418 FIELD CROPS 



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 beetles cause an immense loss to 

 the potato crop throughout the United States every year. 

 Potato beetles 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 

 thoroughly to all parts of the plant, and in sufl&cient strength 

 to be sure to destroy the beetles. The use of a poor grade 

 of poison or of a weak solution may make the work ineffective. 

 Early and effective spraying is imperative. Spraying for 

 both bUght and beetles may be accomphshed by mixing poi- 

 son with the Bordeaux mixture, instead of with water, and 

 applying both at one operation. 



IMPROVEMENT OF THE CROP 



570. Crossing. Improvement in potatoes is conunonly 

 accomplished in two ways, by selecting new varieties grown 

 from seed and by selecting the best tubers from the best hills 

 of some of the common varieties. If seed produced on potato 

 vines is planted, there will be great variation in the plants 

 which are obtained. This variation gives the breeder a wide 

 range from which to select. Crosses between two varieties 

 of known characters are sometimes made artificially with a 

 «70w to combining in one variety the good qualities of both. 

 The desired results are not always secured, as the poor quali- 



