Semipermanent soil sterilization in humid areas requires 500 to 2,400 

 pounds of sodium chlorate per acre (3 to 12 pounds per square rod). In 

 semiarid areas, 500 to 1,000 pounds of the chemical per acre (3 to 6 

 pounds per square rod) are required for semipermanent soil steriliza- 

 tion. Sodium chlorate leaves the soil unproductive for 1 to 4 years, de- 

 pending on the precipitation, prevailing temperatures, soil type, and other 

 soil and climatic factors. For semipermanent sterilization, higher rates 

 of application are required 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 (LD^q = 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 solu- 

 tions, must be handled with extreme caution. Any inflammable mate- 

 rials, 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 from carelessness or failure to observe this pre- 

 caution. 



BORON COMPOUNDS 



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

 boron trioxide, anhydrous sodium biborate, and mixtures of these com- 

 pounds with 2,4-D, sodium chlorate, and/ or a substituted urea compound 

 are used to control deep-rooted perennial weeds, and for temporary 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 semipermanent soil sterilization in humid areas. In 

 arid regions the rates required are usually higher--4,800 to 6,400 pounds 

 per acre (3 to 40 pounds per square rod). The soluble borate compounds 

 are effective at lower rates of treatment. Addition of 2,4-D, sodium 

 chlorate, or a substituted urea herbicide to boron compounds will greatly 

 influence the rate of application required for killing all vegetation. Boron 

 compounds normally are applied as dry granular formulations, but mix- 

 tures of boron and 2,4-D, and boron and sodium chlorate, also are for- 

 mulated for spray application. 



ARSENICALS 



Arsenical herbicides include sodium arsenite, arsenic trioxide, arsenic 

 pentoxide, dis odium methyl arsonate, and other formulations of arsenic 

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

 sively to kill submerged aquatic weeds and as a semipermanent 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. 



