Friday, April 1, 2011

Itchy, Irritating Ivy!

The Environmental Protection Agency, the EPA, defines an invasive species as a plant whose "introduction does or is likely to cause economic or environmental harm or harm to human health." In biology classes we often think first of invasive species as introduced, super competitors that are out competing native species and essentially removing them from our ecosystems. While this is true there are also plants, as defined by the EPA, that cause harm to human health and are therefore invasive species. The first plant that comes to my mind is poison ivy, Toxicodendron radicans. Deer can graze on this plant and many birds feast on its berries in the fall, but humans can get a nasty, itchy, oozing rash caused by an allergic reaction with the oil, called uruishol, located in its leaves and stems. Many people can also have this reaction in their respiratory systems after burning poison ivy and creating smoke that carries the oil which is breathed in. Another negative to this plant that results in more interactions with humans is that it prefers to establish itself in areas that have been disturbed which also happen to be recreation areas such as trials, parks, and yards.

How can you tell if you are looking at poison ivy? Remember the old nursery rhyme that I'm sure you have heard before: "Leaves of three, let it be!" However, it is often difficult to determine whether or not you are looking at poison ivy due to the fact that many plants have compound leaves of three. The center leaf of the compound structure is often symmetrical and has toothed edges on either side. Leaves that flank this center leaf are often shaped like a mitten with the "thumb" side of the leaf toothed. While this is common of many poison ivy plants that I have seen, these characteristics are not indicative of ALL plants! Poison ivy can be found growing up the trunks of trees in hairy vines, growing on the ground, or growing in shrub form. When flowering, poison ivy has blooms of up to 25 off-white flowers which produce yellowish-white berries in the fall. These berry supplies make many species of birds very happy! Poison Ivy is distributed widely throughout the eastern part of the United States.

Methods of control are important with this plant as allergic reactions can become serious if large portions of the body are covered in the rash, if the rash becomes infected, or if the rash is located on delicate respiratory tissues. Please wear gloves and cover any exposed skin before trying ANY of these control techniques! The cheapest way to control poison ivy is to remove the entire root of the plant from the ground by uprooting it. If this process is done in the late fall after the leaves have fallen, you are less likely to encounter the harmful oils. After pulling the plant, allow it to dry out before bagging it and throwing the plants AND your gloves in the trash. Do not ever compost these plants as resprouting can occur and never burn the plants as harmful smoke can be produced. Herbicides, while the are more expensive than the other method, can also be used. Glyphosphate or 2,4-D are the most effective herbicides for the job.

There are many myths in the rumor mill about poison ivy. Some people claim to be immune to the oils. While this can be true for a snapshot of their life, immunity can change. As a particular person who is immune to the poison ivy oils ages, they can become less and less immune. Eventually, that particular individual will have an allergic reaction to the oils. The oil will also stay potent forever. So, if you think a piece of clothing you wore came in contact with the urushiol oil, wash it in cold water or just throw it away! Finally, if you are exposed to the oil, wash the area with cool water and never take a hot shower directly after contact. A hot shower will only open your pores and spread the oil and rash even more quickly. If you ever have a rash from a poison ivy reaction that persists more than 3 weeks or covers wide areas of your body including your face, please go see a doctor!


  1. Interesting and very informational! I actually have never heard of the "Leaves of three, let it be," but now I will know for the future. :) I have always been confused between the 3-leaved plant and the 5-leaved plant, so I just avoided both. That was also interesting that immunity can change. I have a friend who can roll around in the stuff and not feel any effects. Some day his luck may change.

  2. I am not sure whether I would call poison ivy invasive in terms of disrupting native ecosystems, but it does fare well in disturbed areas and definitely affects people. An article I read a while back stated that many vines will do well with climate change, and poison ivy seems like a good candidate to be one of them!

    Yes, immunity can change. I know one person who used to pick poison oak (a close cousin) to show to botany students, but who ended up in the hospital one year with a severe case!