Integrated Use of Fluridone and a Fungal Pathogen for Control of Hydrilla.

Abstract

Combinations of the herbicide fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl) phenyl]-4(1H)-pyridinone} and the microbial pathogen Mycoleptodiscus terrestris (Gerdemann) Ostazeski ( Mt) were tested for efficacy under controlled-environment conditions against dioecious hydrilla ( Hydrilla verticillata (L.f.) Royle. Fluridone rates of 2, 5, and 12 µ g/L, Mt rates of 25, 50, 100 and 200 colony forming units (CFU) per ml, and integrated treatments of 2, 5, and 12 µ g/L + 100 and 200 CFU/ml, and 12 µ g/L + 25 and 50 CFU/ml were tested. Although a dose response was noted among fluridone rates, all treatments resulted in linear decreases in biomass, photosynthesis (PTS) and chlorophyll from 14 through 94 days posttreatment. In contrast, Mt applications of 25 and 50 CFU/ml were ineffective throughout the study. Mt at 25 and 50 CFU/ml + 12 µ g/L fluridone showed no differences from the 12 µ g/L fluridone treatment alone. As Mt rates were increased to 100 and 200 CFU/ ml, severe initial injury was noted within 5 d; however, PTS and chlorophyll showed strong signs of recovery by 14 d and biomass was fully recovered by 28 d posttreatment. Fluridone at all rates + Mt at 100 and 200 CFU/ml produced rapid injury and biomass reductions of > 90% by 28 d posttreatment. The lack of intact viable tissue prevented sampling of physiological variables past 28 d. No differences were noted between the integrated treatments, indicating a lack of dose response. Mt at rates of 100 and 200 CFU/ml resulted in rapid plant injury; however, only short-term control was achieved. Continuous exposure to fluridone resulted in a steady reduction in biomass over time. Integrating fluridone with Mt at rates of 100 and 200 CFU/ml greatly enhanced control, reduced exposure requirements, and increased susceptibility of hydrilla to fluridone at a rate (2 µ g/L) that was not otherwise lethal.