328 WEED FLORA OF IOWA 



Smaller Ragweed (Ambrosia artemisiifolia L.). 



Description. — A puberulent or hirsute annual, branched, 1-3 ft. 

 high; leaves thin, 1-2 pinnatifid; upper leaves alternate, lower 

 usually opposite, pale or canescent beneath ; flowers monoecious, 

 staminate above and pisillate in lower axils of the leaves; fertile 

 heads obovoid or globose ; short-beaked, 4-6 spined ; trichomes sev- 

 eral-celled, cells short or long. 



Distribution. — Ragweed or hogweed is originally from Europe 

 but is common throughout eastern North America; also found in 

 the Rocky mountains, the Pacific northwest, and in Mexico, West 

 Indies and South America. It is common throughout the state of 

 Iowa in gardens and fields and is abundant in pastures. 



Extermination. — This weed is too common in pastures, along 

 roadsides and in waste places. The weed is easily exterminated by 

 cutting the plants off below the surface of the soil. The commonly 

 used cultivator will destroy most of the young plants in a corn 

 field. 



Clark and Fletcher recommend the following treatment: "Sow 

 clean red clover seed. Stubble lands where this weed is prevalent 

 should be shallow plowed directly after harvest, or, if seeded, the 

 autumn growth should be closely cut with a mowing machine 

 within two weeks after the grain crop is cut. 



Wallaces' Farmer says concerning this serious pest of the pas- 

 ture: "We suggested that the reason why the ragweed grows in 

 the blue grass pastures is because for some reason the stand of 

 grass has been weakened and thus the ragweed seeds, which are 

 present in all cultivated soils in the west in great abundance, have 

 a chance to grow. We suggested further that the stand of grass 

 may have been weakened by overpasturing in a dry time, thus giv- 

 ing the sun opportunity to burn the roots and lower their vitality. 

 We suggested also that it may have been weakened by the ravages 

 of larvas of the various insects known as the white grub worms. 

 We suggested still further that blue grass, not being able to ob- 

 tain nitrogen from the atmosphere, was nitrogen hungry, and there- 

 fore weak. 



To meet all these various suggestions we proposed that farmers 

 who have blue grass pastures of long standing should re-seed them 

 next year with one or other of the various kinds of clover, filling 



