Scientific Name: Patinaca sativa.
Origin: Introduced from Europe and Asia.
Lifecycle: Biennial, reproducing by seed.
Identification: Stem is somewhat hairy, grooved, and two to five feet tall. Leaves are course, with saw-toothed edges. Flowers are yellow and arranged in an umbrella shape; appearance is somewhat like the ornamental Queen Anne's Lace.
Distribution: Found throughout the United States.
Habitat: Found in fields and roadsides, and occasionally in wet pastures.
Control: Several herbicides exist that provide adequate control of wild parsnip. However, repeated applications may be needed for control. Most weeds are better controlled by herbicides when they are small. Larger plants may need to be removed by hand pulling, as stems become woody and adequate control with mowers and herbicides will be difficult. If controlling wild parsnip by hand, be sure to wear gloves and protective clothing, as contact with wild parsnip can cause severe blistering of the skin. When using a herbicide, be sure to follow all grazing restrictions and other pertinent information stated on the herbicide label.
Toxin: Wild parsnip may contain chemicals called furanocoumarins.
When Toxic: All growth stages of the plant, when eaten fresh or dried in hay. High concentrations of furanocoumarins have been founds in the seeds as well.
Toxicity: The toxic dose of wild parsnip is not known. The toxic dose of other plants known to accumulate furanocoumarins has not been established either.
Signs and Effects of Toxicosis: Severe sunburn (photosensitivity) occurs in people and animals ingesting furanocoumarins if they are exposed to UV light after ingestion. Sunburn occurs after ingestion due to the furanocoumarin circulation in the blood vessels just below the skin. The UV light exposure is almost always from the sun. Severe sunburn occurs on the white or other light skinned areas, but not the black, brown, or other dark skinned areas, because melanin in the dark skin absorbs the UV light and prevents it from reacting with the furanocoumarins. Consequently, severe sunburn in livestock ingesting furanocoumarin-containing plants is reduced if the livestock are shaded from the ultraviolet sunlight.
Treatment: Remove the plant source. Move animals to an area where shade is available. Topical treatments can be used for the skin lesions.
Other: See the Feeding Clover fact sheet for additional causes of photosensitivity in horses.