Predicting Poststorage Scald on 

 Delicious: Where Do We Stand? 



Sarah A. Weis and William J. Bramlage 



Department of Plant & Soil Sciences, University of Massachusetts 



For some years we have been collecting data 

 relating to scald incidence on Delicious. The 

 major factors explored are 1) harvest date, 2) 

 number of preharvest hours/days in which the 

 temperature falls below SCF, and 3) starch 

 score at harvest. These factors have been 

 shown to influence scald susceptibility. Later 

 harvest, more hours/days below 50°F, and 

 higher starch scores (more mature fruit) all 

 result in less scald after storage. Harvest date 

 is an important factor, but since scald severity 

 varies greatly from year to year even when fruit 

 are harvested the same month and day, other 

 influences clearly are also important in 



determining scald susceptibility. 



Rather than trying to predict the exact 

 probability of a fruit developing scald (an 

 impossible task), we divide fruit into three 

 categories: lots from which more than 60% of 

 fruit are likely to scald, lots from which fewer 

 than 20% of fruit are likely to scald, and those 

 in between. A lot, for our current purposes, is a 

 bushel of apples harvested from adjacent (up to 

 5) trees of the same age, strain, and rootstock. 

 The idea behind these divisions is that if over 

 60% of fruit will scald without treatment, then 

 it is probable that in order to control scald 

 effectively, the maximum concentration of 



O 



o 



Q. 



E 



CO 



0) 



E 



z 



100 



> 60% Scald, prediction wrong 



< 60% Scald, prediction wrong 



< 60% Scald, as predicted 



> 60% Scald, as predicted 



HRC 



Orchard 2 Orchard 3 



Overall 



Figure 1. Predicting severe scald (>60% of fruit) on Delicious, 1995. Equation was devel- 

 oped from data collected at the University of Massachusetts Horticultural Research Cen- 

 ter, 1988-93. If [8.4 - 0.32(day #) + 0.055 (days < 50"F) - 0.055(starch score)] > 0, then it 

 is predicted that > 60% of the fruit will scald. 



Fruit Notes, Volumc 61 (Number 4), Fall, 1996 



