Crosses between `Humble' and five other blackberry cultivars were made to determine the efficacy of `Humble' as a source of resistance to rosette (incited by Cercosporellarubi). Seven cultivars and three selections were planted at a disease free location and at a location where rosette is known to occur to determine the effect of double blossom on yield, berry weight, and ripening date. `Cheyenne' X `Humble,' `Humble' X `Brazos,' and `Navaho' X (`Humble' X `Brazos') produced progenies with various levels of resistance. Promising selections were made from the latter two crosses. Genotype X location interaction was significant for yield and not significant for either Julian date of 50% ripe fruit or weight per berry. These results suggest that rosette reduces yield but has little if any effect on weight per berry or ripening date. `Shawnee' and `Choctaw' were the highest yielding cultivars under disease free conditions; however, their yields were low in the test where they were infected with rosette. `Brazos,' `Choctaw,' and `Rosborough' were the earliest ripening and `Navaho' was the latest ripening cultivar.