COMPOSITAE (COMPOSITE FAMILY) 



457 



be continued late, as it is the plants that bloom and fruit after 

 cultivation has ceased which are most certain to foul the soil. 



PERENNIAL RAGWEED 

 Ambrosia psilostachya, DC. 



Native. Perennial. Propagates by seeds and by rootstocks. 



Time of bloom : June to September. 



Seed-time: July to October. 



Range: Illinois to the Northwest Territory, southward to Texas, 



Mexico, and California. 

 Habitat : Rich prairie soil ; invades all crops. 



This is a much harder weed to combat than its annual relatives, 

 for one must have a care in cultivation 

 not to break up and spread abroad the 

 creeping rootstocks and thus increase 

 the plague. 



The plant looks very like the smaller 

 Ragweed, but is stouter and grows two 

 to six feet high. Leaves once or twice 

 pinnatifid, with lobes usually acute, 

 thick and bristly instead of thin and 

 soft. Male flowers very abundant, 

 on numerous long racemes, the invo- 

 lucres deeply cup-shaped ; fertile flowers 

 mostly solitary, the small, brown achene- 

 like fruits obovoid, hairy, short-pointed, 

 with fewer tubercles than the preceding 

 species or sometimes none at all ; they 

 are often found in grass and clover 

 seed and in baled hay. (Fig. 319.) 



Means of control 



Newly infested areas, if not so large 



as to make the method impracticable, 



FIG. 319. Perennial Rag- 



should have prompt treatment with a wee d (Ambrosia psilostachya). 

 strong herbicide caustic soda or hot x \. 



