Weed du Jour – Poison Ivy

Whenever I go out into fields or a wooded area, I’m always keeping an eye out for leaves with three leaflets. I don’t want to have any encounter with poison ivy.


Poison Ivy in a Bed of English Ivy

Poison ivy (Rhus radicans) is a member of the Cashew family that’s native to North America. This perennial can grow as a vine along the ground, it can climb trees, shrubs and posts, reaching up to 100′ in the air and in full sun, it can take on a shrub-like characteristic. The most well know feature of this plant is that every leaf is made up of three leaflets, each about half as wide as they are long. These leaflets always have pointed tips but the edges may be wavy, smooth or with lobes. In addition the leaves grow from the stem in an alternating pattern. (This helps to distinguish poison ivy from the non-toxic box elder which has similar leaves with three leaflets but the leaves are in opposite pairs along the stem). Poison ivy is a dioecious plant, meaning that there are male plants and female plants. The male plant produces pollen which is spread by insects to the female flowers which produce berries.

Poison ivy is spread by birds that eat the berries and spread the seeds in their droppings. It also spreads by developing roots along its stem wherever it touches the soil.

Sometimes people confuse this weed with other “poison” plants, specifically poison oak and poison sumac. Here in Pennsylvania there is no poison oak – this plant grows to the south and west of the state. Poison sumac only grows in marshy areas so in most of the forests and fields of  PA, the only “poison” you’ll find is poison ivy.

What makes this weed so toxic is an oil that it produces called urushiol. The only parts of poison ivy plant that don’t have urushiol is the pollen and the inner wood of older stems. It isn’t only the leaves of poison ivy that can give you a rash; urushiol is also present in the stems, roots and sap of the plant. When urushiol makes contact with the skin, it binds to the outer layer and causes a rash in many people. It’s often said that washing after contact with poison ivy will prevent a rash from forming. Unfortunately, the urushiol binds almost immediately to the skin so washing quickly and very vigorously might limit the poison but is unlikely to remove all of it.

This oil is non-volatile but very stable. Because it’s non-volatile, the good news is that you can’t get poison ivy by being close to a plant; you have to touch it or come into direct contact with the urushiol. But since it’s so stable, the oil can be carried and remain active on garden tools, clothing and the fur of dogs and cats. Also it’s stability make burning poison ivy something that is warned against in every publication that I read. If you burn any part of a poison ivy plant, the urushiol becomes airborne and can settle on your skin and eyes and can even get into your lungs – yikes!

I was also shocked to see that one old wives’/woodsman’s tale is that to become immune to poison ivy you should eat a leaf of it. This won’t protect you from poison ivy but will pretty much guarantee a trip to either the ER or the morgue!

Since the reaction to the urushiol in poison ivy is an allergic reaction, just because you’ve never had it before doesn’t mean that your immune. Each exposure to poison ivy produces antibodies in the body so you can start getting poison ivy at any age after any number of exposures.

Fortunately poison ivy doesn’t generally grow in cultivated areas but it can be a problem in woodlots and undisturbed areas. If you have poison ivy growing on your property, getting rid of it is a difficult process. If you pull the plants – being sure to protect yourself from contact – any small pieces of root left in the soil will sprout and grow new plants. It’s said that mowing can control it but I wouldn’t touch poison ivy with a mower – think of the toxic clippings that would come flying out of it! There are herbicides that can control this weed but you have to remember that even if the plant is dead, the urushiol is still present in the dead tissue. If you have a poison ivy problem, I’d contact your local extension office to see what they’d recommend.

I think you can tell I really don’t like this weed. But the truth of the matter is that poison ivy does have some uses. It’s great for erosion control and the Dutch have actually planted it for this purpose. Some native Americans used it medicinally. Also a lot of animals eat poison ivy and others use it for protective cover. You see, we’re the only animal that’s affected by this weed!

After many encounters with poison ivy in my teens and twenties, I’ve gained a healthy respect for this weed. I’ve also developed a sixth sense that’s able to spot this weed before I come in contact with it. I’ve made that old adage my motto – leaves of three, let them be!


2 responses to “Weed du Jour – Poison Ivy

  1. Do we or do we not have poison ivy in Germanny. I’s swear it is.

    • You might! While poison ivy is native to North America, some sites report that people took it to the UK, Europe and Australia because of it’s fall foliage. As a result, there could be some growing in Germany. If there’s any doubt, leaves of three, let them be!

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