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Tuesday, August 4, 2015

Wild Parsnip


Source: Nathan Winter, University of Minnesota Extension

Wild parsnip (Pastinaca sativa) continues to spread throughout Minnesota. This plant is considered an invasive species and the Minnesota Department of Agriculture considers it a prohibited noxious weed on the control list. Prohibited noxious weeds must be eradicated or controlled in accordance with the Minnesota Noxious Weed Law (MN Statues 18.75-18.91). This law defines a noxious weed as an annual, biennial, or perennial plant that the Commissioner of Agriculture designates to be injurious to public health, the environment, public roads, crops, livestock, or other property. This weed is on the same prohibited noxious weed list as Canada thistle (Cirsium arvense (L.) Scop.).

According to eXtension.org, the Minnesota Department of Agriculture, and the Ohio Perennial and Biennial Weed Guide, wild parsnip is a biennial/perennial herb that can grow up to 5 feet in height.  Most often this plant is a biennial and is typically 3-5 feet tall. Leaves are alternate (1 leaf per node), compound (5 to 11 leaflets), and branched with jagged teeth. Leaflets are yellowish-green, shiny, oblong, coarsely-toothed, and either mitten- or diamond-shaped. Flowering occurs from May to June, when hundreds of yellow flowers develop. Flowers are arranged in an umbel. Fruits are dry, smooth, slightly winged, and flattened on back. Fruits each contain two seeds, which are dispersed in the fall. Wild parsnip reproduces through seed. Wild parsnip is native to Eurasia and occurs in sunny areas with varying degrees of soil moisture.  Typically, this plant is found in ditches and in perennial non-cultivated landscapes. Some similar species that look similar include golden alexander and giant hogweed.

According to the University of Minnesota Extension Wild Parsnip publication regarding toxins and toxicity, wild parsnip may contain chemicals called furanocoumarins. There is toxicity during 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. The toxic dose of wild parsnip is not known. The toxic dose of other plants known to accumulate furanocoumarins has not been established either.  The publication continues:

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.

Problems can also occur when in contact with wild parsnip. Sap contact with the skin in the presence of sunlight can cause a rash that often leads to blisters and discoloration of the skin (phytophotodermatitis). Be sure to wear gloves, long sleeves, and pants when in contact with wild parsnip.

The University of Wisconsin Extension Wild Parsnip publication highlights some of the control strategies and effectiveness in season and following season after treatment. Pulling or cutting the root out 1-2” below the surface is 90-100% effective in season and 70-90% the following year. Mowing after the emergence of flower heads, but before the seeds enlarge is 90-100% effective in season and 50-70% the following year. Prescribed burning in the spring is 50-70% effective in season and less than 50% the following year. Grazing during the midseason is 50-70% effective in season and less than 50% the following year. Remember that grazing can cause photosensitivity if they consume large amounts of wild parsnip.

Foliar herbicides can be applied directly to plants or broadcast across an infested area. The University of Wisconsin Extension suggests the following herbicides for control of wild parsnip: 2, 4-D, aminocyclopyrachlor + chlorsulfuron, chlorsulfuron, dicamba + 2, 4-D, glyphosate, and metsulfuron. Remember to read and follow the label for proper application and use. Some herbicides are selective and others are non-selective in regards to the control of weed and desirable plants. Typically, herbicides are going to be the most effective when utilized in the spring and fall on smaller plants. Wild parsnips is a biennial/perennial and they will typically be a smaller (6”) in the rosette stage. Control during this stage will help alleviate the number of larger mature plants the following year. Be sure to follow the label if you intend to hay or graze areas that have been treated with an herbicide. Some restriction periods may apply.

Desired weed control can be achieved over time and it will probably include a combination of non-chemical and chemical control. Plan a strategy to control these weeds for more than one year. Once under control, continue to watch for new problem areas.




Photo Credit:
Schaefer, Kristine. Wild Parsnip. N.d. Iowa State University Extension Integrated Crop Management Image Gallery. Wild Parsnip | Integrated Crop Management. Web. 29 July 2015. 

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