Growth Response of Myriophyllum spicatum and Hydrilla verticillata when Exposed to Continuous, Low Concentrations of Fluridone

摘要

The objective of this study was to determine the minimum sustained (threshold) concentrations of fluridone required to control the growth of Eurasian watermilfoil (Myriophyllum spicatum L.) and hydrilla (Hydrilla verticillata Royle). A diluter system was used to deliver five different concentrations of fluridone to five sets of four test aquaria. Another set of four reference aquaria received only filtered well water. Each aquarium contained meristematic cuttings of M. spicatum and H. verticillata planted in beakers containing either a natural, fine-textured, organic substrate or a mixed sand-peat substrate (70:30 volume). Plant injury was assessed after 12 weeks of continuous exposure to the various fluridone concentrations. Results of this study suggest that the threshold fluridone concentration required to control M. spicatum growing on both substrates was estimated to be between 10 and 20 micrograms/l. When root and shoot biomass data and percent injury ratings were considered for H. verticillata, the fluridone threshold concentration necessary to provide greater than 50-percent control was estimated to be 20 micrograms/l. However, 100-percent control of H. verticillata was not achieved, based on percent injury and chlorophyll results.