St. Augustinegrass [Stenotaphrum secundatum (Walter) Kuntze] is a popular warm-season turfgrass in the southern United States. Gray leaf spot (GLS), caused by the fungal pathogen Pyricularia oryzae Cavara, is one of the major diseases in St. Augustinegrass. Although previous studies have reported polyploid lines with resistance to GLS, no comprehensive evaluations of sources of resistance have been performed in the genus. Such evaluations will enable breeders to identify resistant parents for cultivar development. In this study, 58 genotypes of St. Augustinegrass and two genotypes of pembagrass [Stenotaphrum dimidiatum (L.) Brongn.] were screened for resistance to three different P. oryzae sources of inoculum under controlled environmental conditions. The parameters evaluated were incubation period, number of leaves with lesions, mean lesion length, area under the disease progress curve (AUDPC), and area under the lesion expansion curve (AULEC). Significant differences among genotypes were identified. Polyploid genotypes PI 365031, PI 290888, PI 300129, PI 300130, and cultivar ‘FX-10’ and diploid genotype PI 410353 consistently showed high levels of resistance across trials, inoculum sources, and parameters. The identification of resistance genes in diploid genotypes is of great importance for future St. Augustinegrass breeding efforts, as this germplasm pool can be more readily exploited because of the lack of reproductive barriers with most commercial cultivars and plant introductions.