|Poison Ivy (Toxicodendron radicans) – "leaves of three, let it be."|
One study suggests that poison ivy might get itchier and more plentiful in our changing atmosphere. Here's what to watch out for.
Poison ivy has a compound leaf with three leaflets, the centre one having a long stalk. This is key. Note that in all the images here.
Beyond that, plant characteristics can be quite variable, which can make it hard to spot. For example, the leaf margins or edges can be smooth, such as the biggest leaf in the photo above, or toothed, such as some of the smaller leaves behind it. The plant can grow as a low groundcover, just at about itchy ankle height, but can also grow with an upright, shrublike habit and can even climb trees as a vine. Walter Muma's Ontario Wildflowers website has an excellent set of illustrative images and info.
His Ontario Trees & Shrubs site offers equally good info on Poison Sumac (Toxicodendron vernix) as well as Poison Ivy's non-toxic lookalike cousin Fragrant Sumac (Rhus aromatica), a native shrub with excellent red fall colour. In fact, Toronto has extensive plantings of fragrant sumac bushes along the eastern Lakeshore Avenue and Leslie Street sections of the Martin Goodman Trail.
Not everyone is susceptible to the allergens in poison ivy. As many as 3 in 10 are unaffected. If you find yourself with the characteristic wavy-lined rash that seems to grow, then you might have come into contact. Here's Health Canada's advice about what to do.
If you find it on your property, you can control it with pesticides such as Round-Up (never burn poison ivy!) – one of the few cases when homeowners can use pesticides under Ontario's Pesticide Ban. (Here is David Suzuki's plain-language summary of the Pesticide Ban.)
|As a ground-hugger, Poison Ivy likes to grow at the edges of paths. Keep your eyes open for those stray plantlets.|
|Often, the leaflets droop downward and seem almost folded at the centre. New leaves contain the strongest irritants.|
|Stressed or autumn leaves show their cousin-ship to the sumac family by turning a bright red.|
[UPDATE:] If you'd like to hear further tips on Poison Ivy, and hear a delightful Alabaman accent, listen to this short podcast from Backyard Wisdom. A few details don't apply; for example, poison oak isn't found in our Northern climes. However, tips on how to deal with exposure are quite useful.