130 AGRICULTURE 



This is prepared by mixing one pint of formalin with 

 thirty gallons of water. The seed potatoes are soaked 

 in the solution for two hours, and then planted without 

 allowing them to come into contact with bags or utensils 

 in which scabby potatoes have been kept. 



Leaf, or early blight. Leaf blight is another c-ommon 

 potato disease. It attacks the leaves and stems, first show- 

 ing about the time that the tubers begin to form. Its pres- 

 ence may be detected by the presence of grayish brown 

 spots on the leaves, the part of the leaf attacked soon be- 

 coming hard and brittle. Within three or four weeks the 

 leaves are all killed, and the stem is also affected. The tubers 

 grow but little after the leaves are first attacked; hence 

 the crop is ruined unless the blight can be checked. 



The ravages of leaf blight can be almost if not wholly 

 prevented by spraying the plants with the Bordeaux mixture 

 (see page 249). This solution is applied with a spraying 

 machine at the rate of about fifty gallons to the acre. From 

 three to five sprayings during the season are required when 

 leaf blight threatens. One pound of Paris green to the 

 acre at the first spraying, and the same amount later in the 

 season will also destroy the potato beetles, which often prove 

 such a pest. 



Late blight, or rot. The blotches and blackish 

 streaks often seen running through tubers are caused by 

 late blight, or potato rot. This disease first attacks the 

 leaves and stems, causing them to soften and decay, pro- 

 ducing a bad smell. Late blight often appears suddenly, 

 and spreads through a field with great rapidity. A green, 

 healthy-looking field may turn almost black in a day or two. 



The treatment for late blight is the same as for leaf 

 blight, and should never be neglected in regions where 

 blight is common. . It is far better to begin the spraying 



