History & Introduction
Corydalis incisa, commonly known as incised fumewort, is an annual or biennial herbaceous spring ephemeral plant in the poppy family native to Asia. It was first detected in the U.S. in the Bronx in 2005 and in Westchester in 2014, though its means of introduction is unknown. Since its introduction, it has established additional populations in D.C., Virginia, Pennsylvania, North Carolina, Illinois, and several other states. Current distribution in New York State is limited to Staten Island, the Bronx, and Westchester County, most populations of which are located along the Bronx River which disperses the seeds. Due to its limited distribution, incised fumewort is both a LIISMA and State Tier 2 Species with the goal of local and statewide eradication. In 2017, the USDA deemed incised fumewort a “high-risk” invasive species due to its potential to become widespread and inflict significant ecological damage.
In the spring of 2024, LIISMA visited and confirmed reports of incised fumewort on Staten Island. The population is located at the head of a trail in a park with an abandoned greenhouse. This may support the theory that fumewort has been introduced via contaminated nursery materials. The population is also along a stream that may have already transported seeds which established new, not yet detected, populations nearby. Efforts are underway to work with the NYC Department of Parks and Recreation staff to develop a management plan for the incised fumewort.
Identification & Biology
Incised fumewort can be identified by its low growing habit (up to 2 feet high) and bipinnately compound leaves reminiscent of parsley. Its compound leaves are divided into three leaflets, which are also subdivided into three smaller leaflets. Leaves may be highly serrated, lobed, or incised, giving the plant its name. Incised fumewort is shade tolerant and can grow near waterways, floodplains, and disturbed areas, and in particular, thrive in “mesic and alluvial areas,” where it may carpet the understory.
As early as February*, incised fumewort emerges as a spring ephemeral plant, growing rosettes of its double compound leaves from a small tuber. It produces racemes of 10 – 16 tubular purple flowers that bloom in mid to late spring and soon begin producing oblong pods of seeds. Seed capsules are ballistically dispersed, exploding to shoot seeds up to nearly 10 feet from the parent plant when confronted with movement from people, animals, or strong weather. Seeds also contain an elaiosome, or protein and fat-rich structure on the seeds which entice ants to eat part of the seed and disperse them in the process. Seeds are also known to be spread by flowing water, which is evident by incised fumewort’s distribution along the Bronx River. Incised fumewort will die back in early summer as temperatures rise, and go dormant until fall. A rosette of leaves will then reemerge from the tuber and overwinter.
*Much of the research and practical knowledge surrounding C. incisa as an invasive species originates from cases in more southern climates including the National Capital Region, where it is a common problematic invasive species. Since its abundance is limited in the Northeastern States, further research and field study is needed to confirm the phenology of C. incisa in New York, including time of emergence and overwintering state.
Look-alikes: Incised fumewort resembles the native plant, Corydalis flavula, or yellow fumewort. C. Flavula can be distinguished by its yellow flowers and less heavily divided lobed leaves, which range from grayish blue-green to green. Incised fumewort may also have white spots on its leaves and can have up to 200 teeth on one leaflet, as compared to no more than 90 on its native counterpart.
Damage and Concern
Incised fumewort can form dense carpets along forest floors, woodlands, and riparian areas. Here it can suppress and outcompete native species and increase the density of the herbaceous layer. Depending on the time of emergence, incised fumewort may pose a threat to native spring ephemeral plants, which are increasingly uncommon due to threats such as deer overbrowse, invasive species, and general habitat degradation. It is a prolific seeder with the ability to disperse seeds explosively great distances and by ants and moving water. It is shade tolerant and self compatible. Populations have been found and confirmed in at least seven states in addition to D.C. Incised fumewort appears to be resistant to some forms of manual management, including hand pulling and weed torching.
The Maryland Department of Agriculture estimates that approximately 37% of land in the U.S. could be suitable habitat for incised fumewort and is at risk of colonization by this plant. The department concludes that while incised fumewort is highly capable of spreading, its impacts are uncertain due to its relatively recent introduction to the U.S. circa 2005. It is estimated that similar biennial species dispersed by ants can nearly double the size of their populations each year, and the growth rate of incised fumewort may be comparable or greater.
Management & Control
Manual/Mechanical Control
Hand pulling and digging can be implemented on second-year or older plants. Its small tuber should be removed to prevent regrowth when possible. First-year individuals should not be hand-pulled, as the small tuber is likely to break off and lead to further spread. While incised fumewort is said to be somewhat resistant to manual control methods, it may be suppressed and its spread may be limited by these methods.
Other manual control methods including weed torching, solarization, smothering, and mowing may be viable controls, but further research is needed to determine efficacy. Mowing several times throughout the growing season could suppress incised fumewort and prevent it from setting seed.
Manual control should take place in early spring before the plant begins to seed to prevent further dispersal. Properly dispose of plant materials in a garbage bag when possible and practice Play Clean Go, brushing seeds off boots and clothes after managing this plant.
Chemical Control
Herbicidal control methods such as foliar spraying or wicking may be effective in controlling incised fumewort. Bugwood.org recommends a 3% solution of glyphosate applied as a foliar spray. Further information is needed on local case studies controlling incised fumewort with herbicides.
Incised fumewort’s preference for floodplain and wetland adjacent habitats may pose a challenge in safely applying herbicides. Applying herbicides in areas close to wetlands may have negative non-target effects or require special permissions to implement. Carefully consider whether manual control would be a viable option when approaching the management of incised fumewort in wetland adjacent areas and floodplains. If chemical control is required and legally permissible, select the method that utilizes the least amount of herbicide used in the most targeted way to minimize non-target effects, such as wicking.
Repeat treatments using any of the above methods may be necessary. When using any chemical control, always read the entire pesticide label carefully, follow all mixing and application instructions, and use all personal protective gear and clothing specified.
Monitoring & Reporting
LIISMA is currently monitoring incised fumewort as part of our Early Detection and Rapid Response Program. As reports of the species are collected, LIISMA is working with partners to delineate and manage any early emerging infestations before they become widespread. Incised fumewort is currently a Tier 2 species on Long Island, prioritized for early detection and containment.
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