348 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. 



must do to save our crop entirely, there will be no winter spores formed 

 and, therefore, no use in spraying for them. 



Winter treatment, moreover, cannot be completely effective because, 

 however well done, it cannot destroy all the resting spores, because 

 most of them are in the soil, and if but a few escape, they are capable 

 of infecting the whole vineyard when the weather conditions are favor- 

 able. Sulfuring, therefore, is necessary even when winter spraying is 

 practised. 



There is reason to believe, moreover, that winter treatment is com- 

 pletely ineffective. Every other vine in a small patch of vines at 

 Berkeley was treated last winter with bluestone, iron sulfate, or Bor- 

 deaux mixture. In the spring just as much mildew was found, on its 

 first appearance, on the treated as on the untreated vines. 



A still more convincing experiment is described in the "Revue de 

 Viticulture," No. 655, page 12. This seems to prove as well as a single 

 experiment can : First, that the fungus does not pass the winter to 

 any extent in the summer form under the bud scales ; and second, that 

 the most thorough winter treatment is useless if no winter spores are 

 formed, and completely ineffective if they are. 



Mr. Pacottet says in the article quoted : "In 1904 we observed that 

 the spring attack of Oidium occurred first precisely in those hothouses 

 of Nanterre where perithecia had been found in the autumn of the pre- 

 vious year. The same fact was observed in 1905. This led us to make 

 careful observations the following year on the manner and time of the 

 appearance of the Oidium. 



"Oidium appeared at the end of March, 1906, and only in those 

 grape houses, to the number of 20, where the presence of winter spores 

 had been noted in November of the previous year. In these houses the 

 fungus appeared with such intensity that nearly every leaf showed 

 simultaneously several patches. 



"These observations acquire especial importance when considered 

 in connection with the various hypotheses which have been advanced 

 regarding the modes in which the Oidium passes the winter, especially 

 as regards the hibernating of fragments of mycelium (summer form) 

 adhering to the canes and capable of vegetating anew in the spring. 



"At Nanterre the disinfection of the vines is as complete as it is 

 possible to make it. After removing the old bark they are treated with 

 boiling water and swabbed with a 30 per cent, solution of iron sulfate. 

 They are then covered with a paste of lime and sulfur. * * * Be- 

 fore the starting of the buds, the walls, glass, and casings are disin- 

 fected with strong washes and the air with the fumes of burning 

 sulfur." 



