674 WEED FLORA OF IOWA 



PERCENTAGE CONTEXTS OF DRY MATTER. 



Sow thistle (Sonchus oler- 

 aceus) 



Cornflower ( Gentaurea cy- 

 anus) 



Spurrey (Spergula arven-, 

 sis) 



Wild Radish (Raphanus 

 raphanistrum) 



Persicaria or red-shank 

 (Polygonum persicaria) . 



Yarrow (Achillea millefol- 

 ium) 



Average of six weeds 



14.95 

 8.12 



10.12 

 5.22 



10.58 



9.61 

 9.76 



4. WEEDS PULL DOWN THE CROPS. 



Weeds like morning-glory, bindweed, wild buckwheat, and others, 

 pull down a cultivated plant and then prevent the formation of a 

 good crop. 



5. WEEDS ARE INJURIOUS BECAUSE IT IS DIFFICULT TO RE- 

 MOVE THE SEEDS. 



It is difficult in many cases to remove weed seeds from seed of 

 various kinds. Buckhorn can be removed with difficulty from 

 clover seed ; peppergrass with difficulty from timothy seed ; greater 

 ragweed from wheat ; wild oats from oats ; quack grass from brome 

 grass; cockle from wheat. These impurities often greatly reduce 

 the quality of the grain or seed. 



6. WEEDS HARBOR INSECTS. 

 Long gives the following insects found on weeds: 



