SUGGESTED GUIDE FOR CHEMICAL CONTROL 



OF WEEDSi 



Safe and effective herbicides are available for the control of many weeds 

 growing in varied environments including croplands; rangelands; noncrop 

 areas; and potable, irrigation, drainage, and navigable waters. The successful 

 and safe use of herbicides depends on strict adherence to the details of 

 appropriate treatnnent methods. These details differ by localities because of 

 differences in soils, clinnate, crop varieties, cultural methods, and weed 

 species. Methods described herein are given as a broad general guide to 

 current information on weed control. Specific information on application 

 techniques required for the successful use of herbicides under local condi- 

 tions can be obtained from local agricultural authorities. 



Ne'w and improved methods of weed control are available to solve many 

 weed problems on farms and to aid in the nnechanization of crop production. 

 Basic and applied weed control research is underway on a broad front and 

 will continue to provide practical solutions to weed control problems. 



Chennical w^eed control is an economical aid to mechanization of crop 

 production. Maximum effective results w^ith herbicides can be achieved only 

 when their use is accompanied by the use of effective cultural techniques. 



Suggestions on rates of herbicide use given in this publication are based 

 upon the active ingredient or acid equivalent contained, and not upon the total 

 weight of any comnaercial formulation. 



I. CHEMICALS USED FOR WEED CONTROL 



Many herbicides are being used for weed control, and nnany others are being 

 evaluated experinnentally to determine their usefulness. Only those of current 

 general interest and usefulness are described in this report. 



Available information on the degree of toxicity of herbicides to warm- 

 blooded animals is listed in the descriptions of chennicals used for weed 

 control. The symbol L1D50 (lethal dosage that kills 50 percent of the experi- 

 nnental aninnals) precedes each number that indicates relative toxicity. For 

 exannple, the single acute oral dose for sodium arsenite, LD50 = 10 nig. /kg., 

 indicates a relatively high oral toxicity. The larger the LD^q number, the 

 less toxic the herbicide. 



All L1D50 values listed in this guide are based on a single dose of material 

 orally adnninistered to aninnals, followed by observation of the treated ani- 

 mals for a definite period of time. However, these findings do not indicate 



iThe technical information in this publication was compiled and reviewed by L. L, Danielscn, D. L. Klingman, 

 W. C. Shaw, F. L. Timmons, W. B, Ennis, Jr., and associated personnel of the Crops Research Division, Agricultural 

 Research Service. 



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