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Learn to recognize poison ivy

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Poison ivy (Toxicodendron radicans)
Photo: Jardin botanique de Montréal (Roméo Meloche)  

The best way to protect yourself from poison ivy is to be able to identify it properly, so that you can avoid it!

Description and habitat

The scientific name for poison ivy is Toxicodendron radicans, but it is still sometimes referred to by its older name, Rhus radicans.

Poison ivy is tricky! It grows in many forms: shrubby, low-growing and ground-covering, or climbing. It is a woody perennial that forms dense colonies along the borders of woods, in fallow fields, along roadsides and near water. It spreads by means of seeds and underground stems (rhizomes).

It has shiny, alternate leaves, each made up of three leaflets. The stalk of the central leaflet is much longer than the stalks of the two side leaflets. Their margins may be smooth or toothed and they have very prominent veins. The leaves are reddish when they emerge in spring and change to dark green in summer. In fall, they turn yellow, red or orange. They vary greatly in size.

In June and July, poison ivy produces clusters of small whitish to greenish flowers, often hidden by the leaves. In September, waxy, round berries, about the size of a dried pea, appear. They turn from green to yellowish-white. The fruit clusters may remain on the bare plants all winter long.

Contamination and symptoms

Poison ivy sap contains urushiol, an allergen that causes a painful skin rash (allergic contact dermatitis) in about 85% of people. Urushiol is present in all parts of the plant, except the pollen. The offending substance is released when the plant is damaged. Since urushiol is oily and non-volatile, it can easily stick to tools, clothing and pet fur. It can also remain toxic for a very long time.

Since urushiol provokes an allergic reaction, people aren’t affected the first time they come into contact with it. Most people become sensitized at that point, however, and may develop dermatitis the next time they are exposed to it.

In sensitized individuals, symptoms usually appear within 24 to 48 hours of coming into contact with the plant or a contaminated object or pet. The severity of the reaction depends on the individual’s sensitivity, the amount of sap that comes into contact with the person’s skin and the parts of the body exposed to it.

The first sign is intense itching and redness. There may also be swelling and blistering. The blisters may burst, ooze and form scabs. Contact with oozing sores cannot spread the dermatitis.

In most cases, the symptoms disappear within 7 to 10 days. Recovery from severe reactions may take 3 weeks or more, however.

Cross reactivity

People who are sensitive to poison ivy may develop a similar dermatitis reaction to related plants or some of their products, including mango rind, Japanese lacquer, India ink markers, the oil from cashew nut shells, and the fruit pulp of ginkgo trees.

Treatment

  • Wash all exposed regions as soon as possible – including under the nails – with cold water. Soap dislodges the sap more effectively, but it also temporarily removes the natural protective layer that prevents urushiol from penetrating the skin.
  • Wash all contaminated clothing and objects several times in hot, soapy water. Wear heavy-duty rubber gloves when handling all such objects. Pets should also be bathed with soap and water.
  • To alleviate the itching, apply cool water compresses or compresses soaked in a baking soda solution. Oatmeal baths may also be soothing. Some over-the-counter drugs may also offer relief. Consult a pharmacist.
  • If the symptoms are severe or extensive, or if there is fever, consult a doctor.

Eradication

To get rid of poison ivy, you have to be as tenacious as it is!

  • Dig up the plant, remove all visible rhizomes and turn the soil over frequently to prevent it from propagating. It is important to wear suitable protection when doing this work and to thoroughly wash all clothing and tools used afterward.
  • You can also smother poison ivy with old carpeting, thick black plastic or other long-lasting material for at least one year. Be sure to cover the soil at least 2 metres around the plant.
  • As a last resort, use a low-impact herbiicide with sodium chloride as the active ingredient.  
  • Dispose of all the plant material in a properly labelled garbage bag or bury it deeply in the soil. Never compost or burn it. Inhaling the smoke from the burning plant material can cause a severe pulmonary reaction.

See for yourself! Come take a look at the poison ivy growing in the Toxic Plants Garden at the Botanical Garden. That way, you will be able to recognize it the next time you spot it in the wild!

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