SUMMER OUTDOORS Beware of the poison ivy: It's everywhere

The itchy rash affects 10 million to 50 million Americans each year.
SCRIPPS HOWARD NEWS SERVICE
Like many people who spend a lot of time outdoors, Mark Wallace knows to cover his arms and legs when he hikes in the woods.
As stewardship director of the Western Pennsylvania Conservancy's community conservation program, he's equally vigilant when he's helping to plant the 150 or so flower gardens the nonprofit organization puts in each spring in 19 Pennsylvania counties.
Despite the long pants and sleeves and heavy gloves, he inevitably contracts at least one case of poison ivy every year.
Even when you know what to look for, Wallace notes somewhat ruefully, this ubiquitous, highly poisonous weed, which grows almost everywhere in the United States, can escape a person's notice.
"Lots of times I'll be in the middle of something and then realize, too late, I'm standing in it," he says.
This year, Wallace, 37, will be in good (or at least itchy) company.
Anywhere from 10 million to 50 million Americans each year develop dermatitis from these wild plants, according to the American Academy of Dermatology. Poison ivy, poison sumac and poison oak are the most common cause of allergic reactions in the United States.
Know your enemy
The irritating and sometimes insanely itchy rash and fluid-filled blisters are caused by a colorless, sticky oil called urushiol (pronounced yo-ROO-shee-ol). It's in the leaves, stems and roots of the plant. You don't have to touch the plant to develop the rash. You can get it indirectly by brushing against something else that has been exposed, such as a gardening tool, a glove or even your pet. And because the oil remains active for years, you can get the rash even from dead plants.
Spread by birds, which eat its tiny white, waxy berries, poison ivy most often grows as a vine with hairy looking roots on tree trunks and other vertical surfaces. It also can develop as a free-standing, upright shrub or creep across the landscape as ground cover.
Little wonder, then, that some people have trouble identifying it.
While poison ivy is best known for its three divided leaflets ("leaves of three, let them be"), the leaves vary in size, shape and color. New leaves are very shiny and have a reddish tint; as they mature, they turn a dull green, notes Mike Masiuc, extension agent for the Penn State Cooperative Extension of Allegheny County.
In fall, they turn a vivid reddish-purple or yellow.
And while the leaves, which range from two to four inches, are most commonly egg-shaped, their edges can be wavy, lobed or toothed.
Because it thrives in full sun, poison ivy is particularly fond of roadsides, paths and the edges of fields and gardens. As sneaky as it is irritating, it can blossom among shrubs and ground covers.
And it's most dangerous in the spring and early summer when the urushiol content is the highest.
Avoiding poison ivy
The best way to avoid being stricken, of course, is to steer clear of the plant. Getting rid of a patch of poison ivy without also taking all the nonpoisonous plants around it is easier said than done.
Spray-on herbicides can be effective, but they kill everything else that catches the spray, says Margie Radebaugh, director of education at Phipps Conservatory and Botanical Gardens in Pittsburgh. So you may want to apply it to individual leaves with a paintbrush or small bottle.
If the plant is small, you can yank poison ivy out by its roots. Radebaugh suggests covering your hands with two plastic supermarket bags, grabbing the plant and turning the bag inside out as you pull. Make sure you get the entire root because the plant will resprout from even the tiniest root section. And wash your hands afterward.
Don't burn it. That will produce toxic smoke that can severely irritate those who are sensitive to poison ivy.
The best time to get rid of the weed, says Masiuc, is in the late summer when the plant's carbohydrates are moving from the leaves to the roots.
"Timing is important," he says. "That's when the weed killer will be carried to the roots."
According to the dermatology academy, 15 percent of people are resistant to poison ivy; the rest will break out within 12 to 48 hours after contact. The severity of the rash depends on your sensitivity to the oil.
Sensitivity also can change over time. Someone who has had no reaction at a younger age can develop his or her first rash later on.
"Keep a keen eye for it any time you're out in Mother Nature," cautions Wallace, "because it comes back every year."