186 The Sugar-Beet in America 
lambsquarter, and cocklebur, are breeding plants of many 
of the most serious pests. Clean culture that would 
eliminate these weeds greatly lessens the injury due to 
insects. Rotation of crops is practiced by many of the 
beet-farmers, but a few maintain the one-crop system until 
the enemies of the beet become so numerous that the crop 
no longer can be grown. Much loss is occasioned by 
planting beets after grass or similar crops that harbor 
some of the worst beet enemies, such as the cutworms and 
wireworms. Fields are not ordinarily kept as clean of 
insect-harboring rubbish over winter as might be wished. 
In sections where cutworms give difficulty it should be 
known that plowing either in the fall or in the spring 
lessens injury from this insect. When attacks of insects 
become acute, sprays and insecticides save much injury. 
Two general classes of insecticides are available: (1) 
contact solutions for insects such as plant-lice and leaf- 
hoppers, which obtain their food by piercing the plant 
and by sucking its juice; and (2) poisons applied in solu- 
tion to the leaves of the plant to kill such insects as cater- 
pillars, beetles, and grasshoppers, which feed on the out- 
side of the leaves. The most effective contact spray is 
made of a solution of tobacco. For biting or chewing 
insects, sprays containing a poison such as the arsenicals 
are employed, the insects being killed by eating a part 
of the plant covered by some of the poison. The latter 
type of spray should contain a very active poison which 
will not easily run off the leaves of the plant and be 
wasted, as frequently happens when not properly applied ; 
hence arsenate of lead is one of the best sprays. 
Insect troubles vary from. section to section; some of 
