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Milfoil in MN

Posted by [email protected] on October 30, 2012 at 9:50 AM Comments comments (0)

Management of Eurasian Watermilfoil in Minnesota

Most problems caused by milfoil can be managed with conventional methods such as treatment with herbicides or mechanical removal of plants. The DNR supports management methods that cause as little damage to native aquatic plants as possible. The DNR protects native plants because they provide many benefits to lake ecosystems, such as stabilizing lake sediments, and increasing habitat for fish and wildlife. In addition, widespread destruction of native plants can lead to an overall increase in the amount of Eurasian watermilfoil in a water body because milfoil is very effective at invading disturbed habitat.

The DNR's experience using herbicides to eradicate milfoil is consistent with experience elsewhere, which indicates that efforts to eradicate this invasive with herbicides are "...rarely, if ever, likely to succeed" (Smith and Barko 1990). Our experience in attempting to prevent the spread of milfoil within a lake with herbicides is also consistent with the observation by Smith and Barko (1990) that efforts to prevent the spread of milfoil within a lake may slow its expansion, but rarely prevents its dispersion within a lake.

The DNR has done research on the potential to use fluridone, an aquatic herbicide, to manage milfoil. The results of an evaluation conducted by the DNR in the mid-1990s and other information available at that time suggested that application of this herbicide to whole lakes or bays at an intermediate rate of 10 parts per billion (ppb) causes unavoidable damage to native vegetation and has the potential to affect other aspects of lake ecosystems (Welling et al 1997).

The results of subsequent investigations of fluridone in Michigan suggested that application of the herbicide at the low rate of 5 to 6 ppb may provide more selective control than has previously been observed in Minnesota. In an attempt to reproduce those results in Minnesota, the DNR will subject three Minnesota lakes to experimental whole-lake treatments with fluridone in 2002. The results of these treatments will help guide our approach to the possible use of this herbicide in the future.

Grants for management

Potential cooperators on lakes with a public water access, which have widespread Eurasian watermilfoil, may apply to the DNR for grants to support efforts to manage milfoil. The goals of this grant program are to reduce nuisances caused by Eurasian watermilfoil and to slow the spread of the invasive to other lakes. Management done with State funds usually involves control of Eurasian watermilfoil in areas that are located either off-shore or near public water accesses. These areas are commonly used by the general public, as opposed to near shore areas adjacent to privately owned property, which are used primarily, if not exclusively, by owners of that property. This grant program is described in the Minnesota Department of Natural Resources Financial Assistance Directory.

Biological Control of Eurasian Watermilfoil

Since 1992 the State of Minnesota has funded research into potential insect biological control agents for Eurasian watermilfoil. Work has been primarily focused on a weevil (Euhrychiopsis lecontei), which is a native insect. Declines of Eurasian watermilfoil in some lakes have been associated with weevils. Unfortunately, other lakes with weevils have not experienced declines in Eurasian watermilfoil. Current research is focused on attempts to determine what factors or conditions limit the abundance of weevils and prevent the insects from controlling milfoil. Much of this research has been done at the University of Minnesota by Dr. Ray Newman and his colleagues. Information about his work is available on his Biological Control of Eurasian Watermilfoil web site.

The use of biological control agents to reduce Eurasian watermilfoil could minimize the need to use herbicides. Nevertheless, experience has shown that development of biological controls may require research conducted over a period of ten years or more. Consequently, the Invasive Species Program's evaluation of the potential for biological control of Eurasian watermilfoil is considered to be a long-term effort, the outcome of which cannot be guaranteed.

Milfoil Article- Information

Posted by [email protected] on October 30, 2012 at 9:40 AM Comments comments (0)


Since there is no way to completely eradicate Eurasian watermilfoil from a lake once it has been introduced, control efforts must instead focus on: controlling newly introduced infestations, preventing further spread of the plant, or reducing the nuisance level of the problem. Some methods are more appropriate for well-established populations, while others are better suited for those that are recent introductions.


The State of Vermont is concerned about the impacts certain milfoil control methods could have on the environment. Bottom barriers, all mechanically powered devices (harvesters, hydrorakes), herbicides, and biological controls require permits from the Department of Environmental Conservation before they can be used to control nuisance aquatic plant growth. Contact the Department  to determine if your proposed control method requires a permit and to obtain permit applications.



Bottom Barriers, specially made sheets of materials such as fiberglass, polypropylene, or polyvinyl chloride (PVC), anchored to a lake bottom will prevent plant growth by blocking sunlight. Bottom barriers are most appropriate to control growth in localized areas such as in swimming areas, around docks or to create boat lanes out to deeper water.


With diver operated suction harvesting, scuba divers use suction hoses powered by a surface compressor to selectively remove milfoil from the lake bottom. Although too labor intensive on a large scale, this method has proven to be highly successful at combating newly established infestations in Vermont lakes.


A hydrorake removes plant roots and shoots by raking the lake bottom. Any removed material must then be deposited on shore. Hydroraking has had limited use in the state but is most practical for providing short-term relief from dense milfoil infestations.


