precipitation, prevailing tennperatures, soil type, and other soil and clinr^atic 

 factors. For semipernnanent sterilization, higher rates of application are re- 

 quired on the sandy soils of humid regions than on the heavy soils of lower 

 rainfall areas. To kill all vegetation, higher initial rates of application are 

 necessary on the heavy soils of arid regions than on soils of humid areas. 

 Toxicity persists for longer periods in arid regions because there is less 

 leaching and slower decomposition than in humid regions. 



Sodium chlorate has low oral toxicity (LD50 = 7,000 mg./kg.) for rats. 



Caution . The manufacturer's directions for use of sodium chlorate should 

 be followed carefully. This chemical, particularly in spray solutions, nnust 

 be handled with extreme caution. Any inflammable nnaterials, such as 

 clothing, shoes, hay, wood, or weeds, that have dried after having been wet 

 with a sodium chlorate solution become violently inflammable and even 

 explosive. They can be ignited easily by friction, sparks, or even by the 

 heat from the sun. Serious injury or property damage may result fronn 

 carelessness or failure to observe this precaution. 



BORON COMPOUNDS 



A number of boron connpounds, including borax, sodium pentaborate, boron 

 trioxide, anhydrous sodium biborate, and mixtures of these compounds with 

 2, 4-D, sodium chlorate, and/or a substituted phenylurea compound are used 

 to control deep-rooted perennial w^eeds, and for tennporary and semipermanent 

 soil sterilization to prevent growth of all vegetation. Boron compounds should 

 be applied at rates of 2,400 to 4,800 pounds of borax equivalent per acre 

 (15 to 30 pounds per square rod) for control of all vegetation and semi- 

 permanent soil sterilization in humid areas. In arid regions the rates re- 

 quired are usually higher--4,800 to 6,400 pounds per acre (30 to 40 pounds 

 per square rod). The soluble borate connpounds are effective at lower rates 

 of treatment. Addition of 2, 4-D, sodium chlorate, or a substituted phenylurea 

 herbicide to boron compounds will greatly reduce the rate of application re- 

 quired for killing all vegetation. Boron compounds normally are applied as 

 dry granular formulations, but mixtures of boron and 2, 4-D, and boron and 

 sodiunn chlorate also are formulated for spray application. 



ARSENICALS 



Arsenical herbicides include sodium arsenite, arsenic trioxide, arsenic 

 pentoxide, disodium mononnethylar sonate (DMA), and other formulations of 

 arsenic acid. Sodium arsenite (the most commonly used arsenical) is used 

 extensively to kill submerged aquatic weeds and as a sennipernnanent soil 

 sterilant to control all vegetation on driveways, tennis courts, railroad 

 rights-of-way, industrial storage sites, and on other nonagricultural areas 

 inaccessible to animals. It leaves the soil unproductive for 1 to 4 years, 

 depending on soil type and climatic conditions. 



Areas frequented by livestock should not be treated with sodium arsenite 

 because of hazard of poisoning. Sodium arsenite is highly toxic for mammals 

 (LD50 = 10 to 50 mg./kg.) when administered orally. 



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