Biocorrosion is also known as microbiologically influenced corrosion (MIC). It is often caused by sulfate reducing bacteria (SRB) biofilms. More effective biocide treatment methods are desired due to environmental regulations and increasing costs. Recently, several publications revealed that some D-amino acids are signaling molecules for bacterial biofilm dispersal. In this work, tetrakis hydroxymethyl phosphonium sulfate (THPS) was combined with D-methionine for the mitigation of Desulfovibrio vulgaris (ATCC 7757) biofilm in the full ATCC 1249 medium and a modified medium with only four ingredients, i.e., magnesium sulfate, sodium lactate, ferrous ammonium sulfate hexahydrate, and yeast extract at concentrations 1/4 of those in the full medium, as well as MIC pitting of C1018 carbon steel. D-Methionine alone even at a concentration of 1000 ppm w/w and 50 ppm (active concentration) THPS alone were both found ineffective. However, a synergistic biocide combination consisting of 50 ppm THPS and 100 ppm D-methionine was highly effective and even better than 500 ppm THPS used alone. Although D-methionine alone has no biocidal effects, its biofilm dispersal effect can convert sessile cells to planktonic cells under a biocide stress. This is very useful in biofilm treatment because planktonic cells are much easier to treat than sessile cells using biocides.