INSECT PESTS OF POTATOES 441 



for the growing of potatoes but once in several seasons on 

 the same soil is also effective. 



577. Scab. Scab, which attacks the outside of the tu- 

 bers, causing rough, unsightly blotches, also does immense 

 damage throughout the country. The disease may be car- 

 ried over in the soil or on the seed. As it works on the out- 

 side of the tubers, it may be controlled by treating the seed. 

 Potatoes that show any indications of scab should be treated 

 before they are cut. Mix 1 pound of 40 per cent formalde- 

 hyde in 30 or 35 gallons of water and soak the seed potatoes 

 in this solution for two hours. If the soil is infected with 

 scab, potatoes should not be planted on it for several years. 

 Plowing under green manure crops which will develop acid 

 in the soil is somewhat effective in destroying the spores. 



578. Insects Injurious to Potatoes. There are a num- 

 ber of insects which affect the potato crop. Cutworms, 

 wireworms, and grubs often attack the crop on sod land. 

 The control of these pests has been discussed under corn. 

 By far the most troublesome insect is the potato bug, or 

 Colorado beetle. The mature beetle lays its eggs on the 

 under side of the leaves of the potato. The larvae feed on the 

 leaves and if not checked will strip the plant, thus prevent- 

 ing further growth. These bugs cause an immense loss to 

 the potato crop throughout the United States every year. 



Potato bugs are usually controlled by spraying the vines 

 with Paris green, arsenate of lead, or arsenite of soda. By 

 far the most common poison is Paris green. This is mixed 

 in water at the rate of from 1 to 4 pounds in 50 gallons, and 

 sprayed on the vines either by hand with a whisk broom, 

 with a small knapsack sprayer, or by a large horse sprayer 

 that will spray several rows at a time. The machine em- 

 ployed usually depends on the extent to which the crop is 

 grown. It is important that the solution be applied quite 



