INVASIVE WEED MANAGEMENT Frequently Asked Questions

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Simply put, all of us use the entire bay and we bring the invasives back into our area.  Like dandelions, if you neighbor doesn't treat then we will continue to have to do our individual treatments each year.  This program is designed to decrease the amount of invasives that need to be treated every year with the goal being that you personally will not need to have your lakeshore treated for these invasive weeds.  Does it mean that all the weeds will be gone? NO!  Aquatic vegetation is needed to keep our bay healthy.  We will only be treating the invasive, non-native weeds.  

With our plan for the fall milfoil treatment it is anticipated that less then 20% of the milfoil will return in the 2nd year which will significantly reduce our cost to treat our bay in year 2.

We pay a lot of taxes to be on Lake Minnetonka and it is frustrating to have to foot the bill for bay AIS treatments.  What we have found is that if we don't advocate for our bay then no one is concerned about our weeds or our water quality.  We have begun conversations with the City of Mound, the Minnehaha Creek Watershed, the DNR and the Lake Minnetonka Conservation District to determine ways to tap into state, county and city funds.  The goal of establishing a bay association is to be in front of these organization and to draw on our state representatives to help us to protect our bay and all of Lake Minnetonka.

For this years treatment we will be applying for grants through the DNR and the LMCD to help offset some of the cost.  If we have dollars left from our fundraising it will roll into 2023 treatment.

No.  A weed free bay is a dead bay.  Native plants are an important part of a healthy lake's ecosytems.  Currently the Lake Minnetonka's Bay Treatment Program specifically targets non-native, invasive Eurasian watermilfoil,  Curly Leaf Pondweed and flowering rush.  These non-native weeds make recreation and boating difficult and are harmful to fish habitat and aquatic life.

 Once established, invasive weeds  are hard to control. Generally, after the first few years of treatment, the acreage needed to be  treated decreases significantly. Most invasive weeds reproduce from fragments, so boaters and  water currents can spread weeds from bay to bay. Annual weed surveys and spot treatments will  be needed to prevent large weed beds from reestablishing. 

 Only herbicides approved as safe by  the US Environmental Protection Agency and the MnDNR are used by the HBA. Herbicides are applied at or below the recommended rates. Herbicides containing  glyphosates are not used. The Lake Minnetonka Association hires only trained and licensed  applicators for its Bay Treatments. 

Our applicators use state of the art equipment and application methods to pinpoint exactly where  to treat and what amount of herbicide to use. This way, we save money, use less herbicide, treat  only the areas necessary, and get better results. Our applicators work closely with the University  of Minnesota and other researchers to continually improve the bay treatments.  

More Info from our applicator - PLM:

First and foremost, PLM is committed to providing services to our most precious resources that are in the interest of improving the ecological value of the resource.  It is our goal to restore and protect our waters in a way that management efforts are minimalized over time.  We too share some of the same concerns as the residents, however I feel confident that the products we are using and the rates we are using have been thoroughly assessed and labeled not only by the Federal Environmental Protections Agency but further assessed by Minnesota’s Department of agriculture.  These assessments and studies were conducted with the most rigorous standards as outlined in the memorandum you shared. This document was supplied as part of the re-registration of Diquat Dibromide which must occur every 15 years. 

As part of the re-registration the following eligibility decision document was released by the EPA which states the information summarized behind the decision to label and allow use of the product.  That can be found at this link.  https://archive.epa.gov/pesticides/reregistration/web/pdf/0288fact.pdf

If we look at the application concentrations in Harrison Bay, we applied at a .256 mg/l which is nearly 4 times lower than the “questionable” study indicated in even the longest exposure time.

 There are no fishing restrictions following bay  treatments. The herbicides used do not accumulate in fish.  

The bay treatments are restoring native plants.  Bays enrolled in the Bay Treatment Program are seeing an increase in the diversity and density of  native plants. Research shows that healthy native plant populations can prevent new, non-native  invasive weeds from becoming established and can help to improve fisheries and habitat for  aquatic species.  

 It is generally recommended  not to swim for 24 hours after treatment. While almost all of the herbicides used on Lake  Minnetonka do not have a swimming restriction, the state of Minnesota requires a notice be posted the day of treatment in areas treated within 100 feet from shore. Therefore, if your  property does not have a notice (sign in the yard) you do not have a swimming restriction. Also,  offshore areas of the lake (deeper water) will be safe for swimming and boating after treatment. 

It depends  on the treatment. Some of the herbicides used may have turf and ornamental flower irrigation  restrictions. The restrictions can range from 3 days to 14 days. If you use water from the lake to  irrigate, please read posted signs carefully to determine your irrigation restrictions after a treatment. It is also recommended that homeowner turn off weed blowers for 24 hours following treatments. 

