summer (after the plants are in full leaf, but before the soil has dried out) or in the early fall (after the first rains but before the first frost). Spray only according to label directions. Herbicides can damage surrounding plants, so use care.

For more information on "Poison Oak and Poison Ivy," (PNW 108), visit our on-line catalog. Our publications and video catalog at: http://extension.oregonstate.edu/catalog/ shows which publications can be viewed on the Web and which can be ordered as printed publications.

Author: Peg Herring
Source: Susan Aldrich-Markham