INSECT CONTROL 325 



(6) Time of Planting. Early planting or the use of early- 

 maturing varieties often enables the fanner to secure a crop 

 before its pests have become most abundant. This has been 

 repeatedly demonstrated with the cotton boll weevil and the 

 cotton bollworm or corn earworm. Early cabbage plants 

 seem to be less injured by maggots and early varieties of 

 peas escape the aphis. On the contrary, late planting some- 

 times enables a crop to escape its enemies, as in the case 

 when wheat is sown too late in the fall for the Hessian fly 

 to lay its eggs on it. 



(c) Weeds. In many cases immature insects feed upon 

 some common weed and the adults attack a cultivated crop, 

 or they may multiply on weeds in neglected fields and then 

 migrate to a crop. "Volunteer" plants of the host crop 

 should be considered as weeds, for they afford food to insect 

 pests in the same way. Thus the corn root-aphis lives on 

 the roots of smartweed and other weeds and grasses until 

 corn is available, and cutworms feed on whatever vegeta- 

 tion is found before corn is planted, so that these pests are 

 more or less starved out on land kept free from weeds. The 

 cotton boll weevil feeds on volunteer cotton in the early 

 spring and the Hessian fly oviposits on volunteer wheat in 

 late summer and early fall. Seedling apple, peach and 

 cherry trees may also be considered as weeds from the 

 standpoint of insect control. 



(d) Fertilization and Culture. There seems to be no evi- 

 dence that any of our common fertilizers have any effect as 

 insecticides, but it is well known that plants which have 

 been weakened from any cause are more subject to insect 

 attack, while vigorous plants will often survive injury, so 

 that liberal fertilization is often of considerable importance, 

 particularly with insects affecting the roots or boring in the 

 stems. In the same way, thorough preparation of the soil 