 Bay treatments are more cost effective than weed cutting. Research  shows that cutting weeds can increase the rate of growth and the density of invasive plants such as  Eurasian watermilfoil and flowering rush. Furthermore, cutting weeds increases the risk of  spreading new invasive weeds lakewide. 

The applicator we are using has a contract with the Lake Minnetonka Association and is highly recommended by the DNR.  The company is PLM Lake & Land Management.  Per their permit communication to the DNR, they indicated that treatment will depend on what vegetation is found on the spring delineation survey.  They propose using diquat for areas with just Curly Leaf pondweed and Diquat/Procellacor combination for areas where milfoil is present.  Per the Lake Management Plan for HBA, we are only allowed to use herbicides that are approved by the EPA.

Diquat Dibromide Screening Profile: https://www.health.state.mn.us/communities/environment/risk/docs/guidance/dwec/screening/diquatdibromide.pdf

Diquat Fact Sheet: https://dnr.wi.gov/water/wsSWIMSDocument.ashx?documentSeqNo=158277108

The products we are using and the rates we are using have been thoroughly assessed and labeled not only by the Federal Environmental Protections Agency but further assessed by Minnesota’s Department of agriculture.  These assessments and studies were conducted with the most rigorous standards. 

As part of the re-registration for Diquat Dibromide (which occurs every 15 year) the following eligibility decision document was released by the EPA which states the information summarized behind the decision to label and allow use of the product.  That can be found at this link.  https://archive.epa.gov/pesticides/reregistration/web/pdf/0288fact.pdf

To address the concerns about fish (walleye) here are some interesting studies out there.  One study that has received a lot of traction specifically regarding walleye has been a subject of debate since its release and it has been challenged due to inaccuracies, insufficient data and quoted "limitations of study" by the EPA. https://www3.epa.gov/pesticides/endanger/litstatus/effects/redleg-frog/2010/diquat/appendix-h.pdf

If we look at the application concentrations in Harrison Bay, we applied at a .256 mg/l which is nearly 4 times lower than the “questionable” study indicated in even the longest exposure time.

There are some questions regarding why Europe banned Diquat, and it has not been banned elsewhere that I am aware of.  It appears that this was done due to re-entry into fields treated with diquat and exposure to the product after its application.  Terrestrial applications are very different from aquatic products and break down much slower than aquatic applications. Diquat has an aquatic field dissipation half-life of 24-48 hours.  After that period diquat is undetectable which shows its rapid adsorption rate making it much less persistent than other products.   

Finally, and most interestingly there are many studies where Diquat has been used to cure fish diseases.  Hear is that link.  Note that the concentrations in this study was at 18 mg/l which is nearly 70 times higher than what we applied in  Harrisons bay. 
https://www.fws.gov/sites/default/files/documents/DRIB-50-Efficacy-of-Reward-to-Control-Mortality-Associated-with-Columnaris-Disease-in-Walleye.pdf

One more good link:
https://journals.flvc.org/edis/article/view/120226/118459

Information from our applicator -  PLM Lake and Land Management

ProcellaCOR aquatic herbicide is not a PFAS.  The US Environmental Protection Agency does not classify ProcellaCOR as PFAS based on its chemical structure and the regulatory science and evaluations validates it does not have the characteristics of long environmental persistence and toxicity risks common to long-chain PFAS (“forever chemicals”).  Further, florpyrauxifen-benzyl, has been granted a tolerance exemption on all food commodities from US EPA because of its non-toxic safety profile for use on and around food- and feed-use sites, including the use of irrigation water for food crops previously treated with ProcellaCOR aquatic herbicides. ProcellaCOR can continue to be applied to control invasive aquatic weeds in lakes following the federal and state approved label and permits.   

Some states are in the process of developing their own PFAS definitions. The Minnesota Department of Agriculture (MDA) has issued a preliminary list of PFAS pesticides active ingredients.  Florpyrauxifen-benzyl, the active ingredient in ProcellaCOR, is included on the MDA preliminary list simply because they are using the broadest interpretation of their definition of PFAS, which classifies any active ingredient containing a fluorine molecule as PFAS, regardless of its environmental persistence or toxicity characteristics.  Minnesota’s broad definition of PFAS classifies >90 pesticide active ingredients as PFAS, most of which do not have the characteristics of “forever chemicals.”  MDA makes no distinction between long-chain PFAS such as PFOA, PFOS, PFHxS, PFNA, and HFPO-DA that have long persistence in the environment and pesticide active ingredients that have been through many years of development and rigorous regulatory review by EPA to ensure safety for humans, wildlife, and the environment. 

• Treatment of the Curly leaf pondweed is done early in the spring when bay oxygen levels are higher
• The plant is smaller so there is less plant material to decompose
• The decomp rate of the plant material is slower when the water is cold
• In the current situation, the CLP can grow to 15 feet tall and then dies off in the warm water around early July leaving more material to be decomposed at the height of water temperatures.