MAISRC graduate student thesis examines effect of herbicides on curlyleaf pondweed and native plants
A thriving native aquatic plant community made up of diverse and abundant plants is essential to maintaining a stable aquatic ecosystem. Native plants stabilize shorelines, reduce sediment resuspension, and balance the water chemistry by taking in phosphorus and releasing oxygen.
However, these delicate systems can be disrupted by the introduction of invasive aquatic plants such Eurasian watermilfoil and curlyleaf pondweed, both of which are becoming increasingly common in Minnesota lakes. (For reference, in 2004 Eurasian watermilfoil was found in 160 lakes in Minnesota; today, that number is over 300.) Curlyleaf pondweed presents issues in Minnesota lakes because it grows very dense stands that displace native species and produces hardy turions (a plant bud that allows the plant to survive in winter without setting seeds) for reproduction that are viable for two or more years,
How these aquatic invaders can be stopped without harming native plants became the focus of Dr. Ray Newman’s advisee, John Jaka, who recently earned his master’s degree and wrote his thesis on this issue. Jaka’s research worked to address three specific objectives:
- The magnitude of the effect of herbicide treatments on curlyleaf pondweed;
- How native plants respond to curlyleaf pondweed herbicide treatments; and
- If reductions of curlyleaf pondweed abundance, biomass, and turion densities in the sediment will allow the native plant community to expand.
Jaka selected two lakes in the Twin Cities metro area – Lake Riley and Lake Susan – as well as one control – Mitchell Lake – on which to conduct his research. The lakes were treated with Endothall, an herbicide commonly used to control aquatic plants, for two consecutive years. Data were compared to several years’ worth of pre-treatment data, including biomass (weight) and turion densities of both native and invasive species.
After observation and data analysis, Jaka found that low-dose, early-season endothall herbicide treatments successfully controlled curlyleaf pondweed within treatment years while having no measurable negative effects – judging by the frequency of plant occurrence, turion density, and overall biomass– on the native plant community. Curlyleaf pondweed frequency of occurrence, biomass, and turion production all declined by 90% or more in both treatment lakes. However, as in previous studies, native plants did not show big increases. Read the full paper here.
While this research did shine light on the effectiveness of this particular herbicide, what remains unknown is how to best enhance the response of native plants, particularly in lakes with poor water clarity.
Additional MAISRC research is working to address this through post-treatment monitoring and transplanting native plants to treated areas. The ultimate goal of this work is to reduce invasive aquatic vegetation and encourage a diverse aquatic plant community that provides forage and shelter for waterfowl, fish, invertebrates, and algae-consuming zooplankton; improves recreational opportunities for swimmers and boaters; and results in the most resilient overall system.
Thank you to the Riley Purgatory Bluff Creek Watershed District for their funding and support of this work.