THE MONTHLY BULLETIN. 49 



Canada thistle is found in many parts of the East and Middle "West, 

 in Canada. Europe, Australia and the Orient. Nearly every state in 

 the Unit i'd Slates has passed laws for the purpose of keeping it out. 

 Nearly every European country has wrestled with it, and the Canadian 

 government has carried on a very persistent fight against it, Without 

 doubt it is one of the worst weed pests known to agriculture. It does 

 not even have the redeeming feature that it can be eaten by stock, 

 as its leaves are so sharp and thorny that few animals will touch it. 

 It is a perennial plant, growing from long, deep-rooted underground 

 stilus or root stocks. It spreads from these root stocks very much as 

 does Bermuda grass or Johnson grass, each cut joint being able to 

 produce a new set of plants. 



Description. 



Canada thistle (Cirsiitm arvensis) is one of the true thistles as 

 distinguished from many so-called thistles like Russian thistle and 

 others. It can easily be recognized by its sharp, spiny, vivid green 

 leaves and bright purple flowers and its long underground roots. In 

 the spring a dense cluster of long irregular leaves first appears close 

 tn the ground ; the margin of each leaf is lined with sharp spines. Later 

 the flower stalks appear. These are at first somewhat weak and spindly 

 but later strengthen. The branches blossom profusely, resulting in 

 a very attractive plant. The plants are partially dioecious, usually 

 having male flowers on one plant and the female on another. The male 

 flowers are much more globular than the female, and of a deeper color. 

 They are nearly always purple, though occasionally white flowers will 

 be found. The seed is comparatively smooth, of a light brown color, 

 generally slightly curved. The apex is cup-shaped, with a pointed 

 tubercle in the center. The body of the seed tapers slightly to the base, 

 which is rounded. Due to its dioecious habit a considerable portion of 

 the seed is sterile. The root of Canadian thistle is what makes it such a 

 serious pest. It grows rapidly and extends into the soil, sometimes to 

 a depth of two and three feet. When cut it is capable of reproducing 

 new plants without any apparent check to the growth. 



Methods of Dissemination. 



Like all thistles the seeds of Canada thistle are spread by winds, birds, 

 threshing machines, sheep and hay, in agricultural seeds and in manure. 

 To eliminate distribution by means of seed the most important thing 

 is to prevent seed development. 



The underground roots provide another means of dissemination. Any 

 cut portions of these will produce new plants. Careless plowing, thresh- 

 ing machines, harrows and plows passing from field to field often 

 spread the roots over a wider territory. In this way many infestations 

 of Canada thistle, as well as morning glory, Johnson grass, star thistle, 

 and quack grass have been spread from farm to farm. It is unwise to 

 allow any farm machines, especially hay balers, threshing machines 

 and the like, to come onto the farm without being cleaned. Greater 

 care in farming will mean fewer weeds. 



