Poison ivy alert
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
Lurking between the ground cover, under the shrubs and, yes, even high overhead, poison ivy is one of the most persistent three-leaved vines known to gardeners. The old adage “with leaves of three, let it be...” is correct.
Few vines fall into the three-leaved category, and if you find one with three, better off not second guessing it. What’s more, poison ivy is abundant in Michigan and can be found in some places you would least expect. You may think of poison ivy appearing only along roadways, forgotten farms or shady corners of obscure camping areas, but I’ve noticed it popping up in dozens of parks, swimming holes and golf courses. The funny thing is, people including gardeners, don't always recognize it.
What is it that makes this skin-irritating vine so difficult to recognize for gardeners? Poison ivy is commonly found along with other twining plants such as five-leaved ivy (Parthenocissis) or brambles. Some woody seedling plants may have three leaflets upon emergence and appear to the causal observer as poison ivy too. One reason for identity confusion would be its trait of exhibiting "polymorphism" – or different shapes to the leaves. Poison ivy's glossy green leaflets have a reddish tinge to the new growth, and they do not have evenly serrated edges but rather, coarse lobes, appearing jagged or tattered. Don’t be fooled by one that is without lobes though. As this plant matures, leaflets are smooth or "entire."
The other fooling factor is that poison ivy doesn't always stay on the ground. It can be a very aggressive woody vine, easily growing up the trunk of a nearby tree. (see photo) The stem is easy to identify as it ages because of its brown, hairy adventitious roots covering the trunk. It can sprout limbs that extend out six to eight feet from its "hitching post" appearing as an extension to the leafy tree. I have known people who have reached up into a canopy of what they thought was a tree and ripped off leaves to take a look at them. Oops!
Poison ivy is hard to control with out persistence. The best time to control any woody weed is the fall when it is storing carbohydrates in its root system for winter. In the summer, several applications of a broad-spectrum herbicide such as Glyphosate should give you a leg up on it. After you have gotten rid of most of it, spot treating new sprouts will help keep it under control.
For a free bulletin to help you identify and control poison ivy, send a self-addressed envelope to the Kent County MSU Master Gardener Lawn and Garden Hotline at 775 Ball NE, Grand Rapids, MI 49503.