No Herbicide in the Lake This Summer

In 2008 Proserpinaca palustris (Marsh Mermaid Weed) was found in Lake Fairlee.  Its presence was recorded, but was not considered when our application to use the herbicide triclopyr in the lake was considered and granted in 2010.Early this year we proposed to treat a much smaller area of the lake with the same product.  In March we were advised that the presence of the rare species Proserpinaca palustris would “trigger further review”.


Mermaid Weed

The concern was that the mermaid weed might be susceptible to the triclopyr, as it is in the class of plants (dicots) that are affected by this class of chemical.  The other plant in this category commonly found in the lake is the pond lily.  These were somewhat affected by the 2010 application (link), but survived and have completely recovered.  Scientists from SePRO, the company that manufactures the herbicide we use, had no experience with mermaid weed and their product.  They had never been asked, probably because P. Palustris is widespread and abundant in other states.

In April the Department of Environmental Conservation made it clear that our chemical treatment was conditioned on somehow ensuring that the mermaid weed would not be harmed, and detailed how we might do this.  In mid May scientists from Lycott and from the State visited the lake and mapped the locations where milfoil and mermaid weed are growing (link).

Since then we have been gathering information and determining how to proceed.  In addition to the cost of the herbicide and its application, we now have to fabricate two custom 400 foot sections of plastic barrier to isolate the area where the mermaid weed is growing.  They will have to be installed the day before the herbicide, and then removed two days later.  In part because of how quickly we need them, they will be very pricey.  As we added up the costs it became apparent that protecting the mermaid weed would almost double the original cost of killing off a relatively small area of milfoil.

Therefore we have decided that we will not use chemicals in the lake this year.  We will pay instead for divers to hand pull the milfoil, and probably to deploy our bottom barriers in areas where the plants are growing densely.  Herbicide treatment remains a possibility for future years.  This year we will measure the efficacy of mechanical control, and will have more data about our ability to control the milfoil by non-chemical means.

At the same time we plan to work on two fronts to open the possibility to treating without special protection for the mermaid weed next summer.  Now that we know where and how P. palustris likes to grow, we can look in other Vermont lakes, and invite residents of other lakes to join us.  If we can demonstrate that it is not as “rare” as previously thought it will not require special treatment.  Also we will gather data on how tolerant the mermaid weed is to triclopyr.  We will engage SePRO to conduct controlled experiments with P. palustris in measured concentrations of the herbicide.

It is our belief that the careful use of triclopyr is safe, and that is is a cost effective way to control dense growths of Eurasian milfoil.  It is likely that in future years we will employ it again.

Mermaid Weed – A Correction

In an earlier post we mistakenly stated that Proserpinaca palustris is categorized “S1” by the State of Vermont.  This would mean that it is “Very rare (Critically imperiled): At very high risk of extinction or extirpation due to extreme rarity (often 5 or fewer populations or occurrences), very steep declines, or other factors.”

In fact P. palustris is listed as “S2”, a slightly less extreme category, meaning “Rare (Imperiled): At high risk of extinction or extirpation due to very restricted range, very few populations (often 20 or fewer), steep declines, or other factors.”

The source for this information is the Natural Heritage Information Project of the Vermont Department of Fish and Wildlife.  You can find it on the 13th page of their document Rare and Uncommon Native Vascular Plants of Vermont.  An explanation of the status codes and their legal implication s can be found here.

Taking Care of the Mermaid Weed

On Wednesday, May 16th, scientists from the State and from Lycott visited Lake Fairlee to inspect the area near the mouth of Middle Brook where the milfoil was growing densely at the lend of last season.  They were looking in particular for the presence of mermaid weed, which was identified in that area in 2008, and which is designated a rare plant in Vermont.

The red dots in the picture below show where E. milfoil was found this week.  The red line delineates the area proposed to be treated on June 6th.

click above for larger image

Mermaid weed was found in abundance, which is evidence that it survived the triclopyr treatment in 2010.  The green dots in the aerial view above indicate where it was found this week.  The red dots show where E. milfoil is growing.  To protect the mermaid weed from the effects of the herbicide we are planning to install a plastic barrier (yellow lines above) extending the full height of the water column — only about 12″ to 18″ here.

Lake Restrictions for Herbicide Treatment

A small 10 acre area of Lake Fairlee will be treated with the herbicide triclopyr in early June, hopefully on the morning of the 6th.  The treatment area will be near the mouth of Middle Brook, off to the right as you look at the lake from the boat launch ramp.  Much of the lake will be closed to ALL use for two days, and water use from the lake will be restricted  until the herbicide concentration has diminished.

