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Poison Ivy

Introduction
Poison ivy is the major cause of allergenic dermatitis in the eastern United States. All parts of the plant contain resinous compounds, known as urushiols, which cause inflammation of the skin, blistering, and itching. You can not catch poison ivy by "just walking in the vicinity of a plant." The toxic compounds can be transmitted in smoke (from burning the plant) and by direct contact with any of the plant parts. In addition it is possible to contact the toxic compounds through objects or animals, which have been exposed to the plant, including gardening tools, pets and clothing. Some feel that you can "catch" poison ivy only during the spring and summer when the leaves are present. This is not true, dermatitis response can occur year round including if you contact stems and roots during the winter months. Just because a poison ivy plant is dead does not make it incapable of causing allergenic dermatitis. The urushiols can remain active on dead plants and even other objects for over a year.

Description of the Plant
Poison ivy is a deciduous vine, which grows on or just under the soil surface as well as climbing up objects such as trees and fences. As a vine it attaches to surfaces via aerial roots and can climb as high as 20 to 33 feet into trees or other objects. Poison ivy has alternate compound leaves with 3 leaflets per leaf. The margins (edges) of the leaflets can be toothed, lobed or entire (smooth). The leaflets can vary in shape (Figure 2), but are most commonly egg-shaped.

The following lettered descriptions refer to the line drawing in Figure 1 and 2. Leaves alternate (1 per node) (a), compound (b), each compound leaf consisting of 3 leaflets (c) at the tip of a long leafstalk (d); the middle leaflet has a longer stalk (e) than the 2 side leaflets (f); overall leaflet shape and type of toothing highly variable between leaflets on the same stem, as well as among plants within a patch and between patches; leaflets ranging from narrow to broadly ovate with a smooth margin (A, C), to a few scattered, shallow, teeth which give the leaflet a lobed appearance (E); leaves purplish to reddish when unfolding in spring (May to early June), bright green and often shiny (with a varnished appearance) in summer and turning a vivid orange-red to wine-red in autumn in sunny areas, but often lacking the bright color in shaded places; leaves smooth and hairless on both surfaces except for small tufts of brownish hair on the underside of the leaflet along the midvein and in the angles formed by the midvein and some of the lower branching veins; flowers small, white or greenish, with 5 sepals and 5 petals (g), in branching clusters from the leaf axils (angles between leafstalk and stem); flower clusters inconspicuous because they are often hidden below the dense leaf canopy and because many plants do not flower every year; each flower in the cluster (B) followed by a whitish to dull greenish-yellow, dry berrylike fruit (h) about 1/5 in. diameter with lengthwise ridges and somewhat resembling a peeled orange. Flowers in June and July, berries produced by September but often remaining on the low leafless stems all winter.

Habitat
Poison ivy can be found growing in landscapes, disturbed sites, woodlands, and wet lands. It will invade these sites via its creeping woody stems and through seeds dropped by birds. It thrives under a variety of conditions and is often seen in seashore areas on Long Island.

Management
Poison ivy may be uprooted by pulling it out of the ground when the latter has been softened by freezing and thawing in spring, usually in March. Remember that the toxic compounds are present in all plant parts year-round so obviously, all precautions and great care must be taken to insure that the skin does not come in contact with the toxic compounds, either directly or from clothing or tools. A person who knows he or she is quite sensitive to poison ivy should not attempt this means of control. Poison ivy pulled out in this manner should never be burned to avoid spreading the toxic compounds in smoke.

In areas that can be plowed, poison ivy may be effectively controlled by close mowing followed by plowing. It may be necessary to repeat the plowing or to follow it with a cultivated crop to kill or starve out the pieces of stem and root that were buried in the process.

If necessary non-selective herbicides such as glyphosate or triclopyr can be used to kill poison ivy. Because these herbicides usually kill all vegetation that is treated (thus the term non-selective) they should be used with discretion and caution to avoid killing nearby desirable plants. Read and follow all label instructions.

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Last modified: Wednesday February 06, 2008.