Poison Oak and Ivy - Identification
The first key to avoiding and managing Poison Oak or Poison Ivy plants is being able to identify them.
Both poison oak and poison ivy are members of the cashew or sumac family, and they appear similar.(1,2) The most significant differences are that they grow in different parts of the country, and the tips of poison ivy leaves are acutely pointed while the poison oak leaves are more rounded and oak-like.(2) Poison oak grows west of the Sierra and Cascade mountains and in the southeast. Poison ivy is widespread, but is not typically found in California or western Oregon and Washington. Either plant can grow as a shrub or vine.(1) They do not tend to grow above 4,000 feet in elevation.(3)
The plants are distinguished by their leaves which grow in groups of three on a shared petiole (stem). The leaves resemble oak or ivy leaves, often turn red or orange in the fall, and usually appear shiny and leathery.(1,2) The best advice to follow is the old saying - “Leaves of three, let them be.”(1) In the spring, the plants have greenish-white little flowers and white berries with hard seeds inside.(2,4) The berries are toxic to humans.(3) In the winter, when the leaves are gone, the plant is harder to identify. It probably will have its berries and is still dangerous. Stems and stalks contain their troublesome oil year-round. When parts of the plant are bruised or broken, the sap turns black and sticky.(5) It is a good idea to mark the plants or areas containing the plants in the leafy seasons, so you can avoid, manage, or remove them later.
1. Daar, S. 1991. Safe ways to outwit poison ivy and poison oak. Common Sense Pest Control. VII(4): 7-14.
2. Callihan, R.H. 1990. Poison ivy and poison oak: Biology, toxicity, and management. Univ. of Idaho Coop. Extension. Current Information Ser. 856.
3. Hauser, S.C. 1996. Nature’s revenge: The secrets of poison ivy, poison oak, poison sumac, and their remedies. New York: Lyons & Burford.
4. Walters, C. (1991). Weeds: Control without poisons. Kansas City, MO: Acres USA. Pp. 248-249.
5. Mitich, L. 1995. Poison-ivy/poison-oak/poisonsumac—the virulent weeds. Weed Technol. 9:653-656.