What is the safe and environmentally sound way to eradicate cow parsnip?
Since cow parsnip propagates by seed, and is not known to propagate vegetatively, it can be removed by digging up or severing its roots. (For some people, combined exposure to sap and sunlight causes a painful skin irritation known as phytophotodermatitus. Wear clothing that will prevent skin contact with the sap.) As a further precaution against contacting the sap, I suggest first cutting the stalk down into a few manageable sections, starting at the top and handling this material with a garden fork. Be sure to discard flower heads that may contain mature seeds. Next, dig up the root, or destroy it by slicing through it with a sharp shovel. New shoots of cow parsnip that emerge next spring will be susceptible to a broadleaf herbicide. Alternatively, dig them up or destroy with a shovel. If you have more questions, feel free to contact me directly.
Thank you Matthew for the quick response. Now, the follow-up question we have is "what is a safe broadleaf herbicide that we can use?" Thanks again.
An effective choice for controlling cow parsnip in Alaska is a systemic herbicide containing the active ingredients triclopyr+2,4-D ("Crossbow" is an example of such a product). West Virginia University's wild parsnip publication (https://extension.wvu.edu/lawn-gardening-pests/weeds/wild-parsnips) contains further information about controlling this plant.
When planning your pesticide application, remember that cow parsnip will be most susceptible to treatment during its first year of growth, early in the spring when growth begins. Choose a product that lists the site you intend to use it on, and follow all label instructions to make a safe and effective application.