Dave Anderson's Forest Journal: Poison ivy is a plague you learn to avoid

June 22. 2013 2:42AM

I've made my peace with poison ivy. It took four decades to come to terms with P.I. after the misery I suffered from this humble, tenacious and all-too-common plant.

As a lad, I was constantly plagued with itchy, weeping poison ivy blisters and slathered with Calamine lotion. (Why did it have to be so . pink?) I was briefly hospitalized from a secondary infection inside my fingers. Poison ivy made me suffer.

My grandfather's cure instructed my parents to take me to the beach to spend the day in astringent, icy-cold salt water. He said to be sure to use a stiff scrub brush to open blisters and lather up with a cake of old-fashioned, brown laundry soap. The lye and salt water burned worse than any itchy rash.

Eventually our family doctor prescribed cortisone steroid shots to lessen my allergic reaction. Now I rarely even get a faint hint of a rash. Of course now I also avoid poison ivy like the vegetative plague it is.

Poison ivy is easy to avoid once you learn to recognize it. Identify poison ivy by its glossy three leaves and its common habit of forming a dense, nasty mat of multiple stems and fence- or tree-climbing vines.

"Leaves of three? Let it be! Berries white? A poisonous sight!" was a familiar rhyme that nevertheless didn't keep me out of the woods of my youth.

More important is to learn poison ivy's preferred habitats.

Some plants are fussy specialists with tight-growing site tolerances for sun vs. shade, wet vs. dry and poor, sandy soils vs. rich, deep loam. Poison ivy is a generalist. It wins by default on all disturbed sites, including dry riverbank sand and rich, fertile silt in the deep shade of forest edges. The shifting soils of riverbanks, beach dunes, sand pits, as well as roadside medians and ditches just beyond fences and guardrails, are where poison ivy thrives. It spreads in a low carpet, and it can climb fences, buildings and trees with its thick, reddish-hairy vines.

The oily, glossy leaves of noxious plants in the genus "Toxicodendron" employ chemical warfare tactics. Vines, stems and leaves produce pale yellow oil called urushiol that causes contact dermatitis, the familiar poison ivy rash.

Before oil is absorbed by the skin, it can be removed with soap and water if caught immediately. But as much as 50 percent of the oil may be absorbed in the first 10 minutes after contact. Once oils penetrate skin, the immune system activates lymphatic defenses that dispatch white blood cells of a type called T-cell lymphocytes to the area of contact to wage an allergic-reaction response that damages skin through the formation of weeping blisters.

The American Academy of Dermatology estimates up to 50 million cases of urushiol-induced rashes annually.

One local mom, Heather Moran, recently passed along her family's natural remedy for poison ivy rash. Ingredients: cosmetic clay, fine-grain sea salt and peppermint essential oil. Make a paste with clay and a pinch of sea salt in a small bowl, and add one or two drops of peppermint. Apply the paste to the rash, and let it dry. Keep re-applying until the rash stops oozing.Urushiol is the plant-specific "oleoresin" contained in poison ivy sap and released when plant tissues are damaged or crushed. It seeps to leaf surfaces in late autumn to form a black lacquer in contact with oxygen. Oleoresins are valued for production of certain varnishes, sticky adhesives and glazes. Urushiol lacquer is used to produce the traditional Chinese, Korean and Japanese lacquer-ware pottery. Poison ivy grows in the temperate regions of Asia. In North America, it grows in the states east of the Rocky Mountains. It is most common in the suburban and exurban regions of New England, as well as Mid-Atlantic and southeast states.

As earlier noted, poison ivy dominates sites altered by natural and human-caused disturbances. It thrives in dry sand and gravel, and in the rich silt edges of parking lots and roadside ditches. In near-coastal forests and sandy dunes of pine and oak, poison ivy becomes the ubiquitous understory because it tolerates salt-spray and brackish flood tides. It rapidly colonizes areas in the aftermath of severe storms, including hurricane tidal surges. One legacy of more frequent severe weather events will include the creation of more and better poison ivy habitats.

By human standards, poison ivy is a nasty, noxious weed. Ironically, people have done more to favor its recent success within its native range than nature otherwise would have provided.

Poison ivy is far more common now than four centuries ago when Europeans first arrived in North America. People opened the forest canopy to sunlight and scraped-away damp, spongy, humus layers of soil.

Today, countless thousands of fallow acres of disturbed sites lie in full or partial sun - on the fringes of forests, in areas under intensive cultivation as agricultural fields, and on asphalt and lawn acreage of commercial and residential real estate. Creation of these extensive "edge habitats" has favored expansion of poison ivy beyond its former limitation to rare edges of dense eastern deciduous forests.

We've brought this plant curse entirely upon ourselves.

Each summer, new generations of suburban kids find ways to escape the civilized confines of tidy playgrounds and manicured back yards to unintentionally become acquainted with this humble three-leaved plant. Poison ivy is weedy, opportunistic, tenacious and highly successful. It chemically teaches self-defense and adaptability. Poison ivy mirrors us. It follows us.

Alert Barbara Walters: If humans could collectively be any plant, we'd likely be poison ivy.

"Forest Journal" appears every other week in the New Hampshire Sunday News. Naturalist Dave Anderson is director of Education and Volunteer Services for the Society for the Protection of New Hampshire Forests. Email him at danderson@forestsociety.org or through the Forest Society Web site: forestsociety.org.

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