OIDIUM OR POWDERY MILDEW OF THE VINE. 349 



Now, even with such thorough winter treatment as this, which it 

 would be quite impracticable to apply in a vineyard, no apparent effect 

 was obtained in the control of the spring infection. The spring infec- 

 tion was due, therefore, to spores which were not on any part of the 

 vine, and from which no kind of spraying or swabbing of the vine 

 would be any protection whatever. 



Pacottet concludes, therefore, that practically all the spring infec- 

 tion is due to spores which have passed the winter in the soil. These 

 are the spores contained in the perithecia which have dropped in the 

 autumn with the leaves on which they are formed. His advice for hot- 

 house treatment is to gather all these leaves before they fall and to burn 

 them. 



This again is impracticable in a vineyard, and we are forced again 

 to the conclusion that no form of winter treatment is of any use in the 

 control of Oidium in vineyards, and that the only practicable method 

 is proper sulfuring of the vines in spring and summer. This will' pre- 

 vent injury to the vines, and if thorough will prevent the formation of 

 winter spores. 



SUMMAEY. 



Oidium is one of the most serious diseases of the vine and the only 

 serious fungus disease of vines in California. 



It is capable of destroying the whole crop in most vineyards in bad 

 seasons if not controlled. 



Much more damage is done to vines and grapes in California than 

 is usually supposed, but the control is much easier and more certain 

 than in most vine-growing countries. 



The disease attacks leaves, canes, and fruit during the growing 

 season. 



It grows only on the exterior green surfaces of the vine and passes 

 the winter in the form of resting spores in the soil. 



Certain varieties of vines are very susceptible and others compara- 

 tively resistant. 



Moist warm atmosphere favors the growth of the fungus. 



Methods of training, cultivation, and irrigation which keep the vine 

 dry by thorough aeration minimize the danger of attack. 



Dusting the vines with sulfur is the cheapest and most efficient 

 method of control in California. 



The weather and the season when the sulfur is applied are of great 

 importance. 



