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2013 Aquatic Technology End of Year Report

 

Aquatic Control Technology

11 John Road Sutton, MA 01590-2509 (508) 865-1000 Fax (508) 865-1220 info@aquaticcontroltech.com

December 5, 2013

Lake Mishnock Preservation Association

c/o Dan Albro, President

P.O. Box 240

Coventry, RI 02816

Re: 2013 YearEnd Report for Nuisance Aquatic Plant Management Program at Lake Mishnock

Dear Dan:

Aquatic Control Technology was contracted by the Lake Mishnock Preservation Association (LMPA) to perform an

invasive aquatic plant treatment program for the ninth consecutive season in 2013. The program continued to

focus on areaselective control of invasive variable milfoil (Myriophyllum heterophyllum). The following report

summarizes the results of the 2013 treatment program and provides ongoing lake management recommendations

for next year.

2013 TREATMENT PROGRAM SUMMARY

For the third consecutive season, we recommended the use of 2,4D liquid herbicide for milfoil control. In 2012,

there was considerable milfoil regrowth seen within two months of the initial 2,4D liquid application. This was

believed to be due to the lateness of the initial application, which didn’t occur until late June due to permitting

delays. The biomass and maturity of the milfoil plants at the time of that treatment resulted in incomplete control

and a considerable amount of detached milfoil stems that floated throughout the lake. After documenting active

regrowth of milfoil in late August, a followup spottreatment was planned for early September. The followup

treatment appeared to be effective, but there was regrowth seen in many of the same areas by late May 2013.

After evaluating available herbicides with LMPA last winter, it was agreed to continue maintenance treatments

with 2,4D liquid in 2013, because is considerably less expensive than the available granular products. Again in

2013, we recommended increasing the amount of acreage being treated to insure that a lakewide lethal dose of

2,4D was being applied in hopes that this would provide more complete and longer term control. Details of the

2013 treatment program are provided below.

Chronological Summary of 2013 Management Activities

Approved Permit issued by RI DEM (#A1215) ..................................................... completed in 2012

Pretreatment inspection......................................................................................................May 21st

Liquid 2,4D herbicide spottreatment in Big and Little Mishnock.......................................June 10th

Posttreatment inspection ................................................................................................... July 16th

Late season survey .................................................................................................... November 26th

The permit issued by DEM in 2012 was valid for one calendar year, which allowed for treatment to be performed

up to June 19, 2012. This was confirmed with DEM over the winter of 2012/2013, and it was made clear that

future permits would only be valid during the calendar year that they were issued. As a contingency, a new permit

application was prepared and submitted in case additional treatment was requested later in the summer, but due

Lake Mishnock – YearEnd Report 2013 2 ACT

to new review processes at DEM and their request for specific well information from the residences that abut

Mishnock Lake, the review process was delayed and eventually suspended. No additional permits were issued by

DEM in 2013.

Active milfoil growth was documented during the May 21st inspection. The majority of growth was found in the

typical “hotspots” including the south and southeast coves on Big Mishnock and the southern end of Little

Mishnock. The “footprint” of milfoil growth had contracted from what was seen in 2011 and 2012, so the

treatment areas were modified accordingly.

Treatment areas for first application on 6/10/13

DMA 4 IVM (2,4D liquid) herbicide was applied at an application rate of approximately 4 ppm to approximately 10

acres on June 10th. The liquid herbicide was diluted and injected subsurface using weighted hoses and a calibrated

spraysystem in one of our airboats. A GPS unit was used to provide realtime navigation during the treatment and

insured that the herbicide was applied in the right locations.

A posttreatment inspection was performed on July 16th, approximately 5 weeks posttreatment. By that time, all

of the treated milfoil plants had collapsed to the bottom and the majority of the biomass had already

decomposed. We did not observe decaying milfoil plants floating around the lake, like what was seen in 2012. We

attribute this to the earlier treatment date and reduced milfoil biomass at the time of treatment. Occasional

reports that we received from LMPA later in the summer indicated that the milfoil control was more complete and

longer lasting that had been achieved in the prior two years.

During our final late season survey on November 26th, we did observe new growth of milfoil in several of the areas

that were treated in June. Most of the plants were only 12 feet tall and they had thin, bright green stems which

are usually seen when new shoots develop. Again, the milfoil footprint appeared to be reduced from what was

seen during the pretreatment inspection, but milfoil had definitely survived and was recovering.

Lake Mishnock – YearEnd Report 2013 3 ACT

ONGOING MANAGEMENT RECOMMENDATIONS FOR 2014

Since 2009, we have been relying on various formulations of 2,4D herbicide to control variable milfoil in Lake

Mishnock. Over the past five years we have been experimenting with several formulations and treatment

strategies at several locations in Rhode Island, Massachusetts and New Hampshire. We took a critical look at

different products and formulations that were used at 30 different sites in NH in 2013. The results can be

summarized as follows:

Optional herbicides for variable milfoil control:

Chemical Formulation Trade Name Attributes Limitations

2,4D BEE ester Granular Navigate

(recommended)

Best activity on variable milfoil Can “plug” in mucky bottom

sediments, resulting in

incomplete release of active

ingredient

2,4D amine Liquid DMA 4 IVM;

Clean Amine,

etc.

