Chemical Treatment For Aquatic Invasives May Hurt, Not Help, Native Lake Plants

Jun 30, 2020

Eurasian watermilfoil.

Lake managers might be hurting native aquatic plants – instead of helping them – when they use chemicals to control invasive plants on entire lakes.

New research by DNR Lakes and River Team Leader Dr. Alison Mikulyuk shows native plant communities can struggle when chemicals are used to target invasive Eurasian watermilfoil.

It appears the effects on native plants are worse than if there were no treatment at all.

“If the herbicide treatment could be applied in a case where it would only target the Eurasian watermilfoil, there would be no downside. But we do see negative effects associated with treatment itself,” Mikulyuk said.

DNR Lakes and River Team Leader Dr. Alison Mikulyuk.
Credit UW-Madison

Some wisdom has suggested whole-lake chemical treatment of Eurasian watermilfoil opens a window for native plants to thrive. But Mikulyuk’s research indicates the opposite is true.

“Surprisingly, our study associated more native species declines with lake-wide herbicide treatment than with EWM,” she said.

Mikulyuk reviewed more than 600 surveys on 442 Wisconsin lakes.

She suggested lake-wide treatments of the invasive milfoil might only be appropriate in the most pressing of circumstances.

“Unless there’s strong evidence of high impacts, so ecological, social, economic impacts for an invasive species, this idea of aggressive chemical control conducted at a lake-wide scale might do more harm than good,” she said.

Mikulyuk said she hopes biologists, lake groups, and individuals can use her research when making decisions about chemical treatment.

For a closer look at the debate over using chemicals on part of Anvil Lake in Vilas County, read last week’s The Stream.