A new race of the downy mildew pathogen (Peronospora farinosa f. sp. spinaciae) on spinach was first identified in November 2012 in Imperial Valley, CA, U.S. This race overcomes the resistance of several important varieties. The isolate was designated UA4712 and was characterized with a standard set of differential varieties. Subsequently, isolates with the same reaction pattern on the differential set have been found in numerous locations. After careful evaluation of the significance of this development to the spinach industry, the International Working Group on Peronospora farinosa (IWGP) has denominated isolate UA4712 as race Pfs: 15.