164 DISEASES OF ECONOMIC PLANTS 



Result of Bla.ck Rot Experiments in 1908 



Powdery mildew, uncinulose ( Uncimda necator (Schw.) 

 Burr.). — This mildew, a native of the United States, first 

 noted in Europe about 1845, near London, and shortly after 

 in Belgium and France, is said to have reached every grape- 

 growing country of Europe l^efore 1851. It increased in 

 severity until 1854 when it began to be held in check by 

 sulphur applications. It is known in all parts of the United 

 States. 



The powdery mildew attacks all parts of the plant except 

 the roots, showing first upon both the upper and lower 

 surface of young leaves as whitish circular spots, which ap- 

 pear somewhat as though dusted with flour. These spots 

 enlarge, coalesce, and may cover the whole leaf. The af- 

 fected leaf is retarded in growth and becomes distorted. 

 Mildewed blossoms fail to set their fruit, and fruit that 



