Garden Blitz

If it seems that poison ivy is getting more vigorous every year, it’s not just your imagination. It’s a scientific fact that poison ivy is thriving on the increasing levels of carbon dioxide in our air.

Lewis Ziska, a plant physiologist at the U.S. Department of Agriculture, published a study in 2007 documenting this phenomenon. Local conservation ecologist Gigi La Budde reminded me of that study recently when we were joined by fellow dog-owner Sue Clearfield. We were digging spotted knapweed, a non-native, invasive species out of the Spring Green Dog Park. As we dug, we also pondered the crop of poison ivy growing in a nearby treeline.

Although all plants use carbon dioxide to grow, some are especially efficient at it. CO2 might as well be steroids when it comes to poison ivy. Thanks to climate change, poison ivy is producing more leaves and stronger, farther-reaching vines than ever before.

What’s more, poison ivy is becoming more potent. The plants respond to increased carbon dioxide levels by producing higher concentrations of urushiol. That’s the toxic oil that causes the rash that makes you want to scratch your skin right off.

As if that’s not bad enough, poison ivy was once largely limited to woodlands. Now, however, it’s escaping to urban areas where CO2 levels can be as much as 30 percent higher by some estimates. Poison ivy is now growing in parks and school yards, along fences, up the sides of buildings and even in concrete rubble.

Gigi says that, in fairness, I must point out that poison ivy isn’t all bad. More than 60 species of birds think the fruits of poison ivy are a delicious and important food source. Duly noted. Still, for those of us who are sensitive to poison ivy — and that’s most of us — it’s not welcome news that climate change is a boon to this plant.

At this time of year, poison ivy takes on a brilliant red fall color. That makes it easier to spot and target for removal. If you decide to eradicate it, be sure to do so carefully.

The best approach is to use an herbicide specially formulated for poison ivy. I use Roundup Poison Ivy Plus. Spray the leaves thoroughly on a day when there’s no wind, no rain in the forecast and the temperature is between 60 and 80 degrees. Remember that the herbicide will kill any plant material it touches, so spray carefully. It won’t do you any good, either, so be sure to wear gloves, cover up and consider wearing protective eye covering.

Whatever you do, don’t burn poison ivy. Urushiol will become airborne. The smoke can carry enough oil to give you a rash. If you inhale it, you can be in serious trouble.

Even when the vines are leafless in winter, urushiol is still active. Tearing the vines down with your bare hands can result in an itchy, blistery, miserable mess.

Don’t believe in climate change? Poison ivy doesn’t care. It’s sucking up CO2 and getting ready to take over the world. This obnoxious plant is gearing up to get the last laugh. There’s no blitz in that.

Patrice Peltier lives in Spring Green and writes regularly for Wisconsin Gardening, Chicagoland Gardening and The Landscape Contractor magazines. Her work has appeared in Better Homes and Gardens and Midwest Living magazines.