Mark Czarnota, Ph.D., Ornamental Weed Control Specialist
Departments of Horticulture and Crop Science, 1109 Experiment Street
Griffin, GA 30223
Biology of Poison-Ivy
Poisonous Principles of Poison-Ivy
First Aid for Poison-Ivy
Cultural Control Methods for Poison-Ivy
How to Control Poison-Ivy with Herbicides
Poison-ivy (Rhus radicans) is a common poisonous plant in Georgia. Its preferred habitats are moist, deciduous forests and wooded areas. It is also found in pastures, fence rows, ornamental plantings and various types of noncropland areas. Poison-oak (Rhus toxicodendron), a related species that may actually be an ecotype of poison-ivy, is also found in similar habitats. Chemicals (urushiols and others) found in special cannels of poison-ivy and oak cause contact dermatitis (redness, rash, blisters, itching) to thousands of people. The American Medical Association estimates that in the United States poison-ivy and Pacific poison-oak (Rhus diversiloba) cause more cases of contact dermatitis than all other plants and household and industrial chemicals.
Every person who works outdoors with plants or participates in hiking, camping or other outdoor activities should be able to identify poison-ivy. Failure to do so can lead to severe allergic reactions.
Poison-ivy is a woody perennial that belongs to the Cashew (Anacardiaceae) family. It may grow as a small shrub or as a high climbing vine with aerial rootlets on trees, fence rows and buildings (Figure 1). In contrast, poison-oak usually grows as a small shrub. Poison-ivy reproduces by creeping roots and seed. Leafy shoots can arise from the creeping roots several yards away from the parent plant.
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| Figure 1. Poison-ivy vine (Rhus radicans) with aerial rootlets on tree. |
The leaves of poison-ivy are alternately arranged on the stem. Each compound leaf consists of three, bright green, shiny leaflets (Figure 2). Leaflets are elliptic to egg-shaped and 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 pubescence (presence of hairs) is highly variable. Leaves with different shapes may be found on the same plant or on plants near to each other. People may incorrectly identify poison-ivy when observing a poison-ivy plant with an unusual leaf shape. Always follow the old saying, “Leaflets three, let it be.” While this approach may cause unjust suspicion of a harmless plant, people must consider their sensitivity to poison-ivy.
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| Figure 2. Poison-ivy (Rhus radicans) leaf with three leaflets. | Figure 3. Box elder (Acer negundo). Leaves are often confused with poison-ivy. | Figure 4. Virginia creeper (Parthenocissus quinquefolia). Leaves are often confused with poison-ivy. |
A plant found in Georgia that is often confused with poison-ivy is box elder (Acer negundo) (Figure 3). Seedlings of box elder have a leaf with three leaflets that resembles 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 viny plant similar in growth habit and appearance, may also be confused with poison-ivy (Figure 4). Virginia creeper, however, has compound, palmate leaves with five leaflets. Occasionally Virginia creeper plants have three to seven leaflets.
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 in color, nearly round in shape, about 3/16 inch in diameter and contains a single seed. More than 55 species of birds are known to consume poison-ivy fruits.
Symptoms of contact with poison-ivy include skin inflammation and blistering. All parts (stems, leaves, roots, flowers and fruits) are poisonous at all times of the year. A toxic, or sensitizing, oily compound (urushiol) is contained in specialized resin ducts in the various plant parts. The toxin is not normally found on the outside surface of intact leaves and stems. The toxin is quickly exuded, however, if the leaves or stems are crushed, bruised, brushed, chewed by insects, or otherwise damaged.
Humans are commonly exposed as they brush against the plant and bruise the leaves. Exposure also occurs when sensitive people contact the toxin by touching equipment, clothing or animals that have been in contact with poison-ivy. Dogs and cats frequently transfer the toxin to people. Additionally, the toxin can be carried on soot particles in smoke from burning poison-ivy and cause severe allergic reactions.
Sensitivity to poison-ivy varies among individuals. Some are extremely allergic; others are not as sensitive. Following contact with the poison-ivy toxin, 12 to 48 hours usually elapse before symptoms occur. With some individuals, however, symptoms may not appear for several days.
If contact with poison-ivy is suspected, wash the skin with cold water as soon as possible. If done with-in 5 minutes, cold water may keep the urushiol from contacting your skin. Within the first 30 minutes, use soap and water. If contact is suspected, wash clothes with detergent. Clothes can transfer urushiol to furniture and other household items.
Only the oily toxin can spread the rash. The fluid contained in blisters is non-allergenic.
Numerous topical ointments and lotions are available for treating the symptoms of poison-ivy. Consult a physician or pharmacist for the appropriate treatment.
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. Several clippings during the year and for several years are often necessary to control poison-ivy. 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 from the lawn. In order to prevent future encroachment into the lawn, control poison-ivy in the adjacent wooded area.
Digging, or “grubbing out” poison-ivy plants and roots can be used as a control method in small beds of landscape ornamentals. Always wear water impermeable gloves when handling poison-ivy plants (including the roots) to prevent poisoning.
