536 FIELD CROPS 



as has already been recommended for land which is to be 

 planted to cultivated crops. Great care should be taken 

 to insure the sowing of clean seed. It is of little use to harrow 

 and disk land to clear it of weeds and then put on a new sup- 

 ply of weed seeds with the seed grain. The harrow or weeder 

 may often be used in fields of drilled grain to destroy small 

 weeds during the first few weeks of spring; the harrowing 



Fig. 160. Blossom and root of wild mustard; also (1) the ripe seed pod; (2) the 

 blossom, and (3) the seeds. 



should be done with the drill rows rather than across them. 

 Harrowing broadcast grain will help to keep down weeds, but 

 it will also reduce the stand of grain. Ragweed and other 

 weeds which come up in grain fields after harvest may be 

 prevented from seeding by mowing them when they first 

 come into bloom, by pasturing, preferably with sheep, or 

 by disking the land. 



