Institute of Food and Agricultural Sciences
Hendry County Horticulture News
Poison Ivy - Bane of the Great Outdoors
Although gardening is generally thought of as an enjoyable and healthful outdoor activity, the outdoor enthusiast should be aware of a few hazards that can really spoil an otherwise pleasant pursuit. One of the most frequently encountered, poison ivy, and its relatives, poison oak and poison sumac have plagued lovers of the great outdoors for ages. Poisonous plants have been a problem since before the first settlers arrived in this country. Native American populations rubbed the juice of plants on their skins to counteract the rash caused by poison oak and ivy. Captain John Smith recorded poison ivy as a true ivy in his writings in the 1600s. Although early settlers found the glossy greenery attractive, they soon learned otherwise.
Poison ivy (Rhus radicans), a native of North America, is a very variable species. It may occur as a tall vine that clings to its supports by means of rootlets; as a dense ground-cover; and as an erect nonclimbing shrub. Each leaf is composed of three leaflets which vary in shape from oval to round. Their tips are pointed and their edges (margins) may be entire or distinctly lobed or toothed. The leaf surface may be glossy or dull. Flowers are borne in clusters as are the white waxy berries which follow. (See photos below) Gardeners and others are well advised to recall what most boys in Scouts learned in preparation for their first outdoor adventure- "Leaves of three, leave it be--- Berries of white, you'd better take flight!"
Although poison ivy is the common name correctly applied to the species (Rhus radicans), there is some confusion with poison oak. Poison oak (Rhus toxicodendron and Rhus diversiloba) is typically a shrub or sometimes a vine climbing to about 8 ft. high. Poison sumac (Rhus vernix), is a shrub or small tree typically found in swampy places. Both species cause skin rashes like poison ivy. Fortunately for local residents, only one of these, poison ivy, is found in south Florida. The range of poison oak and poison sumac extends only to north Florida.
Poison ivy is a pest because of its aggressive character and because, upon contact with it, or with objects that have touched it, many people develop a painful dermatitis, or rash commonly called ivy poisoning. This condition is caused by urushiol, a gummy resin contained in the sap of the roots, stems, leaves, and unripened fruits.
Urushiol is an allergen, not a poison. Urushiol bonds with your skin cells creating something your body recognizes as an alien. In an effort to eliminate the invaders, your body takes a series of unpleasant and painful measures to get rid of those modified skin cells - fast.
Not everyone reacts to it. If you're allergic to the resin, however, and either touch the plant directly or come in contact with clothing or pets that have been exposed to it, you'll develop a rash of itchy, oozing blisters, sometimes with swelling. The sap must contact the skin to produce ivy poisoning. Handling dogs and other animals that have run where the plant occurs is a common cause of infection; other cases have been traced to handling shoes and clothing worn by people who have been in contact with poison ivy plants. Smoke from a fire in which poison ivy plants are burned may also cause dermatitis.
The degree of sensitivity varies greatly. Massive exposure often sensitizes the victim so that for the rest of his or her life, he or she will be poisoned by the slightest contact with the poisonous sap. Even individuals who consider themselves immune can be poisoned by extensive exposure and be made sensitive to lesser contacts later.
No satisfactory method of preventing dermatitis following exposure is known. Avoiding contact with the plant is the most important preventive measure. In some instances, immediate and thorough washing of the exposed area with detergents can remove sap before a rash occurs. In serious cases, medical attention should be sought. In lesser cases, various lotions and other preparations sold to relieve itching and cause the blisters to dry are helpful.
Special injections to produce immunity, seem to produce favorable results with some people. In addition, several blocking creams and lotions on the market are some what effective in keeping the sap from bonding with the skin and causing ivy poisoning.
Poison ivy can be controlled in the landscape with herbicides such as Brushkiller or Garlon or Roundup. Care should be taken when using herbicides near or under desirable species as they may be killed also. Poison ivy should be treated when it is actively growing. Always read and follow herbicide labels for correct application procedures.
Poison ivy may be mechanically controlled by pulling or cutting. Poison ivy may need to be pulled or cut several times as it will regenerate from root stock. Remember that gloves and tools used to remove the poison ivy will be contaminated and can cause an allergic response.
Encountering a plant with three distinct leaves does not necessarily mean the worst - Virginia Creeper - a native plant beneficial to Florida wildlife is often mistaken for Poison Ivy. Its compound leaves usually have five leaflets, but they may also have three, or seven. Both plants display red color in fall and winter. The fruit of Virginia creeper is a berry and resembles its grape cousins, dark blue to black in color. A close look at the compound leaves of Poison Ivy will reveal three leaflets with distinct petioles, while the leaves of Virginia creeper typically have five leaflets and the petioles are so short that the leaflets appear almost sessile, or unstalked.
Don't let your time outdoors be spoiled by poison ivy - learn to recognize it and avoid or eliminate it. Good luck and good gardening.
Photos courtesy of Mary Nason, 2000
Gene McAvoy is the horticulture agent with the Hendry County Extension Service. Direct your horticulture questions to PO Box 68, LaBelle, FL 33975, e-mail - firstname.lastname@example.org or phone 863-674-4092 or 863-983-1598. You are also welcome to visit the Hendry County Extension Office at 225 Pratt Blvd., LaBelle. Office hours are from 8:00 - 5:00.
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