the possible hazards that may arise from skin contact or inhalation of the 

 substances. Likewise, these data do not accurately predict the toxicity of a 

 fornnulation which may differ according to the solvent or diluent ennployed. 



PHENOXY COMPOUNDS 



Several connpounds in this group, including 2,4-dichlorophenoxyacetic 

 acid [2,4-D], 2,4,5-trichlorophenoxyacetic acid [2,4,5-T], 2-nn.ethyl- 

 4-chlorophenoxyacetic acid [MCPA], and 2 -(2,4,5-t^ichlo^ophenoxy)p^o- 

 pionic acid [silvex] are used as post-ennergence selective herbicides to con- 

 trol broadleaved weeds in corn, small grains, sorghum, rice, flajc, lawns, 

 and to control brush and weeds in pastures, along roadsides, rights-of-way, 

 and drainage and irrigation ditches. Some of the phenoxy compounds also 

 may be applied to the surface of the soil as a pre-ennergence treatnaent to 

 control grasses and broadleaved weeds in corn and other crops. 



4-{2, 4-dichlorophenoxy) butyric acid [4-{2,4-DB)] and 4-(2-methyl-4- 

 chlorophenoxy) butyric acid [4-(MCPB)] have shown promise for post- 

 emergence control of broadleaved weeds in (a) cereals underseeded with 

 certain forage legumes; (b) establishment of pure stands of forage legumes; 

 (c) forage-legume seed-production fields; (d) flax; and (e) other weedy-crop 

 situations. Legumes that are relatively tolerant to 4-(2,4-DB) include white 

 clover, alsike clover, red clover, alfalfa, and birdsfoot trefoil. 



Phenoxy compoiinds usually are fornnulated and marketed as two basic 

 types. They are of low to intermediate oral toxicity {LD50 = 375 to 1,200 

 nng./kg.) for the various formulations, 



1. Salts 



The most widely used salts of 2, 4-D, MCPA, 2,4,5-T, and other phenoxy 

 acids are the diethanolamine, triethanolamine, dimethylamine, triethylamine, 

 isopropylamine salts, and mixtures of these and others. These amine salt 

 formulations are available chiefly as w^ater -soluble liquids. The amine salt 

 formulations are more phytotoxic per pound of acid equivalent than the other 

 salt forms, and are more effective in controlling a wider range of weeds. 



Some of the phenoxy compounds also are commercially available as sodium 

 and ammonium salt formulations. These connpounds are available chiefly as 

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

 water-soluble liquids. These salt formulations are satisfactory to use on 

 easy-to-kill weeds such as mustard, pigweed, and lannbsquarters. 



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, and amyl esters. These esters of 2,4-D, MCPA, 2,4,5-T, 

 and other phenoxy compounds are liquids w^hich, when properly fornnulated, 

 form emulsions when mixed -with w^ater. Because they are highly volatile. 



