Genetic mapping in polyploid organisms that undergo random pairing during meiosis is a difficult process. Early genetic maps were constructed using single dose allele markers. These markers cannot be used to identify homoeologous chromosomes. Software capable of identifying allelic dosage for SNP markers and mapping software that allows for the use of higher-dose markers has recently become available, allowing for the creation of high-density maps of segmental allopolyploids, like hybrid roses. The unmapped black spot resistance gene Rdr3 was previously identified in the tetraploid rose ‘George Vancouver’. A mapping population was developed by crossing ‘George Vancouver’ with the susceptible tetraploid ‘Morden Blush’. Phenotyping was conducted via a detached leaf assay with Diplocaron rosae race 8 and the population was genotyped with the WagRhSNP 68K rose Axiom array. Allelic dosage assignment and genetic mapping were conducted using the R packages ‘fitPoly’ and ‘polymapR’, respectively. Rdr3 was mapped to a chromosome 6 homoeolog. To date, three additional black spot resistance genes (Rdr1, Rdr2, and Rdr4) have been mapped. Rdr1 and Rdr2 map to a chromosome 1 homoeolog and Rdr4 maps to a chromosome 5 homoeolog. Rdr3 is a unique gene and not an allele of the other genes as it maps to a different region. Mapping Rdr3 demonstrates how new tools can be used to create high-density maps to begin answering complex genetic questions surrounding polyploids.