22 U. S. DEPARTMENT OF AGRICULTURE. 



falls to pieces quite unlike plants affected with slimy soft 

 rot which tend to slip out of one's hand. 



On root crops the rot is not as watery as on leafy tissues. 

 Under dry conditions, evaporation keeps pace with the 

 liberation of water by the fungus and the affected tissue 

 dries out and shrinks. Thus the watery nature of this rot in 

 roots is not as evident as in the case of leafy or succulent 

 tissues. However, under moist conditions, affected root 

 crops exude water freely. The white cottony or matted 

 mycelium and the black sclerotia serve to identify the dis- 

 ease on root crops when the watery characteristics are 

 absent. 



This rot can be differentiated from slimy soft rot by the 

 fact that the latter is a slimy, slippery decay usually accom- 

 panied by a bad odor and lacks the white mycelium and 

 large sclerotia of watery soft rot. The latter can be differ- 

 entiated from gray mold rot by the typical powdery gray 

 moldy outgrowth of the latter. Gray mold rot is generally 

 found on overmature tissues, and is not as watery as the 

 typical watery soft rot caused by Sclerotinia. Watery soft 

 rot progresses at lower temperatures than does the soft rot 

 induced by Rhizopus. Rhizopus rot is prevalent in the sum- 

 mer and in overheated cars in the winter, while watery soft 

 rot develops in refrigerated cars. 



The disease is favored by high humidity and moderate 

 temperatures. The original infection proceeds from the soil. 

 Lettuce grown under glass, or plants grown in crowded 

 quarters, are especially subject to infection. The disease 

 develops and spreads very rapidly in transit and storage, the 

 fungus passing from diseased to healthy tissue by contact. 



Crop rotation and soil sanitation and aeration are control 

 measures which can be applied in the field. Losses in tran- 

 sit and storage may be reduced by sorting out and discard- 

 ing diseased plants and by thorough ventilation. After the 

 diseased portions of affected plants are trimmed off, the re- 

 mainder is edible. It is not advisable to store trimmed 

 plants. 



Ref.: Lettuce (5); (65); (66). 



SUN-SCALD. 



OF CUCUMBER, HONEY DEW MELON, ONION, PEPPER, POTATO, TOMATO, 



AND WATERMELON. 



Cause : Exposure to the hot sun. 



Sun-scald is evidenced by the death and discoloration of 

 a rather extensive area on the exposed surface of the vege- 

 table. In most cases, the lesion is irregular in outline and 

 at first resembles a water-soaked blister, but soon becomes 

 slightly but sharply sunken and distinctly bleached in color. 

 This bleaching is particularly noticeable in peppers, toma- 

 toes, and cucumbers. 



Sun-scald is particularly important from the market 

 standpoint because the scalded areas are very subject to the 



