June 19, 2019

Garden Variety: Tougher poison ivy

Can poison ivy really get any worse?

If you have ever had a reaction to the plant, just the inscribed memory of endless itching might make you doubtful that anything could rival it. For gardeners and outdoor enthusiasts who regularly encounter poison ivy, however, the rumors that the plant is becoming more abundant are starting to look true.

The news about poison ivy (Toxicodendron taxa) is more than rumor, but if you heard it from a friend, it would be easy to put it in a box with old wives’ tales and snake oils. Research at Duke University in the early 2000s started the discussion when the results of a six-year study on the relationship between poison ivy and elevated atmospheric carbon dioxide were released.

The bottom line from the report’s abstract reads: “Our results indicate that Toxicodendron taxa will become more abundant and more ‘toxic’ in the future, potentially affecting global forest dynamics and human health.”

In the study, when atmospheric carbon dioxide increased in a forest, poison ivy was able to photosynthesize better and use water more efficiently, making it grow faster and larger than it would otherwise. In addition, the urushiol (the oil responsible for skin irritation) produced by these plants was more allergenic than in plants at normal atmospheric carbon dioxide levels.

Elevated atmospheric carbon dioxide is related to growth stimulation in other species of plants also, but the rate of increase in poison ivy is higher than most and will help the plant outcompete others as carbon dioxide levels increase.

Unfortunately, little can be done to stop poison ivy besides avoidance and controlling it on your own property. Learn to recognize the plant, characterized by compound leaves with three leaflets. Poison ivy can be a vine, a shrub or something that looks like a perennial groundcover with single leaves coming out of the ground. Along the Kansas River north of Lawrence, large patches of waist-high poison ivy are easy to find. By mid-to-late summer the leaves often have reddish spots on them that make them easier to recognize.

If you encounter poison ivy, avoid touching any part of the plant or contacting it with tools or clothing. Urushiol, the oil produced by the plant, can be carried on objects and cause a reaction later through indirect contact. Urushiol can also be inhaled if poison ivy plants are burned.

According to the Centers for Disease Control and Prevention, 80 to 90 percent of humans are allergic to urushiol, but allergies can develop for those who think they are immune. Urushiol reactions are characterized by itchy red bumps, patches and weeping blisters.

— Jennifer Smith is a former horticulture extension agent for K-State Research and Extension and horticulturist for Lawrence Parks and Recreation. She is the host of “The Garden Show” and has been a gardener since childhood. Send your gardening questions and feedback to Lawrence Living@ljworld.com.

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Garden Variety: Tougher poison ivy

Poison ivy: how to identify and kill it without damaging other plants

QUESTION: What’s the best way to get rid of poison ivy? I have it in two locations. The first is in low-growing ligustrums that border my yard, and the second is along my backyard fence. — Dave Plank

ANSWER: Anyone cleaning out overgrown areas or weeding should beware. Poison ivy (Toxicodendron radicans) may be growing among the plants. Gardeners often come into contact with poison ivy and many contract a bothersome rash as a result. It pays to be able to identify and avoid it.

The plant has a characteristic compound leaf consisting of three leaflets (Hence the saying, “Leaves of three, let it be”). The leaflets are 2 to 4 inches long and dull or glossy green with pointed tips. The middle leaflet is generally larger than the two laterals.

The margins of the leaflets are variable, appearing irregularly toothed, lobed or smooth. The leaves are arranged alternately on the stems. Young foliage often is shiny or oily looking with a reddish tint.

One way to control poison ivy is to spray the foliage with a systemic herbicide. This is only possible when the spray will not get on the foliage of desirable plants (these herbicides will damage any plant).

This should work well on your back fence. If needed, cover desirable plants with plastic sheets or bags to protect them while you spray. Be sure to wet the poison ivy foliage thoroughly with the herbicide solution.

Glyphosate (Roundup, Eraser, Killzall, and other brands) or triclopyr (Brush-B-Gon, Brush Killer and other brands) are commonly recommended for poison ivy control. Herbicides that contain a combination of dicamba (banvel) and 2,4-D also work well.

The dead leaves can still cause rashes and should be handled cautiously with gloves.

For poison ivy vines growing in trees or intertwined in shrubs, such as in your ligustrum hedge, try this method: Cut off each poison ivy vine a few inches from the ground with loppers or hand pruners and immediately treat the fresh-cut stump with undiluted triclopyr (Green Light Cut Vine and Stump Killer and other brands). The cut vine will die because it has no root system. The treated stump will die because the herbicide gets absorbed and translocates to the roots. This method is effective and may be used any time of the year.

Getting poison ivy off your property will take repeated herbicide applications. Older vines in neighboring yards may continue to drop seeds in your landscape. Watch out for this unwelcome plant and be prompt and aggressive in your efforts to control it.

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Poison ivy: how to identify and kill it without damaging other plants

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