Poison ivy (Rhus radicans ) and poison oak (Rhus toxicodendron ) are common poisonous plants in Georgia. Poison ivy and poison oak prefer moist, deciduous forests and wooded areas. They are also found in fence rows and ornamental plantings.
Both contain chemicals (urushiols and others) that cause contact dermatitis (redness, rash, blisters, itching) to thousands of people. Every person who works outdoors should be able to identify poison ivy. Failure to do so can lead to severe allergic reactions.
A frequent question that I get is how to tell the difference between poison ivy and poison oak. Poison ivy might grow as a small shrub or as a high-climbing woody vine with aerial rootlets that can attach to trees, fences and buildings. Poison oak usually grows as a small shrub.
These plants can reproduce by creeping roots and seed. Leafy shoots can arise from the creeping roots several yards from the parent plant.
The leaves of poison ivy and poison oak are alternately arranged on the stem. Each compound leaf consists of three, bright green, shiny leaflets. These leaflets are elliptic to egg-shaped and can have either smooth, toothed or lobed margins. The upper leaf surface is smooth, or lacks hairs, while hairs are commonly found on the veins of the underside of the leaf.
Poison ivy leaf shape and presence of hairs are highly variable. Leaves with different shapes may be found on the same plant or on nearby plants. People might incorrectly identify poison ivy when observing a plant with an unusual leaf shape. However, the old saying, "Leaflets three, let it be" should always be followed.
The flowers of poison ivy are arranged on slender stalks. Each flower is small and has five yellowish-green petals. The fruit of poison ivy is grayish-white, nearly round, about 3/16 inch in diameter and contains a single seed.
A number of plants are confused with poison ivy and poison oak. The seedling stage of box elder (Acer negundo ) has a leaf with three leaflets that resemble poison ivy. Young box elder plants can be distinguished from poison ivy in that seedlings have opposite leaves, while poison ivy has alternate leaves. Virginia creeper (Parthenocissus quinquefolia ), a vinelike plant similar in growth habit and appearance, might also be confused with poison ivy. However, Virginia creeper has compound, palmate leaves with five leaflets.
There are several methods to control these plants, including cultural and chemical controls. Poison ivy will not tolerate repeated tillage, cutting or mowing. Continually clipping the plant at or near the ground level will eventually control poison ivy. But several clippings during the year and for several years are necessary to control it.
Poison ivy shoots commonly encroach from wooded areas into newly established lawns. Herbicide use is not usually necessary, as frequent mowing will eliminate the plant. To prevent future encroachment, poison ivy should be controlled in the adjacent wooded area.
Another cultural control is digging, or "grubbing out" poison ivy plants and roots. This method is used in small landscape beds. Wear water impermeable gloves when handling poison ivy (including the roots). I like to use bread bags or plastic sleeves that newspapers come in.
Herbicides are the other control option. The best time of the year to control these plants with herbicides is late August and September. There are two ways that these herbicides can be applied. The first is a foliage application. The herbicides that work best for this is 2, 4-D glyphosate and triclopyr. When applying these herbicides, care should be taken to shield other plants.
Another option is to use glyphosate and triclopyr as cut-stump treatments. This is done by cutting the plant off above ground level and putting herbicides on undiluted. Follow the directions on the label.
Charles Phillips is a retired Columbia County Extension Service agent and operates Hort Consulting. He can be reached at email@example.com.
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