A SECOND OHIO WEED MANUAL. 



373 



For the first, repeated cutting- with hoe and applications of salt, kerosene 

 (coal oil) or sulfuric acid to the cut stems in the ground will usually prove the 

 cheapest and best method. The treatment, at least the cutting, needs to be 

 repeated as often as green leaves of the thistle show above ground. Cutting 

 alone will be sufficient to destroy them but it will need to be followed for two 

 or more seasons to be effectual. 



In areas too large to be destroyed by hand work, the summer fallow may 

 be used, to be followed by hand treatment to kill out the small remaining areas. 

 The field should be plowed shallow in June and harrowed to destroy all green 

 tops. Upon the appearance of new growth of the thistles it should be cross- 

 plowed and again harrowed. This procedure is repeated thorughout the season, 

 to be followed by carefu 1 tillage the next year in corn, potatoes or some other 

 crop that is to receive all-summer hoeing and cleaning. After this some patches 

 will commonly remain to be killed out as first suggested. Refuse packing or 

 house salt, which is quoted at about twenty-five cents per barrel, is perhaps 

 the cheapest chemical to appJ}- after cutting. Kerosene is sometimes recom- 

 mended, yet costs more, while sulfuric acid is dangerous to handle, although 

 effective in burning up and destroying whatever it may be applied to. 



Smothering with straw is rarely successful, since the thistles finally grow 

 through it, aside from its depriving the owner of the use of the land for a longer 

 time than summer fallow. The correct principle of destruction is, however, of 

 more importance than the mere method. This is to starve out the underground 

 stems. Two or more seasons will be needed. 



379 Common Thistle, Bull Thistle (B) *Carduus lanccolatus L. The 

 common, purple-flowered thistle found in pastures is a biennial, 2 to 4 feet high, 

 with deep tap-root. The plants start in the fall 

 and may be seen during winter waiting for the 

 next summer to blossom and fruit. The cut (Fig. 

 73 , shows the appearance of the head of this 

 weed; these are about one inch across. 



Seeds gray, larg-er than those of the Canada 

 thistle, 1-4 inch long and abundantly supplied 

 with pappus. Common in hay and seeds. De- 

 stroyed by cutting off below crown before blossom- 

 ing, usually not destroyed by mowing. 



380 Tall Thistle (B) Carduus altissimus L. 

 Is a native thistle with downy stems, 3 to 10 feet 

 high, leafy to the heads and leaves white woolly 

 underneath. The flowers are chiefly purple, the 

 heads large, 1 1-2 to 2 inches high. It is found 

 in damp thickets and fields. Destroyed as the 

 preceding. Seeds dark brow r n, 3-16 inch long and smooth. 



381 Swamp Thistle Carduus muticus (Michx. ) Pers. Is another thistle 

 found in swamps; it has the leaves green on both sides and the heads almost 

 without prickles. It is usually not aggressive. 



382 Cotton or Scotch Thistle (B) *Onopordon Aamthium L. This is an 

 abundant weed in the vicinity of Cincinnati. It has a cottony appearance all 

 over and the leaves extending as wings down the stem. Destroyed in the same 

 manner as the common thistle. 



383 BIue=bottle, Corn Thistle (A) * Centaur ea Cyan us L. Is the escaped 

 bachelor's button which sometimes is quite showy in grain fields. It may be 

 removed by hand. Other annual species also are found. 



Seeds bluish-white, oblong, 1-8 inch long with brown, "paint brush" circle 

 of pappus half or more than half as long as the seed body. Conspicuous by 

 reason of this "brush." 



Fig. 



13. Common Thistle. 



After Millspaugh.) 



