Recent research completed on Lake Koronis in Paynesville continues to show a long line of successes and failures in determining the best methods to manage a large-scale Starry Stonewort infestation.

Starry Stonewort is a large, submerged plant-like alga that can form dense mats in water bodies. These mats can interfere with boating, fishing, swimming, waterfowl hunting and other recreational activities. In addition, Starry Stonewort may choke out native plant communities, causing ecological harm. The species can spread by clinging to watercraft, trailers, and equipment.

A 250-acre infestation of Starry Stonewort was discovered in Lake Koronis in 2015. The MN Department of Natural Resources (DNR) performed an algaecide treatment in the Hwy 55 lake access area late fall of that year and again in 2016. Neither treatment had an effect on controlling the invasive algae.

The Koronis Lake Association joined with the MN DNR and experts from the MN Aquatic Invasive Species Research Center and Clemson University (South Carolina) to develop and implement a four-year pilot program to determine if an integrated management effort would yield sustainable results in keeping the infestation below a nuisance level.

In 2016, small plots were established whereby mechanical pulling alone, algaecide treatment alone, or combined actions were demonstrated to separately reduce the mass of Starry Stonewort, allowing normal water activities and opening up heavily infested areas. In 2017, within the same plots, fewer algaecide application were needed to keep Starry Stonewort presence below nuisance levels, demonstrating a sustainable model for the future.

The lessons learned in 2016-17 were ramped up in 2018. Both mechanical pulling and algaecide applications were combined in an integrated manner across the entire 250- acre infested area, including the previous years’ pilot plots. Any infested areas at depths less than four feet were mechanically pulled, including raking around and under docks and lifts. Two algaecide applications followed, spaced throughout the summer. Depths greater than four feet also had two algaecide applications performed. Pre and post-treatment audits were done after every pull and algaecide application to determine effectiveness.

Starry Stonewort was successfully managed to below nuisance levels in all areas where this integrated approach was implemented. Approximately 1,673 cubic yards of Starry Stonewort was removed and disposed of at a local organic farming operation. The use of mechanical pulling greatly increased the effectiveness of algaecide treatments, reducing the need for further algaecide applications.

In 2019, the partners plan to continue the integrated approach used in 2018. Koronis Lake Association now owns the mechanical pulling equipment thanks to the donation of funds from a local shore owner. Clemson University will continue to assist by looking for lower-cost algaecides that work equally as well on Starry Stonewort in an effort to reduce costs.

To date, complete eradication of Starry Stonewort from an infested water has not proven to be successful anywhere in the United States. For more information, visit StearnsCountyMN.gov/Environment/WaterResources/AquaticInvasiveSpecies.

 

 

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