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.