2,4-D and Mycoleptodiscus terrestris for control of Eurasian watermilfoil.

Growth chamber studies were conducted to evaluate the impact of an indigenous fungal pathogen, Mycoleptodiscus terrestris (Gerd.) Ostazeski, and the herbicide 2,4-D applied alone and in combination with one another, on the growth of a nuisance submersed plant, Eurasian watermilfoil ( Myriophyllum spicatum L.). Treatments included 0.25, 0.50, and 1.00 mg L -1 2,4-D; 0.08, 0.16, and 0.32 ml L -1 M. terrestris ; combinations of both agents at all rates (applied simultaneously); and untreated controls. Six weeks after application, all treatments except the lowest rate of M. terrestris , had significantly reduced shoot biomass compared with untreated controls. Herbicide and pathogen combinations provided better control of Eurasian watermilfoil than either agent used alone. Based on the Colby statistic, interactions between the two agents were either synergistic or additive. Rates as low as 0.25 mg L -1