INTEGRATED USE OF FLURIDONE AND A FUNGAL PATHOGEN FOR CONTROL OF HYDRILLA

Combinations of the herbicide fluridone {1-methyl-3-phenyl-5-[3-(trifl uoromethyl) phenyl]-4(1H)-pyridinone} and the microbial pathogen Mycol eptodiscus terrestris (Gerdemann) Ostazeski (Mt) were tested for effic acy under controlled-environment conditions against dioecious hydrilla (Hydrilla verticillata (L.f.) Royle. Fluridone rates of 2, 5, and 12 mu g/L, Mt rates of 25, 50, 100 and 200 colony forming units (CFU) per mi, and integrated treatments of 2, 5, and 12 mu g/L + 100 and 200 CF U/ml, and 12 mu g/L + 25 and 50 CFU/ml were tested. Although a dose re sponse was noted among fluridone rates, all treatments resulted in lin ear decreases in biomass, photosynthesis (PTS) and chlorophyll from 14 through 94 days posttreatment. In contrast, Mr applications of 25 and 50 CFU/ml were ineffective throughout the study. Mt at 25 and 50 CFU/ ml + 12 mu g/L fluridone showed no differences from the 12 mu g/L flur idone treatment alone. As Mt rates were increased to 100 and 200 CFU/m l, severe initial injury was noted within 5 d; however, PTS and chloro phyll showed strong signs of recovery by 14 d and biomass was fully re covered 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 betwee n 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 flur idone with Mt at rates of 100 and 200 CFU/ml greatly enhanced control, reduced exposure requirements, and increased susceptibility of hydril la to fluridone at a rate (2 mu g/L) that was not otherwise lethal.