330 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. 



It is impossible to do the work perfectly in a high wind, but a 

 gentle breeze is an aid in making the sulfur penetrate to all parts of 

 the vine. 



Rain or very heavy and continued winds following immediately 

 after the sulfuring will remove most of the sulfur before it has pro- 

 duced the desired effect on the fungus, and the treatment must be re- 

 peated. Each sulfuring should be followed by from one to four days 

 of warm weather before the sulfur is removed by rain or wind. One 

 or two days at or about 90 F. to 95 F., maximum shade temperature, 

 or four or five days between 85 F. and 90 F. will usually give satis- 

 factory results. If rain comes before the sulfur has been subjected to 

 such temperature, the vines must be resulfured. 



As already noted, sulfuring in excessively hot weather should be 

 avoided on account of the danger of burning grapes or foliage. For 

 the same reason, any cultivation or other disturbance of the vines 

 should be avoided in hot weather immediately following the application 

 of sulfur. 



Proper Season for Sulfuring. The proper season for sulfuring will 

 depend on the number of sulfurings needed. This number will differ- 

 according to locality, weather, variety, and the exposure of the vine- 

 yard and will vary from one to three in the interior valleys to from 

 two to five in the coast valleys, or even as high as six or seven with 

 susceptible varieties, in bad seasons in close proximity of the coast. 



The most necessary and effective sulfuring of all, and one which 

 should never be omitted under any conditions, is at the time when the 

 vines begin to open their blossoms. Even with the most resistant vari- 

 eties, in the least affected districts, this sulfuring should be applied. 

 Even where there is little or no danger of Oidium, the gain in better- 

 setting of the fruit has been so frequently demonstrated that it amply 

 repays the outlay. As all varieties do not blossom at the same time, the 

 mixing of varieties in the same block should be avoided, for this and 

 other reasons. 



Number of Treatments. In the interior, if this sulfuring were reg- 

 ularly and universally applied, it would usually be sufficient. As many 

 growers totally neglect sulfuring, however, there is danger of reinfec- 

 tion from neighboring vineyards during the early summer. The vines 

 should be watched, therefore, and upon the first signs of Oidium, a 

 second sulfuring should be applied. This will usually be at the time 

 the grapes are about the size of buckshot. Later than this there is 

 little danger usually, as the air becomes too hot and dry for the growth 

 of the fungus. The vines should be watched, however, especially those- 



