75 

 lower than normal rates of 2,4-D. Mo costs were included for labor, 

 conversion of the spray equipment to allow the use of GA 3 , or for 

 increased storage and transporation of GA 3 . 



Results and Discussion 



The mean pretreatment biomass (fresh weight) of the Lake Dexter 

 waterhyacinth population was 21.98 kg/sq m (standard error 0.67) and the 

 mean pretreatment number of plants per sq m was 70.76 (standard error 

 2.92). These means are within the ranges reported by Center and Spencer 

 (1981) for mature stands of waterhyaci nths in a North-Central Florida 

 lake during August. At the conclusion of phase one, mean fresh weight 

 and mean number of plants per sq m of the control plots were not signi- 

 ficantly different from the pretreatment levels (a=0.05) which indicates 

 that the plants were physiologically mature and had become space-limited 

 as reported by Richards (1980) and Center and Spencer (1981). 



Tables 3-1 and 3-2 summarize the results of the phase one eval- 

 uations of the 17 treatment combinations of GA 3 and 2,4-D in terms of 

 mean percent change in fresh weight and mean percent change in number 

 due to treatment, respectively. 



Comparisons of Table 3-1 and 3-2 reveals that within 2,4-D rates of 

 0.56 and 1.12 kg/ha and any rate of GA 3 , the mean percent change 

 in fresh weight per sq m was always greater than the mean percent change 

 in number of plants per sq m. This was a reflection of the morphologi- 

 cal response of the waterhyaci nths to the treatments. At the lower rate 

 of 2,4-D, the older leaves became necrotic at the base and readily 

 separated from the plant, such that the only remaining viable tissue was 

 the men' stem, youngest leaves, and roots. However, the plants remained 



