Evaluation of Triclopyr and Mycoleptodiscus terrestris for Control of Eurasian Watermilfoil (Myriophyllum spicatum)

Abstract Growth chamber studies were conducted using 55-L aquariums to evaluate the efficacy of the herbicide triclopyr and the fungal pathogen Mycoleptodiscus terrestris, applied alone and in combination against Eurasian watermilfoil. Treatments included 0.15, 0.40, and 1.50 mg acid equivalent (ae)/L triclopyr, 0.08, 0.16, and 0.32 ml/L M. terrestris, combinations of both agents at all rates, and an untreated control. Plants were exposed to all treatments for a 24-h contact time and plant biomass (shoot and roots) was recorded 6 wk after application. For both triclopyr and M. terrestris applied alone, plant control increased with treatment concentration. Compared with untreated plants, 1.50 mg/L triclopyr and 0.32 ml/L M. terrestris reduced Eurasian watermilfoil by 100 and 91%, respectively. Lower doses of herbicide or pathogen were less effective and plant recovery was observed from surviving plant tissues (stems and root crowns). Although M. terrestris at 0.08 ml/L did not significantly reduce shoot or...