A field reference for outdoor crews covering the five plants most likely to put a Canadian worker in hospital. Identification features, what each one actually does to skin, and the immediate response that changes the outcome — plus a pre-season briefing record for your hazard assessment.
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| Mechanism | What happens | Why the response differs |
|---|---|---|
| Phototoxic (sap + sunlight) | Sap chemicals react with UV light and burn the skin. Not an allergy — anyone exposed reacts. | Getting out of sunlight matters as much as washing. Cover the skin immediately. |
| Allergic contact dermatitis | An oil triggers an immune reaction. Severity varies between people and builds with exposure. | Wash off the oil fast, and decontaminate clothing and tools that carry it. |
| Mechanical | Physical needles or spines inject irritants on contact. | Usually short-lived. Matters most because a startled worker may fall or drop a tool. |
| Feature | What to look for |
|---|---|
| Height | Up to five metres — far taller than anything around it. |
| Stem | Hollow, thick, with coarse bristles and purple blotches. |
| Flowers | Large white clusters, umbrella-shaped, can reach 80 cm across. |
| Where | Roadsides, waterways, disturbed land. Documented in Ontario, BC, Quebec and the Atlantic provinces. |
| Harm | Phototoxic. Sap on the skin followed by sunlight causes severe burns. Symptoms occur within 48 hours and consist of painful blisters. Purplish scars can last for many years. Eye contact with the sap has been reported to cause temporary or permanent blindness, although Ontario notes that permanent blindness cannot be substantiated by existing research. |
| Feature | What to look for |
|---|---|
| Height | Smaller than giant hogweed, typically waist to chest height. |
| Flowers | Flat-topped yellow clusters — the quickest way to tell it from hogweed. |
| Stem | Hollow, grooved, green. |
| Where | Roadside ditches and unmaintained right-of-ways. Reported in all provinces and territories except Nunavut, and abundant along Ontario’s 400-series corridors and rural right-of-ways. |
| Harm | Same phototoxic mechanism as giant hogweed. Responsible for more documented workplace injuries in eastern Canada simply because it is far more common. Mowing an infested area without PPE has produced burns across an entire crew. |
| Feature | What to look for |
|---|---|
| Leaves | Three leaflets on each stalk. Glossy in spring, red in autumn. |
| Form | Ground cover, shrub or climbing vine. |
| Where | Fence lines, disturbed soil, forest margins. Every province except Newfoundland and Labrador. |
| Harm | Urushiol oil causes allergic contact dermatitis. Present in every part of the plant year-round, including dead vines in winter. Most people develop symptoms 24 to 48 hours after contact, and the rash spreads via contaminated clothing, gloves and tools. |
| Plant | Identification | Harm |
|---|---|---|
| Stinging nettle | Toothed leaves with fine hairs on leaves and stems. Moist, disturbed ground across the country. | Hollow silica needles inject formic acid and histamine. Immediate pain, generally short-lived. Main risk is a startled worker falling or dropping a tool. |
| Cow parsnip | Native, smaller than giant hogweed, white flower clusters. Common in BC and Alberta. | Same phototoxic mechanism, less potent. Treat as hogweed until identified with confidence. |
| Requirement | What good looks like | Y / N / N-A | Evidence or gap |
|---|---|---|---|
| Plants in the hazard assessment | Noxious plants named as a hazard for the areas your crews work. | ||
| Pre-season crew briefing | Delivered before the growing season, with identification photos. | ||
| PPE specified | Impermeable gloves, long sleeves, eye protection for mowing or brushing infested areas. | ||
| Wash facilities available | Soap and water accessible on site or in vehicles. | ||
| Known infestations mapped | Locations recorded and flagged for crews before they arrive. | ||
| Mowing controls | Procedure for mowing or trimming infested ground, including downwind and spray considerations. |
| Location | Plant | Identified by | Date |
|---|---|---|---|
| Name (print) | Signature | Date |
|---|---|---|
Our consultants (CRSP Certified · COR & ISO 45001 Lead Auditors) can adapt this to your workplace or review your safety program with you.
Sources: ontario.ca, Giant Hogweed; ontario.ca, Wild Parsnip; canada.ca, Health Canada, Poison Ivy.
Identification guidance only. When in doubt, do not touch the plant. Seek medical attention for any suspected exposure, and confirm control obligations against the weed control legislation in your province.