Early Season Applications of Fluridone for Control of Curlyleaf Pondweed

Widespread in the Great Lakes region, curlyleaf pondweed Potamogeton crispus L. is an exotic submersed plant that forms dense monotypic stands, and is reported to restrict recreation, suppress native plant populations, and increase internal phosphorus cycling. Because preventing new turion formation is the key to long-term management of this aquatic weed, the effect of fluridone applications on curlyleaf pondweed growth and vegetative reproduction was evaluated in two greenhouse studies. Herbicide doses ranged from 0.5 to 6 micrograms ai Lexp -1, and were applied to plants of different growth stages for varying exposure times. Fluridone doses greater than or equal to 5 micrograms ai Lexp -1 that were maintained for at least 28 days before degrading to less than or equal to 2 micrograms ai Lexp -1 inhibited both shoot growth and turion production. Treatments of 3 and 4 micrograms ai Lexp -1 that degraded to less than or equal to 2 micrograms ai L exp -1 after 28 days reduced turion number, but not shoot biomass. All treatments less than or equal to 2 micrograms ai Lexp -1 were comparable to the reference. Although young plants that were less than 15 cm at herbicide application remained below the water surface, they produced the same amount of turions as mature plants that were greater than 15 cm at the time of application. Sprouting tests determined that turions from all fluridone treatments were viable. Based on these results, strategies for curlyleaf pondweed management may include fluridone applications to young plants using rates that would curtail turion production and either prevent or limit nuisance shoot growth.