Leaves can be glossy or dull, dark or pale green, and hairy or not.
Itching to get out in the garden? Poison ivy (Toxicodendron radicans aka Rhus radicans) includes several subspecies, and is only one of multiple sumacs, many of which are also rash-producing, and the one you’re most likely to tangle with in your own backyard. It belongs to the Anacardiaceae family along with mangoes, cashews, smoke tree (Cotinus sp.), and other desirable relatives, which, likewise, may produce severe allergic reactions.
Our North American “brand” spreads from coast to coast, from Canada through Mexico, Asia to Guatemala, Europe and Australia. Only primates are sensitive to urushiol (the plant’s toxic substance). Cats, dogs, goats, and deer are immune, but they can transfer the problem to humans via their fur.
The rash can also spread through airborne soot and ash, so never burn the plant. People inadvertently use poison ivy twigs for firewood. (Inhaling urushiol particles can cause asthma and swollen eyes.) Once the stricken victim has bathed, the rash is not contagious to others. Many people don’t exhibit symptoms with their first encounter. About 80 to 90 percent of people are susceptible to poison-ivy-induced rashes. People have gotten rashes from 20-year-old herbarium specimens and garden tools they haven’t used for years. We expect problems in spring and summer, when sap and pollen are plentiful, but in winter, dormant plants are equally dangerous.
The axiom “leaves of three” does apply to poison ivy, but the plants can have four, five or seven
leaves as well.
Poison ivy can take the form of a ground cover, a vine, or a shrub. It adheres to trees with hairy roots.
Identifying poison ivy
The familiar “three” leaflets can be four, five, or seven smooth-edged, lobed, or toothed, tiny or large, glossy or dull, dark or pale green, hairy or not, and can form a small deciduous plant, long vine, or huge shrub. Juveniles form ground covers and spread by runners until they find a climbable support structure (such as trees, walls, telephone poles). Mature plants can reach 100 feet with a 6-inch trunk diameter.
Once you’ve had a close encounter of the blistery kind, you’ll soon be able to recognize it in its many sinister disguises. But, even if you never set foot outdoors, handling clothing or any object that has brushed against the plant can bring the poison ivy experience to you firsthand. The oil attaches to skin and cell proteins, causing our immune systems to react. The fluid emanating from blisters is mostly white blood cells and serum produced by our bodies. Almost all body parts are vulnerable to the sticky urushiol that produces the characteristic rash. Places where skin is tender, between fingers for example, are most sensitive.
Killing the rash
Cleansing within 10 minutes of contact may arrest the initial outbreak, and this can help prevent further spread. The rash may appear within a few hours to a week or more after exposure, and most rashes disappear within three weeks or sooner. Water alone can dilute the oil.
Home remedies for poison ivy rashes abound. Success has been reported using various soaps, chlorinated water, Aloe vera, vitamin C, tea tree oil (Melaleuca alternifolia), iodine, vinegar, sassafras leaves, plantain leaves, salicylic acid, even honey or banana peels.
Once a rash develops, aluminum acetate (Burrows solution), baking soda, colloidal or oatmeal baths, aluminum hydroxide gel, calamine, kaolin, zinc acetate, zinc carbonate, or zinc oxide applied to the skin can help, as can corticosteroids and antihistamines used both topically and internally. Menthol, benzocaine, and pramoxine sprays often can numb the itch.
Poison ivy can have red fall color and white berries.
Nevertheless, even “evil” poison ivy has beautiful fall color, and provides a source of cover and food for wildlife. Bees visit the flowers, deer browse the fruits and foliage, and cottontail rabbits feed on the twigs and bark. Its white berries are savory to at least 60 species of birds.
Killing the weed
But you probably don’t want poison ivy in your garden. Using proper personal protection (such as long sleeves and pants, gloves, and eye protection) cut vines and pull them away from trees. Dig up roots. Mow or cut young shoots until the plant dies. Supposedly environmentally friendly herbicides, such as a citrus-based weed killer, and those formulated from soap-based fatty acids can rid large garden areas of poison ivy. Non-selective herbicides with the active ingredient glyphosate, and selective herbicides containing triclopyr also can do the trick. Or enlist one of the lucky 15 percent of the populace who seem to be immune to poison ivy’s charms to weed the plants out for you.
Or rent a goat – they can eat poison ivy with no ill effects.
A version of this article appeared in a March/April 2017 print edition of State-by-State Gardening.
Photography courtesy of Joseph LaForest/bugwood.com and U.S. Department of Agriculture.