The salt formulations of 2,4-D, MCPA, 2,4,5-T, and other phenoxy com- 

 pounds are practically nonvolatile, and are much safer to use near valuable 

 susceptible plants than ester formulations if spray drift is avoided. 



2. Esters 



(a) Relatively high volatile esters .-- This type includes methyl, ethyl, 

 isopropyl, butyl, amyl, and others known to possess relatively high vapor 

 activity. These esters of 2,4-D, MCPA, 2,4,5-T, and other phenoxy com- 

 pounds are liquids which, when properly formulated, form emulsions when 

 mixed with water. Because they are highly volatile, they should not be 

 used under high temperature conditions for weed control in areas adjacent 

 to susceptible plants, such as cotton, tomatoes, grapes, flowers, and orna- 

 mentals. These volatile esters are more phytotoxic per pound of acid 

 equivalent than the amine or other salts of 2,4-D, MCPA, and 2,4,5-T to 

 most crops, annual weeds, and hard-to-kill weeds and brush, especially in 

 the more arid regions and under conditions adverse to rapid plant growth. 

 They penetrate leaves rapidly andtheir effectiveness is not reduced by rain 

 unless it occurs immediately after application. If a range of rates of 

 application is suggested, the esters should be applied at the lower rates and 

 the amine or other salts at the higher rates. 



(b) Relatively low volatile esters . --This type includes the butoxyethanol, 

 butoxyethoxypropanol, capryl, ethoxyethoxypropanol, isooctyl, propylene 

 glycol butyl ether, and other esters known to be low volatile. The low 

 volatile esters are less hazardous than high volatile esters in areas adja- 

 cent to susceptible crops when temperatures are 95° F. or less. When 

 temperatures exceed 95° F., the vapors of both the high and low volatile 

 esters will cause injury. Even under such high temperatures the low 

 volatile esters are less hazardous to adjacent susceptible crops. 



2,4-DICHLOROPHENOXYETHYL SULFATE (Sesone) 



This herbicide is formulated as the sodium salt and is a white crystalline 

 powder that is soluble in water. When applied to moist soils, sesone is con- 

 verted into a herbicide with properties similar to 2,4-D. It is effective as 

 a pre-emergency herbicide for weed control in a number of crops. Unlike 

 2,4-D, however, sesone possesses little or no phytotoxicity as a foliage 

 spray on most plants. Sesone, therefore, is much safer than 2,4-D as a 

 pre -emergence treatment in areas where 2,4-D spray drift, or vapors of 

 esters of 2,4-D, are hazardous to susceptible crops, such as cotton, grapes, 

 tomatoes, and sugar beets. Sesone is not effective as a post-emergence 

 foliage spray; therefore it must be applied to the soil before emergence 

 of the weeds to give effective control. It has been effective as a post- 

 planting spray for weed control in strawberries when applied before emer- 

 gence of the weeds. The herbicide has been erratic in performance during 

 periods of inadequate soil moisture. 



Sesone is of relatively low toxicity (LDcq = 730 to 1,400 mg./kg.) for 

 rats. 



SUBSTITUTED PHENOLS 



The dinitro alkyl phenols and chloro substituted phenols have been used 

 widely as contact selective and nonselective post-emergence herbicides. 

 They have also been used for selective pre-emergence weed control in a 



- 3 - 



