Poison ivy: You can look, but you'd better not touch
Editor's note: This is the latest in a series of biweekly columns from the Becker County Master Gardeners, who are part of the University of Minnesota Extension.
Poison ivy is one of several plant varieties found in Minnesota that can be classified as poisonous, along with wild parsnip, stinging nettles, and sumac. It is a persistent problem for many of us who live in Minnesota, but with proper management it can be controlled.
Peak poison ivy season in Minnesota is between Memorial Day and Labor Day, but it can be found any time of the year. Poison ivy belongs to the Anacardiaceae family of plants. Other members of this plant family are mangos, cashews, and pistachios, to name a few.
All these plants produce an oil called urushiol. When urushiol comes in contact with skin, it can bond with the skin cells and cause a medical condition called contact dermatitis. Symptoms of contact dermatitis may include itching, rash, swelling, blisters, clear yellow drainage, and red skin. These symptoms usually occur 24 to 48 hours after exposure but can happen as long as nine days after exposure. The skin irritation itself is not contagious, but you can transfer it to another person by touch if you have urushiol oil on your skin.
There are three main ways people come in contact with urushiol. First is through direct contact with the plant. Second is through indirect contact by touching any object that had contact with the plant, such as a gardening tool or a pet. Third is through burning the plant, which can release urushiol into the air and cause airborne contact.
The best way to avoid exposure is to avoid contact with the plant. Know what plant to avoid, wear protective clothing, such as long pants and long-sleeved shirts to minimize contact, and wash well if you think you have been exposed.
There are two varieties of poison ivy, Western and Eastern, and Minnesota has both types. Eastern poison ivy usually grows as a rope-like vine, and Western poison ivy as a low growing shrub. Because their geographical areas overlap, they sometimes hybridize (crossbreed) and are referred to as “poison-ivies.” Poison ivies have an extensive root system and propagate by underground rhizomes and seeds.
Most mature plants will flower and produce white, waxy fruit in clusters. The vines or stems are woody, and the leaves occur in threes, called leaflets. The edges of the leaflets can be smooth, wavy, lobed, or toothed and change texture and appearance as the growing season progresses. The stem of the end leaf in each leaflet is at least twice as long as the stem of the other two leaves.
Interestingly, only humans and some primates are adversely affected by the urushiol in poison ivy. Poison ivy is an important food source for many animals. Birds and deer eat the waxy fruit, called a drupe, and insects eat the leaves.
If poison ivy is a problem where you live, you can either avoid it or try to control it. Whenever working near poison ivy, make sure to wear appropriate long sleeved-shirts, long pants, and gloves. Poison ivy can be controlled using manual or chemical methods. For light infestations of poison ivy, small plants, including the roots and rhizomes, may be dug up or cut to the ground. Cutting to the ground requires monitoring the infestation every one to two weeks and cutting it back as new growth occurs. This eventually starves the plant.
Another method to control poison ivy is herbicide use. Effective herbicides include glyphosate, 2-4-D amine, dicamba, mecoprop, and triclopyr. Always follow the instructions on the package and apply as directed. Herbicides work better when applied at the right time. 2-4-D and dicamba work best in late spring or early summer when plants are actively growing. Triclopyr is best after leaves fully expand in the spring but before they change color in the fall. Glyphosate works best as a 2% solution, applied two weeks before and two weeks after full bloom, which is early summer.
- “Poisonous Plants,” 2018, U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health. Accessible at: https://www.cdc.gov/niosh/topics/plants/geographic.html .
- “Poison Ivy, Oak and Sumac Plant Identification, Prevention, and Treatment,” Zanfel, 2019 Minnesota Safety and Health Conference. Accessible at: https://www.minnesotasafetycouncil.org/conf/speakerassets/Poison_Ivy_Oak_and_Sumac.pdf .
- “Poison Ivy, Oak, and Sumac: The Basics,” by Carol DerSarkissian, 2019 WebMD Medical Reference. Accessible at: https://www.webmd.com/skin-problems-and-treatments/guide/understanding-poison-ivy-oak-sumac-basics .
- "Western Poison-ivy (Toxicodendron rydbergii),” by Walter Fertig, Plant of the Week, U.S. Department of Agriculture, Forest Service. Accessible at: https://www.fs.fed.us/wildflowers/plant-of-the-week/toxicodendron_rydbergii.shtml .
- “Toxicodendron radicans, T. rydbergii,” by Robin J. Innes, 2012, U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory. Accessible at: https://www.fs.fed.us/database/feis/plants/shrub/toxspp/all.html .
- “Poison Ivy,” by Bob Polomsky, Debbie Shaughnessy, and Joey Williamson, 2019, Home and Garden Information Center Factsheet HGIC 2307. Clemson Cooperative Extension. Accessible at: https://hgic.clemson.edu/factsheet/poison-ivy .
- “Poison Ivy Identification Guide,” by Katie Licavoli, 2020, Greenbelly. Accessible at: https://www.greenbelly.co/pages/how-to-identify-poison-ivy .