Council Wants To Introduce Weevils To Combat Watermilfoil in Cedarville Bay
The Les Cheneaux Watershed Council has launched a fundraising campaign to raise $34,000 to fight invasive Eurasian watermilfoil in Cedarville Bay, using a tiny insect hoped to bring invasive weed growth under control. The group is seeking tax-deductible donations from private and public sources.
The council plans to purchase native weevils known for their affinity for Eurasian watermilfoil and effectiveness at destroying the plant. Milfoil weevils are native to Michigan and the northern United States, and prefer to feed on the invasive Eurasian watermilfoil over other milfoil species. As demonstrated in the lakes treated with weevils, they will not entirely wipe out Eurasian watermilfoil, but they will significantly reduce the density of the plant growth, making it less of a threat to native plants competing for the same ground as milfoil does.
Eurasian watermilfoil has been identified in local lakes and other states as a growing problem because it is so prolific and competitive. Having few natural predators to keep it in check, the weed is free to expand its range. It easily spreads because if one piece is torn off by a boat motor propeller and carried to another body of water, it can grow and eventually root and establish itself in the lake bottom.
In Cedarville Bay, resident complaints about the overabundant weed growth prompted the Watershed Council and Department of Environmental Quality to survey the vegetation in the bay, and large beds of Eurasian watermilfoil were found there. The plant's range has spread, and many suspect that this is the plant that has been getting caught up in boat propellers as people drive through the bay. As boats tear thought the milfoil beds, they take up pieces of milfoil and carry them to other places in the Les Cheneaux Islands, and even to other bodies of water. Eurasian watermilfoil is now being found as far away from Cedarville as Voight Bay, on the outer shore of Marquette Island.
The milfoil problem has been further exacerbated by excess nutrients in Cedarville Bay, said retired microbiologist and Watershed Council member Robert Smith. Mr. Smith has coordinated most of the water quality testing that identified Cedarville Bay as needing help.
"Cedarville Bay is a naturally shallow bay rimmed with weeds and interspersed with weed beds. In recent years, multiple factors have contributed to increased sedimentation and dense weed growth that lead to accelerated and premature aging of the bay," Mr. Smith said. "Periods of low water have contributed to increased weed growth in the past. Dense weed growth occurred in the bay during low water years of the early 1960s. There are, however, significant differences between the dense weed growth of the 1960s and the intense, choking growth experience today."
The low water levels of recent years have allowed more light to penetrate deeper into the water and contribute to greater weed growth, he said. Another invasive species, zebra mussels, filters its food from the water and has clarified the water even further. Mr. Smith added that
14 years of treated wastewater discharge into Cedarville Bay has added nutrients to the bay that act as fertilizer for existing plants and invasive species like milfoil. Septic system discharge, surface water runoff, and a larger population also add nutrients to the bay.
Part of the Cedarville Bay redemption plan includes treating wastewater at the source: the municipal wastewater treatment facility north of Cedarville. Clark Township Board, the Les Cheneaux Watershed Council, and the Department of Environmental Quality are discussing future solutions, and possible state and federal funding opportunities for removing excess phosphorus from wastewater effluent before discharge in to the bay. Another idea is to end discharge into Cedarville Bay and dump it further out into Lake Huron, beyond the islands, in water as deep as 70 feet.
For the time being, the Watershed Council has decided to move forward with introducing weevils to Cedarville Bay. The group has held two meetings, one in April among water ecology experts and Clark Township Board and Watershed Council members, and another in July to discuss improvement recommendations and to hear what the public thinks.
Since the meetings, the group has considered three treatment options, including herbicide, hydraulic dredging, and weevils. Weevils were selected by the Watershed Council as the best option at this time as it will have the least impact on the environment and other organisms. Some limited herbicide applications are already being used against weeds at private facilities on the bay. Herbicide can be used in Great Lakes waters if one obtains a permit from the Department of Environmental Quality.
First-year costs for the weevil project are an estimated $24,000. The second and final year costs are about $10,000. Milfoil weevils must be purchased from a firm that raises the insects and sells them for about $2 a piece, which includes costs associated with planting them in the bay. Midd-Foil, the company that raises and distributes milfoil weevils, recommends two years of weevil applications before the insect establishes itself.
Once planted, adult weevils will live on the stems of Eurasian watermilfoil. Milfoil weevils are a rare type of insect called "a specialist," meaning that they feed and develop only on one particular plant, so they won't damage other plants.
They will insert their eggs into the milfoil, and once the eggs hatch, weevil larvae remain in the stem of milfoil, where they bore out the stem and weaken it to the point the plant collapses and dies.
When they become adults, the weevils will be about the size of a sesame seed, and eventually move into the shoreline in the fall to burrow in leaf litter along the shoreline. They will remain there through the winter, and in spring will return to the plants in the water. Once the weevils are established, they will reproduce naturally and keep Eurasian watermilfoil populations in check.
Heavy boat traffic in the boat ramp and municipal dock area make early establishment of the weevils difficult. Therefore, limited mechanical weed removal is recommended for these areas until the weevils become established in other parts of the bay. As Eurasian watermilfoil decreases in treated areas, the beetle population gradually will decline to a smaller population.
Additional information about the weevil or wastewater treatment programs can be obtained by calling Clark Township Supervisor Linda Hudson at (906) 484-2672 or Les Cheneaux Watershed Council member Bob Smith at (906) 484-4081.