DNR ramp on Lake Manitou to open July 1

Indiana DNR Release:

The Department of Natural Resources' access site on Lake Manitou, which has been closed since late April to allow for treatment of the highly invasive plant hydrilla, will open July 1.

The DNR decided to open the ramp after a recent survey found no live hydrilla plants in the lake.

Despite the findings of the survey, the threat of spreading the plant to other waters still exists. Signs remain at the DNR site on Manitou to remind boaters to self-inspect their watercraft, motor and trailer for signs of plants when taking them from the water. All plant material should be removed and disposed of at the ramp before the boat is towed. Mud should be rinsed from the boat and trailer before transport, since hydrilla tubers could be present.

Boating equipment should dry for five days before being used in another body of water. These precautions should be performed not only at Manitou but at all waters, to prevent the spread of a host of aquatic invasive species, not just hydrilla.

All other public and private access sites on Manitou will remain closed, including the city boat ramp on the northwest corner of the lake.

"The sites we are keeping closed are very near where the densest hydrilla populations were found when the plant was first discovered in 2006, and still represent the greatest threat of hydrilla still being present," said Doug Keller, DNR aquatic invasive species coordinator.

The herbicide Sonar was initially applied on May 14. Due to frequent heavy rains this spring, additional Sonar was added last week to maintain the concentration necessary to control hydrilla. Rains flush Sonar from the lake, reducing its concentration.

"Through the 2008 treatment, the hydrilla tuber population has been reduced by 93 percent, compared to pre-treatment levels," Keller said.

The need for future additions of herbicide this year will be determined through future testing to determine the level of Sonar in the water. A lethal concentration of Sonar will be maintained in the lake once again this fall, through Oct. 15, since by this date the water temperature should have cooled enough that hydrilla tubers would no longer be expected to germinate

“Hydrilla tubers can sprout at any time water temperature is 55 F or warmer, which requires that a concentration that is lethal to the plant be maintained throughout its growing season to eliminate newly sprouted plants,” Keller said.

Sonar, with the active ingredient Fluridone, is an aquatic herbicide produced by SePRO Corporation of Carmel. Humans, fish and other aquatic life are not harmed by Sonar, especially at the extremely low rate being used at the lake, according to Keller.

Another tuber survey will take place this fall to determine the continued attrition of the tuber bank and another plant survey will be performed mid-summer.