Numerous herbicides are available for control of poison-ivy. Before any herbicide is used, read all label directions. Because poison-ivy has an extensive root system, multiple applications of herbicides are usually necessary for effective control. Make repeat applica-tions at the full-leaf stage of growth.
Glyphosate: Glyphosate is the active herbicidal ingredient in Roundup. Numerous other trade names of glyphosate are sold in retail outlets. Glyphosate is applied directly to the foliage of poison-ivy. The best control is achieved when glyphosate is applied on a warm, sunny day when plants are actively growing. Glyphosate requires a 1-hour rain-free period for maximum activity. It is a systemic herbicide and is translocated throughout the leaves, stems and roots of plants. The best control with glyphosate occurs when it is applied to poison-ivy plants in the flower or fruit stage of growth. Applications at earlier stages of growth are not as effective. Delaying application until the fruit or flower stage, however, may not be practical in many situations. Flowering generally occurs in the early summer months in Georgia.
Glyphosate can cause severe injury if the spray droplet particles contact the foliage or immature, green bark of desirable plants. Do not apply glyphosate on windy days. Use coarse sprays with large spray droplets rather than fine mist applications to minimize drift.
Glyphosate may be used along fence rows, as a spot treatment in turfgrasses and pastures, and as directed treatment in ornamentals, and fruit and nut trees.
In situations where poison-ivy has grown into the canopy of large trees, glyphosate can be used in combination with clipping the vine. In this method, the poison-ivy vines are cut 2 to 3 feet above the soil surface. This will kill the portions of poison-ivy that extend into the tree canopy. One to two weeks after cutting the vine, spray the poison-ivy vines remaining below the cut with a glyphosate solution. Since glyphosate will not penetrate the mature, brown bark of large trees, no injury to the tree will occur. If inspection of the bark reveals green tissue, as is commonly found on deciduous trees that have been planted for 1 to 2 years, do not spray glyphosate on the bark of the tree.
2,4-D: 2,4-D is either sold alone or in mixtures with herbicides such as MCPP, dicamba and triclopyr. 2,4-D is only marginally effective in controlling poison-ivy. Products that contain 2,4-D in combination with dicamba and triclopyr will provide better poison-ivy control than 2,4-D alone. Dicamba (Banvel) or triclopyr (numerous trade names), however, will usually provide better control than the herbicides that contain 2,4-D as one of the components in the mixture. 2,4-D and 2,4-D mixtures are applied at the full leaf expansion growth stage of poison-ivy. Repeat treatments will be needed to control new flushes of growth.
2,4-D and 2,4-D mixtures will not injure most turfgrasses and other grasses. Numerous broadleaf plants (ornamentals, fruit trees, muscadines, grapes, cotton, tobacco and many vegetables), however, are highly sensitive to 2,4-D. Spray drift of 2,4-D can severely injure these plants. 2,4-D drift injury can be minimized by using coarse sprays and by staying several feet away from sensitive plants.
2,4-D products are formulated as either amine salts or esters. Ester formulations of 2,4-D are subject to vapor drift, especially at high air temperatures (>80 degrees F). Volatilization or vapor drift of 2,4-D ester herbicides can injure sensitive plants at considerable distances from the original site of application. Do not use ester formulations during the warm months of the year.
Triclopyr: Triclopyr is a highly effective postemergence herbicide for the control of poison-ivy as well as numerous other woody vines. This herbicide is sold under a wide variety of trade names for use in commercial agriculture, forestry and noncropland areas. Most of these products are not sold in lawn and garden stores and other retail outlets. Ortho markets a brand name of triclopyr called Brush-B-Gon in numerous retail outlets. For most homeowners, Brush-B-Gon would be the preferred formulation of triclopyr.
Like 2,4-D, apply triclopyr to poison-ivy at the full leaf stage of growth on a warm, sunny day. Triclopyr can also injure desirable broadleaf plants by spray droplet drift so avoid use on windy days.
Unlike glyphosate, do not spray triclopyr solutions on the mature bark of trees. Triclopyr can be absorbed through the bark of some tree species and cause severe injury.
Triclopyr (Brush-B-Gon) is recommended for use around homes and fences, and in non-garden areas. It can be used near ornamentals, but do not spray when wind conditions favor spray drift.
Triclopyr is commonly used to prevent the regrowth of sprouts from tree stumps. When used in this fashion, undiluted triclopyr is “painted” on the sides and cut surface of the freshly cut tree stump. This “cut stump” method can be adapted to control poison-ivy. Simply clip the poison-ivy vine near the soil surface and paint the freshly cut surface with undiluted triclopyr. This method is useful for the control of small infestations of poison-ivy in areas that are difficult or not practical to spray. When using the cut stump method, some re-growth of poison-ivy will eventually occur. In this event, repeat the cut stump method.
ATTENTION!
Pesticide Precautions
Trade and brand names are used only for information. Cooperative Extension, University of Georgia College of Agricultural and Environmental Sciences does not guarantee nor warrant published standards on any product mentioned; neither does the use of a trade or brand name imply approval of any product to the exclusion of others which may also be suitable.
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