Poison ivy (Toxicodendron radicans) often grows as a ground cover until it finds a tree. It then becomes a long-lived deciduous vine. Resin in poison ivy leaves and stems causes severe itching that often persists for three weeks. Learn to recognize poison ivy's glossy three-leaflet leaves, and always wear gloves, long pants, and a long-sleeved shirt when working near it. Girdle mature vines by cutting them in several places with a sharp knife. Spray or brush a glyphosate herbicide on all poison ivy foliage within reach. Organic herbicides will weaken poison ivy, but monthly applications will be required to slowly kill it.
Glyphosate herbicide. It is safer to use a strong herbicide to control a dangerous weed such as poison ivy than to engage in hand-to-hand combat. Mix a small amount of glyphosate herbicide according to label directions, and use a paintbrush to ″paint″ weed leaves on a warm day when rain is not expected for at least 48 hours. Be careful, because spills and splatters also will injure or kill other plants. Ready-to-use glyphosate sprays are another option, but spraying with this chemical should be done only in still weather. A small amount of wind can carry the spray to nearby garden plants. As an extra precaution, surround the weed with a bottomless cardboard box before applying herbicide. Do not use glyphosate near water, and limit your use to dangerous plants, such as poison ivy. Glyphosate works by interfering with photosynthesis, so plants die slowly over a period of several days.
Organic herbicides. There are several herbicides made from natural ingredients. Those that contain clove oil (eugenol) give the best control of young broadleaf weeds. Products containing acetic acid, often in combination with citric acid, do a good job on young grasses. Some products contain both clove oil and acetic acid, so they are useful for a broad variety of weeds. Soap-based herbicides dehydrate leaves by cutting through their protective layer of cutin. All of these types of organic herbicides work best on young weeds and pose only a temporary setback to well-rooted perennial weeds. To minimize damage to neighboring plants, spray only in dry, still weather. To maximize effectiveness, spray young weeds when temperatures are above 70 degrees F and the sun is shining brightly. Be aware that repeated applications of a product containing acetic acid (which is very strong vinegar) can lower the soil's pH, making it more acidic.Image courtesy of Jenna Antonino DiMare, National Gardening Association