9 



paratoiT to putting- out the 3 oung crop, and which u.suallj' causes the 

 farmer little concern, is really of vital importance. The farmer rests 

 secure in the knowledge that he can easily kill this growth of weeds 

 and grass later. This is true; but he does not do so until his corn has 

 grown to a size that will permit cultivation, and b}- this time the ants 

 have transferred the root-aphis to the corn. The aphides are then no 

 longer dependent on the roots of the grass and weeds, so that the 

 destruction of the latter at this time does not seriouslj' affect the 

 domestic arrangements of the ants and aphides. 



NATURAL ENEINIIES OF THE ROOT-APHIS. 



While the leaf -aphis is attacked by a host of parasites, the root- 

 aphis does not appear to suffer in the least from inroads of either para- 

 sitic or predaceous insect enemies. This is, perhaps, owing in part to 

 the protection offered l)y the ants. All natural checks must therefore 

 be meteorological influences, and, as previousl}" shown, these also are 

 to a marked degree overcome by the watchful care of attendant ants. 



PREVENTIVE AND REMEDIAL MEASURES. 



Preventive measures deal with the pest prior to its becoming estab- 

 lished on the roots of corn in the fields; remedial measures, with dis- 

 posing of it afterwards. 



CROP ROTATION. 



From the fact that in the midst of the corn belt, and where the 

 root-aphis is known to prove destructive under certain conditions, 

 almost complete immunity is secured where a system of crop rotation 

 has been carried out for many years, involving but one corn crop in 

 the cycle of rotation, it is self-evident that this measure offers the 

 greatest protection from the ravages of this pest. Indeed, it is only 

 where such a system of crop rotation is not practicable that the root- 

 aphis need be considered in farm practice. To the eastward, where 

 there is more general rotation of crops, this pest does but little injury. 



Unfortunately, local conditions, often extending over large sections 

 of country, will not permit of crop rotation being generally adopted, 

 and some other plan more feasil)le nuist be put into practice. Two 

 other methods may be followed. One of these is practicable through- 

 out the corn-growing section of the country in seasons of not more 

 than normal precipitation during the time intervening between the 

 first plowing of the ground and the first cultivation of the young corn. 

 The other is perhaps best adapted to the southern portion of the coun- 

 try on account of the milder winters. 



[Cir. 86] 



