Control of Curlyleaf Pondweed (Potamogeton crispus) with Endothall Herbicide Treatments and the Response of the Native Plant Community in Suburban Lakes

Abstract

Curlyleaf pondweed (Potamogeton crispus) is an invasive aquatic plant often associated with eutrophic lakes. In many cases, curlyleaf develops expansive monotypic stands that shade out and displace native plants. In an attempt to enhance the native plant communities in Lakes Riley and Susan (Carver County, Minnesota), early season endothall herbicide treatments were conducted in May 2013 and 2014. These treatments aimed to reduce invasive curlyleaf pondweed abundance. The purpose of this study was to assess the response of native plant communities to these treatments. Prior to treatment, curlyleaf occurred in 74% of sites sampled in the littoral zone in Lake Riley and 66% of sites sampled in Lake Susan, compared to 23% and 16% respectively after treatment. Posttreatment decline in curlyleaf biomass was similar in scale to the declines observed in frequency of occurrence. Declines in curlyleaf frequency and biomass were statistically significant (p <= 0.05). Total native aquatic plant biomass increased in both Lakes Riley and Susan when comparing pre-treatment to post treatment, however increases were not significant. The frequencies of occurrence for Canada waterweed, bushy pondweed, and American lotus all increased significantly after treatment in Lake Susan. No frequencies of occurrence increased significantly for any native species in Lake Riley. My results suggest that the native plant communities increased slightly after herbicide treatments, however other factors continue to hinder the plant communities in both lakes.