DESCRIPTIVE MANUAL 



155 



Fig. 87-A. Distribution of Jointed Charlock. 



Distribution. — Common; spreading eastward in fields and waste 

 places; reported in grain fields in "Worth and a few other counties 

 in the northern part of Iowa. It is said to have been largely dis- 

 tributed with oats seed. 



Extermination. — Exterminated by cultivation. Sow only clean 

 oats seed in clean fields. 



Mustard or English Charlock {Brassica arvensis (L.) Ktze.). 



Description. — Lower leaves nearly divided to the middle^ with 

 divisions unequal, terminal lobe larger, upper leaves not stalked 

 as a rule, much smaller than the lower; flowers yellow, large and 

 very fragrant; pods 1-2 in. long, irr^ular in outline, appearing 

 somewhat nodose, 3-7-seeded or occasionally more, upper part of pod 

 forming a beak; seeds round, brownish black, darker than in B. 

 nigra and minutely pitted, when moistened becoming mucilaginous. 



Distribution. — ^Mustard or charlock has been known as a pest of 

 the grain fields from the earliest historical record, throughout the 

 grain growing section of the world; common everywhere in Iowa, 

 but most abundant in the grain growing section of northern and 

 northwestern Iowa where it was introduced with flax. 



Extermination. — The first and' most important consideration in 

 connection with the extermination of mustard is that the oats or 

 wheat should be freed from mustard seed. Then this grain should 

 be sown on clean fields, preferably fields that have been in pasture 

 or meadow. Nothing has done so much to remove the weeds from 

 the fields of northwestern Iowa as the pasture and meadow. If the 

 grain is sown in a corn field there should have been no mustard the 