Here are the details:

  • There shall be NO USE of Lake Fairlee, south of the intersection of Burma Road and Route 244, and the outlet stream downstream to its confluence with the Ompompanoosuc River (as indicated in the attached map) FOR ANY PURPOSE, including boating, fishing, swimming, domestic (household) use or irrigation, on the day of and the entire day after the treatment.
  • Swimming/wading, boating, fishing and domestic use (except drinking or for food or drink preparation) may resume the beginning of the second day following treatment.
  • Use of water from Lake Fairlee, south of the intersection of Burma Road and Route 244, and the outlet stream downstream to its confluence with the Ompompanoosuc River (as indicated in the attached map) for drinking or for food or drink preparation shall not resume until water sample analyses reveal that the active ingredient in Renovate OTF (triclopyr) is at or below 75 parts per billion by laboratory analysis.
  • Use of water from Lake Fairlee, south of Idle Pine Drive, and the outlet stream downstream to its confluence with the Ompompanoosuc River (as indicated in the attached map) for irrigation, including use for watering lawns, trees, shrubs or plants, shall not resume for 120 days or until water sample analyses reveal that triclopyr is at or below 1.0 part per billion by laboratory analysis, whichever comes first.

2011 Final Report to the State

Pursuant to our herbicide application permit from the State our consultant/contractor is required to file annual reports detailing milfoil management activities undertaken this year and recommendations for next year.  The complete report may be downloaded by clicking on the image above.  CAUTION: this is 32 page pdf file which is 3.6Mb in size.

Spot Treatment with Herbicide Proposed for 2012

In a prior post we reported on the low incidence of E. milfoil found in the September 2011 survey, but noted that “we are very cautious about the low incidence of milfoil reported here.”  Based on anecdotal information we expected that considerably more milfoil has returned to the lake.  Now we have received a report from Lycott titled  Summary of 2011 Eurasian Milfoil Observations & 2012 Management Recommendations which confirms our fears.

You can download the three page document ay clicking this link, but here are the high points:

  • Milfoil was observed at fourteen locations around the lake this summer.
  • Ten of these exhibit only “sparse” growth.  We believe that these can be managed with hand pulling next summer.
  • Three areas have “moderate” growth.  In these locatirons we will employ either hand pulling or install bottom barriers, as the situation warrants.
  • At the mouth of Middle Brook there is an eight acre patch with heavy milfoil growth.  Lycott recommends that we again apply the herbicide triclopyr to this area for three reasons:
    • The existence of native species in moderate to heavy densities makes finding E. Milfoil difficult
    • Wide distribution of E. Milfoil over 8+ acres will be difficult to target with bottom-barrier
    • Sediment deposits in this area can greatly reduce visibility during hand-pulling and therefore increase the chance that plants will be missed

The report includes maps showing the locations where milfoil was found.

This comes as somewhat of a surprise to us, as we had come to believe that the 2010 herbicide treatment might last a few years. Apparently this is not the case. We are learning that milfoil is a pernicious weed (alright, we already knew that), and that its roots can survive in the ground under the lake for years. We do not know whether the newly grown milfoil is growth from submerged rootstock, if it is newly seeded from introduced plant fragments, or if some if it is coming into the lake down Middle Brook.

Based on this information we are beginning to explore just what this will mean for Lake Fairlee and for the Association.  We will be meeting with representatives of the State DEC to discuss premitting, notifications, testing, and funding.  As we know more it will be posted here.

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In related news, we have learned that our sister Lake Morey intends to apply an herbicide treatment next summer as well.  They treated portions of their lake in the summers of 2007, 2008, and 2009.  Now the area they treated in 2007 is again densely infested with E. milfoil.

Year Two Aquatic Vegetation Survey Report

Lycott Environmental has submitted their Aquatic Vegetation Survey Report to the State.  Jumping to the chase, here is the conclusion of their report:

The surveys conducted in 2011, the year following herbicide treatment of 120 acres of E. Milfoil in the littoral zone of Lake Fairlee, show that the treatment both significantly reduced the distribution of E. Milfoil and allowed for continued growth of non-target, native species. Of the thirteen (13) species observed during the 2009 pre-management survey, more than half were observed at the same or greater densities during the September 2011 survey.

Although E. Milfoil was documented at only one of the data points surveyed during September 2011, growth of this invasive species extends beyond this single point. Additional work conducted by Lycott as part of the Lake Fairlee Association’s management efforts, including diver surveys and hand-pulling efforts, have further mapped distribution of E. Milfoil. The details of these surveys and additional management efforts conducted under 2009-C08 HB will be provided with the forthcoming ‘Final Report for Year Two of Eurasian Milfoil Management in Lake Fairlee’.

The entire report is available HERE.  It is a 23 page pdf file with color graphs and maps.

