Cow parsnip (Heracleum maximum), also commonly called cow parsley, is a native, herbaceous, biennial to short-lived perennial weed of woodlands, grasslands, pastures, riparian (streambank) areas, and roadsides. although it grows best in moist soils. It is more common in northern regions of New York State.
Cow parsnip. Photo by Peter M. Dziuk, via Minnesota Wildflowers
Toxicity
Like the closely related giant hogweed, cow parsnip sap contains furanocoumarins, chemicals that can cause chemical burns due to increased sensitivity to sunlight (phytophotodermatitis). The burns caused by cow parsnip are much less severe than those of giant hogweed, but can still cause a blistering, itchy rash. Furanocoumarins are present in all the aboveground plant parts including leaves, stems, flowers, and fruits. Burns occur when sap gets onto skin that is then exposed to sunlight. This can affect sensitive individuals and animals with thin fur, including recently sheared sheep.
If exposed to cow parsnip, cover the affected area immediately to prevent the reaction and wash the area with cool water and mild soap. Keep the affected area away from sunlight for at least 48 hours. If working in cow parsnip, be sure to cover all areas that may be exposed to sap by wearing long sleeves, pants, and gloves. If pulling cow parsnip, cover the wrist area where gloves and long sleeves may not overlap. In addition to being a skin irritant, ingested cow parsnip by lactating livestock has been found to cause milk tainting, and therefore should be managed within pastures.
For more information on cow parsnip toxicity, please see the New York State Department of Environmental Conservation’s cow parsnip page.
Identification
Seedlings: Cow parsnip seedlings appear in mid to late spring. Seedling leaves are deeply lobed and toothed. For the first and occasionally the second year, cow parsnip will remain in a basal rosette.
Cow parsnip seedling. Image and permission for use by Pamela B. Trewatha, Missouri State University.
Young cow parsnip plant. Photo by Katy Chayka, via Minnesota Wildflowers, via Bugwood.org.
Leaves: Cow parsnip leaves can measure up to 20 inches across. The leaves have a rough feeling and hairs throughout. Leaves have three leaflets, each lobed and toothed. At the base of the leaf where it is connected to the stem, there is a sheath that is typically covered in short, fine, hairs.
Mature plant: After remaining in the basal rosette stage for the first growing season(s), cow parsnip will produce an upright stem and flower. Leaves are arranged alternately on the stem, and are smaller towards the top of the plant. Stems are hollow except at the nodes, and are covered in coarse hairs. Stems lack purple spots, which is one way to tell them from giant hogweed which has purple-spotted stems. At maturity, cow parsnip can grow 6 feet tall, versus the 15 feet of giant hogweed.
Cow parsnip leaf. Photo by Rob Routledge, Sault College, via Bugwood.org
Cow parsnip stem. Photo by Peter M. Dziuk, via Minnesota Wildflowers
Flower/seeds: Cow parsnip typically flowers from May to June, producing small white flowers in umbrella-shaped clusters (umbels) up to 8 inches across. Each individual flower has five petals with notched tips. Fruits are initially bright green and darken to brown when ripe. Fruits are ¼- ½ inch long, flattened, ribbed, finely hairy, and will split into two individual seeds.
Cow parsnip flowers. Image by William M. Ciesla, Forest Health Management International, via Bugwood.org
Cow parsnip seed head. Image by Rob Routledge, Sault College, via Bugwood.org.
Species Similar to Cow Parsnip
Table 1: Shows cow parsnip (Heracleum maximum) similarities and differences in identification compared to its similar species .| Species | Similarities | Differences |
|---|---|---|
| Water hemlock (Cicuta maculata) | white flowers in clusters, purple splotches on stems | narrow leaves with toothed leaf margins, stems with fine and fuzzy hairs |
| Giant hogweed (Heracleum mantegazzianum) | white, flat-topped flowers in clusters; hairy stems | purple splotches on stems, 50 or more rays per flower cluster |
| Poison hemlock (Conium maculatum) | white flowers in clusters, purple splotches on stems | fern-like leaves, smooth stems |
Management
Chemical control
Larger patches of cow parsnip may need to be managed with herbicide applications. A systematic herbicide should be used when there is enough foliage, and the plant is actively growing.
For management in New York agricultural situations, please refer to the Cornell Crop and Pest Management Guidelines.
For specific information on parsnip weeds, you can also reference West Virginia Extension’s page on the management of parsnip weeds. As herbicide regulations vary from state to state, make sure to check your state’s regulations before settling on a management strategy.
Non-chemical control
The most effective strategy for controlling cow parsnip is early detection, especially in areas with livestock exposure. If detected before it is well established, it’s much easier to manage. Small patches can be hand removed. As noted, protective clothing should be worn when removing this plant. When hand pulling, aim to remove as much of the taproot as possible. Bag removed cow parsnip plants and dispose of them in a landfill to prevent exposure to people or livestock. Mowing is also a possible means of control, but will spray the sap and mowed plant parts so protective clothing is important for this method. Mow before plants begin to seed to avoid spreading the infestation. Repeated mowing through the growing season can deplete the taproot’s reserves.
References
Cornell University Turfgrass and Landscape Weed ID- Weeds and Human Health: The Severe Seven http://turfweeds.cals.cornell.edu/weeds-and-human-health
Cornell University’s Weed Ecology and Management website. Contains a wealth of information on ecological management of agricultural and garden weeds. Look for a revamp of this site in 2021.
Golden Gate National Parks Conservancy – Cow Parsnip https://www.parksconservancy.org/conservation/cow-parsnip
New York State Department of Environmental Conservation- Cow Parsnip https://www.dec.ny.gov/animals/105388.html
New York State Department of Transportation- Cow Parsnip (Heracleum maximum) https://www.dot.ny.gov/dangerous-plants/cow-parsnip
North Carolina State Extension – Heracleum maximum https://plants.ces.ncsu.edu/plants/heracleum-maximum/
Minnesota Wildflowers: Heracleum maximum (Common Cow Parsnip) https://www.minnesotawildflowers.info/flower/common-cow-parsnip
West Virginia Extension Service- Wild Parsnips https://extension.wvu.edu/lawn-gardening-pests/weeds/wild-parsnips
Teton County Weed and Pest District: Cow Parsnip and Giant Howeed https://www.tcweed.org/giant-hogweed-and-cow-parsnip-which-is-which-and-why-you-should-care/