254 FARM FRIENDS AND FARM FOES 



A great many different kinds of powdery mildews are 

 found upon wild and cultivated plants. One of the most 

 abundant of these is the Cherry Powdery Mildew, which 

 occurs also on apples and other fruits. It is especially de- 

 structive to young trees in nursery rows. The Gooseberry 

 Powdery Mildew is another widespread and destructive 

 disease. It is especially likely to attack English varieties 

 of gooseberries when grown in America. The Grape 

 Powdery Mildew is also more or less injurious over most 

 of the United States, and the Powdery Mildew of the Bean 

 is likewise widely injurious. 



The powdery mildews live externally upon the leaves 

 and stalks of plants more than is the case with most para- 

 sitic fungi. Hence we would expect that they could be 

 easily prevented by spraying with fungicides, and this is 

 true. These mildews are checked by applying almost any 

 of the fungicides. 



OTHER FUNGOUS DISEASES 



A considerable number of fungous diseases are due to 

 parasites, the complete life histories of which have not yet 

 been discovered. Such fungi are commonly classified 

 under the heading Fungi Imperfecti or Imperfect Fungi. 

 The imperfection, however, is found chiefly in our lack of 

 knowledge. As the diseases are more carefully investi- 

 gated, the parasites are being transferred to the various 

 groups to which they belong. 



The Potato Scab is one of the most important of these 

 diseases. It is caused by an inconspicuous fungus that in 

 freshly dug potatoes may often be seen as a coating of fine 

 white threads over the scabby surface. The disease occa- 

 sionally occurs upon beets and other root crops. Spores 

 are produced among these threads. It is now well estab- 



