21 



marked waves of disease ; one in the spring soon after 

 the foliage is full grown. The second wave appears soon 

 after midsummer, and attacks the leaves and shoots 

 of the new growth (see Plate I.). 



During an average season the spring wave of 

 disease is usually of a mild character, and apt to be 

 overlooked, or, at all events, neglected. This neglect, 

 however, may lead to serious results, for the scattered 

 patches of mildew furnish the spores that infect the 

 flower buds and at a later stage set up the second wave 

 of disease, which is mostly confined to the new growth. 



The white summer fruit is alone produced during 

 the first wave of infection in the spring, as the wood of 

 the previous season cannot be infected, and the winter 

 fruit is only produced on the mildew growing on the 

 shoots. For this reason the late summer wave of infec- 

 tion is most dangerous, inasmuch as it furnishes the 

 fungus fruit that starts the disease the following season. 

 As previously stated, the winter fruit appears on the 

 white cottony tufts of mycelium growing on the young 

 wood, rarely on the fruit, never on the leaves. 



PREVENTIVE MEASURES. 



(i). Cleanliness. As will have been gathered from 

 the preceding account, the extension of mildew depends 

 on summer spores produced on the leaves being con- 

 veyed by wind and other agents to other healthy leaves. 

 This risk is met by spraying, which will be dealt with in 

 the next paragraph ; on the other hand, the appearance 

 of mildew during the following season depends entirely 



