Wild chervil sounds like an exotic salad herb, but is in fact a Class B noxious weed in Washington, regulated in many counties including King County, due to its nasty habit of being invasive and taking over fields and pastures. Weed specialists first discovered wild chervil in King County in 2011 along Highway 410 near Enumclaw.
Wild chervil (Anthriscus sylvestris) is not very conspicuous at first, but when it gets established it forms a solid mass of white-flowering fern-like plants that is hard to miss. Since 2011, we have discovered several more infestations on roads and private properties, including several large populations on the Enumclaw plateau. Fortunately it is still limited to the southeastern part of the county, but it proving to be more widespread than we had realized. We are very interested in finding out where this plant is growing, so please report it online if you see it growing in King County.
Wild chervil is thought to have been introduced to North America from Europe in wildflower seed mixes and is now found in across large parts of northwestern and northeastern North America. Interestingly, it is also an invasive plant in some very cold places, such as Alaska, Iceland and Greenland. For some scary photos of infestations in Iceland, see this NOBANIS – Invasive Alien Species Fact Sheet.
Wild chervil is mostly found on roadsides and disturbed areas, but it is also a successful invader of fields, pastures and forest edges. It is somewhat shade-tolerant and tends to prefer rich, moist soils, although it can tolerate a wide range of habitats.
Dense patches of chervil can shade out lower growing vegetation and can expose sloped soils to erosion.
There are economic impacts as well. Wild chervil acts as a host for viral diseases that infect other plants in the same family, including carrots, parsnips, and celery. Also, although wild chervil is not toxic to livestock, it can cause problems for hay growers because it takes a very long time to dry after being cut.
On a positive note, the plant is also used for medicinal purposes. According to the NOBANIS factsheet, wild chervil has been used for the prevention and treatment of various diseases and as an analgesic, and contains chemical compounds which have been reported to have anti-tumor and anti-viral activities against human cancer cells.
April to June is the best time to spot wild chervil. However, it resembles several other plants in the carrot family so identification can be tricky. It is an upright, leafy, tap-rooted biennial/perennial that grows 1 to 3 feet tall. The flowers are white, in umbrella-shaped clusters about 3 inches across, and generally appear starting in April.
Wild chervil leaves are divided and fern-like with pointed leaf segments. Plants are leafy from top to bottom but the upper leaves are smaller in size.
Wild chervil stems are hollow, ridged and entirely green with no purple spots. They are hairy on the lower portion and hairless on the upper portions.
Wild chervil closely resembles bur-chervil, poison hemlock, and wild carrot. There is a great video on identification. The main identifying feature is the early spring flowers. Wild chervil typically flowers well before hemlock and wild carrot or other similar plants.
It is hard to get rid of wild chervil once it is established because plants spread both by seed and root buds. After a plant goes to seed, the main plant dies and its daughter rosettes that grew from root buds become independent, thus extending the life and size of the population. Also, wild chervil seeds can germinate right through grass and other vegetation, allowing this plant to invade established grasslands.
The deep taproot makes killing wild chervil particularly difficult. If plants are isolated and not mixed in with grass roots, it is possible to dig up individual plants. It is crucial to remove the entire root to effectively control the plant. For larger infestations or where the plants are growing mixed in with grass, digging up the plants with a shovel won’t be very effective.
Disk tilling before flowering provides good control of wild chervil. The tilling breaks up the roots and brings them to the surface to dry, ultimately killing the plant. Unfortunately disc tilling only works in highly accessible areas. Re-seeding of tilled areas with appropriate grass mixes should occur in the fall.
Most of the chervil sites in King County occur in mixed pasture/forest lands where tilling alone is not possible due to terrain and access with equipment.
In these types of area, applying imazapyr herbicide with a surfactant can be effective. Imazapyr has provided excellent control of the wild chervil, due the ability to translocate into the deep taproots.
There have been several studies on control methods, one being this study by Dr. Timothy Miller from WSU Extension. This study showed that a combination of herbicide treatment, disc tilling, and re-seeding grass works well to control chervil. This is a great example of Integrated Pest Management and using multiple control strategies to reduce infestation sizes and get the targeted species infestations to a more manageable size.
In early April, the plants are still small and low to the ground so it’s a good time to treat them with imazapyr while avoiding impacting the grass, which is also killed by imazapyr. Areas treated with imazapyr shouldn’t be re-seeded until the following year because this herbicide stays active in the soil for many months. Currently, an informal herbicide efficacy trial is being carried out by our staff to try to find a selective herbicide that provides good control for grassy areas.
There are many useful websites with identification and control information about wild chervil including:
King County Noxious Weed Program
Washington State Noxious Weed Board
UW Burke Museum
and an excellent NOBANIS fact sheet about Iceland.