Thu, Aug 05, 2021:On Demand
Background/Question/Methods
Hydrilla (Hydrilla verticillata) is an aquatic nuisance species that was introduced to the US in the 1960’s and has spread throughout the eastern seaboard. Hydrilla negatively affects the aquatic ecosystems where it establishes by altering pH and dissolved oxygen, nutrient cycling, disrupting boat access, and clogging intakes. We report the results from field collections that explored the effects of herbicide on tuber production and experiments that tested for the interaction between temperature and season on hydrilla germination and growth in two reservoirs on the Chattahoochee River. Field collections revealed that hydrilla tubers were less dense and smaller from sites treated with herbicide compared to untreated sites.
Results/Conclusions Subsequent experiments found no effects of herbicide application on tuber germination rate or plant growth suggesting no carry over effects of herbicide application on tubers sprouting from the sediment. Hydrilla grew faster in organic matter than in sand substrates suggesting management efforts should concentrate control efforts in areas with substantial organic matter in order to slow the spread of their propagules. Planting tubers in the fall that had been exposed to air (i.e., drying) did induce them to germinate, but germination rates were relatively low (~50%) across all of our experiments compared to other studies using monecious hydrilla. These results indicate that Columbus, at N32° latitude, may represent a southern boundary for the expansion of the monecious variety of hydrilla. Experiment timing could have reduced germination rates, but also reveals that exposure to air, regardless of season, induces germination and could be used as a management strategy. Extending the drying time did not alter germination rates. Taken together, repeated drawdowns that induce tuber germination in seasons that are not favorable for growth combined with herbicide treatments will result in the reduction in biomass and spread of hydrilla.
Results/Conclusions Subsequent experiments found no effects of herbicide application on tuber germination rate or plant growth suggesting no carry over effects of herbicide application on tubers sprouting from the sediment. Hydrilla grew faster in organic matter than in sand substrates suggesting management efforts should concentrate control efforts in areas with substantial organic matter in order to slow the spread of their propagules. Planting tubers in the fall that had been exposed to air (i.e., drying) did induce them to germinate, but germination rates were relatively low (~50%) across all of our experiments compared to other studies using monecious hydrilla. These results indicate that Columbus, at N32° latitude, may represent a southern boundary for the expansion of the monecious variety of hydrilla. Experiment timing could have reduced germination rates, but also reveals that exposure to air, regardless of season, induces germination and could be used as a management strategy. Extending the drying time did not alter germination rates. Taken together, repeated drawdowns that induce tuber germination in seasons that are not favorable for growth combined with herbicide treatments will result in the reduction in biomass and spread of hydrilla.