41 

 reported synergism of GA and 2,4-D for the control of waterhyacinths in 

 an outdoor environment in order to eliminate the "greenhouse" effect 

 reported by Hitchcock et al . (1949) and Koch et al . (1978). 



Materials and Methods 



Waterhyacinths used in this study were collected from Lake Ocklawaha 

 near Palatka, Florida, and a small tributary stream of the St. Johns 

 River in Jacksonville, Florida. Plants were maintained in outdoor pools 

 prior to experimental use or placed directly into the experimental con- 

 tainers after field collection. Regardless of initial source, all plants 

 were allowed to remain in the experimental containers for a period of 

 three to four days prior to initial weighing and treatment. Experiments 

 were conducted during the 1980, 1981, and 1982 growing seasons. 



Initial experiments were conducted outdoors in full sunlight in 

 approximately 70-liter metal barrels lined with polyethylene bags. All 

 barrels were filled with tap water to within 2.5 cm of the top. Eight 

 grams of commercially prepared 20-20-20 soluble plant nutrients and 

 micronutrients were dissolved in the barrels to yield a calculated 

 nitrogen concentration of 20 to 22 mg/1 (approximately equivalent to 10.0 

 percent Hoagland's solution). Solution levels were maintained as 

 necessary by addition of tap water. Experiments were set up in three 

 replications of five to six plants each, depending upon size and weight of 

 the plants. Waterhyaci nth plants used in the experiments were selected 

 on the basis of appearance, freedom of disease, and uniformity in size. 

 Prior to placement into barrels, all dead plant material, flower 

 spikes, and daughter plants were removed. Plants were allowed to drain 

 and were lightly shaken by hand in order to remove excess water from the 



