184 GRAPK CULTURE AND 



come dried and roll up, attacked, the herbaceous parts 

 blacken, cease to grow, and end by withering and drying up. 

 This latter extreme is rarely attained in California. The 

 growing berries are attacked as readily as other parts, giving 

 the whole a languishing and unhealthy aspect. The young 

 branches also present blotches of a powdered nature which 

 ultimately cover the greater part of the surface exposed to the 

 sun, and where badly affected also taking on a whitish, pow- 

 dered and eventually chapped appearance, which causes them 

 to crack open and cease to grow. Thus it will be seen that the 

 oidium, unlike other fungus, affects the crop directly as well 

 as indirectly through damage to the foliage. The parasite 

 first appears abundant in June, though frequently commencing 

 its attack in May, at or after the time of flowering. 



The conditions favoring the oidium are moisture and 

 warmth, the latter playing the most important part. The 

 moisture here meant is not the extremely humid condition of 

 the atmosphere which appears with or immediately follows a 

 rain or heavy fog continue, a condition often incorrectly named 

 as favorable to oidium, but merely the moisture to be found 

 in sea breeze after it has traveled ten, twenty or even thirty 

 miles inland. An atmosphere which produces a light dew at 

 night is sufficiently moist to favor to the utmost the propagation 

 of oidium. Quite different in this respect is the peronospora 

 and Anthracnose which require the deposition of heavy rain, 

 fog or excessive moisture to produce their growth. For this 

 reason, I believe, California has been comparatively free from 

 the true Mildiou, a disease which of late years in France, 

 where summer rains are frequent, has threatened the vine- 

 yards to as great an extent as has the- dreaded phylloxera. 



Our principal vegetable parasite thus far has been the oidi- 

 um, one especially favored by our dry, warm climate, and one 

 easily destroyed by the timely application of sulphur. 



As before remarked, excessive moisture is unfavorable 



