MINNESOTA WEEDS 



WEEDS IN GENERAL 

 DEFINITION 





The word weed has been defined in many different ways. A 

 fairly comprehensive definition is the following: "A weed is a plant 

 which grows where it is not wanted;" in other words, "an undesir- 

 able plant citizen. " A plant may be a weed at one time and useful 

 at some other time, depending upon its environment. For instance, 

 a wheat plant may appear in the cornfield. It is then a weed. Then 

 again one corn plant may be a weed to another corn plant. For 

 instance, if eight plants come up in a hill where only three are desired, 

 five of these plants are really weeds. This, then, is the broad con- 

 ception of the term weed. 



KINDS OF WEEDS 



Weeds may be classified in different ways. One of the most 

 useful classifications is based on the length of time the weeds live. 

 This gives three classes: (1) annual, (2) biennial, and (3) perennial. 



An annual weed is one that starts from the seed in the spring, 

 develops into a plant which flowers and seeds the same year, and then 

 dies; or, in other words, an annual weed is one that lives but one 

 growing season. Most of our weeds belong to this class. It includes 

 wild mustard, foxtail, wild oats, pigweed, Russian thistle, corn cockle, 

 kinghead, ragweed, and many others. 



Some plants are known as winter annuals. Their seeds ripen 

 early in the summer, fall to the ground and germinate, reaching a 

 certain stage of growth before frost. As soon as the frost is out of 

 the ground the next spring, they continue their growth and ripen 

 seeds very early in the spring. Such plants are, in a sense, biennial 

 in their habits, though not real biennials. Some weed examples of 

 winter annuals are French weed, peppergrass. and shepherd's purse. 

 These plants are also annuals, however, just as winter wheat is a 

 winter annual, but, if sown in spring, is an ordinary annual. 



Note. — In this bulletin the terminology in regard to seeds and fruit is that of the farm and 

 seed trade. For instance, a Canada thistle "seed" is in reality a fruit. Adhering to the strictly 

 accurate botanical terminology leads only to confusion and complexity in a bulletin intended for 

 practical farm use. 



The term pod is used in the common sense of a capsular fruit, and not necessarily to designate 

 a legume. 



The drawings in this bulletin are all original. The drawings of seedlings were made by 



E. W. Norcross and G. D. George, those of mature plants by G. D. George, and those of seeds by 



F. H. Hillman. 



