10 FARMERS' BULLETIN 891. 



METHODS OF CONTROL. 



Most of the measures for the prevention or control of the corn 

 root-aphis are methods which not only are effective in reducing or 

 eradicating this and other insect pests, but constitute the more ap- 

 proved cultural practices and for this reason are doubly important. 



ROTATION OF CROPS. 



A rotation which avoids having two successive crops of corn on 

 the same land is effective not only in preventing injury by the corn 

 root-aphis, but also in controlling other serious pests. In the cotton 

 belt it is important also to avoid following cotton with corn, or vice 

 versa, since both plants are hosts of the same aphid. No other cul- 

 tivated field crop is seriously affected by this insect; consequently 

 corn may follow^ any other field crop with reasonable safety. Oc- 

 casionally corn is damaged in spring following other crops, such as 

 clover, but in these cases it will be found that smartweeds and other 

 wild plants preferred by the aphis have occurred in the field in abun- 

 dance the year before. Damage during late spring or summer may 

 occur in corn following a crop other than corn or cotton, the infesta- 

 tions sometimes coming from neighboring heavily infested fields, 

 but usually such damage occurs only in years unfavorable to corn 

 growing and is of rare occurrence. 



CULTURAL PRACTICES. 



The most complete and effective means of controlling the corn 

 root-aphis is thorough stirring of the soil previous to planting. The 

 object of this procedure is to disturb the ant colonies and scatter and 

 kill the aphids so as to permit the plants to make a substantial 

 growth before the ant and aphid colonies can become reestablished, 

 and in addition to prevent the growth of weeds upon which the 

 aphids live, making it necessary for the ants to carr}^ the surviving 

 aphids to new fields. Infested fields which are to be replanted to 

 corn should be plowed to a depth of 6^ or 7 inches in the spring, 

 after March 15 in the latitude of central Indiana and Illinois; then 

 they should have 3 or 4 diskings to a depth of 4 or 5 inches with a 

 16 or 20 inch disk, the number of cultivations and the intervals 

 between them varying according to the length of the period between 

 plowing and planting. When it is necessary to replant early injured 

 corn the field should first be plowed deeply and thoroughly and then 

 disked deeply 3 or 4 times at intervals of 2 or 3 days. '' Though 

 these practices necessarily involve additional labor, they not only 

 prevent injury by the corn root-aphis, but also put the field in a 

 much better physical condition. Plowing in the fall before the ant 

 colonies go below the plowline is sometimes as useful as spring plow- 



