Septoria nodorum blotch is a wheat foliar and glume disease caused by Parastagonospora nodorum, a necrotrophic fungal pathogen. Snn1-SnTox1, Snn3-B1-SnTox3, and Tsn1-SnToxA are three important interactions between wheat necrotrophic effector sensitivity genes and P. nodorum effectors. I evaluated a recombinant inbred population that segregated for these three necrotrophic effector sensitivity genes with P. nodorum isolates containing various combinations of the three corresponding necrotrophic effectors. The Tsn1-SnToxA and Snn3-B1-SnTox3 interactions explained up to 32.7 and 21.2% of the disease variation, respectively, when present. For most isolates the Snn1-SnTox1 interaction did not show a significant effect, however for some isolates, the interaction explained up to 30.2% of the disease variation. Necrotic flecking was observed on leaves of lines containing Snn1 and corresponded to the Snn1-SnTox1 interaction. The results from this study suggest that the amount of disease explained by each interaction varies by isolate and may be due to differential gene expression.