80 MINNESOTA WEEDS 



deeply enough to bring the roots to the surface. The best time to 

 plow is just as the thistles come into blossom. Discing and surface 

 cultivation may be used during the early fall to prevent the growth 

 of the plants. Then replow late in the fall leaving all the roots pos- 

 sible exposed to the action of the frost. Following this preparatory 

 treatment the adoption of a three-year rotation of barley, clover, 

 corn, or other cultivated crop will be found most satisfactory where 

 clover will grow and corn can be made use of. Barley would, there- 

 fore, be the first crop on the land. The land should be prepared for 

 it by double discing at least once before sowing the barley. Clover 

 seed should be sown with the barley at the rate of eight or ten pounds 

 per acre. Needless to say it should be free from Canada thistle seed. 

 The clover will occupy the land during the fall and, if a good stand 

 is secured, will crowd the thistles badly during the next season. The 

 first crop of clover can be cut by June 25 to July 10 before the 

 thistle seeds have a chance to ripen. The second crop will come on 

 rapidly and will again prevent the thistles from spreading much or 

 going to seed. The land should be plowed soon after the second crop 

 of hay is cut. The following spring thorough preparation for the 

 corn crop, clean cultivation, a careful watch for stray plants, and hand 

 hoeing when necessary until October will practically complete the 

 eradication. A repetition of the rotation will be wise, however, 

 to prevent possible reinfestment. 



Where clover can not be grown, some other crop, as millet or 

 Canada field peas, may take its place. In strictly grain -growing 

 districts, bare fallowing for a year, discing and cultivating frequently 

 and thoroughly, so as to prevent the leaves from appearing above 

 ground, for at least six weeks during July and August will prove 

 effective though expensive. 



Bull Thistle {Carduus lanceolatus L.) 



Other common names. — Plume thistle, bank thistle, horse thistle, 

 bell thistle, bird thistle, blue thistle, and button thistle. 



Description. — The bull thistle is a biennial weed which is often 

 mistaken for Canada thistle. It is, however, much larger and more 

 rugged The stem is from half an inch to an inch in diameter. The 

 leaves are woolly beneath and spiny above, resembling a cat's tongue. 

 The plant blossoms the second year, forming purple flowering heads 

 which are about one inch in diameter It has a tap root instead of a 

 running root like the Canada thistle. The seed is grayish in color, 

 often striped with brown or purple, and larger than the seed of the 

 Canada thistle. 



