FACTORS INFLUENCING DPA RESIDUES ON APPLES 



William J. Bramlage 

 Department of Plant and Soil Sciences 



Most apple growers in New England use diphenylamine (DPA) as a postharvest dip 

 or drench to control scald on apples. Although these treatments have been generally 

 effective in controlling scald, results of a given treatment are not always the same. 

 One reason for this is that fruit vary considerably in their susceptibility to scald, 



depending on variety, fruit maturity, fruit nutrition, and growing conditions especially 



the temperature that occurred during the days shortly before harvest. 



Another reason for variable results is that a number of factors affect the amount 

 of residue left on fruit by a treatment. (It is this residue that protects the fruit from 

 scald during and following storage.) A recent study by Drs. Shih-Lo Lee, Asela Carag, 

 and Hesh Kaplan of Decco Tiltbelt Division, Pennwalt Corporation, Monrovia, California 

 (1) demonstrated some important factors influencing this residue. 



Most of their studies were with Granny Smith apples, which are very sensitive to 

 scald, and most employed No Scald DPA EC-283®, 31% a.i., as the test material. Their 

 results can be summarized as follows: 



1. Effect of DPA solution temperature. Cold apples were dipped in solutions at 41°, 

 55°, 70° and 95° F for 30 seconds, 1 minute, or 2 minutes. When dipped for 30 

 seconds, solution temperature had no effect on DPA residue, but when dipping 

 time was 1 minute a solution temperature of 95° F. doubled the residue left by 

 solutions at the lower temperatures. It should be noted that solutions of 41°, 55°, 

 and 70° F. all left approximately the same residue regardless of solution temperature 

 or treatment time. 



2. Effect of fruit temperature. Cold apples were kept at 40°, 55°, or 72° F. for 10 

 to 12 hours to warm before dipping in a 70° F. solution for 1 minute. The coldest 

 apples (40° F) retained the least residue, but there was no difference between those 

 at 55° and 72° F. 



3. Effect of dipping time. Apples were dipped for periods varying from 15 seconds 

 to 4 minutes. A dip of only 15 seconds produced less residue than the other dipping 

 periods, but all periods of 30 seconds or more produced the same residue. 



4. Effect of DPA concentration. When apples were dipped in concentrations of DPA 

 varying from 500 to 2500 ppm, the amount of residue increased with concentration. 

 There was twice as much residue from 2500 ppm as from 500 ppm, but perhaps 

 of greater interest is the finding that there was about one-third more residue from 

 2000 ppm than from 1000 ppm, since our recommendation usually calls for use of 

 "1000 to 2000 ppm". 



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