53 

 differences (a=0.05) between the GAo treatment levels at 2,4-D rate of 

 0.00 kg/ha; however, the differences were not in proportion to the rate 

 of GAo. It was also observed that when 2,4-D rates were held constant, 

 the addition of GA3 increased the mean response of waterhyacinths and 

 this response was frequently significant particularly at 2,4-D rates of 

 0.28 and 0.56 kg/ha. This observation supports the observation that 

 the effect of GA3 on waterhyaci nth sensitivity to 2,4-D recorded for 

 this series of observations was additive rather than synergistic. 



Summary 

 Based on regression analysis, the response of waterhyacinths grown 

 outdoors in 70-liter containers to treatments with combinations of 2,4-D 

 and GA^ does not indicate a synergistic effect or interaction between 

 GA 3 and 2,4-D either in terms of the percent change from initial biomass 

 or a percent change from the initial number of plants. However, at lower 

 rates of 2,4-D, the response does appear to be additive. These findings 

 are not in agreement with results reported for the effects of GA3 and 

 2,4-D on waterhyacinths by Pieterse et al . (1980) and Pieterse and 

 Roorda (1982). However, differences in experimental design and environ- 

 mental controls (greenhouse versus non-greenhouse, open air situations) 

 may account for the lack of agreement. 



