Poison Ivy Growing Faster, More Virulent

Lewis Ziska, plant physiologist for the U.S. Department of Agriculture's agricultural research service, says rising carbon dioxide levels and forest disruption are making poison ivy spread faster, grow larger, show up in new places and become more toxic. He tells host Michele Norris what makes the plant uniquely affected and how to treat skin that's been exposed.

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ROBERT SIEGEL, host:

From NPR News, this is ALL THINGS CONSIDERED. I'm Robert Siegel.

MICHELE NORRIS, host:

And I'm Michele Norris.

We've long known that poison ivy is nasty stuff. Even if you barely brush up against it, you can get an angry, weeping, contagious, red rash that takes weeks to heal. Well, it turns out that poison ivy, along with its voracious cousins poison oak and poison sumac, is even more of a nuisance this summer. The plants are spreading faster, growing larger, showing up in new places and becoming more toxic. It's the kind of thing that's so scary, it almost deserves its own soundtrack.

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NORRIS: At the very least, it deserves more examination. And to find out why the poison plants are even more of a threat this year, we turn to Dr. Lewis Ziska. He's the plant physiologist for the U.S. Department of Agriculture's Agricultural Research Service. Welcome to the program.

Dr. LEWIS ZISKA (Plant Physiologist, Agricultural Research Service, U.S. Department of Agriculture): Thank you.

NORRIS: Why is the plant spreading more and becoming more voracious? Why is it growing larger?

Dr. ZISKA: One of the things that we think is occurring is that as carbon dioxide is increasing in the atmosphere - carbon dioxide, as everyone knows, is a basic greenhouse gas, but it's also plant food. And plants take that carbon, and they convert it into sugars and carbohydrates and so forth.

But not all plants respond the same way to that resource, and we think that vines, particularly vines like poison ivy or kudzu or other noxious weeds, seem to show a much stronger response to the change in CO2 than other plant species. So on average, the poison ivy plant of, say, 1901, can grow up to 50 to 60 percent larger as of 2010 just from the change in CO2 alone, all other things being equal.

And as a result of that change, we see not only more growth but also a more virulent form of the oil within poison ivy. The oil is called urushiol, and it's that oil that causes that causes that rash to occur on your skin when you come into contact with it.

NORRIS: Is this happening all over the country or is it a bigger problem in some parts than others?

Dr. ZISKA: We tend to see it more in areas where forests have been disrupted. If you go to sort of an old-growth forest that is intact and it's very shaded, you tend not to see much poison ivy there because there's a certain light requirement in addition to the carbon dioxide. But as forests become fragmented as a result of land use change, then that in addition to the carbon dioxide change is causing a faster, more rapid growth of poison ivy.

Some of the work that was done at Duke University showed that of all of the different species, when you gave them CO2, in the forest understory, poison ivy was the number one responder.

NORRIS: Now, it's always been said that about 15 percent of the population is not affected or not vulnerable to poison ivy. They don't see to show up in this rash. Because the plant is producing more oil, does that mean that more people are vulnerable to exposure?

Dr. ZISKA: What we see is that as the toxicity of the oil goes up, then yes, it means that more people would be more vulnerable to getting a rash. But also as the plant grows more and spreads more, then the chances of coming into contact with it also increase, as well.

NORRIS: What do you do if you do come in contact with poison ivy? What's the best way to treat it and to keep it from spreading to other parts of your body and to other family members?

Dr. ZISKA: The best thing you can do is to wash with soap and water as fast as you can. After about eight to 10 minutes, the poison ivy, the urushiol, has actually been absorbed into your skin and there isn't anything you can do.

So if you do come into contact with it and you have access to a place where you can wash, wash as quickly as you can. Once it's absorbed into your system, there really isn't much you can do, other than to put the chamomile and other things on that will relieve some of the itching.

NORRIS: Lewis Ziska, thanks for coming in.

Dr. ZISKA: You're welcome.

NORRIS: Lewis Ziska is plant physiologist for the U.S. Department of Agriculture's Agricultural Research Service.

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