The durability of stem rust resistance in wheat varieties is strengthened by the use of polygenic, and broad-spectrum sources of resistance. Adult plant resistance (APR) was observed in the mid-20th century Ecuadorian bread wheat cv. Morocho Blanco (PI 286545) in field tests at Njoro, Kenya, and at St. Paul. Morocho Blanco was susceptible to races TTKSK, RCRSC and TPMKC at the seedling stage. A doubled haploid (DH) mapping population was created from a cross between Morocho Blanco and the susceptible line LMPG-6 to identify loci associated with APR phenotypes. Eighty-eight DH lines were genotyped with approximately 90,000 SNPs using a custom Infinium assay from Illumina. Sixty-seven additional DH lines were used to verify SNPs associated with reduced stem rust levels. Severity and infection type were assessed on adult plants at the stem rust screening facility in Kenya in 2013 and 2014, and in two single race nurseries inoculated with races RCRSC and TPMKC at St. Paul in 2014. Two identified and verified QTL reducing stem rust severity were located on chromosome arms 2BS and 6AS. The QTL on 6AS also reduced infection type at Njoro, but a similar reduction was not observed at St. Paul suggesting a genotype x environment or genotype x race interaction. The QTL on 2BS was associated with reduced stem rust severity at both Njoro and St. Paul. It is a strong candidate for use in breeding for APR to stem rust.