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Predicting Delicious Apple Storage Scald

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Scald can be an important post-harvest storage disorder of Delicious apples in New England (see picture). Although the exact causes of scald are not known, research has shown that:

  • late harvested fruit scalds less than early harvested fruit (within a cultivar)
  • the riper the fruit at harvest, the less likely they are to scald
  • scald susceptibility varies from year to year among fruit, even from the same tree
  • year to year variation in scald susceptibility is a function of weather (at least partly)

As a result of extensive research on scald susceptibility of Delicious apples in New England, UMass researchers Sarah Weis, and Drs. William Bramlage and William J. Lord developed prediction equations for determining scald susceptibility based on:

  • harvest date
  • the number of days when minimum temperatures were less than 50 degrees F
  • the average starch-index at harvest.

These equations proved very reliable for predicting low, intermediate, or high susceptibility of New England Delicious apples to scald in air storage. Therefore, the formula(s) can be used to predict the most efficient use of a DPA scald prevention treatment:

  • highly susceptible fruit require a 2000 ppm. pre-storage DPA treatment
  • moderately susceptible fruit require only 500 ppm
  • low susceptibility fruit need no pre-storage DPA dip

Use the equations below (start with Equation 1) to fine tune your requirement for scald-preventive DPA treatments, saving both money and chemical use on stored fruit.

Apple Scald Prediction Calculator for New England Delicious Apples

Equation 1: To identify scald-susceptible Delicious fruit (more than 60% likely to scald)

<--- In September enter day of month fruit is harvested, or in October 30 + day of month harvested

<---Number of days minimum temperature less than 50 degrees F. since August 1

<--- Starch Index average value of ten fruit sample (using Cornell generic starch-index chart)

Now INDEX

If INDEX greater than zero, more than 60% of fruit are likely to scald. Pre-storage treatment with DPA at 2,000 ppm. recommended. If INDEX is less than zero, use Equation 2 to determine if fruit have low or intermediate susceptibility to scald.

Equation 2: To identify scald-resistant Delicious fruit (fewer than 20% likely to scald)

<--- In September enter day of month fruit is harvested, or in October 30 + day of month harvested

<---Number of days minimum temperature less than 50 degrees F. since August 1

<--- Starch Index average value of ten fruit sample (using Cornell generic starch-index chart)

Now INDEX

If INDEX greater than zero, fewer than 20% of fruit are likely to scald. No pre-storage treatment with DPA is advised.

If INDEX is less than zero, more than 20% (but possibly less than 60%) of the fruit are likely to scald. You should use Equation 1 to fine tune the need for DPA treatment -- if Equation 1 suggests more than 60% are likely to scald, follow the 2000 ppm. recommendation. If Equation 1 and Equation 2 both produce an INDEX less than zero, then an application of at least 500 ppm. DPA is recommended.

Author: 
S. Weis, W. Bramlage, & J. Clements
Last Updated: 
Sep 17, 2012
Topics: 
Agriculture
Agriculture topics: 
Fruit
Post Harvest Handling