February, '21] mccolloch: corn leaf aphis 91 



Indirectly, this aphis may also be considered injurious to corn, since 

 the honey dew secreted by it forms one of the main sources of food for 

 the moths of the corn earworm and other insects of the corn field. It is 

 also generally associated with physodermal disease of corn and there is a 

 strong possibility that it may be concerned in the transmission of this 

 disease. 



Injury to Sorghums 



The injury to sorghums, while general throughout the state, appears 

 to increase westward. Mr. J. H. Parker of the local Agronomy Depart- 

 ment, after a trip through western Kansas in September, 1919, examining 

 sorghum fields, reported that the com leaf-aphis had ruined the crop 

 in that section. The heads were very heavily infested and the grain so 

 badly shriveled that much of it was worthless. 



All kinds of sorghums are attacked by the aphids, although there is 

 apparently a difference in the injury of the different varieties. The 

 percentage of plants showing appreciable injury in a test of seventeen 

 varieties conducted in 1919 by Mr. W. P. Hayes, varied from 3.1 percent, 

 in the case of Sudan grass to 96.5 percent, for feterita (Table I). 



T.\ELE I. — -Percentage of Plants Showing Appreciable Injury in Variety Test of Sorghums, 



1919 



Percent. Percent. 



Variety plants injured Variety plants injured 



Black hull kafir 77.8 Feterita 96.5 



Dwarf black hull kafir 6.5.0 Freed's Sorghum 78.8 



Dawn kafir 46.2 Red Amber 85.8 



Shrock kafir 91.6 Kansas Orange 25.8 



Sunrise kafir 67.1 Sumac Sorghum 46.4 



Pink kafir 74.9 Dwarf Sumac Sorg. 21.3 



Red kafir 84.5 Hagena 67.1 



Dorse 96.3 Sudan 3.1 



Yellow milo 77.6 



As in the case of com, several distinct types of injury are noted. 

 The infestation usually begins in the developing curl, and the aphids 

 feed on the more succulent part of the leaves. As the heads develop 

 they attack these, sapping the juices from the developing grain. The 

 heads often become covered with the honey dew and later with molds 

 or fungi, which give them an unsightly appearance. The reddish dis- 

 coloration on the sorghums, due to bacterial infections, is usually asso- 

 ciated with A. maidis, and often becomes serious enough to cause the 

 rotting of the whole stalk. In 1920 the stalks of from 7 to 10 percent. 

 of the plants in a kafir field were heavily infested with A. maidis and 

 bacterial blight. The infestation resulted in shrinking the head, 

 causing a loss of about 33 percent, in weight and 50 'percent, in volume. 

 (Plate 3, fig. 6). 



Control 



A. maidis, like many of the aphids, presents ntmierous difficulties 

 in the way of control. The great rapidity with which it increases, its 



