Japanese hedgeparsley is a biennial plant that invades roadsides, rights-of way, and forested areas in the midwestern United States. Interest in managing populations by mechanical or hand-clipping techniques exists, but no information is available on the appropriate timing to maximize mortality and prevent the production of viable seed. To assess that, we applied clipping treatments at five periods throughout the summer to three Japanese hedgeparsley populations in southern Wisconsin and measured the number and viability of seeds produced by each plant during the year of treatment and the survival of plants clipped. Japanese hedgeparsley plants began producing seed by mid-July, but production was not maximized until early August. Viable seeds were not produced until early or mid-August, coinciding with the presence of ripened brown fruit. Clipping at any timing resulted in > 95% mortality by the fall of the treatment year. All plants that resprouted were in the vegetative stage when clipped, and no plants survived the following year. Results indicate that clipping Japanese hedgeparsley plants when they are in a reproductive phase before fruit turns brown is an effective management strategy for this invasive plant.
Nomenclature: Japanese hedgeparsley, Torilis japonica (Houtt.) DC. TOIJA.
Management Implications: Japanese hedgeparsley is actively invading full sun and forested habitats in the midwestern United States. Little is known about how to manage populations, but mechanical or hand removal is of interest because populations are appearing along areas easily accessed by people or equipment. We compared the effectiveness of clipping populations at five timings in southern Wisconsin to determine when viable seed is produced and whether plants resprout after clipping requiring further management to prevent seed production. We found that Japanese hedgeparsley was capable of producing more than 6,000 seeds plant−1, but viable seed were not present until the fruits turned brown in color. In Wisconsin, that occurred in early to mid-August, depending on the location. Clipping populations before that time not only prevented the production of viable seed, but < 5% of clipped plants resprouted. The few plants that did resprout were in the vegetative stage when clipped, but none produced viable seed. Results indicate that clipping is an effective control strategy for this invasive plant, and management should be conducted when plants are in the reproductive stage, but before fruit turn brown to avoid dispersal of viable seed. Although resprouting after clipping was minimal in Wisconsin, populations should be monitored carefully as the consistency of this response in other regions is unknown.