38 

 a slow rate (maximum amount in six days); and (c) almost entirely 

 towards the newly developing leaves (20.8 percent of total applied). 

 Singh and Muller (1979a) used radioactively labeled 2,4-D to 

 demonstrate that three hours after spraying single waterhyacinths at a 

 rate of 0.75 kg/ha in a spray volume of 800 1/ha, 53.3 percent of the 

 total sprayed solution was in the water culture medium. It was also 

 shown that waterhyacinths grown in culture medium containing labeled 

 2,4-D can absorb and translocate sufficient 2,4-D from treated water to 

 result in their death if the 2,4-D concentration is above 1.0 mg/1 . 

 Thus, Singh and Muller (1979a) suggested that immediately after spraying 

 2,4-D in the field, the upper surface layer of water, if exposed, might 

 contain concentrations of 2,4-D which would be readily available for 

 uptake by waterhyacinth roots. Others have suggested that 2,4-D which 

 is added to the water surface from spray drift or runoff has an added 

 effect and may be a factor in explaining why waterhyacinths grown in 

 small containers in greenhouse experiments appear to be more sensitive 

 to lower rates of 2,4-D as compared to field studies (Hildebrand, 1946; 

 Hitchcock et al . , 1949; Koch et al . , 1978). 



Koch et al . (1978) reported an aerial application rate of 4.5 kg/ha 

 in spray volumes as low as 15 1/ha in the White Nile River, Sudan. This 

 rate was deemed effective due to the low relative humidity and high tem- 

 peratures in southern Sudan. The reliability of applications was also 

 deemed to be reduced at spray volumes <100 1/ha. Public agencies 

 responsible for aquatic plant control in Florida routinely apply 2,4-D 

 to waterhyacinths at rates of 2.24 kg/ha in aqueous spray volumes of 457 

 to 934 1/ha for ground applications and up to 4.48 kg/ha in spray vol- 

 umes of 56.7 1/ha for aerial applications. The U.S. Army Corps of 



