An effort to use the herbicide fluridone to reduce problems caused by the invasive curly-leaf pond weed without harming native vegetation got underway in April at Lake Benton, a 2,850-acre lake in Lincoln County, according to the Minnesota Department of Natural Resources (DNR).

It is the first time that fluridone has been used in Minnesota to control the prolific curly-leaf pondweed, which displaces native plants. Past fluridone treatments of lakes infested with Eurasian watermilfoil have produced mixed results.

"Curly-leaf sprouts early, giving us a window of opportunity to impair its growth without harming native plants," said Wendy Crowell, DNR aquatic biologist. "This is a chance to see if we can switch from a curly-leaf infested lake to a lake with a healthy plant community."

Under a permit issued by the DNR, the Lake Benton Lake Improvement District will apply low levels of SONAR, a brand name for fluridone herbicide, to the entire lake. The first treatment took place April 11 and another is scheduled for May. The lake has been infested with curly-leaf pondweed since the early 1990s.

If this summer's treatments are effective, they will be repeated twice each year for the next three to four years. "A decline in curly leaf pondweed with a corresponding increase in native plants such as coontail and sago pondweed should be visible by then," Crowell said.

According to the U.S. Environmental Protection Agency, fluridone poses minimal risk when used according to label directions. Fluridone prevents plants from capturing light energy needed for photosynthesis by destroying their chlorophyll. It does not harm fish or animals. Because it affects plants, it can harm plants irrigated with treated lake water.

The lake was posted with signs and lakeshore property owners were notified of the first fluridone treatment. This notification explained when it was safe to use lake water for irrigation. Similar notification will precede the final treatment for the year in May. While the herbicide label carries no restrictions on swimming, fishing, or drinking water treated with SONAR fluridone, the DNR recommends a one-day restriction on swimming to allow the herbicide to disperse throughout the entire water body.

"If treatments are successful, it is likely that curly-leaf pondweed will return to nuisance levels in localized areas in the lake at some point," Crowell said. "Hopefully, smaller spot treatments will be able to control the plant in those areas when that time comes."

A similar test treatment is being done on Weaver Lake in Hennepin County this spring.