Potatoes 1387 



BLIGHT 



Taken altogether, the most serious foe to the potato is the blight. 

 It is so insidious in its attacks that if preventive measures are not 

 employed early in the season it will often ruin a potato crop in 

 twenty-four hours. The late blight is the one most in evidence 

 and most destructive. It is peculiarly a wet weather disease, the 

 spores of which, so far as is known, live over winter only in the 

 old tubers. When such infested tubers are planted and the earth 

 becomes warm and moist, these spores multiply and burst from 

 their cells, so that the soil literally swarms with them. Many, of 

 course, die ; some find their way to the surface. Often, when the 

 plants are five or six inches high, a heavy rain will beat them down 

 to the earth where they come in contact with the blight spores. 

 If the weather continues wet, these multiply and penetrate the 

 leaf. Later they spread to other leaves and live on the leaf tissues. 

 When weather conditions are favorable, i. e., wet, they increase at 

 an enormous rate, and so destructive are they that a field will often 

 turn black in a day. If the wet is excessive, these spores are 

 washed from the tops to the ground, and so to the tubers again, 

 and rot often follows — always infection. Here is another reason 

 for deep planting. Tubers are less exposed to the spores and be- 

 ing deeper and cooler in the spring, fewer spores germinate and 

 come to the surface. There is no cure after the spores are estab- 

 lished, but it can be prevented by what is known as the bordeaux 

 mixture, viz., 5 pounds of copper sulphate (blue vitriol), 5 pounds 

 of lime and 50 gallons of water. If this is thoroughly applied 

 early, before the leaves are contaminated, it copperplates them, as 

 it were, and the blight spores die because they can not gain an 

 entrance. It must, therefore, be applied in season, thoroughly, so 

 as to protect the whole plant, and often enough to cover the new 

 growth. Sometimes one spraying before the spores come from 

 the ground has been sufficient. Usually three give excellent re- 

 turns. Again, five are even more profitable. Much depends on 

 the season, as well as on the time and thoroughness of the work. 



There is no question as to its practicability, in proof of which 

 I call attention to Bulletins No. 32,3 and 349 of the Ts T ew York 

 State Experiment iStation, which may be had for the asking. 

 Briefly stated, the facts are these: For seven years the station 



