It has been the year of weeds, according to complaints Master Gardeners have heard. One of the culprits that is becoming more prevalent is poison ivy.
Even though it is a native species and a valuable food source for wildlife and should not be eliminated, it is still on the noxious weed list. Because it is harmful to humans (but not wildlife), it is deemed a noxious species that should be controlled near homes and yards, along rights of way, trails, public accesses and on business properties where people can be exposed to its effects.
Poison ivy roots, stems, and leaves contain urushiol, an oily resin that can cause severe blisters, rash, swelling and intense itching when your skin touches it. Pets who pick up the oil on their fur can also be a source of exposure. If plants are burned, inhaling the smoke can cause serious respiratory problems. Recognizing the plant is the first part of the strategy to dealing with this horticultural hazard.
“Leaves of three, let them be,” is a memory rhyme directing behavior toward poison ivy. The plant has compound leaves that have three egg-shaped leaflets with pointed tips and smooth to irregularly tipped edges. The alternate leaves are glossy green that are now turning yellow and, later in the fall, to dark red. In early summer it has clusters of diminutive yellow to green flowers. Once pollinated, small green to greyish white berries form in little clusters. They are waxy-looking and turn yellow, white or tan later in the season. It is a shrub that is 1 to 2 feet tall. In other areas of Minnesota and further south and east in the country it can grow as a vine. On the East Coast, I swung on thick vines that hung 30-40 feet in the air thinking it was woodbine -- only to learn that it was climbing poison ivy. It is a good idea to learn about the indigenous vegetation before you make stupid choices!
Poison ivy reproduces by both seeds and roots. Animals transport the seeds and they also can be moved by wind or water. It has extensive shallow underground roots and vining above ground. It is a perennial plant and all parts can cause the harmful effects.
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To control this plant there are four things to keep in mind: first, do not burn it; second, avoid touching it with your bare hands or arms; third, wear long sleeves and pants and wash them in hot, sudsy water after exposure; and fourth, wear rubber gloves. In fact, hand control should be avoided. You can reduce the spread of the plant and its population by mowing it continually. There are various herbicides that also can be used to control it. According to the University of Minnesota Extension “several herbicide active ingredients are effective in poison ivy control. Products containing a combination of the selective broadleaf herbicides, 2,4-D, 2,4-DP, MCPP, MCPA, dicamba and triclopyr can effectively control poison ivy.” Repeated applications may be necessary to control this persistent plant. Read the labels and ask questions about the best product for your situation before purchase. Always read and follow chemical directions carefully, wear protective clothing and boots, and avoid application on hot, windy days. You also must be careful to avoid contact with desirable plants.
To learn more about controlling this plant, an extensive article on weed control strategies is at www.extension.umn.edu/garden/diagnose/weed/idlist.html#16 . Other information can be found at www.extension.umn.edu/garden .
