FACTORS IN WHEAT PRODUCTION 103 



the choice of wheat, corn, oats, rye, flax, and 

 barley./ 



Enemies -and Diseases that affect Wheat Pro- 

 duction. - - Related to both soil and climate, and 

 seriously affecting the production of wheat, are 

 its enemies and diseases. Like all living things, 

 wheat must struggle to live. It is hindered by 

 weeds, plant diseases, and insects. 



From Rlley, 7th Missouri Report. 



FIG. 59. The chinch bug : adult, a, b, eggs ; c, newly hatched larva with 

 enlarged tarsus at d ; e, larva after first molt ; /, larva after second molt ; 

 g, pupa ; h, i, j, leg, tarsus, and beak of adult bug. 



Weeds. - - Weeds interfere with the growth of 

 wheat by choking it out, thus lessening the yield, 

 and reducing the quality of the grain. Of the 

 many weeds that attack wheat fields the most 

 persistent are those commonly known as Chess, 

 Russian Thistle, and Wild Mustard. In these the 

 seeding methods are so well perfected that their 

 extermination is difficult. The general methods 

 employed in combating weeds and thus prevent- 



