302 The Spraying of Plants. 



presence of the parasite by portions of the leaf turning a lighter 

 green than that of the normal tissue. Later, these parts turn 

 yellow, and when the destruction of the tissue is complete, the 

 parts affected are of a brown color. If the under surface of 

 such leaves is examined, it will be found that there is a frost- 

 like substance projecting from the discolored part of the leaf 

 after the upper surface has begun to turn yellow. This appear- 

 ance is due to the formation of fungous threads which project 

 beyond the leaf surface and bear the summer spores of the 

 parasite. This appearance assists materially in identifying the 

 disease. 



The fruit is also very susceptible to the attacks of the downy 

 mildew; but when that is affected, the vine does not suffer so 

 much as the grower does. In case of diseased foliage, the crop 

 of the next year, as well as that of the present, is threatened ; 

 but with diseased fruit it is only a matter of the present year, 

 which is all-sufficient to make the grower anxious to know 

 what can be done. 



In the southern states the mildew appears during June, but 

 in the North it is not feared before July. The young berries 

 suffer very extensively. They are generally attacked before 

 they are one-half grown. The name " brown rot " has been 

 applied to such fruit on account of the brown color which sup- 

 plants the green. Later, as the fungus matures, the affected 

 berries become covered with a whitish powder, the fruiting 

 threads and the spores of the parasite, and this gives the ber- 

 ries a gray color, from which has come one of the popular names 

 of the disease. Both forms of the rot are nevertheless caused by 

 the same organism, although the external characters differ. 



Treatment. The downy mildew of grapes may attack the 

 vines throughout the growing season, and for this reason it 

 is more essential that applications be made earlier in the 

 year than those necessary for the control of the black rot. 

 Where downy mildew is found, an application made when the 

 shoots have grown from six to ten inches is a very important 

 one. The second should be made after the vines have blos- 

 somed, and later ones should succeed each other at intervals of 

 two to four weeks, taking the same precautions against stain- 

 ing the fruit as mentioned under BLACK ROT. The treatments 

 should be preventive rather than curative. 



