A Poison Ivy Primer

Photo: https://hort.extension.wisc.edu/articles/poison-ivy/

Young poison ivy leaves (left) can have smooth margins, while mature poison ivy leaves (right) often have serrated or lobed leaf margins.

Poison ivy (Toxicodendron radicans) is the one plant the proves the point that not all native plants are pleasing. It is a perennial, woody plant native to Wisconsin and all of North America.  It is quite adaptable, prefers to climb, but will creep along the ground if it cannot find something upon which to climb. 

Poison ivy is in the plant family Anacardiaceae, as are mangos, pistachios, and cashews. Fortunately eating those plants do not cause the same allergic reaction that poison ivy does, although the stem of them mango fruit can cause a reaction. However, that is not generally the part of the fruit that is consumed.

Poison ivy is typically a woody vine, but it can also be shrub-like, especially when in full sun. When growing up a tree, it becomes thick and develops adventitious roots to hold fast. It becomes so branched that it almost looks like part of the tree. However, it does not damage the tree. It grows in pastures, woodlands, fields, farms, along streams, and in home landscapes. It spreads rapidly by both underground rhizomes and seed. It is deciduous, dying back in the fall and emerging again in May.

Does poison ivy have any redeeming value?  Yes. The berries are an important food source to wildlife, particularly songbirds and small mammals, during the fall and winter months. Deer will browse on the brightly colored leave during the fall with no ill effects.  The persistent roots provide erosion control, particularly on slopes.

However, given the fact that roughly 90 percent of the human population has an allergic reaction when contact is made with this plant, it is not something most people want in the landscape.  The entire plant is poisonous because all parts, leaves, stems, and roots, contain the irritating, resinous, colorless, oil urushiol. This cannot be removed by simply washing with soap and water, but requires something stronger like naphtha soap or alcohol. Contact does not have to be made directly with the plant but can be picked up on tools, clothing, and the fur of pets. It is important to never burn the plant as the smoke can also contain the oil; breathing it can result in serious consequences. 

The best defense against a reaction to poison ivy is learning to identify the plant. The old adage “leaves of three, beware of me” is a good guideline. The leaves are positioned alternately on the stem and the margins can be either smooth, serrated, or lobed. Virginia creeper (Parthenocissus quinquefolia), another native and very common Wisconsin plant, is often mistake for poison ivy.  However, it has compound leaves with five leaflets.  

Controlling poison ivy can be challenging. Goats are experts at consuming the plant, but since that is not a good option for most people, most have to resort to herbicide controls. Herbicides containing glyphosate and triclopyr are effective.  Foliar sprays should be used when the plant is fully leafed out and actively growing.  Remember, these are non-selective herbicides and they will kill all vegetation they contact. Alternatively, sever the vine and immediately apply the herbicide to the cut end. Follow the label directions and always wear appropriate personal protection gear. Clean up any cut vines by bagging and disposing them.  Do not burn or compost any debris.  Cover any exposed cut vine stubs with several inches of wood mulch to prevent inadvertent contact.

Carol Shirk

Certified Master Gardener