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    Milfoil Removal in Marina Bay
    Aquatic Weed and Algae Control Case Study

    Location and Acreage:
    Wolfeboro, NH | 34-Acres

    Project Timeframe: 
    2018

    Project Manager:
    Pete Beisler, Environmental Scientist 

    Key Staff:
    Kara Sliwoski, Aquatic Biologist & Regional Manager
    Eric Kuhn, Environmental Scientist

    Site Description:
    This site is a 34-acre bay located on Lake Winnipesaukee in Wolfeboro, NH. The bay is relatively shallow, averaging about six feet deep. It serves as a valuable resource to the surrounding community by providing excellent fish and wildlife habitat, as well as recreational opportunities, such as fishing, boating, wildlife viewing, a competitive tournament water skiing course/jump and a designated model sailboat racing area. There is also a marina and numerous boat docking areas in the bay.

    watermilfoil-before-case-study    after-watermilfoil-case-study

    Historically, this bay has suffered from the excessive growth of invasive variable milfoil (Myriophyllum heterophyllum), which is likely due to highly organic substrates and historical sawdust inputs, which provide favorable growing conditions with nutrient-rich sediments. Variable milfoil has been treated eight times since 1991, with seven of those treatments occurring between 2005 and 2015. Also, some degree of diver hand pulling/suction harvesting has occurred every year since 2008.


    Variable milfoil is a highly invasive exotic plant that is threatening waterbodies in the northeast U.S. Milfoil is capable of spreading rapidly through established root systems and fragmentation/auto fragmentation. The plant flourishes in shallow areas with high boating and recreational activity and nutrient rich sediments. If left unmanaged, it not only has the ability to impair ecological balance, but will readily spread to other areas of Lake Winnipesaukee and surrounding waterbodies, as it can be easily transported by heavy downstream water flow and on the boats and trailers of unsuspecting boaters.

    Scope of Work:
    The primary goal of this project was to utilize an herbicide treatment program to mitigate the dense growth of variable watermilfoil, which had significantly impaired conditions for recreational uses of the bay. To combat this invasive plant, the SOLitude team decided to utilize a new “Reduced Risk” aquatic herbicide that had just recently been registered in NH. This herbicide is highly selective to milfoil, while using much less herbicide than necessary in past treatments. The aquatic invasive plant management program consisted of permitting, aquatic herbicide treatment, monitoring and reporting.

    Project Description:
    SOLitude implemented an effort to control the aggressive nuisance plant growth while preserve native vegetation. Past treatments had utilized an herbicide that has been used for years in NH for control of variable milfoil. Although these treatments were generally successful, SOLitude felt like the newly registered herbicide that has never been used at this site would be an excellent new approach, eliminating the possibility of any of the plants being herbicide resistant.

    The management approach involved treating the entire bay (~33 acres) with a properly concentrated dose of the new herbicide (designed to quickly and specifically target the invasive plant species). The herbicide application was made in early to mid-September 2018.

    A post-treatment survey of the treatment areas was performed to assess the level of target plant control achieved and to document impact to non-target plants. This survey will be performed in accordance with Special Permit conditions.

    SOLitude hired an independent, NELAC accredited laboratory to collect and analyze water samples for herbicide residues following the treatment, in accordance with Special Permit conditions.

    During the post-treatment inspection there was no viable milfoil found in the bay. No adverse impacts to non-target plants or other aquatic organisms were observed directly in or immediately adjacent to the treated areas during the post‐treatment survey.

    A project-completion report was prepared that detailed the treatment program performed, provided results of the herbicide residue testing and summarized results of the treatment program. The report was prepared and submitted to the State of NH in accordance with Special Permit conditions.

    While preventative measures are the preferred management approach, success of this treatment demonstrates a new and exciting expected long-term focused management strategy that can be employed throughout the country in areas where this highly invasive plant has already taken over.

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