224 DRY FARMING 



tcr gives the plants a set-back and the deep plow- 

 ing when they have not entirely recovered, gives 

 them another. Surface cultivation as needed may 

 then be given to prevent green leaves forming on 

 any that may remain. This plan, or some modifica- 

 tion of it, is generally used for the Perennial Sow 

 Thistle. 



2. Deep plowing as soon as the weather turns warm in 

 May, then sowing thickly to a leafy crop like oats 

 or barley. This often gives very satisfactory re- 

 sults with Quack Grass. 



3. Mowing and removing the weeds just after blos- 

 soming when they are least able to stand a check, 

 then deep plowing followed by deep, thorough and 

 frequent cultivation to keep the land black. This 

 is frequently used for the control of Canada 

 Thistle. ' 



177. How to Prevent the Introduction of Weeds to the 

 Farm. With the exception of a few native weeds all 

 those now on our farms have grown from seeds that 

 were introduced to it by human or other agencies. The 

 prevention of weeds coming to the farm is the big prob- 

 lem of men on virgin soils, and not an unimportant 

 problem for all other farmers. Among the means of 

 prevention are : 



1. Using only clean seed unclean seed is chiefly res- 

 ponsible for the weed evil. 



2. Buying only such feed grain as is free from Wild 

 Oats, Mustard and other weed seeds, and such 

 forage grasses as are free from Canada and Peren- 

 nial Sow Thistles. 



3. Controlling soil drifting. A man cannot, of course, 

 farm his neighbor's land and he cannot keep the 



