Gibberellin Synthesis Inhibitor Effects on Submersed Aquatic Weed Species

A laboratory bioassay showed that inhibitors of gibberellin synthesis (flurprimidol, paclobutrazol, and uniconazole) reduced plant height but did not affect physiological parameters such as photosynthesis, respiration, and chlorophyll content in two weedy submersed aquatic plants, hydrilla and Eurasian watermilfoil. Eurasian watermilfoil was sensitive to these compounds at concentrations as low as 0.75 μg L−1. Hydrilla sensitivity was in the range of 75 to 750 μg L−1. The three compounds reduced main and lateral stem lengths in hydrilla; however, at 75 μg L−1 the number of lateral stems and roots was greatly increased over untreated controls resulting in a stoloniferous growth habit. Dominant growth form of treated Eurasian watermilfoil was a single shortened stem with numerous compacted buds. Photosynthesis, respiration, and chlorophyll content were not affected in either plant at nontoxic dosages in which stem reduction was obtained. Both plants required only a 24-h exposure to maintain main stem length reduction for 6 wk after transfer to untreated medium. Our results indicate that these gibberellin synthesis inhibitors would be effective in reducing plant height in aquatic systems.