The objectives of this study were to determine the effect of ferulate and its analogs, and factors which may affect the toxicity of ferulate to Oscillatoria cf chalybea, the cyanobacterium presumed to cause musty flavor in farm-raised catfish. Rapid bioassays utilizing 96-well and six-well cell culture plates were used to monitor the toxicity of ferulate analogs and potential ferulate stability factors toward O cf chalybea. The additions of low concentrations of the oxidizing compound sodium carbonate peroxyhydrate with ferulate did not help control O cf. chalybea. Of three forms of ferulate tested, trans-ferulate was most toxic towards O cf chalybea. Light enhanced the toxicity of ferulate, indicating that weather conditions and the time of day could influence the success of ferulate applications to fish ponds to control O cf chalybea. Ferulate was less toxic to O cf chalybea in six-well culture plates than in 96-well plates, indicating that higher concentrations of ferulate should be used in field trials, due to possible reduction of ferulate toxicity towards O cf chalybea in large, aquatic environments (ie fish ponds). These studies provided fundamental information on potential ferulate toxicity towards O cf chalybea to be considered before conducting field trials (ferulate applications to fish ponds). © 1999 Society of Chemical Industry