University of Maryland Extension

Poison ivy

Poison ivy
Toxicodendron radicans

poison ivy

How to identify poison ivy - Learn to recognize the many look-alikes.

Key Points

  • Poison Ivy, Rhus (Toxicodendron) radicans, is a common native plant found in woodlands, fields, pastures, farms, and home landscapes. In natural areas, its berries provide nutritious food for migrating birds
  • Poison ivy is typically a deciduous woody vine that attaches itself to trees or other objects for support. But it can take on different growth forms depending on its age and growing conditions. When growing in a tree, mature vines become thick and develop dark brown hairy holdfast growths (called adventitious roots). The vines often develop extensive branches that look like the branches of the tree. Poison ivy vines do not harm the trees that are attached to. 
  • In some cases, it can also grow as an upright shrub without support. Shrub forms typically develop when grown in the full sun.
  • The leaf forms also can vary even on the same plant. They all have the characteristic three leaflets but the leaf margins can be smooth, wavy, lobed, or toothed.
  • Some leaves may resemble oak leaves. Many people call the leaf form that resembles oak leaves ‘poison oak’. In reality, the true species of poison oak, Rhus diversiloba, is found in the Western U.S.
  • The entire plant is poisonous because all parts, leaves, stems, and roots, contain the irritating oil urushiol. Urushiol (pronounced, ‘you-roos-sheol’) is a colorless or slightly yellow oil and is very potent.
  • It often grows in shrubs and groundcovers making it difficult to spot. 

Life cycle
Reproduction
Poison Ivy Exposure
Common Myths about Poison Ivy
Controlling and Protecting Yourself from Poison Ivy

Life Cycle 

  • Begins as an herbaceous perennial and becomes woody vine. Can also  be shrub-like.  
  • Poison ivy is deciduous (it loses its leaves in the fall). Leaves have yellow or red fall color that begins to turn in early fall. 
  • Vines leaf out again, usually in May.
Poison ivy leafing out in May
Young leaves on a poison ivy vine
Photo: Rob Routledge, Sault College, Bugwood.org 
Red fall color on poison ivy leaf
Fall color
Steve Dewey, Utah State University, Bugwood.org

Reproduction 

  • By seeds which are quickly spread by birds and other animals that eat the small fruits. Poison ivy can get started in the landscape and in a short time become a widespread problem.
  • Most mature poison ivy plants will flower and produce fruit. The small flowers appear in the summer. White, waxy fruits develop in late summer or fall and are attached in clusters on slender stems that originate in the axis of the leaves along the side of the smaller branches 
  • Poison ivy grows fairly quickly and also propagates itself by underground rhizomes.
white poison ivy flowers
Maturing poison ivy flowers
Photo: Karan A. Rawlins, University of
Georgia, Bugwood.org
chipmunk eating mature white poison ivy berries
Chipmunk feeding on ripened berries
Photo: Gary P Bell, Bugwood.org

Poison Ivy Exposure

  • Some people are more sensitive than others to the effects of poison ivy. However, sensitivity can change from time to time so that someone who was not affected by it at one time can get a reaction at another time.
  • The oil (urushiol) penetrates the skin within about ten minutes of contact. If you suspect contact with poison ivy, wash the exposed area immediately after contact or as soon as possible. 
  • Washing with running water is recommended. Using soaps that contain emollients or bath oils, such as complexion soaps, can actually spread the irritating oil and make the rash more widespread.
  • There are specially prepared poison ivy cleansing agents on the market that remove the rash-causing oil if applied according to label directions.
  • For those sensitive to the oil, a linear rash, resembling small insect bites, will usually appear within 12 to 48 hours of exposure. The rash progresses and blisters will form. Allergic reactions may take up to two weeks to appear and skin-to-plant contact is not necessary for a reaction to occur.
  • The plants are most dangerous in spring and summer when oil content is highest. The oil can remain active for months on objects.
  • Even dead plants may cause allergic reactions for a couple of years.
  • If burned, the oils in the smoke can also cause severe allergic reactions and respiratory problems.
  • The rash can be picked up on tools, clothing, and the fur of pets. Therefore, anything that may be carrying the oil should be carefully washed with soap and water. Tools can also be cleaned with alcohol. 
  • Contact your physician if you have severe swelling, blistering, or itching, or if the rash is present on a sensitive area such as your face. 

Common Myths about Poison Ivy

  • Scratching poison ivy blisters will spread the rash.
    This is not true. The irritating oil is spread by hand only before the rash begins.
  • Poison ivy rash is catching from one person to another.
    This is not true. The rash cannot be transferred from person-to-person.
  • Once allergic, always allergic.
    False. An individual’s sensitivity can change over time even from season to season.
  • Leaves of three, let them be”.
    This is usually true for poison ivy, but occasionally its leaves may be in groups of 5,7 or even 9. There are a few plants that also have three leaflets very similar to poison ivy. For example,  boxelder trees and Virginia creeper look very similar to poison ivy.

Controlling and Protecting Yourself from Poison Ivy

  • Always cover all exposed skin by wearing long-sleeved shirts, long pants, protective gloves, and boots when working around poison ivy. Launder your work clothes separately from the rest of your laundry. 
  • Early in the season, identify seedlings. Digging, cutting, and hand pulling of small plants is effective. Its root system is not deep. 
  • On trees, sever vines growing up the trunk to eliminate the flow of moisture from roots. Or spot spray the foliage (but never direct the spray overhead) or cut the vine and immediately apply the herbicide directly to the cut end using a non-selective herbicide containing glyphosate or triclopyr. These are commonly labeled as poison ivy or tough brush killers and are easy to find in hardware stores or plant nurseries. Use herbicides with care. Read the label directions, follow all safety precautions, and protect surrounding valuable plants.
  • Chemical control is most effective during active growth periods especially in early to mid-summer. The chemicals are most efficiently absorbed and translocated through the plant at these times.
  • Never burn the plant as toxins can be inhaled in smoke and cause severe respiratory problems.

    Mention of trade names in this publication does not constitute an endorsement by University of Maryland Extension.

Additional Information

Climate Central - Poison Ivy in a Warming World

(PDF) The Ohio State University - Poison Ivy Information

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Based on publication HG 34 Poison Ivy, author Ray Bosmans, Professor Emeritus University of Maryland.

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