Low cost

Initial concentration can be

established immediately

Subject to dilution

Not effective for spottreatment

2,4D amine Granular Sculpin G Less dense granule will not sink

into the mud

Complete herbicide release

within 24 hours

Subject to dilution

Not effective for spottreatment

Higher cost than liquid

2,4D amine &

triclopyr amine

Granular Renovate Max G Less dense granule will not sink

into the mud

Complete herbicide release

within 24 hours

Good control when wholelake

concentrations are established

and maintained for 2 weeks+

Long restriction on irrigation for

gardens and ornamentals

Subject to dilution

Not effective for spottreatment

Higher cost than liquid

Triclopyr Granular &

Liquid

Renovate OTF &

Renovate 3

Less dense granule will not sink

into the mud

Complete herbicide release

within 24 hours

Good control when wholelake

concentrations are established

and maintained for 2 weeks+

Long restriction on irrigation for

gardens and ornamentals (120

days or <1 ppb)

Subject to dilution

Not effective for spottreatment

At least 3x more expensive than

2,4D

Diquat Liquid Reward

(recommended)

Low cost

Rapid mode of action, effective

for spottreatments

Controls bladderwort and milfoil

Short water use restrictions

(maximum 5 day irrigation)

Not systemicacting so it does

not kill the roots

Flumioxazin Liquid Clipper Rapid mode of action, effective

for spottreatments

Low toxicity, no drinking

restriction, maximum 5day

irrigation restriction

High cost

Does not provide complete

control of variable milfoil alone,

but works well in combination

with Diquat

Fluridone Liquid &

Granular

Sonar Systemicaction provides

complete plant control

Effective on multiple species

High cost

Requires long contact time (60

90 days)

Long restriction on using water

for irrigation

The liquid and granular formulations of the 2,4D and triclopyr amine products (2,4D liquid, Sculpin, Renovate,

etc.) are effective when adequate herbicide concentrationexposuretime could be maintained, but are less

Lake Mishnock – YearEnd Report 2013 4 ACT

effective in areas subject to dilution and mixing with untreated water (i.e. shoreline areas, highflow areas, small

areas with a lot of flow, etc.). Despite seeing good initial control following the 2,4D liquid treatment in 2013,

complete milfoil control did not appear to be achieved in some of the smaller, more exposed treatment areas,

which was most likely due to dilution with untreated water.

The herbicide concentrationexposuretime required for Navigate (2,4D BEE) does not appear to be as long as it is

for the 2,4D amine products, but dilution can still be an issue, and Navigate granules have a greater potential

“plug” in soft bottom sediment because they are smaller and denser and this may reduce treatment efficacy. Most

of the areas with stubborn milfoil growth in Lake Mishnock have mucky bottom sediment, so granule plugging

could be a problem.

Another issue with all of the 2,4D products are the concerns associated with adjacent wells that were raised by

DEM in 2013. Even though it is highly unlikely, 2,4D is capable of migrating through the sediment under the

proper conditions. In MA, the use of 2,4D is restricted in wellhead protection areas. We believe that 2,4D will

raise more concern with DEM than some of the other available herbicides.

Reward (diquat) was used at Mishnock between 2005 and 2008. It should provide control of targeted milfoil for

the majority of the summer growing season. Diquat requires minimal exposure time so good control of target

plants can be achieved in areas that might be subject to dilution with untreated water. Diquat will also provide

some control/thinning of the native bladderwort growth which appeared to be robust in 2013. Diquat has no

mobility in soil, so we do not expect that it will raise as much concern with DEM. Treating with diquat will break

the cycle of repeat 2,4D treatments and help avoid the possibility of any herbicide tolerance from developing.

The maximum water use restriction periods for drinking and irrigation following treatment with Reward are only 3

5 days. Diquat treatments also carry a lower cost than treatment with 2,4D granular products.

For the reasons provided above, we recommend spottreating with Reward (diquat) during the 2014 season. We

also recommend seeking contingent permit approval for the use of Navigate (2,4D BEE granular) herbicide in the

event that <10 acres require spottreatment in 2014. We will continue to evaluate available herbicide alternatives

for future treatments at Lake Mishnock.

A recommended budget for a maintenance herbicide treatment program during the 2013 season is provided

below:

Prepare and file permit application with RI DEM ...................................................................................$150

Perform early season survey with the Association to determine if treatment is

warranted, posttreatment survey and prepare brief yearend letter/report........................................$450

Reward (diquat) herbicide treatment for milfoil control (20 acres) ....................................................$3,400

ESTIMATED PROGRAM TOTAL .............................................................................................................$4,000

Feel free to contact me or Keith Gazaille if you have any questions or would like to discuss our report or

recommendations in greater detail. We value your business and look forward to assisting LMPA with your

ongoing lake management efforts.

Sincerely,

AQUATIC CONTROL TECHNOLOGY

Marc D. Bellaud

President/Aquatic Biologist

 

 

 

 

 

 

 


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