Laboratory experiments were conducted in 55-L aquaria to evaluate the efficacy of the aquatic herbicide endothall and the fungal pathogen Mycoleptodiscus terrestris (Gerd.) Ostazeski, applied alone and in combination against hydrilla. Treatments included 0.25, 0.50, and 1.25 mg ae/L endothall, 100, 200, and 400 colony-forming units (CFU)/ml M. terrestris, simultaneous integrated treatments of 0.25, 0.50, and 1.25 endothall + 100 or 200 CFU/ml M. terrestris, sequential integrated treatments of 100 and 200 CFU/ml M. terrestris + 0.25 and 0.50 mg ae/L endothall, and untreated controls. By 42 d after treatment (DAT), all treatments had significantly reduced shoot biomass levels of hydrilla compared with the untreated controls. Combining the two lowest herbicide rates with M. terrestris provided better hydrilla control than either treatment alone. Based on these results, an outdoor mesocosm study was conducted to evaluate the efficacy and selectivity of endothall and the pathogen applied alone and in combination against hydrilla, Illinois pondweed, American pondweed, and vallisneria. Treatments included 0.25 and 0.50 mg ae/L endothall, 100 and 200 CFU/ml M. terrestris, integrated treatments of 0.25 and 0.50 mg ae/L endothall + 100 and 200 CFU/ml M. terrestris, and untreated controls. Unlike the laboratory results, none of the treatments controlled hydrilla 100%. The combined treatments worked better than either treatment applied alone. By 42 DAT, all the combined treatments except 0.25 mg ae/L endothall + 100 CFU/ml M. terrestris had reduced above-ground hydrilla biomass by ≥ 90% compared with the untreated controls. All nontarget species sustained varying amounts of injury from endothall and M. terrestris applied alone or in combination.