December 2014

Invasive Watch: Wild Parsnip (Pastinaca Sativa)

What to Look For
Wild parsnip acts as a biennial, forming a rosette of basal leaves the first year, overwintering and flowering in the second year. The basal rosette consists of large, pinnately compound leaves that resemble celery leaves. Plants grow up to 6 inches in the rosette stage. Sharply toothed or lobed, egg-shaped leaflets run along both sides of a common stalk. The lower leaves have leaf stalks (petioles), where the upper leaves attach directly to the stem. The hollow, deeply grooved stem can grow 2 to 5 feet tall.

Flat-topped, broad flower clusters bloom from June through late summer. Five-petaled flowers are small, predominantly yellow and arranged in an umbel spanning 2 to 6 inches. Seeds are small, flat, slightly ribbed and straw-colored.

Plant parts contain a substance called psoralen, which can cause a condition known as phytophotodermatitis. A reaction occurs when plant juice gets on the skin and the skin is exposed to sunlight, which causes the skin to redden, develop a rash and, in severe cases, blister or burn. Dark red or brownish skin discoloration develops where the burn or blisters first appeared and can last for several months.

Where It's Found
Wild parsnip inhabits roadsides, pastures, field edges or natural areas. It favors calcareous soils and sunny areas, but adapts to different environments. It can be found throughout most of the United States and Canada. Wild parsnip produces a large amount of seed, which contributes to the plant’s persistence and spread. Seeds take three weeks to ripen before they can reseed, but they are viable in the soil for up to four years.

How to Treat It.
To effectively treat wild parsnip, apply Opensight® specialty herbicide at 2 to 3.3 ounces per acre to the vegetative stage prior to bloom. Use the higher rate when weeds are larger. The goal is to eliminate seed production. Because flowering does not occur all at once, the area must be monitored for several weeks.