FUNGI AFFECTING THE POTATO 



The Downy Mildew, or Late Blight 



Phytoplwra infestans 



A sufiBciently full account of this disease has already 

 been given in the Introduction (pp. 6-10). A large pro- 

 portion of the potato maladies in the United States have, 

 until lately, been attributed to this fungus ; but recent 

 observations indicate that other asrencies are at work — 

 particularh' the fungus known as Jfao'osporium solcmi, 

 and apparently certain bacteria. The downy mildew 

 disease has been called, by Professor Jones, of Vermont, 

 the ^'late blight," to distinguish it from the ^^ early 

 blight,'' caused by the MacrosjDorium. The late blight 

 fungus generally ajjpears rather late in the season ; and 

 its attack is frequently sudden and fatal, affected plants 

 beino" entirely destroyed in a few days. The tubers are 

 also commonly affected, rotting and producing, during 

 the process, a foul smell. This disease is most destruc- 

 tive during warm, moist weather, at such times spread- 

 *ing very rapidly. It commonly begins as a single spot 

 on a leaf, from which it spreads throughout the plant, 

 and produces on the lower leaf-surface a mildew-like 

 growth, to be distinguished by the naked eye. This dis- 

 ease can be j^revented by sj^raying several times with the 

 Bordeaux mixture. 



The Early BHght, or Leaf=spot Disease 



Macrosporium solani 



This disease appears early in summer in the shape 

 of small browuj brittle spots, scattered over the leaf. 



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