FRIENDS AND ENEMIES OF PLANTS 



177 



Annuals grow, mature their seed, and die within a year. Among 

 these are the ragweed, cocklebur, horseweed, burgrass, dog's 

 fennel, wild lettuce, Russian thistle, pigeon grass, etc. Annuals 

 may be held in check by frequent tillage and by preventing 

 them from seeding. In an open, uncultivated field they may be 

 mowed or pastured with sheep. They follow tilled crops. 



Biennials do not finish their growth and mature their seed 

 until the end of their second year. The most troublesome 

 ones are the wild carrot, the bull thistle, 

 and the burdock. They can be checked by 

 grubbing them out or plowing them under 

 from time to time. 



Perennials grow from year to year, and 

 many of them are reproduced both by run- 

 ning roots and by seeds. These include 



Oxeye daisy. 



Long-leaved plantain. 



quack grass, sow thistle, Canada thistle, dandelion, horse nettle 

 or sand brier, nut grass, white daisy, English plaintain, sour 

 weed, wild onion, etc. 



Perennials are very difficult to eradicate, and they have to be 

 fought in many ways. Constant and clean cultivation will do 

 much to subdue them, but sometimes farmers have to smother 

 out the weeds by sowing some crop that makes a quick, heavy, 

 luxuriant growth. Cowpeas are often used for this purpose and 

 prove quite satisfactory. These weeds must not be given a start. 



PRAC. AGRICUL. 12 



