2008 Year-End Report from Aquatic Control Technology
Aquatic Control Technology, Inc.
11 John Road ● Sutton, MA 01590-2509 ● (508) 865-1000 ● Fax
(508) 865-1220 ●
October 23, 2008
Lake Mishnock Preservation Association, Inc.
c/o Dan Albro, President
P.O. Box 240
Coventry, RI 02816
Re: 2008 Year-End Report for Nuisance Aquatic Plant Management Program at Lake Mishnock
The fourth consecutive year of the Nuisance Aquatic Plant Management Program was completed at Lake Mishnock
during the 2008 season. The program continued to focus on the control of invasive variable watermilfoil (Myriophylum heterophyllum) growth throughout the lake.
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
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
A summary 2008 treatment program is provided below, followed by recommendations for an ongoing aquatic plant
management program at Lake Mishnock.
Chronological Summary of 2008 Management Activities
• Prepared and submitted
Pesticide Permit Application with RI DEM.....................................................April 2nd
• Received approved
Permit from RI DEM............................................................................................ April 28th
inspection ...................................................................................................May 22nd and June 6th
• Reward herbicide
spot treatment in Big Mishnock ............................................................................... June 16th
• Late Season Survey/final
post-treatment inspection ...................................................................September 29th
Summary of 2008 Program
Two initial pre-treatment surveys were conducted on May 22nd and
June 6th to verify the extent of milfoil growth in Big Mishnock and to establish final treatment
areas. As expected patches of dense contiguous milfoil growth were observed within the proposed treatment areas in Big
Mishnock, while only a few strands of milfoil were found at the southern end of Little Mishnock.
Lake Mishnock – Year-End Report 2008 2 ACT, Inc.
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.
Our final post-treatment inspection was performed on September 29th. The survey was conducted from a jon boat
using visual observations through polarized lenses and a throwrake. At the time of the survey a few small patches of milfoil
were found in the southern end of little Mishnock. Native bladderwort (Utricularia spp.) was found both rooted and floating throughout Little Mishnock and a few patches of native large-leaf pondweed (Potamogeton amplifolius) were found near the western
shore. In addtion, a small patch of Common Reed (Phragmites australis),
an invasive emergent plant species, was found growing on the eastern bank of Little Mishnock.
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
Lake Mishnock – Year-End Report 2008 3 ACT, Inc.
Recommendations and Expectations for 2009
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.
Lake Mishnock – Year-End Report 2008 4 ACT, Inc.
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
AQUATIC CONTROL TECHNOLOGY, INC.