Although they provide contrasting color, size and texture, not all plants that produce large, vivid blooms are desirable in a garden. Certain weeds that belong to the carrot family (Apiaceae) should be avoided because of their toxicity and ability to cause dermatitis. Wild parsnip (Pastinica sativa) and cow parsnip (Heracleum maximum) are among the weedy parsnips that can be found planted in West Virginia gardens.
Wild parsnip is a relative of the cultivated parsnip and can be seen growing in early spring along roadsides, ditches and the perimeter of fields. Wild parsnip is a biennial capable of producing vivid, yellow flowers upon bolting during its second year of growth. They grow in umbels, or flower clusters, that form into a flat or curved surface, and their leaves have saw-toothed edges.
All parts of the plant are toxic to mammals because of secondary metabolites called furocoumarins. Secretions can cause dermatitis upon contact and photodermatitis (rash caused by exposure to sunlight).
Cow parsnip is another biennial plant with succulent stems that produce large white umbels during the second year or subsequent years (it may grow as a short-lived perennial). Cow parsnip is not as toxic as the wild parsnip, but it can also cause rashes upon contact with the plant sap.
Other Weedy Biennials
Giant hogweed (Heracleum mantegazzianum) is a non-native invasive capable of causing severe dermatitis. It is a close relative of weedy parsnip and can sometimes be mistaken for the Angelica plant (Angelica sylvestris). Fortunately, giant hogweed is yet to be documented in West Virginia, although it is present in Ohio and Pennsylvania. Giant hogweed produces larger flowers and leaves with deep lobes (as fingers in a palm) as opposed to the three major lobes found in cow parsnip.
Poison hemlock (Conium maculatum), water hemlock (Cicuta virosa), and wild carrot or Queen Anne’s lace (Daucus carota) are other weeds with varying degrees of toxicity. These weeds, however, are not typically planted in a garden.
Managing Weedy Parsnip
The best time to manage weedy biennials in pastures is during the vegetative stage in the first year’s growth. Mechanical removal works for managing small populations, while herbicides are more effective in controlling larger infestations.
Apply a systemic herbicide when they have sufficient foliage and are actively growing.
Herbicides such as Grazon P+D (picloram + 2,4-D; restricted use pesticide), Weedmaster
(2,4-D + dicamba) or Crossbow (triclopyr+2,4-D) are effective options. Contact
your WVU Extension county agent for questions regarding safe and proper
use of pesticides.