INSECTS 191 



likely to be destroyed by certain insects than those that are 

 weak. For example, wheat plants that make an early, vig- 

 orous growth, as npon richly fertilized land, are less likely 

 to be greatly injured by the jointworm than are weak, slow- 

 growing plants. Mineral fertilizers and soil amendments 

 such as kainit and lime seem to have a direct effect upon the 

 control of certain insects. For example, insects infesting sod 

 land may be partially controlled by heavy applications of 

 kainit and lime. This treatment, when applied in the spring, 

 has the added advantage of stimulating the growth of the 

 grass. 



Community cooperation. Certain insects migrate from 

 one farm to another and therefore cooperation among the 

 farmers of the community is necessary for the control of 

 them. For example, wheat should not be sown early for 

 pasture or volunteer wheat allowed to develop in wheat 

 fields when the Hessian fly is bad. Such a practice is likely 

 to injure the neighboring farmer who is making an effort to 

 save his next crop of wheat from the fly. 



Other methods of control. Clean farming, including 

 clean cultivation and the destruction of weeds and rubbish, 

 has its influence in keeping insects under control. Corn 

 shocks standing over winter may afford means of hibernation 

 for chinch bugs; old cabbage stalks and leaves may furnish 

 protection for the pupae of the cabbage butterfly and the 

 cabbage maggot; weeds and other plants along fence rows 

 and on other parts of the farm may harbor the Hessian fly, 

 the chinch bug, the jointworm and many other insects. 



Some varieties of plants are less liable to insect injuries 

 than others. When possible such varieties should be used, 

 provided they have other desirable qualities. The phylloxera 

 of the grape vine, a plant. louse injuring the roots and some- 



