THE SUNFLOWER FAMILY 171 



out the crops almost completely. It is much worse in this respect 

 than any of the other thistles. In Manitoba Perennial Sow 

 Thistle is considered the worst of all weed pests; in some cases 

 it has rendered whole fields unfit for grain production. If left 

 undisturbed, its seeds ripen before the grain is cut and are carried 

 long distances by the wind. The seed is sometimes present in 

 clover and grass seeds and seed grain. 



Remedy: The fight against this aggressive, pernicous pest 

 will continue indefinitely in localities where it has become 

 established unless extreme measures are taken, and continued 

 from year to year,* to prevent it maturing and distributing its 

 seed from waste places and the lands of careless farmers. Every 

 farmer should be sufficiently familiar with this plant to distinguish 

 it from the other sow thistles, as it is a much more dangerous 

 weed. It should be given special attention by municipal govern- 

 ing bodies and weed inspectors. 



Small patches may be eradicated by digging out the 

 roots as thoroughly as possible and destroying them. This 

 rhay have to be done several times during a season. Great 

 care must be taken not to distribute pieces of the rootstalks 

 over the fields by harrows or other implements. To exterminate 

 Perennial Sow Thistle, some system must be adopted which 

 will prevent the development of leaves for a period sufficiently 

 long to kill the roots by smothering them. When a field is 

 badly infested it requires special treatment for a season and 

 close attention for a number of years. One of the most effective 

 methods is to plow lightly immediately after the hay or grain 

 crop is removed and follow with frequent use of a broad-shared 

 cultivator. Late in the fall plow again, somewhat deeper. In 

 the spring give frequent cultivation, so "as to prevent the develop- 

 ment of any leaves and thus weaken the roots to the greatest 

 possible extent. About the middle of June or first of July sow 

 rape in drills at the rate of about 1 Ibs. per acre. Cultivate 

 between the drills as soon as possible and repeat at short intervals 

 until the rape completely covers the ground. Some hand hoeing 

 may be necessary to keep all the thistles down. This should 

 pretty well exterminate the pest but if some plants still remain 



