MARKET DISEASES OF FRUITS AND VEGETABLES 47 



for fungi causing such diseases as pink mold rot, fisheye rot, and 

 blue mold rot. 



CONTROL MEASURES 



Spray schedules for scab vary considerably in different parts 

 of the country. Under ordinary conditions in most sections the 

 disease is controlled by applications of sulfur or ferbam, one of 

 the new organic fungicides. The recommendations of the local 

 agricultural experiment station should be followed in any specific 

 section. 



(See 9, 59, 65, 69, 100, 1U, 131, 138.) 



Scald 

 occurrence, symptoms, and effects 



Scald, one of the most serious storage and transit diseases of 

 apple, occurs on fruit grown in all apple-producing sections of 

 the country. No variety is entirely immune, but there is a wide 

 variation in susceptibility. Among the varieties most seriously 

 affected are York Imperial, Grimes Golden, Arkansas (Mammoth 

 Black Twig), Rome Beauty, Rhode Island Greening, Baldwin, 

 Wagener, Stayman, Yellow Newtown, and Winesap. 



Scald affects chiefly the skin of the apple and is largely confined 

 to the greener side (pi. 8, D, E). Bright-red areas are rarely 

 affected. In mild cases the disease appears as a mere superficial 

 browning of the skin; in more severe cases the entire skin 

 layer is killed (pi. 8, F) and sometimes broken down so much 

 that it sloughs off readily from the underlying tissue. In some 

 instances the flesh of the apple becomes dead and brown to a 

 depth of % inch or more and has an appearance much like rotted 

 tissue; but true rots usually spread down into the flesh in more 

 or less conical shape, whereas scald is diffuse. 



Apples usually show but little scald while held continuously 

 in cold storage (30° to 32° F.), but fruit that is apparently free 

 from the disease at those temperatures often becomes badly 

 scalded after short exposure to warm air. The higher temperature 

 does not cause the scald ; it merely brings out what was already 

 latent in the fruit. 



Scald is worse on immature than on mature fruit and also 

 worse on apples from heavily irrigated trees than on those from 

 trees receiving moderate irrigation. It develops more rapidly at 

 high than at low temperatures and is worse in tight than in 

 more open packages. Open stacks with air spaces that permit 

 good circulation of air in the storage room contribute to the 

 prevention of scald, but cannot be relied upon for the control of 

 the disease. 



Delaying storage may greatly increase the development of 

 scald, especially if the fruit receives little ventilation during the 

 delay. If immature fruit is adequately ventilated a delay in 

 storing sometimes reduces the development of scald. 



CAUSAL FACTORS 



Scald is believed to be caused by accumulation within the apple 

 tissues of certain gases that are produced by the apples themselves 

 as a result of their respiratory activity. These gases can be at 



