220 MANUAL OF AMERICAN GRAPE-GROWING 



until the berries are at least half grown. Soon after the ravages 

 of the fungus become apparent on the berries, the fruits turn 

 black, shrivel and become covered with minute black pustules 

 which contain the summer-spores. Figure 44 shows the 

 work of black-rot. In the winter and spring, another form 

 called the winter- or resting-spore is produced upon these old, 

 shriveled, mummied berries, and these carry the disease over 

 from one season to another. 



Since the disease is carried through the winter in mummied 

 fruits and diseased wood, the desirability of destroying these 

 mummied grapes and the leaves and prunings of infected vines 

 as soon as possible is apparent. This treatment, however, 

 is not sufficient, and the disease can be effectually controlled 

 only by thorough spraying with bordeaux mixture (4450). 

 The first application should be made just before the grape 

 blossoms ; the second, shortly after blossoming. The amount 

 of material applied matters less than evenness in distribution 

 and fineness of the spray as applied. In rainy seasons, perhaps 

 a third or a fourth application should be made in regions where 

 the disease is serious ; the third is made when the berries are 

 the size of a pea ; the fourth, as the berries become large enough 

 to touch each other. 



Downy-mildew . 



Downy-mildew (P'asmopara viticola) rivals black-rot for 

 first place among fungous diseases of the grape. It is found 

 in all grape regions east of the Rocky Mountains but does most 

 harm in northern localities. Like black-rot, downy-mildew 

 attacks all the tender growing parts of the vine, but is chiefly 

 found on the foliage and is usually less destructive than black- 

 rot. As first seen on the foliage, the work of the fungus appears 

 as greenish-yellow, irregular spots upon the upper surface which 

 later become reddish-brown. At the same time on the under 

 surface of the leaf, a thin, white downy growth puts forth. 



