396 



Bulletin 266. 



wet season, or succession of such seasons, is the only condition necessary 

 to bring about another epidemic of the disease. 



LIFE HISTORY OF THE FUNGUS 



{Guignardia hidwellii.) 



This opinion bears more weight when certain facts in regard to the 

 life habits of the fungus are considered. In 1908, the writers published 

 a bulletin from this Station which, among other 

 things, contained a statement of the known facts in 

 regard to the method of conservation, propagation, 

 and dissemination of the fungus. Epitomizing briefly 

 it may be stated that the specific cause of the Black 

 Rot disease is a microscopic fungous parasite {Guignar- 

 dia bidwellii (E) V. & R.). The fungus passes the 

 winter on the old mummied berries, either clinging to 

 wir^s or lying on the surface of the ground; on the 

 clinging tendrils or leaf petioles; and on the canes 

 bearing the fruit-buds (Fig. 99). The fungus on such 

 parts perishes when covered by a few inches of soil, 

 but it is obviously impossible to treat the canes in 

 such a manner and impracticable to remove tendrils 

 from the wires. 



The spores, or reproductive bodies of the fungus, 

 are encased and protected in a receptacle which pre- 

 vents their being killed by a contact spray. Spores 

 are discharged by a purely mechanical process re- 

 quiring the presence of precipitated moisture. The 

 water is absorbed by a gelatinous substance surround- 

 ing the spores and by the swelling of this substance 

 Fig. 99. — Black the spores are mechanically forced from the receptacle. 

 year-ddTam. ^Th'e Under natural conditions this happens only when 

 minute black pint- there is a rain of sufficient duration to thoroughly 



&e^ftJt!hi!m^ ^^'^^^"^ the parts bearing fungous receptacles. The 

 inwhich spores may spores thus discharged must be borne by the wind or 

 hve over winter spattered by a breaking drop of water to some green 

 and growing part of the vine in order to be able to produce an infec- 

 tion, and, even then, such an infection is possible only when the spore 

 has the necessary moisture for a sufficient time to permit of germina- 

 tion. It was found further that, after the entrance of the germ tube of 

 the spore, at least ten and often as many as twenty days are necessary 



