New research shows algaecide treatments knocked back starry stonewort but failed to kill bulbils

New research findings from MAISRC show that algaecide treatments that targeted starry stonewort reduced its biomass, but failed to kill — and may have even increased the abundance of — bulbils, the alga’s primary means of reproduction. 

Treatments for starry stonewort were piloted by the Koronis Lake Association last summer on Lake Koronis, the first lake in Minnesota where starry stonewort was found. MAISRC researchers partnered with the association to evaluate the effectiveness of these treatments. Different areas of the lake were subjected to mechanical harvesting only, algaecide only, or harvesting plus algaecide. Additionally, untreated reference areas were monitored to provide a baseline for comparison. The algaecide treatments included granular copper-based formulations which are specifically intended to kill bulbils.

By sampling in the lake before and after these treatments and conducting further experiments in the lab, researchers found that bulbils treated with the granular algaecide were just as viable (and therefore able to sprout and reinvade) as bulbils from untreated areas. Not only that, areas only treated with algaecide actually showed a large spike in bulbil density, which the reference and mechanically harvested areas that were not treated with algaecide did not have.

The overall biomass of the plant – which can form dense mats on the surface of the water that are hard to swim and boat through – did decrease following these treatments. However, since bulbils remained viable and abundant, the relief may only be temporary.

“Although the treatment results were somewhat disappointing, there is a lot we can learn from this,” said lead researcher Dr. Dan Larkin. “For starters, it’s good for lake users that the overall biomass decreased following treatment. We also now know that this particular algaecide regimen was not effective at killing bulbils. Going forward, we’ll be conducting lab trials on different herbicides to better target the bulbils.”

This project is part of a broader effort to evaluate treatment effectiveness in starry stonewort-invaded lakes throughout Minnesota, and research findings will be shared with herbicide producers, applicators, and lake associations. Learn more about starry stonewort and MAISRC’s research here.

Read the full February 2017 newsletter here.