-2- 



5. Effect of additives. Addition of calcium chloride at 24 lbs. per 100 gallons did 

 not affect DPA residue, and neither did the addition of a surfactant. 



6. Differences among varieties . The authors compared Granny Smith apples with 

 Golden Delicious, Delicious, Jonathan, and Rome Beauty. When the fruit were 

 all dipped under identical conditions, the residues were similar on all varieties 

 except Delicious, which retained almost twice as much residue as did the other 

 varieties. 



7. Effect of DPA formulation. Three different commercial formulations of DPA 

 were tested under identical conditions, and one of the formulations left twice as 

 much residue as did the other 2 formulations. 



Conclusions 



These results indicate that apples should be treated for at least 30 seconds, but 

 that prolonged periods provide no additional benefit unless the dipping solution is hot. 

 They also show that cold apples will retain less residue than warm ones. However, 

 the temperature of the dip solution is of little consequence unless a quite warm solution 

 is used, which will greatly increase the amount of residue. They also illustrate that 

 the same treatment can protect different varieties to different extents, and that 

 different DPA formulations can produce different results. Within the solution itself, 

 DPA concentration was highly important, but addition of CaCl2 or surfactant had 

 no effect on DPA residue. Addition of fungicides to the solution was not tested. 



The results of this study should be of considerable interest to apple growers, who 

 are frequently concerned about how treatment conditions affect scald control. 



Literature Cited 



1. Lee, S-L, A. Carag, and H.J. Kaplan. 1984. Factors influencing the uptake of 

 diphenylamine by apples. HortScience 19(l):94-95 



POMOLOGICAL NOTES 



William J. Lord 

 Department of Plant and Soil Sciences 



Response to chemical thinning. The primary effect of chemical thinning is a reduction 

 in the number of smaller apples rather than a large increase in the size of the remaining 

 fruits. Thinning does not change a potentially small apple into a large fruit but helps 

 to insure that a potentially large apple will size properly. 



