Reservoir souring remains a challenging problem for the oil & gas industry, especially in aging assets where H2S and microorganisms from the reservoir can pose a serious risk to the integrity of producing wells and equipment. Nitrate treatment is commonly used to control SRB activity in the reservoir, but it is not always effective due to poor subsurface definition and increasing volumes required over time. In this study, we evaluated the use of a biocide to replace nitrate injection in reservoir conditions when nitrate is no longer effective to control SRB activity. We used sour, sand-packed reactors to evaluate a biocide formulation applied prior to and after nitrate cessation. Measurements of VFAs, nitrate, sulfide and genomic analysis were used to assess souring and changes in the microbial population. The results indicated that biocide was successful to remediate souring when applied before AND after the nitrate treatments. However, the cumulative amount of generated sulfide was higher when the biocide was applied after nitrate cessation, indicating the need of temporary co-injection of nitrate and biocide to prevent a H2S wave period. Genomic analysis indicated that this formulation specifically targeted the SRB rather than broadly killing the microbial population. Taken together, this study highlights a new strategy to control reservoir souring and potential corrosion issues in producing wells.