Recognizing the ”leaflets three” that characterize poison ivy can spare you the painful consequences of a brush with this weed.
While it seldom is encountered in urban or metropolitan areas these days, isolated plants may sprout unnoticed in even well-groomed yards. Certainly it still persists in woodland and undeveloped suburban areas, especially in swamps or bogs.
It may be found growing as a vigorous vine climbing trees, poles or fences, or as a bushy plant. Either form can be a serious irritant to susceptible people who come in contact with it.
Heeding the adage ”Leaflets three, let them be” can help you avoid the plant in the spring and summer. Because there are some look-alike plants, play it safe and stay clear of them, too.
Poison ivy (Rhus toxicodendron radicans) is a member of a large plant family that, incidentally, includes poison sumac (Rhus vernix). An oily substance called urushiol, which produces the rash associated with poisoning, is found in the roots, stems, leaves and even on the plant’s grayish-white berries.
Poisoning usually occurs through direct contact with plant parts, but some sensitive people may incur it by simply handling clothing worn in the field, petting a dog or cat that brushed against the plant or from the smoke of burning brush that includes plant stems and foliage.
Among plants most commonly mistaken for poison ivy are the Virginia creeper (Parthenoissus quinquefolia), also known as woodbine and American ivy, and the bitter nightshade vine (Solanum dulcamara), a pesty woody vine.
A positive clue to the identity of poison ivy is, of course, its compound, trifoliate leaves, the margins of which may be straight, toothed or lobed. Each leaflet can vary from 2 to 4 inches long, with a dull or glossy green, smooth or hairy surface.
Although Virginia creeper has five leaflets on its larger compound leaves, confusion about its identity often occurs because each leaflet resembles those of the ivy. Leaves of both plants take on orange to scarlet hues in autumn.
The nightshade vines can be distinguished from poison ivy by their alternate, deeply lobed leaves and profusion of small violet and yellow flowers, which are followed by showy red berries. The berries are toxic to humans but a treat for the birds, which spread the seeds in annoying abundance. Foliage is not harmful to the touch, as with the ivy.
The toxic effects of poison ivy are greatest in spring and summer when the sap is flowing. The simplest control measure when it is found in your yard is application of brush killers or other appropriate herbicides. Never try grubbing out plants with a hoe or by hand or risking contact with the plants by burning them.
One of the worst pests for gardeners is ground ivy that, though nontoxic, creeps and spreads with such abandon that it overtakes everything in its path.
The weed (Glecoma hederacea) is also known as gill-over-the-rock, field balm and other names unfit to print, and often incorrectly as Creeping Charlie (Lysimachia nummularia), which has yellow flowers and round leaves.
Ground ivy, which covers itself with tiny purplish-blue flowers, is genuinely attractive in early growth. Soon, however, its thready, elongated stems entwine around desirable or cult ivated plants, threatening to choke them out. When it moves into lawn areas, it knits a veritable cover over the turf in ever-enlarging patches.