When done properly, pulling milfoil plants by hand is highly effective for controlling small, newly introduced milfoil populations.



Mechanical harvesters cut off the milfoil (and any other plants) below the water surface, gathering the cut material as they move through the plant bed. Milfoil roots are not removed in this process. Mechanical harvesting, like lawn mowing, merely reduces the height of plant growth temporarily in order to make the lake more usable. Removing the plant material from the lake does however, prevent the plants from contributing to the sediment which rapidly accumulates under dense aquatic plant beds. Mechanical weed harvesting has been used on several heavily infested Vermont milfoil lakes.


Other potential milfoil control methods include rotavating, chemical herbicides and biological controls such as grass carp.


Rotavating involves a machine that "tills" the lake bottom, dislodging both the roots and stems of the plant. Plants are either collected by a mechanical harvester or, if conducted in the late fall, are allowed to wash ashore and dry over the winter. This method has yet to be used in Vermont.


There are a number of federally registered aquatic herbicides that control Eurasian watermilfoil. Considerations for use include cost, the potential need for repeated applications, and product label restrictions that prevent their application in lakes used as water supplies



Biological controls such as insects, bacteria or fungi that will impact milfoil are in the experimental stages only. Their use as a milfoil control method may prove to be the control of the future. The use of plant-eating fish such as the grass carp, a native to China, is currently illegal in Vermont.


The VTDEC has been working with the watermilfoil weevil Euhrychiopsis lecontei since 1989. The weevil was responsible for at least one Eurasian watermilfoil decline in Vermont, in Brownington Pond in Brownington. It has been found naturally occurring in many other milfoil-infested lakes in Vermont. The weevil, a native aquatic insect, has shown promise as a potential biological control agent for Eurasian watermilfoil, and is currently the subject of ongoing research.

Lake Weeds Summer 2012

Posted by blmn on June 26, 2012 at 1:20 PM Comments comments (0)

From Kay Botko re: spring 2012 inquiry on status of Bryant Lake

After chatting with a number of neighbors and learning of our collective concern about the condition of the condition of our lake - the quality of the water, the numbers of dead fish, and th incredible layers of weeds seemingly choking off areas of the lake, I decided to track down someone who might give us some answers.

Finding a "real person" to talk to was no small task, as I was shunted from Three Rivers employees, to Highland Park, to "that number is no longer in use" to a litany of extensions that didn't deal with such issues.  Finally, a nice gal in charge at highland's offices of Three Rivers directed me to Rich Braich (he is the fellow quoted in today's paper regarding lakes/algae growth/water quality in the Twin Cities.  He principally deals with Water Resources (763-694-2061) and is not reachable but does return calls.  I called, explained my concerns and awaited an answer.

He was fairly prompt in his response, and in fact mentioned that in the interim he was in the process of dispatching a sampling crew to Bryant Lake, so he called their attention to my inquiry regarding the east side of the lake.  This testing crew apparently tests the water of the lajke every two weeks.  Their testing has shown that the quality of the water is not only very clear, but has a good quality of oxygen levels in the water.  The water had received an alium(?) treatment earlier and all of the data indicates that the quality of the lake water is very good.  They keep records of this data relative to state standards and it would be available should anyone want to see it.

It seems that the vegetation condition of the lake is what is causing the greatest concern for the residents as we see whole bays virtually impassable to the boat traffic.  He was aware that it is principally the Eurasian milfoil that is the culprit.  There is also a broadleaf plant, whose name I couldn't recall, coontail, and pikeweed-both of which are good for fish habitat.

Historically, residents have taken care of their frontage-in various ways:  pellets, approved chemical spraying and divers "weeding" the lakefront.  Our park does chemically treat the weedy areas when they encroach on the beach.

I mentioned that of particular concern also was the inordinate number of dead fish last week.  He said that a certain number of dead pan fish is an annual occurance-nothing out of the ordinary.  When I mentioned that we had, however, seen a number of larger fish, bass, and a huge muskie....he said that that would be of concern to the DNR and would prompt their further inquiry.

Apparently at issue also is:  Is this current heavy weed problem an anolomy?  Something that happens once every ten or twenty years?  (Some basis on climate change indication, as well as an incredibly unusual winter and early spring growing season)  Or, is this the: " new normal".  We may have to manage the symptoms or agree to harvest.  It may require group action if it continues.  What is the role of the Three Rivers District?  The DNR?   Well...those are the fellows that I hven't been able to reach.

It was suggested that a guy by the name of Kevin Bigalke is the guy to talk to and he is on vacation until June 18th.  It was also suggested that the DNR at Shakopee is the place to call.  We need to talk to Darryl Ellison at 952-496-4141, extension #222 for further information.  He doesn't answer, but I was assured that he will return the call.

NOTE:  I don't know of the accuracy of my "recall" on this conversation, so don't quote it as gospel.  Rich was very nice, spent almost 20 minuttes with me, so this is a "capsule'.  We need to follow up.

Kay Botko, June 12, 2012