A plant dwells among us of such ill repute and so feared by lovers of the outdoors that in eastern Pennsylvania it is commonly referred to as "poison," short for poison ivy.

Actually, it is not an ivy at all, but a member of the cashew family. Its Latin name is "rhus." Outdoor enthusiasts take heart: avoiding or promptly dealing with exposure to the poison or toxin in this plant can eliminate a lot of the discomfort that you fear.

All parts of poison ivy contain a toxin called urushiol, which can cause an allergic reaction, most notably the feared rash or dermatitis, ranging from reddened and itchy skin to major swelling, blisters and weeping wounds. If leaves are swallowed, the mucous and digestive tract can be irritated and the reaction can be so severe that death may result. Smoke from the burning plant can also carry urushiol into a person's eyes, nose and throat.

The best offense is a good defense. If you are exposed, get the toxin off your skin as quickly as possible by thoroughly washing with soap and water, hopefully within 10 minutes. Better yet, avoid exposure entirely by learning to identify the plant, avoid it, and eradicate it, if possible. Teach children to be aware of and avoid poison ivy.

Don't forget to wash and decontaminate clothing, tools, pets or anything else which has come in contact with the plant. Remember, the toxin can remain potent for years. It is possible to recontaminate yourself from contact with anything which still carries traces of urushiol.

Clothing and other articles can be decontaminated by thorough washing in several changes of strong soap and water. Don't forget objects like door handles or steering wheels. Do not wash contaminated clothes with other clothes. Beware that sending contaminated clothes to the dry cleaner may expose unsuspecting workers.

Back to a plan for defense. Learn to identify the plant. So widespread and versatile is this plant that it can be found in woods, disturbed habitats, along fences or streams and around buildings or in yards in urban areas. Its usual form is that of a vine, but you may find small plants that seem to stand alone and other plants that look more like shrubs 6- to 30-inches tall.

The vine stems can, over the years, grow quite woody and to several inches in diameter. These vines have no problem climbing trees, stone walls or buildings. While, in general, they will not damage trees or structures, the plant can affect so many people and is so bothersome to eradicate that it is wise to remove it as soon as possible.

One of the problems in identifying poison ivy is that the shape of its leaves is quite variable, even on the same plant. However, there are always three together and only one three-part leaf leads off from each node on the twig. They never occur in pairs along the stem.

If the plant does produce greenish-white flowers anytime from May to July, they are inconspicuous, located in clusters just above where the stalk of three leaves joins the stem.

If the flowers produce fruits (August to November), they are grayish-white or cream colored and waxy in appearance and have rather distinct lines marking the outer surface, like the segments in a peeled tangerine or orange. Sometimes the fruit has a fine, hairy or downy appearance. These fruits are most likely to be noticed in fall, winter and early spring. They may be the only way to identify the plant at these times.

Poison ivy may also intertwine itself with ornamental shrubs and vines, again making it difficult to spot. Some people end up mistakenly encouraging its growth because the plant, with its shiny green leaves and brilliant red or reddish-yellow color in the fall, is actually quite attractive.

Poison ivy is frequently confused with plants such as Virginia creeper, also known as woodbine, and Boston ivy. Virginia creeper, which also turns purple-red to crimson in the fall, has five leaves in a cluster and its fruit is bluish-black and berry-like.

Since so many people are sensitive to urushiol, getting rid of the plant is tricky. If you happen to have the services of someone who is not sensitive to this plant, try getting his or her help. Herbicides work well. The plants should be sprayed or the leaves painted with herbicide during spring or summer.

Vines should be cut off at the base and the stump treated with a herbicide such as glyphosate. Take care not to expose other desirable plants, however. If you attempt to dig out the plant, be sure to get all the roots.

What does one do with the plant material which has been removed? Don't put it in the compost pile or take it to the recycling center. Wrap and put it in the trash or bury it. Never burn poison ivy. The urushiol in the smoke can cause severe reaction if inhaled or in contact with the mucous membranes of nose or eyes.

In summary, remember these facts:

Poison ivy plants contain the skin irritant urushiol all year long.

The plant must be bruised or broken for the toxin to exude from the plant.

The toxin is not airborne except when carried in smoke or particles generated by burning the plant.

Weeping wounds and blisters do not spread poison ivy over the body.

New blisters are the result of delayed response at the site of infection, renewed contact with the plant, or recontact with irritant-contaminated articles.

After contact, symptoms may appear within hours or up to a week.

If exposed to the toxin, you can prevent or reduce a reaction or recontamination by immediately and thoroughly washing any exposed areas or articles.

"Growing Green" is contributed by Lehigh County Extension Office Staff and Master Gardeners. Lehigh County Extension Office, 610-391-9840; Northampton County Extension Office, 610-746-1970.