Leaflets three, let it be! It's probably poison ivy, a serious health hazard to those who are susceptible to its poison. If touched, rash and blisters may form accompanied by persistent painful itching.

All parts of the plant are toxic, particularly the sap. The toxic agent, urushiol, is easily transfered from one object to another and by pets that run through poison ivy plants.

The smoke of burning poison ivy is even more dangerous than the plant. The poisonous oils produced by the plant are volatilized by the heat of the fire and carried in the smoke. If the smoke comes into contact with the skin or is inhaled, it's almost certain to cause harm even to the most resistant person.

After exposure, thorough washing with alcohol or strong soapsuds may prevent poisoning if it is done promptly enough. Many solutions and lotions are available for treatment, but these may do no more than relieve the burning and itching temporarily.

The best way to avoid poisoning is to learn to recognize the plant and avoid it. It should not be allowed to grow in lawns and gardens, school grounds, along public roadways, or in parks, especially those frequented by children.

It can show up in the most unexpected places. It forms clusters of white berries in late summer, and many kinds of birds use them for food. At least some of the seeds pass through their intestinal tract. The seeds germinate readily, and seedlings can become established and grow unnoticed among other vines and plants around the home.

One of the best chemicals for control of poison ivy is Amitrole (sold as Amitrole, ATA Weedazole, etc.). Amitrole is absorbed by stems and leaves of plants and moves to meristeamatic tissue to inhibi chlorophyll synthesis.

Amitrole is rated as relatively nontoxic to birds and pets and persists in the soil for only a short time. Directions on the label should be read and followed exactly.

It may kill other plants if it touches them. To treat poison ivy growing in a hedge, mix a solution in a tin can and use a long-handled brush to paint it onto the leaves of the poison ivy. Paint at least a dozen leaves on each stem.

Poison ivy may grow as an erect shrub or as a vine climbing fences, walls or trees. There are three leaflets on a stem, the leaves may have a glossy or dull surface or may even be somewhat hairy, especially on the lower surface. o Q: We planted crocuses in our lawn last fall. They have bloomed beautifully and we don't want to do anything that will spoil them for next year. Should they be fertilized? A: Your problem is, when the grass is cut the first few times, their foliage will be cut also and that will spoil them for next year. Like daffodils, tulips and hyacinths, crocus foliage must be allowed to produce food until it turns yellow and starts to droop in May or June. Q: Our dwarf red maple is red and beautiful in the spring, turns green in early summer ans stays that way the rest of the season. Is there anything we can do to make it stay red for us ? A: Most red maples, including many of the Japanese, start out in the spring with red foliage which turns green by early summer. It's a genetic characteristic and nothing can be done about it. The variety Atropurpureum has dark red leaves that stay red throughout the growing season, and the variety Sanguineum bears light red leaves that remain that color throughout the season. But even seedlings of these two may have leaves that turn green when hot weather starts.