Circular no. 751 



December 1946 • Washington, D. C. 



UNITED STATES DEPARTMENT OF AGRICULTURE 



Blue Mold Decay of Delicious Apples 

 in Relation to Handling Practices 



By Harley English, formerly assistant pathologist, A. Lloyd Ryall, horticulturist, 

 and Edwin Smith, senior horticulturist, Division of Fruit and Vegetable Crops 

 and Diseases, Bureau of Plant Industry, Soils, and Agricultural Engineering, 

 Agricultural Research Administration 



CONTENTS 



Page 

 Importance of decay and con- 

 tributing factors 1 



Materials and methods 3 



Factors related to blue mold in- 

 fection 4 



Lenticels 4 



Miscellaneous infection 



courts 7 



Holding fruit in orchard or 

 warehouse prior to wash- 

 ing 8 



Cold-storing fruit prior to 



washing 11 



Kind and temperature of 



washing solutions 12 



Page 



Factors related to blue mold in- 

 fection — Continued 



Size of spore population 12 



Packing wet or dry 14 



Fruit variability 14 



Decav in commercially packed 



fruit 16 



Development and types of 



decay 16 



Spore population of washing 



solutions 16 



Fungi isolated from infected 



fruit 18 



Literature cited 19 



MAo^ y M^ 



IMPORTANCE OF DECAY AND CONTRIBUTING 



FACTORS 



Delicious apples now constitute a large proportion of the commercial 

 crop in Washington, and many of them — about a third in 1940 — are 

 marketed after February 1. This fact, together with the increased 

 awareness among shippers that high quality in the Delicious variety 

 can be maintained through a long storage season only by prompt cool- 

 ing to 30° to 32° F., has necessitated changes in some of the older 

 handling practices. Under present conditions Delicious apples are 

 harvested faster than they can be packed, with the result that much 

 of the fruit must be held either in the orchard or the warehouse at 

 high temperature or in cold storage prior to washing and packing. 

 Such holding in cold storage has the decided advantage of maintain- 

 ing dessert quality, but some plant operators contend that passing 

 cold, turgid fruit through heated washing solutions results in increased 

 injury and subsequent decay. 



The extension of the storage and marketing season for Delicious 

 apples has increased the hazard of fungus decay, most of which is 



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