Lake Maspenock Weed Treatment Management Report

Pre-Treatment Survey

On June 04, 2024, a Biologist from SOLitude conducted an early-season survey at Lake Maspenock. The objective of this study was to evaluate the composition and distribution of aquatic vegetation before the planned herbicide treatment. During the survey, four invasive species were observed in trace to moderate densities: Eurasian Watermilfoil (Myriophyllum spicatum), Variable Watermilfoil (Myriophyllum heterophyllum), Curly-leaf Pondweed (Potamogeton crispus), and Fanwort (Cabomba caroliniana). See figures 1a, 1b, and 1c.

Click to see a larger image (L-R, Figure 1a, Figure 1b, Figure 1c

Invasive Species Density and Dist, Eurasian Watermilfoil, Lake Maspenock, Hopkinton, MA — Figure 1a: Invasive Eurasian Watermilfoil

Invasive Species Density and Dist, Variable Watermilfoil, Lake Maspenock, Hopkinton, MA — Figure 1b: Invasive Variable Watermilfoil

Invasive Species Density and Distribution Fanwort, Lake Maspenock, Hopkinton, MA — Figure 1c: Invasive Fanwort

In addition to the non-native plants, the native species observed at this time included Clasping-leaf Pondweed (Potamogeton perfoliatus), Thin-leaf Pondweed (Potamogeton pusillus), American Tapegrass (Vallisneria americana), common waterweed (Elodea canadensis), stonewort (Nitella spp.), Slender Naiad (Najas flexilis), and Yellow Waterlily (Nupharvariegata). See Figure 2.

Click to see a larger image: Figure 2

Native Species Density and Distribution — Figure 2: Native Species

Herbicide Treatment

Based on the established treatment plan, an herbicide treatment to control the invasive watermilfoil, curly leaf pondweed, and nuisance levels of native species was conducted on June 17, 2024. A SOLitude Senior Applicator conducted this herbicide treatment utilizing Tribune (diquat) and Aquathol K (endothall) to reduce the targeted species. See Figure 3.

Click to see a larger image Figure 3

Treatment Area, Lake Maspenock, MA — Figure 3: Treatment Area

A total of 64.5 acres of the lake were treated with 60 gallons of Tribune (diquat) and 125 gallons of Aquathol-K (endothall). The application was executed using an airboat outfitted with a calibrated spray system. This system was designed to apply the herbicide below the water’s surface through weighted hoses, effectively minimizing the risk of aerial drift. A GPS unit was utilized to conduct the application in a precise manner. At no time during the treatment were fish mortalities or significant non-target impacts to other aquatic organisms or wildlife observed or reported.

Post-Treatment Survey

On July 7, 2024, a post-treatment survey was conducted to evaluate the distribution of vegetation species and to assess the efficacy of the herbicide treatment. The survey identified Fanwort as the only invasive species (refer to Figure 4), which was found in several trace-sparse patches. Neither Eurasian Watermilfoil nor Variable Watermilfoil was observed during this survey. Furthermore, a desirable reduction in native species was recorded.

The native species identified during the survey comprised Bladderwort (Utricularia spp.), Slender Naiad (Najas flexilis), American Tape Grass (Vallisneria americana), acroalgae (Nitella and Chara), and both yellow and white waterlilies (Nuphar variegata and Nymphaea odorata). See Figure 5.

Click to see a larger image Figure 4. Figure 5

Post Treatment Invasive Species Fan wort, Lake Maspenock, Hopkinton, MA — Figure 4: Post Treat Invasive Fanwort

Post Treatment Native Species, Lake Maspenock, Hopkinton, MA — Figure 5: Post Treat Native Species

Ongoing Management Recommendations

Results from the late-season survey indicate that this year’s treatment was overall successful. The targeted species experienced significant reductions. We defer to the Town to determine the management needs, if any, for 2025 but do recommend assessing the lake’s vegetation assemblage at a minimum.

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