GENERAL CONSIDERATIONS IN THE USE OF HERBICIDES 



BASIS FOR PURCHASING HERBICIDES 



The effectiveness of herbicides is largely dependent upon the active in- 

 gredients they contain. One of the best general guides to use in purchasing a 

 commercial herbicide is the price per pound of active ingredient. The con- 

 tainers for all commercial herbicides have labels that state the annount of 

 active ingredients contained in the nnaterial. The ingredients are expressed 

 in percent by weight, or as pounds of active ingredients per gallon. 



"Acid equivalent" is commonly used to express the active ingredient of 

 2, 4-D and certain other herbicides. Usually the concentrated formulations 

 are most economical to use. For example, 2, 4-D formulations that contain 

 4 pounds of acid equivalent per gallon usually ■will cost less per pound of 

 2, 4-D acid than a formulation containing only 1 or 2 pounds of 2, 4-D per 

 gallon. 



Another important consideration in purchasing 2, 4-D or 2,4,5-T herbi- 

 cides for certain weeds and special situations is the type of herbicide formu- 

 lation--amine or high-volatile or low-volatile ester. When vapors from the 

 herbicide are likely to cause injury to adjacent crops or plants, either an 

 amine salt formulation or a low- volatile ester should be used. Esters of 

 2, 4-D and 2,4,5-T are classified as high- or low-volatile according to the 

 degree of vaporization that occurs. In general, methyl, ethyl, isopropyl, 

 butyl, and amyl esters are considered highly volatile. The butoxyethanol, 

 butoxyethoxypropanol, ethoxyethoxypropanol, propyleneglycolbutylether , 



and isooctyl esters and others w^ith a long sidechain are low-volatile esters. 



The carrier components contained in herbicides, such as emulsifiers, 

 solvents, and other adjuvants, often have a bearing on problenns encountered 

 in mixing and spraying and on weed control results. The large variety of 

 these materials available for various purposes nnakes it difficult to give 

 general guides for purchasing. 



SPRAYER CALIBRATION 



The type and operating condition of sprayer equipment used to apply herbi- 

 cides is of utnnost importance to efficient chennical weed control. Uniform 

 distribution of the spray solution is an essential requirennent of good spray 

 equipnnent. A sprayer must uniformly distribute any quantity from 5 to 100 

 gallons per acre, since various weeds and situations may call for a -wide 

 range of dilutions for proper plant coverage. Sprayer output should be deter- 

 mined for each particular spraying operation. A good metliod of calibration 

 is to make initial adjustments to suit the machine and job requirenn.ents, and 

 then make a trial run to determine the actual output of the machine. The 

 herbicide spray mixture then should be prepared accordingly. The calibra- 

 tion should be repeated frequently to check for nozzle orifice wear and other 

 factors affecting performance. This is especially important when wettable 

 pow^ders or other abrasive sprays are used. 



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