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Wild parsnip (Pastinaca sativa) is one of the most common and irritating plant pests in southern Wisconsin. The biennial grows first year rosettes bearing leaves about six inches tall. It develops a long, thick taproot, which is edible. (FYI, it is not an obligate biennial. It is monocarpic (flowers once then dies). The field experience of many people has bore out that rosettes may grow 2-5 years before flowering. The WIDNR invasive species fact sheet discusses this.) The second year the plant produces a single, thick (1 inch diameter) stem, rising up to 5 feet, with hundreds of yellow umbellate (carrot-like) flowers. [source: WDNR - Invasive plant species - Wild Parsnip (Pastinaca sativa) via website]. It favors open sunny areas like roadsides, pastures, and fallow fields. Hikers learn the watery blisters on their skin came from wild parsnip; the rash is easily confused with poison ivy.
Mowing to reduce an infestation may inadvertently promote parsnip, if done at the wrong time of year, by lowering the competition around its basal rosette. If mowed too early, flowering plants will resprout and set viable seed. If mowed too late, seed will ripen and get spread by the mower. If left unmowed during midsummer (a common error now) the plant will set seed in July. Farmers and roadside crews that mow in May and then again in August simply scatter mature seed. The result is a thicket of parsnip along the roads. A similar difficulty presents itself when trying to control parsnip with selective mowing on prairie remnants. The optimum time to mow parsnip in southern Wisconsin, to break its seed production cycle, is in the first two weeks of July.
I learned through conversation with WDNR Natural Area manager Mark Martin that one of the best ways to control parsnip in areas that you do not wish to mow in mid summer was by slicing the taproot and removing the top portion by hand. WDNR did this with garden spades. A sharpened spade was placed near the plant and angled so the blade would slice the root a couple inches below ground. The severed root stub was pulled up by the stem. (Gloves are required to avoid the blister producing sap.) The root fragment left behind dies later since it lacks mass and crown buds to re-sprout.
I sought a narrower shovel for this purpose. I wanted less cutting resistance, lighter weight, and less potential damage to non-target species. Unable to find a suitable model I created various flat stainless experiments mounted on old snow shovel handles. These homemade tools worked well but were unfeasible for mass production. So our chapter located a small, ‘ladies’ type spade (six-inches wide) in a commercial market. We choose the 40-inch model with a D-handle, and modified it in three ways:
We cut away the sides leaving about 3 inches of blade tapering in the middle.
We cut the tip so it was concave (“notched”) for easier centering on the root.
We remounted the D-handle so it was perpendicular to the blade, making it more ergonomic, like a saw.
We left the footrest alone. We sharpened everything else. We called it the Parsnip Predator.
After using them on our prairie plantings we began getting requests for more. We bought more commercial spades, hired a local handicap firm to cut the blade to our design, and to remount the handle, and began selling them at a price to cover our costs.
I am not aware of any studies testing the success of controlling parsnip with this modified design or with any other spade. Removing the root stub by shovel seems to be a popular methods advised in government and academic circles. Reports from our users since we began experimenting in 1998 have been very encouraging.
The tool can theoretically address any tap-rooted plant in any soil. The key is to slice, never to pry. The reduced blade is not strong enough for prying.
We are presently experimenting with a Predator blade mounted on a one-handed medical crutch. An athletic person can jab the ground with one arm and lift the plant out with the other at a rapid pace. Rich Henderson of WDNR Bureau of Science Services conceived the adaptation; we gave him one of these for field-testing and as an accolade for his service to TPE. He says “it works great! It is the cheetah of the parsnip predators.”
We sell the Parsnip Predator at TPE events. We also offer them by mail order. Proceeds go entirely to The Prairie Enthusiasts. The Predator was created for the singular purpose of restoring prairies by removing parsnip. Any handyperson can buy a small shovel and replicate the tool at home.
I would like to acknowledge Julia O’Reilly for championing the Predator and becoming our first production and vending manager, and Nick Faessler who later took over the post.
Wisconsin Natural Resources Magazine June 2000 Wild Parsnip II by David J. Egan:
WDNR - Invasive plant species - Wild Parsnip (Pastinaca sativa):
Wisconsin Vascular Plants: link