Sirch Beyond Your Back Door Blog 10/7/21
Poison Ivy: The Good, the Bad, and the Beautiful
Neotropical birds are migrating south now. Recently, a cold front brought winds from the north. On one evening BirdCast predicted that 300 million birds would fill the night sky.
What do these birds eat to fuel their journey? Many insect-eating birds add fruit to their diet when insect populations decline in the fall. Native herbaceous plants, shrubs, trees, and vines have evolved to be fruiting just at the right time. The birds eat, eliminate, and spread the seeds to new locations with a bit of fertilizer added for good measure!
One such plant is Poison Ivy (Toxicodendron radicans). Despite its effects on us, Poison Ivy is actually a great native plant for wildlife. A woody, deciduous vine, its white berries are ripe right when its leaves turn a brilliant scarlet. Some botanists think the beautiful fall color is a signal to birds, called foliar fruit flagging. I have seen tourism ads, encouraging leaf peepers to travel to New England, that feature Poison Ivy in their colorful photography.
Other than being food for some neotropical migrants, Poison Ivy berries are relished by more than 60 species of birds that overwinter here or that are permanent residents, including the Northern Mockingbird (Mimus polyglottos), Black-capped Chickadee (Poecile atricapillus), Tufted Titmouse (Baeolophus bicolor), Hermit Thrush (Catharus guttatus), Ruby-crowned Kinglet (Regulus calendula), Yellow-rumped Warbler (Setophaga coronata), White-throated Sparrow (Zonotrichia albicollis), Wild Turkey (Meleagris gallopavo), Northern Flicker (Colaptes auratus), Red-bellied Woodpecker, (Melanerpes carolinus), and Downy Woodpecker (Dryobates pubescens). Some mammals also eat these berries, including White-tailed Deer (Odocoileus virginianus), the White-footed Mouse (Peromyscus leucopus), Eastern Chipmunk (Tamias striatus), and Black Bear (Ursus americanus).
Poison Ivy is adaptable to sun or part-shade and prefers a woodland edge. It can grow as a sprawling ground cover, a thick brown wooly vine with aerial rootlets up a tree, and even as an upright shrub, particularly along the coast. You have probably heard the warning rhymes “leaves of three, let them be,” “berries white, take flight,” and “hairy vine, no friend of mine.” The plant has compound leaves (those three leaves are actually leaflets). Its leaves can be shiny or dull, and either toothed at the edges or smooth-edged. One field mark is that the middle leaflet has a longer petiole (the leaf stalk that attaches to the stem) than the other two leaves.
A species similar to Poison Ivy found growing in Connecticut is Western Poison Ivy (Toxicodendron rydbergii). It grows in forests and as a small shrub on cliffs, ledges, and rocky slopes. It can be distinguished from Poison Ivy by its smooth, white berries, unlike Poison Ivy’s slightly hairy, white ones. Poison Sumac (Toxicodendron vernix) is a tall, upright shrub with compound leaves and upright panicles of white berries. It is found ringing the edges of freshwater swamps and bogs.
The explorer Captain John Smith provided the first written account of Poison Ivy in 1624, writing that “the poisoned weed is much in shape like our English Ivy, but being touched, causeth rednesse, iching, and lastly blisters.” Urushiol (pronounced “yoo-ROO-she-ol”) is the allergen in Poison Ivy that causes contact dermatitis (the rash). It is named for Urushi, the highly prized Japanese lacquerware that has been made from the related Japanese Lacquer Tree (Toxicodendron vernicifluum) for centuries. All members of the genus Toxicodendron are in the mango, or cashew, family, the Anacardiaceae. Some people who are allergic to Poison Ivy also have a reaction to eating mangos and cashews.
Urushiol is an oily substance found on all parts of the plant at all times of the year. You can get oil on you from touching a brown mature vine in the middle of the winter or even dead leaves in your compost pile. The oil can be transferred to your body and face from clothing, pets, and tools, or from direct contact with the plant. The colorless, odorless chemical is quite stable and can be viable for years. Increased carbon dioxide levels as a result of climate change are causing an increase in Poison Ivy’s growth rate as well as more potent urushiol.
More than 70% of people are allergic to urushiol. It can penetrate the skin within 10 minutes of contact, so it’s best to scrub right away with cold water and dishwashing liquid or rubbing alcohol. You also can use special soaps and treatments from your pharmacy that are recommended. The rash can appear in as little as four hours or as long as two weeks after exposure. Never burn Poison Ivy, because the oil can become airborne, get into the lungs, and cause a serious reaction.
You can control Poison Ivy in your yard by repeatedly mowing over the leaves, which will keep the plant from growing new leaves and so sap the roots of stored carbohydrates. Another method is to cut the leaves and then cover the area with wet cardboard, followed by 12 inches (30.5 centimeters) of wood chips.
Despite our efforts to control it, Poison Ivy plants often seem to grow rampantly around the edges of our landscapes. Perhaps the food it offers wildlife can be seen as one thing in its favor.