Februarv, '211 



mccolloch: corn leaf aphis 



93 



Referring to Tables II and IV, it will be' noticed that Commercial white 

 shows a marked increase in injury over the other varieties in nearly all 

 the date plots. Likewise, there is some indication that Hildreth is not 

 as susceptible to injury. In order to detennine whether Commercial 

 White was as badly injured when grown in general fields, a comparison 

 was made between a field of it and a field of Pride of Saline, both fields 

 being planted about May 5. The field of Commercial White had 14.9 

 percent, of the plants severely injured, while Pride of Saline had only 

 6.S percent. In addition to these experiments, counts were made of 

 the injur}' in variety tests in the Entomology plots and at the Agronomy 

 farm. The result of these studies are presented in Table V. 



T.\BLE v. — Percentage of Plants Showing Severe Injury in 1919 and Appreci.\ble Injury in 



1920' 



'The varieties are ranked in this table with relation to their apparent susceptibility to injury. 



In summarizing the data presented in Table V, it will be noted that 

 the amount of injury increases with the lateness of the variety. Late 

 maturing varieties, such as White Democrat, Commercial White, 

 Midland Yellow Dent, and Corn Planter, sufi"ered the greatest damage, 

 while such carl\- maturing varieties as Minnesota No. 13, 90 Day, 

 Funk Yellow Dents, and the various strains of Bloody Butcher, had a 

 comimrativeh' low percentage of injurx'. There is also some indication 

 that certain varieties are not infested as badl\' as others, although they 

 have about the same growing period. This is strikingly exhibited b}^ 



