FARM METHODS FOR THE CONTROL OF INSECTS 31 



and wireworms live normally in grass land, and where it has not 

 been plowed for several years they often become exceedingly 

 abundant. If the sod be then turned under and the land planted 

 to corn these insects will attack the corn, and as there are rela- 

 tively few plants to the number of insects which were feeding 

 upon the grass, the injury will usually be serious. To avoid 

 this, sod land should be planted in a small grain, buckwheat, 

 potatoes, or some crop not affected by these pests. Similarly, 

 the insects which affect cabbage usually feed on all the cole crops, 

 and turnips, radishes, etc., following cabbage will be liable to 

 injury by the same pests. Clovers, cowpeas, and other leguminous 

 crops become of importance in rotation in this connection, as 

 they are not usually attacked by the insects affecting other crops, 

 and of course are widely used in every good rotation for the pur- 

 pose of storing nitrogen in the soil through their root tubercles. 



Time of Planting. Planting crops so that they may avoid 

 the greatest abundance of their worst insect enemies is often the 

 best method for their protection. Late-sown wheat is usually 

 exempt from the attack of the Hessian-fly (see page 119) 

 and late-planted corn is much less affected by the stalk-borer 

 (see page 82) than that planted earlier. On the other hand 

 early planting of early-maturing varieties often enables the crop 

 to mature before its pests become most abundant. Thus early 

 planting and early varieties are of the greatest importance in 

 preventing injury by the cotton boll weevil, the cotton boll- 

 worm and corn ear- worm, and early varieties of peas escape the 

 injury of the pea aphis. 



Weeds. Many insects feed upon some common weed in one 

 stage while in another stage they are injurious to a cultivated 

 crop. Thus the flea-beetles feed upon the roots of solanaceous 

 weeds during the larval stage, while the adults attack all sorts of 

 garden crops. In many cases caterpillars, such as the salt marsh 

 caterpillar, army worms, the white-lined sphinx moth, and 

 grasshoppers multiply upon weeds growing in neglected fields 

 until they overflow and destroy crops. Many insects feed on 

 weeds during the early part of the season or after the crop which 

 they injure is harvested, so that the destruction of these weeds 

 may often considerably shorten their breeding season or increase 

 their mortality. Thus the corn root-aphis lives on the roots 



