Forecasting Scald Potential of Delicious Apples in New England

Abstract

Susceptibility to superficial scald on apples varies with season, orchard location, and time of harvest, and is related to seasonal weather variation. If scald potential could be forecast at the time of harvest, then appropriate antiscald treatment decisions could be made. This could result in 1) reduced use of scald inhibiting diphenylamine (DPA) dips, with their accompanying fungicides and 2) reduced loss of stored fruit due to scald. Analyses of scald-related data collected at the UMass Horticultural Research Center (HRC) from 1986 to 1993 have resulted in development of equations relating scald development to harvest date, number of preharvest days in which the temperature fell below 10 °C, and harvest starch score. Equations to identify lots of fruit which were particularly scald susceptible or particularly scald resistant were also developed. These equations were tested in 1995 and 1996 on 'Delicious' apples harvested from orchards throughout New England and stored at the HRC. About 80% of the 182 lots of fruit were placed in the correct susceptibility category. DPA treatments were applied to the Massachusetts fruit in both years, and forecasts were almost 100% effective for determining the appropriate concentration of DPA needed to control scald. Effects of controlled atmosphere (CA) storage on scald development, scald forecasting, and necessary scald control measures will vary according to the atmosphere, but initial data show forecasting trends to be about the same for CA as for air-stored fruit.