92 JOURNAL OF ECONOMIC ENTOMOLOGY [V^ol. 14 



manner of feeding, at least in part, in protected situations, together with 

 the fact that the seasonal history is only indefinitely known, indicate 

 some of the difficulties to be encountered. Experimental tests with 

 nicotine sulphate sprays gave excellent results in killing the aphids, 

 but the problem of spraying corn and sorghum fields is out of the ques- 

 tion. 



Certain observations on the date of planting corn and on variety tests 

 of corn indicate that the injury can be materially reduced, and that 

 further studies along this line may open the way for definite methods of 

 control. 



Time of Planting Corn 



Observations were made in 1919 and 1920 on the number of plants 

 injured in the Time of Planting Corn experiments conducted by the 

 Entomology Department, and also on a date of planting test at the 

 Agronomy farm in 1919. The counts of 1919 include only those plants 

 showing severe injury such as is seen in Plate 2, figure 1, while the 1920 

 counts took into consideration all plants showing appreciable injury. 

 The results, which are presented in Tables II to IV, indicate that with 

 the possible exception of Hildreth, the injury increases with the delay 

 in planting until about the middle of May. 



Table II. — Percentage of Plants Showing Severe Injury, Entomology Plots, 1919 



Date cf Planting 

 Variety of corn April 15 May 1 May 15 June 1 June 15 



Boone Co. White 13.9 lO.G 18.3 18.3 13.8 



Pride of Saline 7.6 11.8 17.0 19.9 13.7 



Commercial White 18.0 21. .3 25.2 27.7 20.2 



Kansas Sunflower 7.6 10.8 14.4 16.6 15.6 



Hildreth 17.8 12.6 12.6 16.0 12.5 



Table III. — Percentage of Pride of Saline Plants Showing Severe Injury, Agrono.viv F.\rm, 



1919 



Date of Planting 

 Method cf Planting April 16 April 21 May 3 May 10 May 20 



Open furrow 4.8 8.6 10.0 15.7 10.0 



Listed 8.9 9.5 18.0 16.9 10.1 



Surface planted 5.6 5.0 10.7 9.8 4.7 



Table IV. — Percentage cf Plants Showing Appreciable Injury, Entomology Plots, 1920 



Date of Planting 

 Variety of corn April 24 May 1 May 8 May 15 May 22 May 29 



Boone Co. White 58.9 58. 1 67.8 63.7 64.5 67. 1 



Pride cf Saline 58.1 45.0 49.2 ,58.3 66.6 56.9 



Commercial White .59.6 65.7 58.1 67.7 65.3 41.4 



Kansas Sunflower 48.2 46.7 .55.1 .56.5 59.1 55.1 



Hildreth 50.0 47.7 46.5 .50.0 57.3 44.0 



Variety Tests of Corn 



The observations on different varieties of corn were similar to those on 

 the Date of Planting Tests in that only severe injury was counted in 

 1919, while all plants showing appreciable injury were noted in 1920. 



