A STUDY OF FACTORS INFLUENCING THE YIELD OF POTATOES 1255 



tively. As shown in these tables, there was no apparent gain in yield in 

 1913 from cultivating more than seven times. In fact, it is question- 

 able whether the small gain shown in most cases from cultivating more 

 than five times was sufficient to pay the extra cost of the labor involved. 

 This means that the average frequency for the year concerned was not far 

 from optimum. The coefficient 0.055 0.039 (fig. 148), while positive, is 



Yield per acre, in bushels 



-? 3 



"es 4 



5 



3 6 



S 7 



| 8 



I 9 



s 10 



14 



12 27 



26 



14 



300 



FIG. 148. 



50 52 76 38 

 r = 0.055 0.039 



CORRELATION OF FREQUENCY OF CULTIVATION AND YIELD ON 300 FRANKLIN AND 

 CLINTON COUNTY FARMS IN 1913 



too small and insignificant to indicate any real correlation of frequency of 

 cultivation with yield. It must be concluded, therefore, that in practically 

 all cases sufficiently frequent cultivation was given so that it was not a 

 factor limiting yield. 



SPRAYING 



Spraying as a factor in potato production must have been first practiced 

 in this country sometime after 1859. This is the date when the Colorado 

 potato beetle (Leptinotarsa decemlineatd) began its movement eastward from 

 the Rocky Mountains (Fraser, 1912). The potentiality of this pest to 

 cause complete defoliation has since resulted in the extensive use of such 

 arsenical insecticides as paris green, arsenate of lead, and arsenite of 

 soda, for its control. The extent to which insecticides have been used in 

 a given locality has depended on the prevalence of the beetles. The fact 

 that growers in a certain locality did not spray for insects during a certain 

 season, is evidence that insects were scarce or almost absent. A study of 

 the influence of spraying with insecticides on yield in a given region, there- 



