TRICHLOROACETIC ACID (TCA) 



There are several salts of trichloroacetic acid (TCA) being used as weed killers, 

 including the anannonium and sodium salts. Sodium TCA is used most widely. It has 

 shown varying degrees of effectiveness in controlling quackgrass, Bermuda grass, 

 Johnson grass, and other annual and perennial grasses. Best results are obtained when 

 it is applied in combination with tillage and cultural practices. Sodium TCA is also 

 being used as a pre-emergence spray for the control of annual grasses and several 

 broadleaved weeds in flax, sugar beets, sugar cane, and certain other crops. The 

 residual toxicity from high rates of TCA for the control of perennial grasses may dis- 

 appear within a few weeks or may persist for a year or longer depending on the rate of 

 application, soil type, temperature, and soil-moisture relations. Sodium TCA is highly 

 soluble in water, somewhat caustic, and will corrode spray equipment. 



2,2-DICHLOROPROPIONIC ACID (DALAPON) 



This relatively new herbicide possesses properties somewhat similar to TCA. How- 

 ever, when applied to the foliage of grasses in the vegetative stages of growth, it has 

 proved less erratic and more effective than TCA for the control of most of the annual 

 grasses and is much more effective on quackgrass, Bermuda grass, Johnson grass, and 

 other perennial grasses. Dalapon possesses higher herbicidal phytotoxicity than TCA, 

 and is often used at lower rates of application than those suggested for TCA. The 

 sodium salt of dalapon, which is highly soluble in water, is the most widely used 

 formulation at present. Research indicates that it is more effective as a pre-emergence 

 or post-emergence spray in controlling perennial grasses when applied in combination 

 with tillage and cultural practices. Dalapon apparently possesses less residual toxicity 

 than TCA, but further research is needed to determine the rate of disappearance of the 

 herbicide from the soil. Dalapon has shown experimental promise for weed control 

 in sugar cane, sugar beets, birdsfoot trefoil, alfalfa, and for spot treatment control of 

 Johnson grass and other grasses in cotton. 



N-1-NAPHTHYL PHTHALAMIC ACID (NPA) 



This chemical is formulated for experimental herbicidal use as the sodium salt, 

 imide, and acid. The sodium salt of NPA is available as a wettable powder and as a 

 liquid concentrate. Its greatest potential use is a pre-emergence herbicide. Presently 

 NPA is being used for pre-emergence control of grasses and broadleaved weeds in 

 cucumbers, squash, cantaloupes, and other crops in the cucurbit group. It has also 

 shown some promise for weed control in irrigated cotton in the West. 



3,6-ENDOXOHEXAHYDROPHTHALLIC ACID (ENDOTHAL) 



In research studies the disodium salt of this acid has show^n promise for the control 

 of certain weeds in turf. It is being used as a pre -harvest aid, a general contact 

 herbicide, and chemical defoliant. 



l,2-DIHYDRO-PRYIDAZINE-3,6-DIONE (MALEIC HYDRAZIDE, MH) 



This chemical is formulated as a water-soluble sodium or diethanolamine salt for 

 use as a herbicide. Ithas shown promise for the control of several annual and perennial 

 grasses when applied in combination with tillage and cultural treatments. It is also 

 being used as a grass inhibitor to reduce mowing on areas such as roadsides. The 

 chemical, however, has performed erratically both as a herbicide and as a grass 

 inhibitor. Additional research is needed to determine the place of this compound in the 

 field of weed control. 



PHENYL MERCURIC ACETATE (PMA) 



This herbicide is available in a number of formulations. It is sometimes impregnated 

 on various carriers such as vcrmiculite, but PMA is also available as a liquid 



- 4 - 