PLEASE NOTE: We are very cautious about the low incidence of milfoil reported here.  This survey collected data only at predefined locations.  We have reason to believe that the “Final Report” mentioned above will show more milfoil.  In addition, we are watching closely the experience of our sister Lake Morey, which will again be treating portions of their lake with tricopyr next summer, as milfoil is regrowing vigorously in the north end of the lake.

Click above to download the entire report

Results of Herbicide Treatment – One Year Later


In June of 2010 we treated the lake with the herbicide triclopyr.  Details of this expensive and politically difficult undertaking can be found elsewhere in this blog.  By the end of the summer we were enthusiastic about the success of our project.  Virtually all of the Eurasian Milfoil was lying dead on the bottom of the lake and decomposing.  The year-end report required by the State confirmed this observation.

This June aquatic biologists from Lycott performed a detailed examination of the lake.  Our program this summer would depend on how much milfoil they found.  It is possible that in the denser beds of milfoil some rootstock may not have had exposed stalks or leaves, and could have escaped the herbicide.  They did indeed find some milfoil, but an amount that can be easily managed this year with hand harvesting.

Our conclusion is that the herbicide treatment was a resounding success. Yes, there is still some milfoil in the lake, but it is substantially all gone. You can read the details of what they found below, but it is a minuscule fraction of the pervasive infestation of the entire littoral area of the lake in recent years.

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LYCOTT aquatic biologists have conducted three (3) surveys during June of 2011.  The first survey was conducted June 14th.  Its primary purpose was to track the effectiveness of the 2010 herbicide treatment.  In an email summarizing their work, the scientist wrote:

Click here for larger image

“E. Milfoil was found in one location during the littoral zone survey and in one of the three areas where Brittany dove.  As you can see from the map, the first location was at the Middle Brook inlet, relatively close to the State boat ramp.  There are plants scattered among the native species in this shallow area.  Attached is a photo of the heaviest growth we found – you can see a lot of Elodea in the background.

Brittany dove at three locations where growth was heavy in 2009 – near Passumpsic Point (?), the beach at Treasure Island, and the large patch that was close to the camp at Lochearn Rd.  As you can see from the map, the second location of growth was off of Passumpsic Point.  She picked everything in her field of view while swimming ~150 ft. and came up with about 5 plants.”

The second survey was conducted June 24th and 25th.  Two SCUBA divers swam the entire circumference of the lake.  their purpose was to direct the proposed 2011 hand-pulling operation.  After the first day the diver wrote:

“So far we’ve identified only three places with milfoil. Two are in Middlebrook Bay and the third is east of Aloha Hive, north of their swim area. Middlebrook Bay has at least one small, dense bed.. other sites are very sparse and fairly unhealthy looking plants.”

And after the second:

“Nothing much more to report. Found scattered plants in Middlebrook Bay along with one small, but dense patch of plants.”

The third visit was by Will Stevenson, the president of Lycott, accompanied by Sarah Miller, a representative of the herbicide’s manufacturer.  I met with them on the lake, and received the impression that they are very pleased by the success of the treatment.

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This Year’s Program

What does this mean for our milfoil program this year?  Here is our consultant’s recommendation:

“Based on the findings of the three June 2011 surveys, LYCOTT recommends deploying a 2-person dive crew to conduct two separate 2-day hand-pulling events to remove Eurasian Milfoil plants. The first event will be conducted in early July to focus on removal of identified plants in the Middle Brook inlet area and the area adjacent to the Aloha Hive Camp, north of the swim area. The second 2-day hand-pulling event will be scheduled for late August to re-survey the littoral area and hand-pull any late-summer growth that emerges.”

The LFA board will likely accept Lycott’s recommendation and hire them to perform the indicated hand pulling.  We also plan to continue our Courtesy Greeter program at the boat ramp. (more here)

Year One Herbicide Report

Report from Lycott Environmental, Inc.

In late August biologists from Lycott conducted another scientific survey of Lake Fairlee, collecting data on plant species at 120 pre-determined points around the lake.  Their report to the State was published yesterday. Since the June 2nd treatment of the lake, the spread of milfoil has decreased from 26% of the lake to just about 0%.  By any measure our treatment has been a success.  There are links to download the complete report below.

We must temper this very good news with caution.  First, the report mentions that several plants which appeared dead were sending out new green sprouts.  We are advised by the scientists that unless these shoots can take root in the bottom of the lake they will not survive the winter.  Nonetheless they represent new milfoil growth, and cause for worry.  Second, we know that even if we start next spring with absolutely no milfoil growing in the lake, it is only a matter of time until it is reintroduced, despite our best efforts to the contrary.

Download the full report here: (these are pdf files)

In sum, we congratulate ourselves and offer heartfelt thanks to our many supporters.  Next year we will start the season with another thorough survey, ready to take whatever steps necessary to prevent the lake from being again taken over.