At this time of year, Credit Valley Conservation (CVC) receives many calls about possible giant hogweed sightings. The majority of these sightings turn out to be cow parsnip, a native relative of the noxious weed.

Cow parsnip and its invasive cousin, giant hogweed, are both members of the carrot family and are commonly mistaken for each other. Cow parsnip flowers from June to August whereas giant hogweed flowers from July to August. Both species have similar looking leaves and stalks, produce white flowers and prefer moist sites. However, several distinct characteristics can be used to help tell them apart.

Cow parsnip usually flowers a full month before giant hogweed. In the Credit River Watershed, cow parsnip is flowering in such places as Rattray Marsh and Meadowvale Conservation Areas. Giant hogweed is not flowering so far. Giant hogweed flowers are umbrella shaped and can grow to be 1.5 m in diameter. Cow parsnip flowers are much smaller and can grow to be 30 cm in diameter. Both species produce white flowers.

Full grown, giant hogweed can grow up to 4.5 m tall while cow parsnip can grow up to 2.5 m tall. Both are extremely large herbaceous species. Giant hogweed has large shiny leaves with deep, serrated edges, which can grow to be 1.5m in length. Cow parsnip leaves are less serrated and duller looking (not shiny).  For more information, please click here.

Just a reminder, never remove giant hogweed yourself.  The sap contains toxins that cause severe burns and blistering if the contacted area is exposed to sunlight. Call CVC at 1-800-668-5557 or 905-670-1615 for help.

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