FUNGI AFFECTING THE POTATO 



The Downy Mildew, or Late Blight 



Phytophora infestans 



A sufficiently full account of this disease has already 

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

 portion of the potato maladies in the United tStates have, 

 until lately, been attributed to this fungus ; but recent 

 observations indicate that other agencies are at work — 

 particularly the fungus known as Macrosjwrium solani, 

 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 ]\[acrosporium. Tho late blight 

 fungus generally appears rither late in tlie season; and 

 icS attack is frequently sudden and fatal, affected plants 

 Ix'inGf entirely destroyed in a few days, 'j'he tubers are 

 also commonly affected, rotting and producing", during 

 I he process, afoul 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 

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

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

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

 ease can be prevented by spraying several times with the 

 Bordeaux mixture. 



The Early Blight, or Leaf=spot Disease 



Macrosporium solani 



This disease appears early in summer in the shape 

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



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