Poison ivy, poison oak, and poison sumac can make summer or fall uncomfortable.
If you have ever experienced blisters, swelling, and severe itching from even the simplest encounters, you can appreciate the capabilities of these plants. Above all other defenses against contact, avoidance should be your priority. But to avoid these plants, you must first be able to recognize them.
“Leaves of Three, leave it be” is more than just a childhood rhyme, it’s a great identifying device, too. Poison ivy develops compound leaves consisting of three leaflets. The leaflets will be 2 to 4 inches long with pointed tips and a pointed base. The leaves may be smooth or hairy, shiny or dull, and their color varies from yellowish green to reddish green.
Poison ivy leaves are arranged alternately on the stem. The sweet-smelling, yellowish-green flowers appear in clusters in early summer and small, waxy white fruits develop in the fall. Poison ivy spreads to cover areas via underground streams and seeds and can tolerate sunny or shady conditions. It may grow as a woody shrub or slender woody vine that extends along the ground and climbs trees and shrubs.
As a vine, it produces “aerial roots” that help it attach to the trunks and give the vine a “fuzzy” appearance. Poison ivy is often confused with Virginia creeper, a non-toxic plant with five leaves.
Poison oak looks like poison ivy but does not climb. It has fuzzy, multi-lobed leaves that are thicker than those of poison ivy. The leaves are pale green and hairy on both sides of the leaves. The stem has no aerial roots. Poison oak prefers dry, sunny locations in woodlands, woodlands, and old fields.
It would be unlikely that you would encounter poison sumac in your backyard without noticing it. This poisonous plant is a shrub that can grow up to 25 feet tall. The leaves are 7 to 15 inches long and are pinnately compound with five to 13 leaflets per stem. They are found mainly in swamps or wet bottomlands. Poison sumac has sweet-smelling flowers in spring and bright red and yellow foliage in fall. Unlike many similar forms, poison sumac has cream-colored berries in the fall.
Avoiding these plants is not always practical, especially when they are growing in your flower beds. Cultural and chemical controls may be necessary in these cases. Hand pulling poison ivy is most effective when the soil is moist. The roots must be completely dug out because regrowth can occur from any remaining root parts.
Wear gloves and long sleeves when pulling this plant and wash your clothes after you’re done. Run a rinse cycle after washing work clothes to prevent contaminating other clothes. If you have a severe allergy to poisonous plants, do not attempt cultural control. To eliminate vines, cut the vine at the base and pull it from the tree.
Use an herbicide, such as Roundup, Spectracide’s Brush Killer Concentrate, or Ortho’s Brush-B-Gone, to treat the regrowth. These chemicals can also be applied to poison ivy and non-climbing poison oak. Care must be taken around desirable plants as damage can be caused by drift or absorption through the roots.
In areas where favorite plants are abundant, you may want to paint the chemical directly onto the leaves of the poisonous plant to avoid contact with other plants. Chemical treatments should be applied while plants are still growing, but repeat applications will likely be necessary. Read and follow herbicide label instructions. Burning is not a recommended method of elimination. During burning, soot particles can carry oils from toxic plants. Contact with smoke can lead to severe poisoning.
The rash caused by poison ivy, oak, and sumac is a direct result of contact with a toxic oily substance within the plant. The plant must be crushed or broken to release these oils. If you touch this area with your hand, you can spread it by touching other parts of your body. Because it is sticky, it can also be applied to garden gloves, clothing, golf balls or pets.
The rash cannot be transmitted by touching a blister. The severity of the rash varies from person to person and may take up to five days to appear after contact. Use calamine lotion, zinc oxide ointment, or a paste made of baking soda and water on the rash or contact your doctor. People who believe they are not affected by poison ivy should know that first exposure to the plant’s oils does not produce a reaction. It often takes several exposures to develop an allergy and see symptoms, so continue to be careful.
P. Andrew Rideout is the UK Horticultural Extension Agent and can be reached at pandrewrideout@uky.edu.