i8o POTATOES 



the mixture to spray one acre. Spraying with Bordeaux 

 mixture may also control other fungus diseases not fully 

 understood at the present time. 



Potato scab is a disease that affects the potato ex- 

 ternally, making ugly blotches upon the surface. The dis- 

 ease is carried by the germs which remain upon the seed 

 potato or are left in the ground, thus affecting the succeed- 

 ing crop. The scab disease lives in the ground for several 

 years. After scabby potatoes have been grown on a piece 

 of land, no more potatoes should be grown on this piece 

 for at least six years. 



Where potatoes have become affected with scab the 

 grower should secure seed potatoes that are free from this 

 disease, or treat the affected ones by submerging sacks of 

 the potatoes for two hours in a solution made by adding 

 one pint of formaldehyde to 30 gallons of water. Other 

 treatments may be used, but the formaldehyde is most 

 simple and effective. Whole potatoes should be treated 

 and cut for seed after treatment. If potatoes so treated 

 are planted on scab-free ground the disease will not be found 

 on the succeeding crop. 



Insect enemies. The Colorado beetle, more commonly 

 known as the potato bug, is the chief insect enemy. 

 Other insect enemies that do more or less damage are the 

 flea beetle, blister beetle, and grasshopper. 



For control of potato insects, arsenical poisons are 

 used. Paris green and arsenate of lead are the poisons 

 commonly applied. A Paris green solution is made by 

 placing 2 pounds of standard Paris green in 50 gallons of 

 water. If sprayed on the potato plants after the dew has 

 dried off in the morning on a day that promises fair, the first 

 batch of insects will usually be controlled. It is often neces- 



