The Indiana DNR is reducing the amount of chemical weed control conducted by lake residents at Lake Tippecanoe in hope of reversing a downward trend in native aquatic plant coverage.

Since 2006, coverage of native plants has declined by 35 percent within the three basins (James, Oswego and Tippy) that make up the 1,133-acre natural lake in Kosciusko County. Biologists are unsure of the cause but say the decrease could have adverse effects on the lake.

“Aquatic plants provide several benefits to lake ecology,” said DNR fisheries biologist Jed Pearson. “They tie-up nutrients, maintain water clarity, buffer the shoreline from erosion and provide fish and wildlife habitat.”

Pearson reviews permit requests for weed control at Lake Tippecanoe and dozens of other area lakes.

According to Pearson, the decline in native plant coverage in Lake Tippecanoe parallels an increase in efforts to selectively control curly-leaf pondweed and Eurasian watermilfoil, two non-native species that plague lakes across the Midwest.

“We’re not blaming the weed-control program,” Pearson said. “The herbicides used and timing of the treatments were designed to target only non-native plants and would not harm native species.”

From 2006 through 2014, the Lake Tippecanoe Property Owners Association hired a state-certified herbicide applicator to annually treat an average of 70 acres of curly-leaf pondweed and 50 acres of Eurasian watermilfoil. The control effort has been paid for in part with funds from the DNR’s Lake and River Enhancement Program and was approved by Pearson.

The DNR is also funding efforts in Lake Tippecanoe to control starry stonewort, another invasive plant that showed up in recent surveys.

“Spraying non-native plants makes sense where they form dense beds or create nuisance conditions that crowd out native plants and impact lake use,” Pearson said.

Native plants should then flourish. But that didn’t happen at Lake Tippecanoe, where native plants also declined.

Native plants once covered 85 percent of near-shore areas at depths where sunlight can penetrate. That figure is now 55 percent. Ideally, they should cover about 80 percent.

Pearson thinks most of the decline is due to weather. The biggest drop occurred during the last two years, after longer winters and colder springs. Similar drops in vegetation have occurred at other lakes.

In a typical year, however, lake residents also have been allowed to remove up to 20 acres of native plant beds along lakefront property and in boat channels connected to the lake. This part of the control program is now under closer DNR scrutiny. Weed control will continue in channels but native plant beds in the main area of the lake will be protected.

“Until we see a return of more native plants in Tippy, we don’t want to exacerbate the problem by spraying them as well,” Pearson said. “Based on what is happening we need to protect native plants and only permit control where someone has a severe problem.”

The DNR will re-evaluate the situation this summer and adjust the weed control program next year if needed.

To view all DNR news releases, see dnr.IN.gov.