372 



OHIO EXPERIMENT STATION: BULLETIN 175. 



378 Canada Thistle, Field Thistle (P) *Carduus mvcnsis L. This field 

 pest is well enough known by name, yet a good many persons are mistaking- it 

 for other plants and calling- other plants the thistle. A complete illustration is 

 shown in Fig. 72. The essential differences from other thistles are the under- 

 ground stems (with numerous shoots coming to the surface as shown in the 

 figure) the lobed and very spiny leaves and the smaller heads. The absence 

 of the thick tap-root alone usually makes us certain that we have to do with 

 the so-called Canada thistle. It is incorrectly so-named, because it is intro- 

 duced from Europe and not from Canada. The specific name "arvensis" means 

 growing in fields, hence field thistle is a much more correct name. Perhaps 

 there is no weed name that carries with its utterance more of dread to the land- 

 owner than that of Canada thistle, yet as I have endeavored to make clear in 

 previous pages, its most noxious feature, that of creeping, rooting, underground 

 stems, is possessed by a dozen or more others, including horse-nettle, toad-flax, 



n ilkweed, ground-ivy, cypress-spurge, nut-grass, 

 periwinkle, bracted bindweed, field bindweed, 

 quack-grass, dogbane and elders. While this is a 

 vile weed it has been over advertised in comparison 

 w r ith some others equally as bad. It has been 

 asserted that the Canada thistle does not mature 

 seeds in any part of Ohio. Though it may not 

 ripen seeds south of the latitude of Columbus, it 

 certainly appears to form viable seeds in this 

 county and to the northward. It springs from 

 seed in many new places each year, and spreads 

 from the underground growth in the others. Its 

 capabilities of forming new plants underground 

 are shown in the four shoots of Fig. 72. Open 

 woodlots are its favorite place to grow from seed. 

 The farmer may rightly be particular in looking 

 such carefully through each year. When a tract 

 of these weeds has been discovered the next point 

 is to destroy them before they spread to a great 

 distance. Railroad rights-of-way and roadsides 

 often become infested and in these, plants have not 

 always received the attention required to kill them out. It is attacked by a 

 rust, Puccinia suaveolens Rostr., which it has been proposed to use to destroy it. 

 The fungus can scarcely be expected to accomplish this end. 



Seeds gray, oblong, 1-8 inch long, striate with obscure lines and with a 

 copious pappus by which they may be carried many miles; present in hay and 

 seeds. In the latter, if known, their presence is a punishable offense. (Sec. 

 7001 Revised Statutes of Ohio). The eradication of Canada thistles is required 

 by their character, but no one can hope to reach this end without continued 

 effort. Sure and swift cures or destroyers may be advertised, yet the nature 

 of the plant including character of growth, makes these claims beyond reason- 

 able expectations. I have often heard it claimed that Canada thistle had been 

 killed by a single treatment, and while this is possible it is very seldom 

 attained. The underground stems must be starved out to kill Canada thistle. 

 This starving is a slow process and we must be content in our measures, to let 

 time operate. Destruction of this weed falls under two plans: 



1. Destruction in small patches. 



2. Destruction in field areas of an acre or more. 



FiG. 72. Canada Thistle. 



The lower figure shows how 



new plants arise from 



rootswcks. 



