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Monday, August 13, 2018

August Weed of the Month: Treatments and Timing of Wild Parsnip

Christina Basch, Minnesota Department of Agriculture

The key to effective invasive plant management is disrupting the lifecycle of the plant. Every plant is different and treatment timing for one plant is completely different from another. Creating a multi-year management strategy that targets timing in the lifecycle is necessary for success.

Before targeting a plant, it is important to understand the plant and its lifecycle. Wild parsnip (Pastinaca sativa) is a non-native biennial plant that produces a rosette in its first year and bolts, producing a seed head in its second year of life. It is spreading throughout Minnesota, and effective management can be tricky. Wild parsnip develops rosettes in its first year, and this is a great time to scout and form a management plan. In late spring to early summer, second year plants will bolt, flower and produce dozens of seeds. Seeds lack substantial germ coatings, and do not persist in soil for extended periods of time.

NOTE: Use caution when working with this plant. Wild parsnip produces a sap, that when combined with sunlight, can cause a blisters and swelling (Phytophotodermatitis). It is very important to use protective clothing, goggles or facemask and gloves.

Mark Renz, an Associate Professor and Extension Specialist for the University of Wisconsin-Madison did a case study on wild parsnip. Here are key management strategies taken from his study:

• Hand pulling and cutting can be efficient as long as a portion of the root has been impacted at least 1-2” below the surface of the soil. This will ensure that the plant will not re-root or produce seed. If seed is present be sure to dispose of the plant effectively and not to spread seed to un-infested areas.
• Mowing is effective if timed properly.  Typically after mowing the plant will re-sprout and still be able to produce a flowerhead and seed. Mowing is most effective if completed after the flowers have emerged but before the seeds are enlarged. Seeds produced at this time will not be viable, and typical regrowth will not develop fertile seeds before weather conditions prevent further growth. A second mowing is needed and common. Mowing can be successful and effective management can be seen typically after 3 years of repeated mowing.
• Herbicides are another useful management tool but have to be timed correctly in order to be effective. There are a range of herbicides that have been proven effective. You will need to consult the herbicide label to understand where it can be used and when it is most effective. If timed properly, chemical application can target flowering second year plants and year seedlings.  If seeds are present on the plant, chemical application is not recommended or effective.

A great resource to help develop a management plan for most specific noxious weeds found in Minnesota is the Minnesota Noxious Weeds Booklet created by the Minnesota Department of Transportation. This booklet has pictures, plant descriptions, management recommendations and a treatment calendar to help you form a plan of what will be most effective at a certain time. Understanding the plant you are targeting, and using different management strategies at effective times, is necessary to develop an effective management plan.

Photo Attached

• Wild+Parsnip+Infestation.jpg

Photo caption: Wild parsnip infestation (Minnesota Department of Agriculture)

MEDIA: For more information on Weed of the Month, contact Allen Sommerfeld, MDA Communications, at allen.sommerfeld@state.mn.us or 651-201-6185.