FUNGI AFFECTING THE POTATO 



The Downy Mildew, or Late Blight 



Pli ytophora infest a ns 



A sufficiently 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 agencies are at work — 

 particularly the fungus known as Macrosporium solaiii, 

 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 Macrosj^oriuni. The late blight 

 fungus generally appears rather late in the season ; and 

 its attack is frequently sudden and fatal, affected plants 

 being entirely destroyed in a few days. The tubers are 

 also commonly affected, rotting and j^roducing, 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 prevented by s}>i'aying several times with the 

 Bordeaux mixture. 



The Early Blight, or Leaf=spot Disease 



^lacrosporium solani 



This disease appears early in summer in the shape 

 of small brown, brittle spots, scattered over the leaf. 



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