150 Diseases of Greenhouse Crops 



than on that grown in the open. In the field it usu- 

 ally attacks fall lettuce. Downy mildew attacks 

 not only lettuce, but also chicory and numerous 

 other Compositae. 



Control. This disease is controlled in the same 

 way as lettuce drop (see p. 151). 



Gray Mold 



Caused by Sderotinia fuckeliana De Bary. 



Symptoms. Gray mold attacks grapes in Europe 

 but in the United States it is commonly met with 

 on lettuce plants which are fully developed and 

 somewhat overgrown. The disease is manifested 

 by soft, watersoaked spots on the foliage, causing a 

 wilting. The spots soon become coated with the 

 fruit of a gray mold. The fungus has two stages, 

 the Botrytis cinera Pers. stage, which is commonly 

 found as a gray mold on wilted lettuce leaves (fig. 

 26, c.) ; the other is the winter or apothecial stage, 

 known as Sderotinia fuckeliana. American botanists 

 have not as yet been able to cormect these two forms. 

 It seems, however, that IstvanfR * was able to con- 

 firm the work of De Bary, who first indicated the re- 

 lationship of Botrytis cinerea with Sderotinia 

 fuckeliana. 



Control, see Lettuce Drop, p. 151. 



Lettuce Drop 



Caused by Sderotinia lihertiana Fckl. 

 Symptoms. The term drop best describes the 



'IstvanflS, G. De, Ann. de I'institut central amp£l. roy. Hon- 

 grois: 183-360, 1915. 



