122 



Diseases of Economic Plants 



Use a dormant spray to clean the bark, trellis, etc. The 

 utility of this first spraying may vary with climatic condi- 

 tions and latitude. Use foliage sprays of 5-5-50 Bordeaux 

 mixture throughout the sunnner. Five or sLx applications 

 are usually necessary. The first should be made when the 

 shoots are 20-30 cm. long, the others at intervals of ten to 

 fourteen days. After the first two applications the spray 

 must reach the clusters to be effective. Spraying each 

 season is necessary; neglect one season brings large increase 

 in the rot the following season. 



The following table shows the benefits of careful, thorough 

 spraying. 



Result of Black-Rot Experiments in 1908 



Powdery-mildew ^^"^^ *°'^ (Undnula necator (Schw.) Burr., 

 Oidium) . — This mildew was first noted in Europe about 

 1845, near London, and shortly after in Belgium and France, 

 and is said to have reached every grape-growing country of 

 Europe before 1851. It increased in severity until 1854 when 

 it began to he held in check by sulfur applications. It is 

 known in all parts of the United States, but is less destructive 

 here than abroad, though in certain localities in New York, 



