The harmful algal species Prymnesium parvum, also known as golden algae, is toxic to many forms of aquatic life. When it blooms it kills fish and other aquatic organisms and can have long-lasting impacts on the ecosystem where it blooms. Many forms of treatments are employed to control P. parvum, including chemical methods. Flumioxazin, the active ingredient of Clipper herbicide, hasbeen effective at controlling P. parvum in small-scale situations. A concentration gradient of Flumioxazin including 50, 100, 200, and 400ug/L was tested in its commercial form of Clipper in a laboratory setting to determine whether it would be effective, considering its supposed inactive and inert ingredients. Varying conditions at the time of application were also examined to aid in decision making processes where Clipper is being considered as a means of control. The conditions examined were season (fall and winter of the southeastern United States) and growth stage (log and stationary) of P. parvum. Through the use of cell counts by light microscopy and chlorophyll-a fluorescence, Clipper was determined to control P. parvum in winter season, but not in fall season, and to be more effective when applied in P. parvum's log growth phase than in its stationary growth phase. This is likely due to P. parvum having an optimum growing temperature closer to the fall season than the winter season of the southeastern United States and that the growth rate of P. parvum in its stationary phase is already low in comparison to its growth rate in log growth.
