INSECTS 189 



grub, wire worm, and cut worm, which infest sod land may 

 remain to injure the corn. Grass furnishes so much food 

 that these insects are not usually noticed when the field is 

 in grass, but they are numerous enough when the corn plants 

 appear to do great damage to corn. This injury may be 

 greatly reduced if measures are taken to get rid of the insects 

 before planting the corn, that is, by early spring plowing 

 and late planting. Another method would be to provide 

 a rotation which would avoid using crops like corn to follow 

 grass. Thus oats, clover, and corn would be a better ro- 

 tation than oats, grass and corn. 



Arrangement of crops on the farm. The arrangement of 

 crops in the fields has an effect on the control of destructive 

 insects. Crops having the same insect enemies should not 

 be planted side by side, for certain insects are likely to migrate 

 from one crop to another. For example, a field of corn beside 

 a field of grass might be injured by the army worms which 

 come from the grass; but if the corn were next to a wheat 

 field it would escape injury from these insects, for army worms 

 are rarely found among wheat plants. On the other hand, 

 if there were danger of injury from chinch bugs, corn growing 

 next to wheat would be especially liable to damage by those 

 insects, if they were numerous in the wheat. 



Neither should crops having the same insect enemies 

 succeed each other, for insects injurious to one crop are 

 likely to live over to do damage to the succeeding crop; 

 corn following grass, mentioned in a preceding paragraph, 

 is an example. Nor should the same crop continue on the 

 same ground two or more seasons in succession; the well- 

 known occurrence of numerous white grubs and wire worms 

 in old meadows and pastures, and of corn-root aphides and 

 corn- root worms in fields where corn is grown for several 

 years in succession are examples. 



