CORN PESTS AND DISEASES 



265 



ticed during the early life. The earliest acquire full 



growth and commence to travel in armies and 

 devastate fields of corn and other 

 crops. They soon afterward descend 

 into the ground, where they trans- 

 form and issue again as moths two or 

 three weeks later. 



The advance of these creatures can 

 be arrested by ditching. To protect 

 a field, however, from the marching 

 horde, a deep furrow should be 

 plowed along the side toward which 

 they are moving, care being taken 

 that the land-side is next the threat- 

 ened crop. The worms being unable 

 to climb this, accumulate in the fur- 

 row, where they can be trapped in 

 post holes dug every ten or fifteen feet, 

 and killed with kerosene, crude pe- 

 troleum, or by crushing. Planks or 

 boards of any kind placed on edge 

 end to end and smeared with coal tar 

 will prove an effectual barrier to them. 

 Paris green, londcn purple, or better, 

 arsenate of lead, sprinkled on the 

 plants in front of a marching host, 

 can be used to good advantage. The 

 most important agents which keep 

 these pests in check are insect para- 

 sities, which attack the worms in great 

 numbers when they appear in march- 

 ing armies. These parasites develop 

 so rapidly it is not an uncommon 



thing at times to find two-thirds of the worms 



parasitized. 



Fig 68— The Army 

 Worm 



Full grown larva ; 

 natural size (after 

 Comstock). 



