APPLE POWDERY MILDEW. 3 



Burrill (5) in 1892 changed the name of the fungus to Sphaero- 

 theca 7)iaU (Duby), identifying it with Eiysiphae inali of that au- 

 thor, but this fungus was later identified as Phyllaetinia corylea 

 (Pers.) Karst. 



Grout (7) accepted Burrill'e identification. He found that the 

 perithecia matured late in the season and were usually found on the 

 shoots, seldom on the leaves, which he suggested might account for 

 the rarity of their collection and the confusion in nomenclature. 



In 1894 Pammel (6) called attention to the disease in Iowa, stating 

 that it was of common occurrence. He recommended the use of 

 Bordeaux mixture instead of ammoniacal copper carbonate as a spray. 

 In a later publication (8) he discussed the confusion in nomen- 

 clature and suggested that it is doubtful whether perithecia of Pod- 

 osphaera oxyacanthae were ever actually seen on the apple in this 

 country. 



The early confusion of the identity of the fungus was cleared up 

 by Salmon (9) in 1900. He definitely referred the fungus to 

 Podosphaera leucotricha. 



The first report of the disease from the State of Washington was 

 by Lawrence (10) in 1905. He described the different species of 

 powdery mildews occurring in the State but did not recognize 

 Posdosphaera leucotHcha. 



In 1910 Stewart (11, p. 318-321) reported that he had found no 

 other species than Podosphaera leucotricha on apples in New York. 

 He found the disease chiefly on water sprouts and nursery stock, but 

 also found it on the terminal growth of trees 36 years old. He noted 

 that the Chenango and Black Ben Davis varieties are particularly 

 susceptible. 



In 1914 Ballard and Volck ( 12 ) published a very complete descrip- 

 tion of the occurrence and control of the disease in the Pajaro Valley 

 of California, where the climatic conditions are particularly favor- 

 able to the development of the disease in serious epidemic form. 

 They found that fully 90 per cent of the foliage of susceptible varie- 

 ties, such as Yellow Newtown and Yellow Bellflower, was frequently 

 diseased. They found that Bordeaux mixture gave very poor mildew 

 control. Copper acetate and copper oxychlorid were effective against 

 the mildew, but caused injury to the fruit and foliage. Dilute lime- 

 sulphur solution and solutions of sulphids in general were likewise 

 injurious. About 125 different materials were tested for foliage 

 spraying, and as a result it was found that sulphur in some finely 

 divided form was the most efficient. Specific directions were given 

 for the preparation of an " iron-sulphid " spray whereby the soluble 

 sulphids so injurious to foliage in that climate were eliminated. At- 

 tention was called to the importance of pruning out diseased twigs 

 as a supplemental aid in control. The important relation between 



