37 

 Efficacy of 2,4-D on Waterhyacinths 



The first recorded use of 2,4-D for the control of waterhyacinths 

 appeared to be in April 1945 near Tampa, Florida (Hildebrand, 1946). 

 Hildebrand (1946) applied 0.059 to 0.125 percent (by volume) 2,4-D solu- 

 tions to 0.006 ha plots and reported nearly complete control. Seale and 

 Allison (1946) evaluated five 2,4-D esters, four 2,4-D amine salts, and 

 five inorganic salts of 2,4-D and reported that the ester formulations 

 were the most effective; however, at higher rates (> 2.24 kg/ha in 

 934 1/ha aqueous solution) the amine and inorganic salt formulations 

 were equally effective. Seale and Allison (1946) reported the first 

 effective aerial application of 2,4-D to waterhyacinths. Hitchcock et 

 al . (1949) conducted extensive evaluations at various rates (2.24 to 

 17.92 kg/ha) and spray volumes (56.0 to 168 1/ha) and concluded 

 that the principal limiting factors affecting 2,4-D efficacy for 

 waterhyacinth control were (a) concentration and rate of application, 

 (b) rate of delivery of spray solution, (c) stage of growth and 

 development, and (d) atmospheric conditions. Application of 2,4-D 

 to mature waterhyacinths with daughter plants attached by stolons 

 resulted in death of the parent plants; however, daughter plants 

 survived (Hitchcock et al . , 1949). Singh and Muller (1979b) used 

 radioactively labeled 2,4-D to confirm these observations by 

 demonstrating maximum transport of labeled 2,4-D to daughter 

 plants from the parent up to the two-leaf stage of the daughter plants 

 and no translocation after the daughter plants reached the four-leaf 

 stage. Singh and Muller (1979a) also demonstrated that radioactively 

 labeled 2,4-D when applied to a single waterhyacinth leaf was 

 transported (a) in small amounts (23.5 percent of total applied); (b) at 



