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Growing Green: Leaves of Three, Let it Be!

Summer is here, the kids are out of school, and everyone is spending more time outside.  Some of my best summer memories involve camping in the woods with my family, some of the most annoying are memories of biting insects, ticks and poison ivy.  I have recently received several calls regarding the identification and eradication of poison ivy.  Here are some tips for finding and getting rid of this pesky plant!

A master of disguise, poison ivy can take the form of a vine, shrub or ground cover. It can have shiny leaves or dull leaves. The leaf edges can be smooth or notched. So how can you spot poison ivy? The phrase "Leaves of three, let it be" is a pretty good rule of thumb. Whether hiking in the woods or playing in a field, beware of any plant with three leaflets. Western Poison Ivy, Toxicodendron rydbergi, is found throughout Minnesota. It grows in all types of soil and under all conditions of sun and shade. 

All parts of the plant contain poisonous oil, called urushiol, that can cause an allergic reaction. The skin rash caused by poison ivy is called allergic contact dermatitis, and can look red, streaky, and include raised areas (hives), or fluid-filled blisters. The reaction can occur when part of your skin comes in contact with the oil, whether it came directly from the plant or not. This can occur through touching objects or clothing that has been in contact with the oil from poison ivy (careful doing laundry!), or even petting your dog or cat after he has romped through a patch.

Poison-ivy is best controlled with an herbicide containing triclopyr, a woody brush-killer. It should be applied directly to the leaves of the poison-ivy, not soaked into the ground. When used according to directions, this herbicide should not injure established grasses, only broad-leafed plants. Apply the herbicide when poison-ivy is growing actively. Temperatures should be in the 60° to 85°F range. Avoid windy days when droplets might drift onto the foliage of nearby trees, shrubbery or garden plants.

You may have to spray more than once since poison-ivy is a tough plant to kill. Wait two weeks or more between applications, and repeat only if weather permits. Don't apply herbicide after poison-ivy foliage begins to show fall color. Wait till new leaves are fully expanded the following spring. Some re-sprouting might occur several months later. Watch the area for at least a year and repeat the treatment as needed. As with any garden chemical, read and follow label directions carefully each and every time you use it.

Be very careful cutting down poison-ivy; all parts of the plant are poisonous. Note, too, that even the dead plants are poisonous. Never burn them! Smoke and ash can carry toxins to the skin causing a rash. Inhaling the smoke can be worse.

Poison Oak and Poison Sumac are not found in Minnesota. However, another rash inducing plant, Wild Parsnip, is an invasive species and noxious weed in Minnesota. The juice of wild parsnip in contact with skin in the presence of sunlight can cause a rash and blistering and discoloration of the skin (phytophotodermatitis).

Robin Trott is a Horticulture Educator with University of Minnesota Extension.