PART 3 - FIELD EVALUATIONS 



Introduction 

 Various public agencies routinely utilize 2,4-D for the control of 

 waterhyacinth in the United States. One such agency, the U.S. Army 

 Corps of Engineers, Jacksonville District, annually utilizes approxi- 

 mately 8,200 kg of 2,4-D at rate of 2.24 kg/ha in a 934 1/ha aqueous 

 solution to control waterhyaci nths on the St. Johns River, Florida 

 (McGehee, 1982). Pieterse and Roorda (1982) reported a ten-fold 

 enhancement of 2,4-D sensitivity of waterhyaci nths when the plants were 

 simultaneously treated with GA3 at 6 to 8 g/ha under greenhouse 

 conditions. It was also suggested by Pieterse and Roorda (1982) that 

 such a large reduction in the amount of 2,4-D would lower the risk of 

 damage to nearby crops or vegetation and may be attractive from an eco- 

 nomical point of view due to the large reduction in the amount of 2,4-D 

 required to control waterhyaci nths. In order to test this possibility, 

 the following investigations were conducted (1) the treatment rates 

 tested in the small plot evaluations (Part 1) were repeated in a natural 

 stand of dense waterhyaci nths; (2) a selected rate of 2,4-D and GAo was 

 evaluated under actual waterhyacinth control operational conditions; and 

 (3) an economic analysis of the use of GA3 in conjunction with 2,4-D was 

 performed utilizing the assumption that GA3 would reduce the amount of 

 2,4-D required for waterhyacinth control by a factor of 10. 



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