168 



WEED FLORA OF IOWA 



Fig. 94-A. Distribution of Marsh Cress. 



Distribution. — In wet places or in low grounds ; frequent in oat 

 fields and meadows; abundant in Iowa especially in northern Iowa; 

 common throughout the northern United States. Not infrequently 

 distributed with clover seed that is grown in Iowa. 



Extermination. — This weed may be exterminated by first drain- 

 ing the soil and then giving clean cultivation. 



Horseradish (Raddcula armoracia (L.) Robinson). 



Description. — A stout perennial with long, deep roots; leaves 

 large, oblong, crenate or pinnatifid, the latter produced in the 

 spring; stem leaves lanceolate, or oblong cordate; flowers with 4 

 green sepals and 4 white petals, not common ; pods short, globular, 

 but fruit seldom found. At least I have never observed any in Iowa. 



Distribution. — Horseradish is native to eastern Europe and in- 

 troduced in west Europe and the United States ; common from the 

 Atlantic to the Pacific; largely an escape from cultivation; found 

 in every part of Iowa. 



Extermination. — The horseradish is one of the most persistent 

 of our weeds ; no other weed will stand such rough treatment. It 

 may be hoed and cultivated and still it persists in coming up. Some 

 years ago we tried the following plan : The land was plowed, then 

 harrowed ; the roots were picked up and the process repeated after 

 the lapse of a week, when young plants again made their appear- 

 ance. After that, young plants were cut off with a hoe below the 

 ground as soon as they appeared. This treatment was kept up for 



