Effect of gibberellic acid and 2,4-D on water hyacinths

Combinations of gibberellic acid (GA₃) and 2,4-dichlorophenoxyacetic acid (2,4-D) were evaluated to determine if GA₃ increased the effectiveness of 2,4-D on water hyacinths (Eichhornia crassipes (Mart.) Solms) under field conditions. Bulbous-leaved water hyacinths were grown outdoors in north Florida in 70-1 containers during the 1980–1982 growing seasons with combinations of GA₃ at 0, 23.5, 47.0, 94.0 and 188 g ha^?1 and 2,4-D at 0, 0.28, 0.56 1.12 and 2.24 kg ha^?1. Significant increases in the effectiveness of 2,4-D in combination with GA₃ were observed at lower rates of 2,4-D. However, these increases appeared to be additive since regression analysis revealed no significant interaction or synergism between GA₃ and 2,4-D at any level.