A statewide survey conducted by Washington State University researchers from February to June, 2016, on fruit harvested in 2015 on 160 grower lots from 10 different counties, provides a comprehensive and accurate assessment on the relative importance of the postharvest threats to apples. Many fungal pathogens cause decay in apples, with significant economic losses for packers. The Washington industry is familiar with pathogens like blue mold, gray mold and bull’s eye rot, but other pathogens, known as the “crabapple disease complex”, Speck rot and Sphaeropsis rot, have emerged in recent years.
Results indicate that blue and gray molds account for almost 72 percent of total decay, with blue mold causing 48 percent. Blue mold was detected in 157 of the 160 lots surveyed, versus 132 lots for gray mold. Usually only one of these two pathogens was predominant in a single grower lot. Bull’s eye rot was found in 52 lots, at frequencies ranging from 1 to 75 percent, whereas the statewide frequency was 4.3 percent. The frequency of Speck rot and Sphaeropsis rot was 2.5 and 1.4 percent, respectively. Additional minor pathogens included Alternaria rot (2.9 percent) and the newly reported yellow rot (2 percent). Other minor or unidentified pathogens accounted for 14.3 percent of total decay.
Blue mold frequency ranged from 31.7 percent to 62.2 percent versus 7.7 to 37.7 percent for gray mold in the 10 different counties surveyed .
