BURDOCK— CANADA THISTLE 73 



Eradication. — The burdock disappears as doorvards and groves 

 are put under cultivation. Continued cutting wil' jxhaust the plants 

 and, in time, exterminate them. The process may be hastened by 

 cutting off deeply below the surface and applying a handful of salt 

 or a few drops of gasoline or kerosene to the root of each plant. Where 

 the trees are not too thick and the yards are badly infested, it will 

 be best to plow the land and grow a crop of corn or potatoes before 

 reseeding. Cutting off below the crown with a "spud" is the best 

 treatment where only a few scattering plants exist. 



Canada Thistle (Carduus arvensis L. Robs) 



Other common names. — Way thistle, cursed thistle, corn thistle, 

 hard thistle, creeping thistle. 



Description. — The Canada thistle is a perennial which ranges 

 from one to three feet in height. The stem is much smaller than that 

 of most other thistles and has few spines. The leaves, however, are 

 very spiny and the margin has a ruffled appearance. The under side 

 of the leaf is somewhat hairy, while the upper side, which is bright 

 green in color, is either smooth or slightly hairy. The flower heads 

 are about half an inch in diameter, and rose-purple in color. A white 

 feathery tuft of hairs is attached to the mature seed which aids in 

 the distribution of the same. The mature seed is brown, nearly 

 cylindrical, and about one-eighth of an inch long. The roots are 

 often found two feet or more in the ground, running parallel with 

 the surface. From these roots shoots come to the surface and form 

 new plants. These roots are light yellow and only about one-fourth 

 of an inch in diameter. The Canada thistle is one of Minnesota's 

 worst weed pests. 



The plant flowers from June to September, but usually matures 

 seed by the middle of July. It is propagated by running roots as 

 well as seeds, and it has been found that a seed planted in the spring 

 will in two years produce enough scattering plants to cover twenty 

 square feet of ground. The seeds are easily carried by the wind 

 and are most commonly found in medium red and alsike clover. The 

 plant thrives in all kinds of soil and is rapidly being introduced into all 

 parts of the State. It is now most prevalent in northwestern Minne- 

 sota. 



Eradication. — The first step in the eradication of the Canada 

 thistle is to prevent all plants from going to seed. It is often neces- 

 sary to go into the grain fields with a scythe or mower and cut down 

 quite large areas of grain in which the thistles are growing, to prevent 

 them from seeding before the main crop of grain is cut. As soon as 

 may be after the grain crop is cut the infested land should be plowed 



