By this point in the season, if you're not weeding on a regular basis, your garden probably looks like an abandoned lot. But in the process of weeding, don't do what my partner, Richard C. Levy, did several weeks ago and accidentally pull out poison ivy or, in the tuneful words of Lieber and Stoller, "Poison ivy, Lord'll make you itch!"

What Richard did was understandable. Poison ivy, botanically Rhus toxicodendron, may look like a number of other plants.

For example, Terry Collier, a student in my landscape design class, recently, brought in a sample from what he thought might be a poison ivy tree. I hesitated to touch the double-bagged specimen because of its characteristic "three-leaflet cluster" appearance. But the sample was box elder, a type of maple--not poison ivy, which is a member of the cashew family.

There's nothing lost and everything gained by being careful.

Right now, Boston ivy looks like poison ivy because of the ivy's young, shiny, reddish leaves; jack-in-the-pulpit (Arisima triphyllum) has a resemblance until it flowers; a hickory seedling, like that of the box elder, can fool you.

You also might confuse wild raspberries because of their three-leaflet clusters, but raspberry canes have thorns.

Poison ivy can occur as a vine, shrub or ground cover and grows equally well in sun and shade. The new growth can be reddish and shiny or appear green and have no sheen to it at all. Because of its adaptability, this is one of the most prolific woody plants on the Eastern seaboard.

Although its leaves usually occur in those three-leaflet clusters, the leaflets may have smooth edges, be slightly lobed or have an undulating margin. The woody stems are tan and, if they're climbing a tree or building, may be covered with reddish-brown hairlike aerial rootlets. The stems can also appear smooth, with no rootlets, if the plant isn't climbing.

If in doubt, get an identification. And when you're bagging a sample to take to a garden center or a county cooperative extension clinic, be sure to keep the leaf and any of its oils on the inside of the bag, or the next person handling the bag could get a rash. The urushiol, the irritant, remains active in the plant, and on whatever it touches, for days.

That includes the family pet. Your dog or cat can get oil on its fur and carry it home. Your pet doesn't get a rash, but the material can rub off on furniture, rugs and you. It also remains on your clothes until you wash them.

A commonly debated issue about poison ivy is whether people become more allergic with repeated exposure.

Early in my landscaping years my doctor counseled, "Learn to recognize it, because the more you contact it, the more your sensitivity to it changes. You can become less allergic, or more, and will never know from one time to another what your reaction will be."

Symptoms can occur within hours or not for days. They may present themselves as a couple of small wart-looking dots that itch or be severe enough to require hospitalization.

Once the rash forms, there's no more danger from the oil. It won't spread from there. Just don't scratch; it has to heal like any other injury. If the rash gets bad, visit a dermatologist.

You can get a rash only by touching the oil, whether on the leaf, your dog or your clothes. You also run the risk of getting internal symptoms from inhaling its smoke, so never burn it.

Cover yourself when working around poison ivy. Wear gloves, long sleeves and long pants, and keep your socks pulled up. Wash your clothes and any skin the plant touched as soon as possible.

The only fully approved protectant for poison ivy is an over-the-counter product called IvyBlock. The preparation coats the skin and will act the same as a clothing barrier once it dries. Wash it off at the end of the day with hot water and soap.

Getting rid of poison ivy on your property is easy. But be sure to spray it only after positive identification.

Carefully cut poison ivy stems that are growing up trees. Cut them near the ground, then wait until the vines leaf out again.

My choice for a herbicide is glyphosate, which is sold under the names Roundup and Kleenup. It's approved for use over the roots of trees, where poison ivy is commonly found. It works in about seven to 10 days. Apply only when the vine is actively growing and has leaves. Follow all label instructions, and the poison ivy will brown slowly and die, roots and all.

Actually, poison ivy has excellent ornamental value. The wildlife love it. Birds devour the tan berries in summer. It's a native that the National Park Service lists as desirable in areas of plant conservation. And you can easily identify it in fall by its gorgeous deep-red-to-yellow- orange autumn leaves.

Even so, let me suggest you keep in mind the old adage, "Leaves three, let it be."

Lerner is president of Environmental Design in Capitol View Park, Md. His e-mail address is lernscap@erols.com