88 WEEDS OF THE FARM AND GARDEN 



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their vitality for long periods. Manure should not be 

 applied on fields until it has been thoroughly composted, 

 and thus the weed seeds contained in it thoroughly de- 

 stroyed. This is not the usual practice. When fresh 

 manure is spread on the field, the straw should be reason- 

 ably clean. Clean seed should be sown. 



In the general treatment of weeds, in order to exter- 

 minate them, it is first always important to prevent the 

 formation of seed and secondly to prevent the formation 

 of roots. This subject will be discussed under the fol- 

 lowing heads: (i) Rotation of crops. (2) Treatment 

 of annual weeds. (3) Treatment for biennials. (4) 

 Treatment for perennials. (5) Treatment for special 

 weeds: a, in meadow and pasture; b, in grain fields; ba, 

 among small grains ; bb, in corn fields ; c, in gardens ; d, 

 on roadsides, in yards; /, lawns; $, summer fallow. (6) 

 Treatment with herbicides. (7) Fungi destructive to 

 weeds. 



Rotation of Crops. It is a well-known fact that a soil 

 long cultivated with the same crop is generally not as 

 remunerative as where rotation of crops prevails. A 

 piece of land grown continually in wheat, oats, or flax 

 will leave the field full of foul weed seeds. The continu- 

 ous cropping of flax and oats in the northwestern states 

 has left the fields so full of mustard that in some places 

 there is almost as much mustard as oats or flax. The 

 continuous cropping with corn, combined with poor cul- 

 tivation, has left many fields in southern Iowa and north- 

 ern Missouri full of cocklebur. The continuous cropping 

 with oats has often resulted in large quantities of wild 

 oats growing with the tame. The continuous use of the 

 pasture without renewal has caused blue vervain to be- 

 come a bad weed. Professor Spillman gives the following as 

 a definite suitable rotation : When sod is plowed, the land 

 is planted in corn, then wheat is sown and grass follows. 

 A freshly broken sod, brought into good condition will 



