October 23, 2008

Lake Mishnock Preservation Association, Inc.

c/o Dan Albro, President

P.O. Box 240

Coventry, RI 02816

Dear Dan:

In 2005 and 2006 Reward (diquat) herbicide treatment programs were performed, which provided good seasonal control of milfoil. While some reduction in milfoil distribution and density of milfoil re-growth was noted, it was evident that annual maintenance treatments would be necessary with diquat to maintain nuisance-level control. In an attempt to break the annual treatment cycle, we recommended the use of the systemic herbicide Renovate OTF (active ingredient triclopyr) in 2007. Two small treatment areas in Big Mishnock and all of Little Mishnock (~13 acres total) were treated with Renovate OTF in late May 2007.

Initially, the small sections in Big Mishnock did not appear to be responding to the treatment, but Little Mishnock looked promising. Unfortunately, milfoil rebounded aggressively in Little Mishnock in August 2007. SePRO, the manufacturer, offered to provide additional Renovate OTF to re-treat Little Mishnock at a higher concentration. A second application was performed in late September 2007 at no additional cost to the Association. By late October 2007, it appeared as if the milfoil had been effectively controlled.

For 2008, we recommended that no treatment be performed in Little Mishnock to determine if multipleyear control was achieved. We did recommend maintenance treatment of Big Mishnock with Reward(diquat) herbicide to provide seasonal milfoil control.

A summary 2008 treatment program is provided below, followed by recommendations for an ongoing aquatic plant management program at Lake Mishnock.

We applied Reward herbicide at 1-2 gallons per acre throughout approximately 17.5 acres around the perimeter of Big Mishnock. The milfoil appeared to respond rapidly to treatment and dropped out of the water column within a matter of a couple of weeks.

In the treatment area located in the southeastern cove of Big Mishnock four small patches and one larger patch of milfoil were observed. A few small patches were noted in the treatment area in the southwestern cove and a three isolated strands of milfoil were found in the northern treatment area. The milfoil patches were all low growing and appeared bright green in color, indicating that the milfoil observed was new posttreatment growth. A large growth of mature milfoil was observed in deeper waters outside of the treatment area near the center of the lake. A thick covering of native bladderwort was observed in both of the southern coves of Big Mishnock and another small patch of common reed was found on the northern side of Big Mishnock.

Milfoil is a stubborn invasive species that continues to threaten desired open-water conditions in Lake Mishnock. Although we expect the density of watermilfoil to be reduced significantly in the 2008 treatment areas some treatment will likely be required in the 2009 season to prevent milfoil from becoming reestablished at nuisance densities.

The second (higher-dose) Renovate OTF treatment performed on Little Mishnock in 2007 did provide fairly good carry-over milfoil control, but some milfoil plants were becoming reestablished at the southern end of Little Mishnock by the end of the year. Considering the dose of Renovate OTF that appears to be required to control variable watermilfoil, it is not a cost-effective management alternative.

Unit costs for treatment are likely to be in the $900-$1200 per acre range. We believe that the Association should consider two alternative treatment options. The first, and least expensive, is to continue with maintenance treatments using Reward (diquat) herbicide. Spot-treating 20-25 acres of the lake with Reward will probably cost in the range of $5,550- $6,000. This should provide good season long control and prevent any milfoil expansion.

An alternative to this option is to discuss with the Department of Environmental Management about the possibility of treating with Navigate (2,4-D granular). Studies performed in NH in recent years by the US Army Corps of Engineers documented that 2,4-D granular provides the most effective control of variable watermilfoil. It was not proposed for use in prior years, due to concerns raised by DEM about the Kent County Water District wells located downstream from the lake. The current permit reviewer DEM appears to be more comfortable with the use of 2,4-D. Where the wells are located over 2,000 feet from the outlet stream, we do not believe that any herbicide used in Lake Mishnock poses a significant risk to the Kent County Water District wells; however, this will be a decision made by DEM. 2,4-D is more expensive than Reward, but we could probably treat smaller areas more effectively. Treatment costs are likely to run between $400-$500 per acre, but two or three years of effective milfoil control should be anticipated.

We would recommend seeking permit approval to use Navigate (2,4-D) and list Reward (diquat) as the back-up herbicide. The permit application should be submitted early, in January 2009 if not before, to allow adequate time for review.

We would also recommend seeking permit approval to use Rodeo or equivalent Glyphosate to control the two small patches of common reed that were noted during our September inspection. This plant had not been observed on Lake Mishnock in previous years, which indicates that these patches are likely to be recent infestations. Common reed can grow aggressively and out-compete many shoreline plants. They can be effectively spot-treated with a foliar application of Glyphosate. Treatment is done late in the summer so that the herbicide is translocated into the roots. Spot-treating the common reed patches should only carry a cost of a few hundred dollars if it can be combined with a regularly scheduled visit to the lake.

Overall, we were pleased with the condition of Lake Mishnock during the 2008 season. Milfoil has been effectively suppressed, but not eliminated. We commend the Association’s efforts so far and look forward to working with you in the future.

Sincerely,

Marc Bellaud

Senior Biologist