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Evaluation of Postharvest Removal of Sooty Blotch and Flyspeck on Apples Using Sodium Hypochlorite, Hydrogen Peroxide with Peroxyacetic Acid, and Soap

Postharvest dips of apples (Malus × domestica) in commercial disinfestants were used to remove signs of the flyspeck (FS) pathogen, Schizothyrium pomi, and the sooty blotch (SB) complex (Peltaster fructicola, Leptodontium elatius, and Geastrumia polystigmatis). Apples were dipped for 7 or 15 min in buffered sodium hypochlorite (Agclor 310 plus Decco 312 Buffer) at 200, 400, 500, 600, or 800 ppm chlorine, a mixture of hydrogen peroxide and peroxyacetic acid (Tsunami 100) at 60 ppm/80 ppm, 120 ppm/160 ppm, or 360 ppm/480 ppm, respectively, or soap (Kleen 440), then brushed and rinsed for 30 s on a commercial grading line. Disease severity was assessed as percent diseased area using a quantitative rating system, and by counting the number of colonies of three mycelial types of SB and FS. Percent diseased area on apples was converted to USDA apple grade ratings and retail values. Both assessment methods provided similar results, but the percent-diseased-area method was less labor intensive. A 7-min dip in 800 ppm chlorine resulted in a mean increase from 25 and 55% to 100% Extra Fancy grade for ‘Jonathan’ and ‘Golden Delicious’ apples, respectively, and increased market value by 31 and 14%, respectively. The 7-min, 200-ppm chlorine dip resulted in an increase from 28 and 45% to 92.5 and 96.5% Extra Fancy after treatment for ‘Jonathan’ and ‘Golden Delicious’, respectively. Blemishes were removed more effectively from ‘Jonathan’ and ‘McIntosh’ apples than from ‘Golden Delicious’. Mycelial types of the sooty blotch and flyspeck fungi were removed differentially by the disinfestant dip treatments.