Pyrenophora teres f. teres, a necrotrophic fungal pathogen and causal agent of net form net blotch (NFNB), is an economically important pathogen of barley (Hordeum vulgare) and has potential to cause significant yield losses in barley production regions of the world. Host resistance is the most desirable means of disease management, yet the genetic nature of this pathosystem is exceedingly complex. With the goal of identifying novel sources of resistance to NFNB, a diverse population of barley accessions was utilized to conduct a genome wide association study which identified a total of 78 significant markers associated with disease reaction to three North American P. teres f. teres isolates, corresponding to 16 genomic loci. Five novel loci were detected and will be of importance for barley breeders for the improvement of elite barley lines. Dominant susceptibility harbored by barley cultivars Rika and Kombar to P. teres f. teres isolates 6A and 15A, respectively, were previously identified to exist in repulsion and mapped at low-resolution. Using 2976 recombinant gametes derived from a cross of Rika x Kombar and markers developed through mining of syntenous genes in Brachypodium distachyon, we mapped the Spt1 locus to ~0.24 cM near the centromere of chromosome 6H. Within the delimited Spt1 region, a receptor-like protein was identified as the primary candidate Spt1 gene designated Spt1.cg. Allele analysis of diverse barley lines exhibited a strong correlation with the presence of a Rika, Kombar, or Morex allele of Spt1.cg and susceptibility to P. teres f. teres isolates 6A, 15A, or Tra-A5/Tra-D10, respectively. Alleles of Spt1.cg appear highly diverged, stemming from selection pressures in wild barley populations and may be targeted by several unique necrotrophic effectors. The barley cultivar Morex rpr2 mutant, previously characterized to have lost Rpg1-mediated resistance to Puccinia graminis f. sp. tritici, also has compromised resistance to P. teres f. teres. Exome capture revealed a 12 base-pair deletion in a gene containing fibronectin and plant homeodomain domains with homology to Arabidopsis VIN3-like proteins. This gene may function in the perception of pathogen effector proteins, that disrupt cell wall integrity, eliciting early damage associated molecular pattern immunity responses.