Scientists Tackle Eurasian Water Milfoil at Lulu Lake

Eurasian water milfoil can ruin your day at the lake. This non-native aquatic plant grows quickly in the spring, forming a thick mass of tangled stems underwater that get caught in boat propellers, rudders, and on boat trailers. The dense mat it forms on the water’s surface makes swimming and fishing almost impossible.

At The Nature Conservancy’s Lulu Lake Preserve in southeast Wisconsin, Eurasian water milfoil (EWM) is a problem for both people and nature. Larger fish can’t swim into the dense mats to lay eggs, and it’s displacing native aquatic plants that waterfowl and other wildlife need.

In 2009, Conservancy Land Steward Jerry Ziegler and Dr. Tim Gerber, Professor of Biology at the University of Wisconsin-La Crosse, teamed up to stop the spread of EWM in Lulu Lake.

“Much of the Eurasian water milfoil was concentrated where boaters enter Lulu Lake through the Mukwonago River from Eagle Springs Lake,” says Ziegler, “so that’s where we focused our efforts.”

With funding the Conservancy secured from the Wisconsin Department of Natural Resources, Gerber mapped the EWM locations in the lake in 2009, and he and other SCUBA divers and snorkelers started hand-pulling it in the summer of 2010. Conservancy interns collected the material along with any broken pieces that floated up and removed it from the lake. By fall 2011, the large populations were under control, but EWM grows back, so constant vigilance would be necessary.

This unfortunate fact eventually led to Gerber’s “hairbrained idea,” as he describes it. What if he and Ziegler could find a way to get native aquatic plants to grow in the places where milfoil was removed and give the invader some competition?

With additional funding from the state, they are working on doing just that. The idea is to weave native aquatic plants like pondweed into a fibrous coconut mat that is biodegradable and then sink the mats into the lake where milfoil has been removed. The fiber mats will suppress milfoil growth, as Gerber and Ziegler have shown in greenhouse experiments, and give the pondweed a chance to establish.

“We’ve successfully grown the native plant mats in the Conservancy greenhouse and placed them in Lulu Lake,” said Ziegler. “We know they work on the calcium carbonate-rich bottom of that lake. We plan to expand this work to Pickerel Lake, another Conservancy project area in the Mukwonago River watershed, to see how the technique works on the sandy, gravely bottom of that lake.

“Early detection, removal and our experimental work with Eurasian water milfoil is part of a broader, long-term effort to manage invasive species in Lulu Lake and the entire Mukwonago River system,” said Ziegler. “This place is truly a Wisconsin treasure, and we need to be innovative and persistent in protecting its health and vitality.”


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