Pyrenophora teres f. maculata causes spot form net blotch (SFNB) on barley and was recently documented in North Dakota. The impact of SFNB on barley, the genetic diversity of the pathogen, and virulence structure are unknown for the state. Yield and quality loss in North Dakota due to SFNB was investigated over eleven year-sites, and simple linear regression of percent yield loss on adjusted percent disease using year-site means of treatments predicted a 0.77% increase in yield loss for every 1% increase in disease. When virulence of isolates of P. teres f. maculata collected from geographically diverse regions in the northern United States was evaluated on differential barley genotypes, few isolates were identical in terms of virulence patterns, and the virulence profile of a population from Idaho differed from other populations. To understand population structure and genetic diversity, SNPs of 140 isolates were generated using genotyping-by-sequencing for analysis of population genetics and structure. Evidence for sexual recombination in each population includes the ratio of mating-type idiomorphs that do not significantly differ from a 1:1 ratio; low index of association values for most populations; and high variation within and low variation among populations. Association mapping detected forty-five significant marker-trait associations of SNPs associated with virulence or avirulence across 19 P. teres f. maculata scaffolds using 82 isolates of P. teres f. maculata from diverse areas in the northern United States. The most significant marker, 01700_198, was found on P. teres f. maculata-scaffold 8 when the population was challenged with four different barley lines. This research demonstrates that SFNB causes significant yield loss; that high diversity exists in the pathogen, with respect to virulence and population genetics; and that association mapping can be used to identify virulence/avirulence marker-trait associations to fill gaps in our understanding of host-parasite genetic interactions in this pathosystem.