Poison-ivy ( Rhus radicans L.) is widespread throughout southern Ontario and reaches north approximately as far as Cochrane and Kenora. It is found most abundantly, however, south of a line from the north shore of Lake Huron through North Bay. This includes the densely populated portions of the province and the popular vacation areas. The plant is often mistakenly called "poison oak", but the true poison oak occurs only in the southern and Pacific states of the U.S.A. and not in Ontario. Prevalence. Prevalance of poison ivy has doubled since 1960, and its potency is rapidly increasing, making this rash a common complaint in dermatology offices. Several factors contribute to this increase in prevalence: Hauser SC. New York, New York: Lyons & Burford Publishing Co.; 1996. Nature’s Revenge. [ Google Scholar]

Figure 1. Poison ivy leaves have three leaflets. Leaflets have scattered, jagged teeth along the edges and may have a larger tooth or lobe close to the bottom edge of the leaflet, giving it a mitten-like shape. There is often a red spot where the bottom two leaflets join together. Fragrant sumac ( Rhus aromatica) is often mistaken for poison oak, and both grow in similar habitats. One difference is that the leaflets of fragrant sumac are attached at a single point, while the terminal leaflet of poison oak has a short stem. Also, the fruit of the fragrant sumac plant is red (figure 10). TCD places a financial burden on our economy and utilizes substantial healthcare resources. For example, outdoor occupations related to agriculture, forestry, and firefighting are at high risk of exposure to poison ivy, and when affected, these workers incur significant monetary expense for worker disability and medical treatments.TCD is responsible for 10 percent of the total US Forest Services lost work time due to injuries. 17 These herbicides are usually most effective if applied anytime from when the foliage is fully developed until the plants begin to go dormant, usually from about June 15 to July 31. Some regrowth of the weed may occur after it has been treated. Therefore, examine the area periodically and the repeat treatment as often as any regrowth appears. In this manner, poison-ivy can often be eliminated from an area. Caution! Even at this stage take care as poisoning may be brought about by handling the dead plants.The increased atmospheric CO2 level caused by global warming not only promotes the growth of these plants (poison ivy and related plants thrive off of CO 2), but also cause the plants to produce more potent forms of urushiol. The number of these plants is expected to double again when atmospheric CO 2 levels, now at 410ppm, the highest in three million years, reach 560ppm. 3 , 16

