NATURE AND CONTROL OF APPLE-SCALD 



By Charles Brooks, Pathologist, and J. S. CoolEY and D. F. Fisher, Assistant 

 Pathologists, Fruit-Disease Investigations, Bureau of Plant Industry, United States 

 Department of Agriculture 



NATURE OF APPLE-SCALD 



EFFECT OF REMOVAL, FROM STORAGE 



It is a quite generally accepted idea that apple-scald is due to the warm- 

 ing up of the fruit after it has been removed from cold storage. This idea 

 comes from an erroneous interpretation of very familiar facts {2)} It is 

 true that apples do not show scald while held continuously in storage at 

 o°C. (32° F.) and that they seldom show it under commercial cold- 

 storage conditions where the air must from necessity sometimes vary 

 slightly from any desired temperature. It is also true that apples that 

 have been stored for several months in tight packages or closed rooms 

 may show very bad scald after a few days' exposure to warm air. Under 

 such circumstances, it is natural to conclude that the warming up of the 

 fruit is the cause of the scald; but the facts of the case are that the 

 apples are already potentially scalded, and the higher temperatures 

 merely allow the death processes of the apple tissue to be carried out. 

 The real cause of the disease is to be found in the conditions of transporta- 

 tion and storage to which the fruit is subjected during the first few weeks 

 after it is removed from the tree. Healthy apples do not develop scald 

 upon removal from cold storage, even when transferred at once to 

 living-room temperatures. 



RELATION OF THE COMPOSITION OF THE STORAGE AIR TO APPLE-SCALD 



The fact that outside air produces such serious results on potentially 

 scalded apples has led to a belief that apples should be kept away from 

 fresh air and air currents as much as possible at all times; but carefully 

 controlled storage experiments have shown conclusively that when the 

 fruit is stored in open packages, scald can be entirely prevented by 

 thorough stirring of the storage air. The question naturally arises as to 

 the nature of the harmful substances that are carried away from the fruit 

 by this air movement. 



Humidity. — Many storage men hold the opinion that excessive mois- 

 ture may bring about apple-scald. The writers have made a number of 

 carefully controlled experiments with apples held under different humidi- 

 ties and, as reported later, have also followed up the moisture conditions 



' Reference is made by number (italic) to " Literature cited," p. 240. 



Journal of Agricultural Research, Vol. XVIII. No. 4 



Washington, D. C. Nov. 15, 1919 



sw Key No. G-179 



(211) 



