188 The Sugar-Beet in America 



periods. Outbreaks of this pest in the beet fields of the 

 western states have at times nearly ruined the crop. With 

 the exhaustion of its usual food in years when it is worst, it 

 migrates from field to field devouring everything in its 

 course as shown in Plate XXI. The larvae which do the 

 injury are naked, dull-striped worms resembling cutworms 

 and closely related to them. Except when moving in 

 armies, the worm is not noticed, because it usually remains 

 concealed in the daytime, feeding mainly at night. When 

 full grown, the worm is about one and one-half inches 

 long, of a dark color except for a yellowish stripe down the 

 back and one down each side. The second brood makes 

 its appearance in the latter part of the summer; as a 

 result, late plantings suffer most. Its normal food plants 

 are certain weeds; hence clean culture will prevent a 

 number of the pests from developing. Poisoning with 

 paris green or arsenate of lead offers much relief when 

 there are a great number of the insects. The poison should 

 be applied as soon as injury is noticed. 



The common army-worm (Leucania unipinicta Haw). 



This species is similar to the above except that it has 

 three yellow stripes instead of one down its back and it 

 winters as a half-grown larva in the ground, emerging in 

 the spring as a dull brownish moth. It more often at- 

 tacks cereals and grasses, but also eats sugar-beets. This 

 worm does its injury in early summer, whereas the beet 

 army-worm is most troublesome in late summer. This 

 insect troubles more crops than the beet army-worm and 

 is more widely distributed. Ordinarily, it is held in check 

 by its natural enemies, but when it becomes excessively 



