Poison Ivy - Manitoba
(Toxicodendron rydbergii (Small ex Rydb.) Greene)

Poison-Ivy is very common across much of southern Manitoba. It is quite variable in size, colour, and leaf shape. It is a short woody stemed plant with with few or no branches typically standing less than 30cm. The leaves, 3-12cm+ in length, are borne near the top of the stem, have long petiols and are divided into three parts. Leaf margins may be lobbed, dentate, or entire. The flowers are tiny white/yellow and grouped in axillary panicles. Berries are clustered off-white (ivory) and usually remain on the stem after the leaves have fallen. In general remember: "Leaves of three, let it be; berries white, danger in sight."

The name comes from: Toxicodendron, from the Latin toxicum, "poison", and the Greek dendron, "tree"; hence "poison tree" rydbergii, from the Latin, "Rydberg's"; named after Per Axel Rydberg (1850-1931), an expert on Western flora. Common names include: Western Poison Ivy, Ryberg's Poison Ivy, Non-Climbing Poison Ivy

Poison-Ivy is common in open woodlands with a moderate amount of sunlight dominated by Bur Oak (Quercus macrocarpa), Green Ash (Fraxinus pennsylvanica), Green Ash/American Elm (Ulmus americana), Bur Oak/Green Ash, or Quaking Aspen (Populus tremuloides). Generally it is found along the edges of open or disturbed areas. It grows in a wide range of moisture and soil conditions from dry gravel ridges (where it is relatively small) to rich mesic lowlands with periodic flooding (where the plants reach their largest size).

Poison-Ivy Dermatitis is a delayed hypersensitivity, allergic reaction, caused by contact with the oil urushiol which is released when the plant is damaged (even slightly). Sensitivity to the oil increases with additional exposure - if you have never had the rash count yourself lucky but watch out since you might still get it. Approximately 85 percent of the population will develop an allergic reaction. The rash can appear within a few hours (typical 12-48hrs) or as much as 10 or more days after contact and last as long as 3-4 weeks. Apparently only humans react to poison ivy.

The oil can last a significant period of time on other objects such as garden tools, pet fur, sports equipment, fishing/hunting gear, and clothing. Even handling dried plant material, leaves, roots, etc... can still cause a rash. Smoke from fires with poison-ivy can also cause a reaction in many people. Oozing liquid from rashes does not spread the rash. New rashes are often caused by contacting items that had not been cleaned after the initial exposure. A friend of mine repeatedly suffered from the rash because he had gotten the oil on the steering wheel of his car after working in the field. Every time he drove the car he spread more oil around until he realized what was happening and washed the inside of his car.

The best way to avoid the rash is to recognize the plant and avoid it. If you do contact or damage the plant then wash with soap and lots of water as soon as possible (within 10 minutes) to remove the oils. Some sources say that washing with lots water is enough and that using soap may spread the oil; swimming or wading in a fast moving stream works well. There are a number of barrier creams made specifically for protection from poison ivy. The effectivness of the creams is quite variable (59%-9% protection) so do some homework before you buy. The American Academy of Dermatology suggests using creams that contain bentoquatam. If you are in an area where you are likely to contact the plants wear long sleeves and pants - remember to wash your clothes. Wet clothing (including sweat soaked) does not make a good barrier.

The rash will usually go away on its own, but it can be uncomfortable. Using a wet cold compresses can soothe the rash. Use of calamine lotion solution helps dry it out. Oral antihistamines can also be helpful in controlling itchiness. If the rash is severe or on your face or other sensitive areas of your body then you should see a physician. Medications, such as antihistamines and corticosteroids may be prescribed. There are a number of treatments on the market - unfortunately I can't recomend any since I have not used (or even seen) most of them but there may be some useful information from the links or articles below.

The berries of Poison-Ivy are a white or cream colour and can stay on the short stems from late summer through the fall and winter.



Plants often confused with PI

There are a number of plants that are often confused with poison ivy. Here are a few common examples. All of these plants often grow with or near poison ivy as well - if you see one you often will see the other.


 

Manitoba Maple Saplings have three leaflets and are on a woody stem.


Bur oak saplings have a woody stem and irregular shaped leaves, but there is only one leaflet.


Wild Sarsaparilla is commonly confused with poison ivy. Look for more than one leaflet, the leaves are not shiny, and the stem is not woody.


Strawberries are nice to eat and grow close to the ground. They do have three leaflets but the surface is not shiny, and may have a hairy appearance.

but be careful because sometimes they grow together with PI.


Virginia creeper has shiny leaves but is usually darker green, in Manitoba it is a vine, and usually has more than three leaflets.


Hog peanut also has three leaflets but it does not have a woody stem and is generally smaller.


Other species that might be mistaken include: Boston or Japanese ivy, Fragrant sumac, skunkbush sumac, raspberries, English ivy, Ash seedlings.


Reference Information:

Some websites with information on poison ivy:

If you like journal articles here is a small sample. The paper by Gladman (2006) is a good review.

Allen, P.L. Leaves of three, let them be: if it were only that easy! Pediatric nursing Volume 30, Issue 2, March 2004, Pages 129-135 PubMed ID: 15185735
Boelman, D.J. Emergency: Treating poison ivy, oak, and sumac. American Journal of Nursing Volume 110(6), June 2010, pp 49-52 PubMed ID: 20505463
Garner, L.A. Poison ivy, oak, and sumac dermatitis: Identification, treatment, and prevention. Physician and Sportsmedicine Volume 27, Issue 5, May 1999, Pages 33-43
Gladman, Aaron C. Toxicodendron Dermatitis: Poison Ivy, Oak, and Sumac. Wilderness and Environmental Medicine Volume 17, Issue 2, 2006, Pages 120-128. PubMed ID: 16805148
Guin, J.D. Treatment of toxicodendron dermatitis (poison ivy and poison oak). Skin therapy letter Volume 6, Issue 7, April 2001, Pages 3-5 PubMed ID: 11376396
McGovern, T.W., Steven R. LaWarre, and Chad Brunette. Is it, or isn't it? Poison ivy look-a-likes. American Journal of Contact Dermatitis Volume 11, Issue 2, 2000, Pages 104-110 PubMed ID: 10908180
Tanner, T.L. Rhus (toxicodendron) dermatitis. Primary Care - Clinics in Office Practice Volume 27, Issue 2, 2000, Pages 493-502 PubMed ID: 10815057


Synonyms:

Just to cause more confusion Western Poison-Ivy (Toxicodendron rydbergii) has been found to hybridize with eastern poison ivy (Toxicodendron radicans (L.) Kuntze) - the kind that climbs. Eastern poison ivy has not been found in Manitoba; it has been found in some parts of Minnesota and southern Ontario.


Poison Oak:

Poison Oak does not grow in Manitoba. (yes that is a period, end of discussion, don't bring it up again - On the other hand all of the species look similar, contain the same oil, and cause the same rash - does it matter that much?)


Finally just for fun:

Geocaching: This write-up was created as part of a geocache called PI in the Woods (GC15J8G) on geocaching.com. At the cache itself there is a brief information sheet about poison ivy


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If you have any questions or comments please send me email at: burc...@cc.umanitoba.ca


Last modified: Sat Nov 6 17:38:11 2010