II. GENERAL CONSIDERATIONS IN THE USE OF HERBICIDES 



BASIS FOR PURCHASING HERBICIDES 



The effectiveness of herbicides is largely dependent upon the active 

 ingredients they contain. One of the best general guides to use in pur- 

 chasing a commercial herbicide is the price per pound of active ingredient. 

 The containers for all commercial herbicides have labels that state the 

 amount of active ingredients contained in the material. The ingredients 

 are expressed in percent by weight, or in pounds per gallon or package. 



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

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

 tions are most economical to use. For example, a 2,4-D formulation that 

 contains 4 pounds of acid equivalent per gallon usually will cost less per 

 pound of 2,4-D 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 

 formulation- -amine or ester (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, the follow- 

 ing are considered high-volatile esters: amyl, butyl, ethyl, isopropyl, and 

 methyl. The low-volatile esters are: butoxyethanol, butoxyethoxypropanol, 

 capryl, ethoxyethoxypropanol, isooctyl, propylene glycol butyl ether, and 

 other long sidechain esters. 



The carrier components contained in herbicides, such as emulsifiers, 

 solvents, and adjuvents, often have a bearing on problems encountered in 

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

 materials available for various purposes makes difficult the forming of 

 general guides for purchasing. 



SPRAYER CALIBRATION 



The type and operating condition of sprayer equipment used to apply 

 herbicides is of utmost importance to efficient chemical weed control. Uni- 

 form distribution of the spray solution is the most essential requirement 

 of good spray equipment. For many weeds and situations, volumes of spray 

 may vary widely (5 to 100 gallons per acre) without affecting results, if 

 adequate coverage and spray distribution are obtained. Sprayer output 

 should be determined for each particular spraying operation. A good method 

 of calibration is to make initial adjustments to suit the machine and job 

 requirements, and then make a trial run to determine the actual output of 

 the machine. The herbicide spray mixture then should be prepared ac- 

 cordingly. The calibration should be repeated frequently to check for 

 nozzle orifice wear and other factors affecting performance. This is espe- 

 cially important when wettable powders or other abrasive sprays are used. 



Individual nozzles should be checked for accuracy of delivery. This may 

 be done by measuring the volume of spray delivered by each nozzle in 1 

 minute. There are many methods of calibrating a sprayer. One method is 

 given below for calibrating each of three different types. 



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