Wild Parsnip (Pastinaca sativa) is an invasive plant from Eurasia that has naturalized across North America, posing a significant health risk to humans and livestock. The danger stems from a toxic sap found in all above-ground parts of the plant. When this sap contacts the skin and is subsequently exposed to ultraviolet light, it triggers a severe chemical burn known as phytophotodermatitis. This reaction, caused by furanocoumarins, can lead to painful blistering, a rash, and long-lasting skin discoloration. Proactive management is required to prevent its spread and reduce the hazards it presents in disturbed areas, roadsides, and open fields.
Recognizing the Plant and Its Life Cycle
Accurate identification is the first step in effective management, especially since the plant’s appearance changes dramatically during its biennial life cycle. During its first year, Wild Parsnip exists as a low-growing cluster of leaves called a basal rosette. These rosette leaves are pinnately compound and coarsely toothed, remaining close to the ground while the plant develops a deep taproot.
In the second year, the plant bolts, sending up a stout, hollow, and grooved stalk that can reach heights of four to five feet. This stalk is topped with flat-topped clusters of small, yellow, five-petaled flowers, which bloom from late spring through mid-summer. This flowering stage is when the plant is most recognizable, and control efforts are time-sensitive to eliminate the plant before it produces viable seeds.
Essential Personal Safety Protocols
Safely managing Wild Parsnip requires strict adherence to protective measures to avoid contact with the sap. Anyone working in or near an infestation must wear long sleeves, long pants, and closed-toe footwear to cover all exposed skin. Recommended gear includes synthetic, water-resistant fabrics, impermeable gloves, and eye protection, such as safety goggles or a face shield, especially when cutting plants at chest height.
Mechanical disruption, such as using string trimmers or mowers, can aerosolize the sap and splatter it over a wide area, increasing the risk of exposure. After any activity, clothing and tools should be washed thoroughly with soap and water to remove residual sap, and the operator should shower immediately. Working during the evening or on overcast days reduces the risk of reaction, but the sap remains active and dangerous.
If accidental contact occurs, the affected skin must be immediately covered to block all sunlight exposure. Promptly washing the area with mild soap and water is necessary to remove the furanocoumarins before they are activated by UV light. The contaminated skin must then remain covered and shielded from sunlight for a minimum of 48 hours to prevent the painful blistering and discoloration.
Manual and Cultural Control Methods
For small infestations or in areas where chemical use is restricted, manual and mechanical methods offer a viable path to eradication. The most effective manual technique is severing the plant’s taproot a few inches below the soil surface. Cutting the root approximately one to two inches beneath the crown prevents the plant from resprouting and completing its life cycle. This is easiest to achieve when the soil is moist or when the plant is in its first-year rosette stage.
Mowing can be used to manage larger areas, but timing is paramount, and it should only be done before the plant sets seed. Mowing after the flowers have developed but before the seeds mature requires careful removal of the cut seed heads, which can still ripen and disperse seeds after cutting. Poorly timed mowing can worsen an infestation by reducing competing vegetation and allowing more sunlight to reach the low-lying rosettes.
Cultural control methods focus on creating an environment that suppresses the growth of Wild Parsnip. Establishing a dense, competitive layer of desirable vegetation can effectively crowd out new parsnip seedlings. Mulching the site immediately after removal reduces light availability, which hinders the germination and establishment of new plants from the seed bank. Consistent monitoring and follow-up removal of any new growth are necessary for several years until the seed bank is exhausted.
Chemical Eradication Options
Herbicides provide the most efficient solution for large-scale infestations, with application timing being the most important factor for success. Systemic broadleaf herbicides containing active ingredients like 2,4-D or triclopyr are effective when applied to the plant’s foliage. Glyphosate, a non-selective herbicide, is also used but requires careful spot application to avoid harming surrounding non-target plants.
The optimal time for herbicide application is when the plant is in its low-lying basal rosette stage, either in the early spring or late fall. During these periods, the plant is actively growing and translocating nutrients to its taproot, allowing the herbicide to kill the entire plant. Applying herbicides when the plant is flowering is ineffective, as the plant is focused on seed production.
Herbicide treatments must be repeated annually for several years because the seeds of Wild Parsnip can remain viable in the soil for up to four years. Following local regulations and the product label directions is imperative to ensure the safe and proper use of chemicals. This includes using the appropriate concentration and avoiding application near water bodies or during windy conditions to prevent drift.