Some of the phenoxy compounds are also commercially available as sodium and 

 ammonium salt fornn.ulations. These compounds are available chiefly as water-soluble 

 powders, but some of these herbicides are also available as water-soluble liquids. 

 These salt formulations are satisfactory to use on easy-to-kill weeds, such as-mustard, 

 pigweed, and lambsquarters, but they are less phytotoxic per pound of acid equivalent 

 than the amine salts and are not as effective in controlling as wide a range of weeds. 



The salt formulations of 2,4-D, MCPA, 2,4,5- T, and other phenoxy compounds 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 .-- These types include the 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 compounds are liquids which, when 

 properly formvilated, form emulsions when miixed 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 ornamentals. 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 con- 

 ditions adverse to rapid plant growth. They penetrate leaves rapidly and their effective- 

 ness is not reduced by rain unless it occurs immediately after application. If a range 

 of rates of application is suggested, the relatively high volatile esters should be applied 

 at the lower rates and the amine or other salts at the higher rates. 



(b) Relatively low volatile esters .-- These types include the butoxyethanol, propylene 

 glycol butyl ether, butoxyethoxypropanol, ethoxyethoxypropanol, capryl, iso-octyl, and 

 other esters knov/n to be low volatile. The low volatile esters of 2,4-D, MCPA, and 

 2,4,5-T are similar to the high volatile esters with respect to phytotoxicity and 

 selectivity on annual weeds and crops in humid areas with nnoderate to low tempera- 

 tures. Under high-temperature conditions, which are conducive to high rates of 

 evaporation, the lo'w volatile esters possess greater persistence and greater residual 

 activity, and are somewhat more effective on some species where sustained residual 

 activity on leaf or soil surfaces is necessary for maximum plant kill. Under most 

 conditions, however, there have been no significant differences in the activity and 

 selectivity of low volatile and high volatile esters of 2,4-D, MCPA, and 2,4,5-T for the 

 control of annual weeds in crops. The low volatile esters are much less hazardous than 

 high volatile esters in areas adjacent to susceptible crops when temperatures are 

 100° F. or less. When temperatures exceed 100°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 injurious to susceptible crops, 



2,4-DICHLOROPHENOXYETHYL SULFATE (2,4-DES) 



This herbicide is a white crystalline powder which is soluble in w^ater. When applied 

 to moist soils, 2,4-DES is converted into a herbicide with properties similar to 2,4-D, 

 It is effective as a pre -emergence herbicide for weed control in a number of crops. 

 Unlike 2,4-D, however, 2,4-DES possesses little or no phytotoxicity as a foliage spray 

 on most plants. 2,4-DES, 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. 2,4-DES is not 

 effective as a post-emergence foliage spray; therefore, it must be applied to the soil 

 prior to emergence of the w^eeds to give effective control. It has been effective as a 

 post-planting spray for weed control in strawberries when applied prior to emergence 

 of the weeds. The herbicide has been erratic in performance in arid areas and also in 

 humid areas during periods of inadequate soil moisture. 



