440 THE SMALL GRAINS 



young cereal plants early in the season. (3) They exhaust 

 the soil of plant-food needed for the crop. (4) They also 

 exhaust the moisture from the soil. In all dry-farming 

 this is the chief source of loss caused by weeds. All inter- 

 tillage of crops and summer tillage preceding cropping 

 is largely of value for the killing of weeds. (5) Weeds 

 harbor injurious insects and parasitic fungi which in some 

 cases sooner or later attack the cereal crop. Some weeds, 

 such as quackgrass and wild barley, are affected by the 

 same fungous diseases as are the cereals. The shade and 

 dampness where weeds are rank, even if they are not 

 themselves infested, will favor the rapid spread of cereal 

 diseases. (6) Weeds reduce the value of the crop for 

 hay, and if the seeds get into the thrashed grain, it is 

 also injured, both for the market and for seed. Often the 

 most serious loss from weeds occurs in this way. (7) 

 Weeds increase the expense of gathering the crop when 

 very numerous, because of extra time and labor required 

 and extra twine needed for binding. (8) They delay the 

 curing of the grain. 



It is estimated that in one of the grain states alone, the 

 damage to wheat due to weed seeds is about 2J million 

 dollars annually. 



478. Habits of growth. In order to combat any 

 enemy properly, animal or vegetable, it is necessary to 

 know its habits, so that means of eradication may be 

 attempted just where and when they can be most effective. 

 There are three classes of weeds as to habits of growth : 

 (1) annuals, (2) biennials, and (3) perennials. Only the 

 principal cereal weed pests of each class will be discussed 

 here separately. 



479. Annual weeds. Weeds which complete their 

 entire growth in a year, then mature their seeds and die, 



