8 HERBICIDAL CONTROL 



sodium arsenite and ammonium thiocyanate were used on marsh 

 plants to a limited extent, but they have been largely superseded 

 by herbicides that are safer and fully as effective. 



Because gas or vapor drift from some spraying operations 

 has proved harmful to farm crops, there are strict laws^ on aerial 

 spraying of herbicides. There is also the possibility of injury to 

 nearby stands of duck-food plants. Coarse sprays, such as those 

 released by low-pressure equipment, are much less likely to drift 

 and cause damage to crop plants than fine sprays produced under 

 high pressure. Furthermore, herbicides consisting of salts or low- 

 volatility esters are safer than volatile esters as regards release of 

 toxic vapors from sprayed areas. 



2,4 -D AND 2,4,5-T 



Two of the most popular herbicides in marsh management are 

 the so-called phenoxy compounds, 2,4-D (2,4-dichlorophenoxyacetic 

 acid) and 2,4,5-T (2,4,5-trichlorophenoxyacetic acid). 2,4-D is 

 cheaper than 2,4,5-T and is used much more widely, but both are 

 comparatively low in cost, and both are effective on many kinds of 

 marsh plants. 



Besides their economy and wide effectiveness, formulations of 

 2,4-D and 2,4,5-T are easy to apply, are somewhat selective in gen- 

 erally being more toxic to broadleaf plants than grasses, and are 

 noncorrosive to spraying equipment. The sensitivity of cotton, 

 tobacco, grapes, tomatoes, and other crops to these chemicals is an 

 important drawback to the use of herbicides in agricultural areas. 



The most commonly used formulations of 2,4-D and 2,4,5-T are 

 amine salts and esters. Under favorable conditions, the salts and 

 esters give nearly equivalent results, though generally the former 

 are slower in showing effects. The salts dissolve readily in water 

 but not in oil, handle easily, and their sprays do not volatilize so 

 readily as esters. On the other hand, the fact that esters can be 

 dissolved in oils is an advantage in low-volume spraying, as in aerial 

 applications. Furthermore, oils such as kerosene and diesel oil 

 have some herbicidal value and their use as diluents enables better 

 residual adherence to floating-leaf aquatics like waterlilies or spat- 

 terdock and on other plants wet by rain shortly after spraying. 



OTHER HERBICIDES 



During the past decade, ammonium sulphamate (Ammate) and 

 TCA (sodium trichloroacetate) have been used to a limited extent 



' Such laws are summarized in Herbicides Law Manual, compiled by the National Agi-icultural Chemi- 

 cal Association, 1145 19th St., N. W., Wasbiiistou 6, D. C. 



