MARKET DISEASES OF FRUITS AND VEGETABLES 17 



tions showed a relation of washing injury and abundance of spores 

 to subsequent decay. It is now recognized that blue mold may 

 enter apples through mechanical injuries, such as cuts by basket 

 rims and stem punctures, through open lenticels, and through 

 lesions in the skin caused by severe washing treatment. Late in 

 the storage season, when the fruit has become weakened by ripen- 

 ing and aging, most varieties have been found very susceptible to 

 lenticel infection by blue mold. This type of lenticel infection may 

 readily result when rotten apples are handled carelessly during 

 repacking late in the storage season. 



Factors that favor the development and spread of blue mold 

 rot may be classed as follows: (1) The extent of the spore load 

 on the fruit, (2) the condition of the fruit, and (3) environmental 

 conditions. The relation between spore load and the amount of 

 blue mold decay has been clearly demonstrated by dipping fruits 

 in a spore suspension prior to storing and comparing the extent 

 of decay with that on fruits carrying only the natural spore load. 

 The presence of open lenticels, mechanical injuries, including 

 bruises, and washing injuries (both skin cracks and injuries 

 beneath open lenticels), along with aging of the fruit, has an 

 important effect on susceptibility. Environmental conditions such 

 as moisture, ventilation, and temperature directly influence the 

 development of decay. The atmospheric moisture necessary to pre- 

 vent apples from shriveling is sufficient for blue mold develop- 

 ment. Lack of ventilation due to tight packing and to lack of 

 air space in stowing increases the moisture about the fruit and 

 slows down the rate of cooling, making conditions unusually fa- 

 vorable for rot development. 



Blue mold develops more rapidly at temperatures higher than 

 the usual storage temperature for apples (30° to 32° F.). Apples 

 that are delayed in going into storage, cooled slowly in storage, 

 stored until late in the season, or held at warm temperatures 

 after removal from storage are particularly subject to infection. 

 The disease is not necessarily prevented or arrested even at 30° 

 to 32°. Rotten spots continue to enlarge, and new infections are 

 initiated at these temperatures. Slow progress in decay is made 

 in the early part of the storage season when the apples are firm 

 and resistant, but in the long months of storage blue mold develops 

 and causes the most serious losses to stored apples. Apples 

 wounded by small pin punctures and inoculated by a spore-sus- 

 pension dip developed small but visible lesions in 30 days at 31° 

 to 32°. By the end of 60 days such lesions had enlarged to % 

 to 1 inch in diameter. 



CONTROL MEASURES 



Some of the more important means of controlling blue mold rot 

 are careful handling, packing-house sanitation, avoiding chem- 

 ical injury in the washing process, and prompt cooling to cold- 

 storage temperatures. Reduction of the spore load carried by the 

 fruit is of great importance. This may best be accomplished by 

 rigid packing-house sanitation. 



Sodium chloro-2-phenylphenate is being used as a disinfecting 

 wash in certain producing districts of the Northwest. (See Pears, 

 Gray Mold Rot, p. 59.) Blue mold rot has been reduced by this 



