Poison ivy contains substances that sensitize a person’s skin. These substances cause the cells of the skin to produce an “antisubstance.” Antisubstances are long-lived and can be transferred from one cell to another throughout the skin. Thus, even though the sensitizing substance originally touched only one portion of the skin, the entire surface of the body can become sensitized to it. When the sensitizing substance and the antisubstance come together, as happens when a person is exposed to the poison ivy plant a second and following times, they react together in a way that produces a small watery blister on the skin at the place where the sensitizing substance or poison contacted it.
Such rashes are usually accomplished by intense itching and in extreme cases may be severe.
Approximately 70% of the U.S. population is likely to acquire dermatitis from casual contact with Toxicodendron radicans (poison ivy) or it’s cousins poison sumac and poison oak. The skin irritant of this group is a nonvolatile phenolic substance called urushoil which is found in all parts of the plant, including roots and fruit, with the greatest abundance in sap. This irritant is very stable, and dead and dried material is as hazardous to sensitive people as an actively-growing plant. It is equally active in the dead of winter. Many people have caught poison ivy from dead poison ivy plants. It usually takes a year or so before the toxic properties weather away. Poisoning is usually, but not always, caused by contact with some part of the plant. A very small quantity of the poisonous substance is capable of producing severe inflammation of the skin and can easily be transferred from one object to another. Sensitive people may contact the irritant from smoke, dust, contaminated clothing and tools, articles and animals.
Poison ivy is a woody plant that shows a tremendous variation in growth pattern and leaf characteristics. Usually, it’s found in the vine form, but growth may be either as an erect shrub; a vine climbing by aerial rootlets on fences, walls or trees; or it may lie prostrate on the ground. Leaves are arranged alternately (one at a node) and are compound with three leaflets. These three leaflets on a leafstalk are usually referred to as leaves in groups of threes. The old saying, “leaflets three, let it be”, is a reminder of the consistent character of the plant. The leaves may have a glossy or dull surface or may even be somewhat hairy, especially on the lower surface. The edges of the leaves are either smooth, toothed or somewhat lobed.
In early spring, emerging poison ivy leaves are an interesting reddish color. After a while they may be a shiny green. They often will be dull green during the summer months but turn yellow or scarlet as autumn approaches. The flowers and fruit are always in clusters on slender stems that originate in the axis of the leaves. The fruits usually have a white, waxy appearance and ordinarily are not hairy. The clusters of small, round, waxy, berry-like white fruit appear in late summer and often persist all win-ter. Seeds germinate freely. Seedlings soon produce creeping stems or rootstocks from the lowest nodes.
Distribution and habitat
Poison ivy is common through Connecticut but is especially abundant in dry, rocky soil, in thickets along the edges of fields, woods, roads and paths. Poison ivy can flourish in the woods where soil moisture is plentiful or in very dry sites on the most exposed hillsides. When the vines grow on trees, the aerial roots attach the vines securely and often give the general appearance of a fuzzy rope. Poison ivy even grows commonly in sandy soils along the sea-shore. Because of its great variation in appearance from place to place, a person who is familiar with poison ivy in one part of the country, may not recognize it in another.
Poison ivy persists and spreads by means of its creeping stems and rootstocks. An effective method of eradication should destroy both the aerial and underground parts, either directly or indirectly. In any treatment, parts of plants may be missed. In an area 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 and starve out the pieces of stem and root that are buried in the process.
The nonselective herbicide glyphosate can be used to control/kill poison ivy according to label instruction. It is a systemic nonselective herbicide, therefore, use it with caution, as it will kill everything it contacts. Treatments should be made in late summer or early fall, when the plant is storing carbo-hydrates in the root systems. Repeat sprays may be necessary, but since glyphosate is systemic, permanent control can be expected with two or three applications. Watch the area carefully and repeat the treatment if you observe any new growth.
Carl A. Salsedo, Cooperative Extension Educator, Horticulture
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