At higher concentrations of fungicide, the heterocyst frequency of the cyanobacteria increased in N₂ as well as NH₄⁺ media except at Bengard (250μg ml-1) concentrations. The normal frequency of heterocyst was seen in 5 - 6% of nitrogen in normal culture condition. This stimulation action in heterocyst formation was observed after a time span of two to six days. Heterocyst did not appear in the fungicide supplemented or Unsupplemented culture in NO₃^- or fungicide interacted with organism, primarily with its N₂ and NH₄+mediated growth conditions. It was found that glucose protect the growth inhibitor effects of the higher concentrations of Bengard (100 - 250μg ml-1) in all inorganic nitrogen media.