56 BOARD OF AGRICULTURE. [Pub. Doc. 



This potato disease is sometimes called the ' ' downy mil- 

 dew," because in favorable circumstances a downy or moldy 

 growth appears on the under surface of the leaves. This is 

 white in color and of considerable density. The upper sur- 

 face of the foliage does not show it, but wherever this frost- 

 like growth is present it is almost certain that the potato rot 

 fungus is present. This external growth consists of the 

 spores and all the parts bearing them. These spores mature 

 very quickly and have the power of immediately propagat- 

 ing the disease. They are small and light and are carried 

 rapidly by the wind. It is these bodies that cause the rapid 

 spread of this potato disease. After maturing from the leaf, 

 some of these spores fall to the ground and by rains, or 

 otherwise, are brought in contact with the tubers under 

 ground ; here the}^ germinate in the same way as upon the 

 foliage. The color of the affected tubers changes, and unless 

 the disease is proceeding with great rapidity, a brown, dry rot 

 takes the place of the normal white color. Under favorable 

 atmospheric conditions the disease may spread with such 

 rapidity that a black, foul-smelling, wet rot results. The 

 decay may take place slowly, and produce black, discolored 

 places throughout the potato, or it may occasion its com- 

 plete destruction. It is, of course, possible that the disease 

 may be communicated to the tuber through the stem, but 

 this is not supposed to be its usual method of attack. 



Fortunately the growth of this fundus, with all its attend- 



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ant ills, can be prevented by the timely and thorough appli- 

 cation of fungicides. Bordeaux mixture is the standard 

 mixture for this as for the great majority of fungous diseases. 

 The same treatment recommended for early blight will be 

 efficacious in preventing the late blight upon the tops and 

 the subsequent rotting of the tubers. 



Leaf Diseases, etc., resembling Blight. 

 Leaf burn or scald sometimes occurs and may be confused 

 with early blight. The tips and edges of the leaves turn 

 brown, and these discolored areas soon become hard and 

 brittle. The burning or scalding may occur at any time and 

 is the result of unfavorable conditions surrounding the plant. 



