MARKET DISEASES OF FRUITS AND VEGETABLES 21 



through handling or washing; thus additional infections may take 

 place through wounds during storage and transit. For this reason 

 sweetpotatoes from an infested field should not be stored with those 

 from a disease-free field. 



CONTROL MEASURES 



Experimental evidence indicates that none of the commercial varie- 

 ties of sweetpotatoes is resistant to black rot. To avoid the develop- 

 ment of this disease in the field, great care should be exercised in 

 selecting disease-free roots for seed purposes. Such roots should be 

 disinfected by immersing them for 10 minutes in a solution made by 

 dissolving 6 pounds of borax in 30 gallons of water. Infested soil 

 should be avoided in the field and the hotbed. 



Control in storage involves careful inspection and discarding of 

 all infected sweetpotatoes previous to storing and keeping those that 

 are harvested from soils known to be infested separate from those 

 grown in disease-free fields. For recommended curing and storage 

 conditions, see page 19. Careful handling to avoid wounds in pre- 

 paring the sweetpotatoes for market is always advisable. Washing 

 the potatoes may spread the disease. 



Blue Mold Rot 



(Penicillium sp.) 



Blue mold rot is most often found in sweetpotatoes that have been 

 chilled or frozen. Potatoes that have been stored at low tempera- 

 ture and moderately high humidity are particularly susceptible. 



The spores of the causal fungus are ever present in the air and on 

 the surface of most fruits and vegetables, but they are unable to cause 

 infection except through wounds or through tissues broken down by 

 other agencies. 



Blue mold rot is a soft decay generally involving large areas about 

 mechanical injuries or lesions of other diseases. In chilled or frozen 

 sweetpotatoes the whole root is soon decayed and the characteristic 

 white and blue-green tufts of mold break through the epidermis. 

 These colored tufts are the most reliable diagnostic character. When 

 many potatoes are infected the whole lot has a musty odor. 



This disease may be avoided if care is used to prevent injury in 

 handling the sweetpotatoes and if proper temperature and humidity 

 are maintained (p. 19). It is especially important that a combina- 

 tion of low temperature and high humidity be avoided. 



(See 46.) 



Charcoal Rot 



(Sclerotium bataticola Taub.) 



Although charcoal rot is most important as a storage disease of 

 sweetpotatoes, it sometimes causes injury to growing plants in the 

 field when the stem becomes infected at the soil line. From the 

 diseased vine the causal organism grows down to the roots and to 

 the developing sweetpotatoes. Decay most often starts at the upper 



