Lake Mishnock Preservation Association

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Livestock watering restrictions unnecesssary

  Date:     July 19, 2010

To:        Ken Brown, Lake Mishnock Preservation Association, Inc.

From:    Marc Bellaud

Re:        Lake Mishnock 2010 Herbicide Treatment Program Summary

Portions of Lake Mishnock were treated with Navigate (active ingredient 2,4-D) herbicide on June 30th.  The treatment was targeting selective control of invasive variable watermilfoil.  The granular formulation of 2,4-D BEE herbicide has been proven to be the most effective herbicide for control of variable milfoil through extensive testing performed by the U.S. Army Corps of Engineers and the States of New Hampshire and Connecticut.   Approximately 12 acres of the lake (~25% of the total surface area) were treated with Navigate herbicide at the application rate of 100 pounds per acre.  A total of 1200 pounds of Navigate was applied.  The 100 pound per acre application rate is half the maximum application rate allowed by the directions for use on the EPA product label.

2,4-D is one of if not the most widely used herbicide worldwide.  It is the active ingredient found in most “weed and feed” fertilizers that homeowners apply to their lawns to control dandelions other weeds.   It is an auxin-mimic herbicide that specifically targets broad-leafed or dicot plants.  In aquatics, variable milfoil is dicot, while many of the desirable native plants are monocots and are not impacted by 2,4-D.  At the rates that are approved for aquatic use, 2,4-D poses “negligible risk” to humans and non-target organisms, which is a requirement for EPA and State registration.  The only temporary water use restrictions listed on the product label are not to use treated lake water for drinking purposes until the in-lake concentrations drop below 70 ppb and not to use treated lake water for irrigation of ornamental and food crops until the concentration drops below 100 ppb (watering established lawns or other crops labeled for direct treatment with 2,4-D is allowed).  These concentrations include safety factors of generally >100x for humans, children and wildlife.  It is an herbicide that specifically targets hormones that are only found in plants.   If there were a significant risk associated with the use of 2,4-D than the State (DEM) would not be able to issue permits for its use . 

Studies have shown that in most cases the levels are below both threshold concentrations within 14 days of the treatment.  There is no restriction on swimming in treated water post-treatment, but we feel it is prudent practice to close the lake to swimming on the day of treatment.   There is no restriction on other uses of treated water.  There is no restriction on livestock watering post-treatment, but this condition was left on the warning posters to be consistent with posters used in prior years at Lake Mishnock.  In more than 30 years of direct experience applying 2,4-D herbicide, Aquatic Control Technology, Inc. is not aware of any well contamination that has occurred or adverse impacts to humans or wildlife following treatment.  The herbicide has a rapid half-life in sediment and is rapidly broken down into its elemental components through microbial degradation.  In 2010 alone, we have treated more than twenty (20) sites on public lakes in New Hampshire and have applied more than 40,000 pounds of Navigate.  All of the sites were tested at 15 days following treatment and most sites reported concentrations that were below the laboratory detection limit and no sites had concentrations above the 70 ppb drinking or 100 ppb irrigation.  This is true for most of the samples that have been collected over the past 15 or more years. 

Samples will be taken from Lake Mishnock during the week of July 19th for analysis of 2,4-D residues.  We expect that the concentrations will be below the detection limit.  Results of the testing will be provided to LMPA as soon as they are received. 


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