334 WEED FLORA OF IOWA 



yards, spreading into north and northeastern Iowa, Mason City and 

 Allamakee county and also in central Iowa, in Boone and Story 

 counties. 



Extermination. — Marsh elder is an annual and hence thorough 

 cultivation for a single season will destroy it, provided it is not 

 allowed to form seeds. 



Cocklebur (Xanthium canadense Mill.). 



Description. — A coarse, rough annual from 1-2 ft. high, stem 

 marked with brown punctate spots; leaves alternate, cordate or 

 ovate, 3-nerved, long petioled; flowers monoecious, staminate and 

 pistillate flowers in different heads, the pistillate clustered below ; 

 involucre of staminate flowers somewhat fiat, of separate scales; re- 

 ceptacles cylindrical ; scales of the fertile involucre closed ; fruit 

 2-beaked, containing 2 achenes; bur densely prickly and hispid, 

 achenes oblong, without pappus. 



The spiny clotbur X. spinosum has spines in the axils of the 

 lanceolate leaves. 



Distribution. — Common in Mississippi valley from Texas to Min- 

 nesota and eastward. Common in fields in many parts of the 

 state, but more common in southern than in northern Iowa. 



Extermination. — The best method of combating this weed is the 

 rotation of crops and clean culture. Where a field is in corn, the 

 field should be thoroughly cultivated and none of the plants al- 

 lowed to mature seed. If they cannot be caught by the cultivator, 

 it may pay to kill the remaining plants with a hoe, or to pull them 

 by hand. The corn should be followed with winter rye, and then 

 oats, using the oats as a nurse crop for clover and timothy. Leave 

 the field in meadow for at least two years and then if possible turn 

 it into pasture. 



Mr. E. B. Watson found in soil badly infested with cocklebur 

 that clover seed would not germinate as well, and it is rather dif- 

 ficult to get clover to start in fields of this kind. 



The Homestead says concerning the eradication of cocklebur : 

 "Needless to say there is no easy way of eradicating the pest. 

 Where the winter wheat can be grown the following plan can be 

 depended upon. Start on fields that have been in small grain and 

 plow the land as soon as the crop is removed. Harrow as often 



