An Easy and Reliable Procedure for 

 Predicting Scald and DPA Requirement 

 for New England Delicious Apples 



Sarah A. Weis, William J. Bramlage, and William J. Lord 

 Department of Plant and Soil Sciences, University of Massachusetts 



The processes which control scald susceptibility 

 and development have been, and are being, studied by 

 many researchers. While the exact causes of scald are 

 not known, it has been observed that a) within a 

 cultivar, late harvested fruit scalds less than early 

 harvested fruit, b) other things being equal, the riper 

 the fruit at harvest, the less they will scald, c) scald 

 susceptibility varies from year to year among fruit, 

 even from a given tree, and d) year to year variation is 

 (at least partly) a function of weather. Cool, sunny 

 weather favors scald reduction, while hot weather may 

 increase scald susceptibility. 



We have been studying the effects of weather on 

 scald variability, both at the University of Massachu- 

 setts Horticultural Research Center (HRC) and at other 

 New England locations in relation to effects recorded 

 at various locations world-wide. Here we will report 

 on recent findings from the New England studies. Our 

 sites were in Ashfield, Belchertown (HRC), Shelbume, 

 Warren, and Wilbraham, MA, Storrs, CT, Putney, VT, 

 Durham, NH, and Monmouth ME. First, it must be 

 recognized that many of the factors purported to 

 influence scald are related to one another. For 

 example, as the harvest season progresses, the fruit 

 ripen, temperature falls, and the days become shorter. 

 However, these factors relate somewhat differently to 

 one another in different years, and in different 

 locations. Our hope was that if we collected data for 

 many years at the HRC, we could identify some of the 

 specific factors influencing scald susceptibility, and 

 then develop a workable general relationship of 

 preharvest factors to scald susceptibility. 



The factors we have concentrated on are the 

 following: 1) preharvest cool temperature as the 

 number of days the apples are subjected to sub-50"F 

 weather between August 1" and harvest; 2) a 

 qualitative measure (sunny, partly cloudy, cloudy) of 



light to which fruit are subjected during the week prior 

 to harvest; 3) fruit maturity at harvest as measured by 

 a starch/iodine test, and 4) harvest date. Because we 

 have been working primarily with Delicious, which 

 are not harvested before late September, we did not 

 experience enough hot (over 80"F) weather near 

 harvest to evaluate that factor, even though we know it 

 could be important. We also have not included a light 

 factor in the reported equations because light measures 

 were only available for the HRC. 



Development of Prediction Equations 



Between 1988 and 1993, we harvested 213 one- 

 bushel samples of Delicious from HRC, stored them 

 20-25 weeks in 32"F air, and then removed the fruit to 

 room temperature for a week before rating them for 

 scald. Scald rating consisted of examining each apple 

 in a box and recording the percent of apples developing 

 scald in that box. A sample was considered very scald- 

 susceptible if more than 60% of fruit in the box 

 developed scald, and was considered scald-resistant if 

 fewer than 20% of the fruit developed scald. It should 

 be noted that any sign of scald was recorded, and some 

 fruit in this latter category would not have been 

 downgraded. The following equations, reported in 

 Fruit Notes 61(4) were generated: 



Equation 1: If [8.36 - 0.320(harvest date as 

 number of days after 8/31) + 0.0546(number of 

 preharvest days < 50"F) - 0.0550(harvest starch 

 score)] > 0, then fruit are very scald-susceptible. 



Equation 2: If [-11.8 + 0.414(harvest date as 

 number of days after 8/31) - 0.0298(number of 

 preharvest days < 50"F) - 0.708(harvest starch 

 score)] > 0, then fruit are very scald-resistant. 



Fruit Notes, Volume 63 (Number 3), Summer, 1998 



