8 



BULLETIN 120, U. S. DEPARTMENT OF AGRICULTURE. 



Very early in the season there is a period when great numbers of 

 what appear to be mild infections establish themselves and cause 

 a characteristic crinkling of the foliage. These infections soon die 

 out and the damage done is not particularly serious, though it is 

 undoubtedly of some importance. 



The climatic conditions of the Pajaro Valley offer excellent oppor- 

 tunity for the establishment and progress of the mildew. The fogs 

 furnish excellent moisture conditions for the germination of the 

 spores, and it is probable that the somewhat peculiar climatic condi- 



Fig. 3. 



-A peritheciuni of Podosphaera leucotricha, showing the two types of appendages. 

 Magnified 90 times. (After Gront.) 



tions of the valley influence the character of the foliage in a way to 

 make it more than normally susceptible to infection. The result is 

 that unless proper protection by spraying is provided, 90 per cent of 

 the foliage of Yellow Newtowns and Yellow Bellflowers may become 

 diseased before the end of the growing season. 



The summer spores, or conidia, that have just been discussed serve 

 only to spread the summer infections. They are not long lived, and 

 therefore are not capable of carrying the mildew over from fall until 

 the next spring. Furthermore, the mycelium on the twigs dies 



