244 DISEASES OF ECONOMIC PLANTS 



should be removed from the beds, since it serves as the ini- 

 tial point of attack for the fungus. Those who are free 

 from the disease should guard against its introduction upon 

 diseased refuse in any form. Compost which may be con- 

 taminated with lettuce refuse bearing this disease should be 

 avoided. Those growing lettuce under glass have found 

 soil disinfection effective and practicable. 



Damping off. See p. 60. 



Gray mold {Botrytis cinerea Pers.). — Gray mold is es- 

 sentially a leaf disease, beginning usually at the leaf edges, 

 and there causing wilted, flaccid patches which soon be- 

 come coated with a straw-colored downy fuzz, the sporifer- 

 ous hyphse. The whole leaf, usually an outer one, may 

 droop and die. 



Weak plants may succumb entirely to such attack, the 

 disease passing slowly from the outer leaves toward the 

 central ones. In all cases the affected parts after death 

 become coated with the dirty fuzzy down characteristic 

 of the disease. This disease may be distinguished from 

 sclerotiniose by the absence of the white mycelium and 

 sclerotia, and by the presence of the gray, dirty, botrytis 

 growth which does not belong to sclerotiniose. The two 

 diseases, while often occurring separate, may both infect 

 the same beds or the same plants. Botryose may also 

 cause damping off. 



High temperature, lack of ventilation, and lack of vigor 

 in the plant, resulting from improper care, are essentials 

 to attacks of botryose. If these be avoided, this disease 

 will do no serious harm. 



Rosette (Rhizodonia sp.). — A moist rot sets in first 

 upon portions of leaves which touch the ground, and 



