3 

 utilized in agriculture, and more specifically, aquatic environments. 

 In order to reduce public concern over use of chemical control agents 

 and to gain more effective control of pest species, two basic approaches 

 have been pursued; i.e., (a) the use of alternate control methods such 

 as biological agents, mechanical harvesting systems, and/or environmental 

 manipulation and (b) modification of herbicide application techniques, 

 equipment, and/or the use of various chemical adjuvants in order to 

 reduce the amount of herbicide actually introduced into the environment. 



This study was designed to determine if the quantity of 2,4-D 

 routinely utilized for large scale control of waterhyacinths could be 

 reduced by simultaneously applying a naturally occurring plant growth 

 substance, gibberellic acid. The study was divided into three major 

 parts. Part one involved small plot evaluations of the efficacy of 

 various rates and combinations of 2,4-D and gibberellic acid for 

 waterhyacinth control. The objective was to determine the presence of 

 an interaction or synergistic effect between 2,4-D and gibberellic acid 

 which would increase the sensitivity of waterhyacinths to 2,4-D. Part 

 two involved growth chamber evaluations utilizing radioactive-labeled 

 2,4-D and unlabeled gibberellic acid. The objective was to ascertain if 

 the cause of increased sensitivity, if present, to 2,4-D was due to an 

 increase in the quantity of 2,4-D translocated to various locations 

 within the plant when also treated with gibberellic acid. Part three 

 involved field application of a combination of 2,4-D and gibberellic 

 acid under routine operational conditions. The objective of this final 

 phase was to determine if a specified combination of gibberellic acid 

 and a reduced rate of 2,4-D would be efficacious in a large-scale, 

 operational waterhyacinth control program. 



