WEEDS AND THEIR ERADICATION 219 



the necessity of working out a system of farm management that will afford 

 weeds the least opportunity to gain a foothold. The problem is not how to 

 rid a farm of weeds, but how to prevent weeds in the first place. This can 

 be solved by a system of cropping which takes into consideration the needs 

 of the different fields as regards weed eradication. This phase of the 

 problem has been discussed under the chapter on "Rotations." 



A few general principles for weed prevention and eradication are here 

 given: 



1. Cut all weeds before seeding, if possible. 



2. Burn all weeds with mature seeds. Do not plow them under. 



3. Practice crop rotations. 



4. Sow clean seed. 



5. Watch for new weeds in your locality. If you can not identify 

 them, send them to your experiment station for identification. 



6. See that the laws in your state dealing with control of weed plagues 

 are enforced. 



A few of the most common weeds are here considered.* 



Canada Thistle. The Canada thistle is a perennial of European origin, 

 and is the most dreaded of all weed pests. It is a common weed of the 

 northern half of the United States. The stems of Canada thistle grow 

 from one to three feet tall ; they are much smaller and smoother than other 

 thistles. The leaves are very spiny and the margin has a ruffled appear- 

 ance. The upper side of the leaves is smooth and bright green in color, 

 while the lower side is downy or hairy. The flowers are rather small, 

 about one-half inch in diameter and of a rose-purple color. The Canada 

 thistle flowers from June to September, maturing the first seed by the mid- 

 dle of July. The seed is smooth and light-brown in color, measuring 

 one-eighth of an inch in length. The seed is easily carried by the wind and 

 is most commonly found in medium red and alsike clover seed. 



Propagation. The Canada thistle propagates by underground root- 

 stocks as well as by seed. The underground rootstocks grow rather deeply 

 in the soil and run parallel with the surface. They are the storehouse of 

 the plants, and are capable of sending up young shoots for some time after 

 the parent plant has been destroyed. This fact explains the persistency 

 of the Canada thistle. As long as the plant is permitted to form green 

 leaves, it will manufacture plant food, which is stored in the rootstocks. 

 As long as plant food is present in the rootstocks they are capable of sending 

 up new plants, and will continue to thrive as long as they grow leaves at 

 the surface. 



Control. The Canada thistle occurs in all crops in the rotation, 

 consequently no one method of control will be effective. The details of 

 control had best be worked out for each particular condition. 



To thoroughly subdue the pest it is necessary to starve out the root- 



* Taken, with modifications, from The Pennsylvania Fanner, prepared by Professor Darst, of The 



Pennsylvania State College. 