Lofgran T, Mahabal G. Treasure Island, FL: StatPearls Publishing; 2020. Toxicodendron toxicity. StatPearls. Last Update: April 19, 2020. https://www.ncbi.nlm.nih.gov/books/NBK557866/ Accessed 17 Sep 2020. [ Google Scholar] For additional information on these and other herbicides, and on the selection, care and use of herbicide application equipment see Ontario Ministry of Agriculture and Food Publication 75, Guide to Weed Control. Harmful Effects Over-the-counter treatments for symptoms of poison ivy include external analgesics, such as benzocaine, pramoxine, and benzyl alcohol; protectants, such as zinc acetate, zinc carbonate, zinc oxide, calamine (a combination of zinc oxide, ferric oxide, mixed with phenol and calcium hydroxide), baking soda, and colloidal oatmeal; aluminum acetate (an astringent); hydrocortisone; Burow solution (an aqueous solution of aluminium triacetate); and oral diphenhydramine. 1 , 9 It is not advised to apply topical antihistamines (e.g., topical diphenhydramine) to the rash due to its potential to worsen the symptoms. 7 Unfortunately, while many of these OTC treatments might assist in drying out the weeping, oozing blisters associated with poison ivy, they often do not provide sufficient relief, especially in severe cases. 1 , 9 , 13 Many plants have been mistaken for poison-ivy because their leaves may also consist of 3 leaflets. These can be distinguished from poison-ivy as follows.Curtisa G, Lewis AC. Treatment of severe poison ivy: a randomized, controlled trial of long- versus short-course oral prednisone. J Clin Med Res. 2014; 6(6):429–434. [ PMC free article] [ PubMed] [ Google Scholar] While there is no entirely satisfactory treatment for TCD other than the “tincture of time,” longer-course glucocorticoid therapy, such as triamcinolone or prednisone, has been shown to be effective in relieving symptoms associated with TCD. 8 Short courses of low-dose methylprednisolone (so-called “dose paks”) are too brief and too weak to offer effective relief. Glucocorticoids should be administered using a 2- to 3-week taper starting with 60mg daily (preferably taken in the morning with food to avoid gastritis) for five days that is reduced to 40mg daily for five days and then down to 20mg daily for five days. 9 , 8 Contraindications for glucocorticoids include concurrent infection, peptic ulcer disease, poorly controlled hypertension, congestive heart failure, and diabetes. 9 Dementia can also be made worse with systemic steroids (so-called “steroid psychosis”). 9 Less serious side effects of systemic glucocorticoids include an increase in appetite, retention of fluid (edema), irritability, and insomnia. Adrenal suppression associated with prolonged systemic steroid use is rarely a problem when using a 2- to 3-week course of glucocorticoid therapy for poison ivy. 9 Nancy Loewenstein, Extension Specialist, School of Forestry and Wildlife Sciences, Auburn University; Amber C. Dunn, former 4-H Regional Extension Agent; and Mark D. Smith, Professor, School of Forestry and Wildlife Sciences, Auburn University. These herbicides can be bought in various concentrations and under many different trade or brand names. Therefore, it is not feasible in this Factsheet to give detailed instructions for mixing and application of each kind. Detailed directions for its use are printed on the label on every container of each herbicide. Follow the manufacturer's directions. For safety's sake, read the label carefully and observe all precautions printed on it. Gladman AC. Toxicodendron dermatitis: poison ivy, oak, and sumac. Wilderness Environ Med. 2006; 17(2):120–128. Accessed September 4, 2020. [ PubMed] [ Google Scholar]

Poison-ivy is a woody perennial. It may grow as dwarf, shrubby plants only a few centimetres high and carpeting the ground ( Figure 1), or as upright plants 60-90 cm (2-3 ft) high, or the vine-like form may twine around trees, shrubs and posts, and reach a considerable distance above the ground. These vines often develop root-like structures which act as attachments, but apparently do not damage the living plants to which they cling. History. Poison ivy is neither poisonous nor a true member of the Ivy family (Hedera). Instead, it is a member of the Anacardiaceae family, which also includes pistachios, cashews, and mangoes. All members of the Anacardiaceae family contain various forms of pentadecylcatechols within their sap, which is collectively termed urushiol, an oleoresin released from the injured leaves, stems, vines, or berries of these plants. 7 The leaves of poison ivy (figure 1) and poison oak (figure 2) have three leaflets. This is where the adage leaves of three, let it be comes from. The leaflets are commonly 2 to 8 inches long and 3⁄4 to 5 inches wide, and they have scattered, jagged teeth along the edges. Some have a larger tooth or lobe close to the bottom edge, giving them a mitten-like shape.

Poison Ivy and Poison Oak

Approximately 10 to 15 percent of people will have reactions severe enough to require medical treatment, often in the form of oral or injected low-dose steroids administered by a doctor. Seek medical help if the rash becomes infected, covers a large part of the body, causes swelling of the face or other sensitive areas, or causes difficulty with swallowing or breathing. Virginia creeper often has 5 or 7 leaflets in other leaves on the same plant and its berries are bluish. Figure 7. Virginia creeper vines are generally less “hairy” than poison ivy vines. There are some short rootlets. Note the clasping rootlets that have what look like small suction cups at the tips. In spring and early summer the young unfolding leaflets are reddish or bronzy green ( Figure 1, left side, below center) and droop or hang limply from the ends of their upraised petioles. Figure 11. Smooth sumac leaves have eleven to thirty-one leaflets. Note that the leaflets have teeth along the edges.