380 WEEDS 



Control. Prevention of Annual Weeds. As the annuals 

 do not have any underground root stalks or other means of spread- 

 ing by vegetative growth, they are disseminated entirely by their 

 seeds. The seed supply is very abundant in annuals. The key- 

 note to prevention of annual weeds, therefore, is to prevent the 

 maturing of seed. The weeds should be kept down in some way 

 until frost kills them. 



Probably the best management for the control of annual weeds 

 is clean tillage. Mowing will accomplish a great deal, but some 

 will produce seed very close to the ground after the higher growth 

 has been clipped off. 



Troubles With Biennials. This group naturally produces less 

 seed, as each plant requires two years in which to develop its crop 

 of seeds. Although the underground parts live for two years they 

 are not disseminated by this means. Most of the biennials are 

 easily destroyed by plowing, hence they are not commonly found 

 in fields that have been plowed recently. For this reason, it is 

 more common to find burdock and similar biennials along fence- 

 rows than along roadsides. In such places the weeds should be 

 prevented from going to seed by cutting them below the surface 

 of the ground with a knife or spading tool, or by keeping them 

 mowed low enough to prevent the development of flowers and 



Wild carrot is a biennial which becomes very abundant in 

 pastures and hay fields. Rotation of crops probably is the 

 best means of curbing it. Mowing the hay crop earty will, to a 

 great extent, prevent seed formation. When such hay is cut 

 twice a year, the crop of wild carrots is largely controlled. 



Eradication of Perennials. Except in special cases, plowing, 

 rotation of crops, and thorough cultivation are the best remedies 

 for the control of perennial weeds. Most perennials do not like 

 to have their root systems disturbed. As already mentioned, a 

 few of the weeds with underground rootstalks are not controlled 

 by such methods. This is true of Canada thistle, Johnson grass, 

 quack grass and a few others. There are numerous perennials 

 with fleshy roots, such as dandelion, true dock and others, that 

 are entirely destroyed by plowing and cultivation. 



In cases where it is impracticable to use these methods for the 

 eradication of perennials, smother-crops may be of considerable 

 value. Grain crops, dwarf Essex rape and other rank-growing 

 crops may shade the weeds, largely preventing their growth. 



