Lake Eden Association
lakeedenvt.org
Eurasian Watermilfoil (EWM) Control Methods
Below are the widely accepted methods of controlling Eurasian Watermilfoil around the country. There are additional methods such as mowing and dredging that are not included below. These methods are only used once an infestation is so widespread that it cannot be controlled at all. These methods are effective in clearing waterways temporarily for boating and swimming use but need to be repeated frequently. Mowing aquatic species needs to be done as frequently as you would mow your lawn.
​
(1) Hand Harvesting
Divers or snorkelers, trained in identifying & removing invasive species, carefully remove the plant and all of its roots by hand. Care is taken to dig down under the surface plant to get the entire root system in order to prevent continued spread in that area. The plants are placed in in a fine mesh bag. Care is taken to catch all resulting fragments with a fine mesh net to prevent fragments from re-rooting and establishing another colony. Volunteers in kayaks and canoes are critically important to help with scooping up any loose fragments.
PRO’S:
-
Environmentally friendly
-
Can reach shallower waters than DASH by snorkelers or divers
-
Immediate removal of plants to clear clogged waterways
-
No impact on other aquatic plants or organisms.
-
Does not require a permit
CON’S:
-
Labor intensive & can be costly if you need to hire dive teams
-
High risk of fragments getting loose and starting new colonies in other areas of the lake.
-
If not done properly and with extreme care, it could make the problem worse.
-
Typically needs to be done multiple times a year and is not considered a permanent control method.
(2) D.A.S.H. (Diver Assisted Suction Harvesting)
Divers are trained to identify unwanted non-native or invasive plants that need to be removed, pull them out by the roots and feed them into a suction tube that transports the plants to a boat to be hauled away. Native plants are left to maintain a healthy aquatic environment. Results are immediate and long lasting. Use of volunteers on the water in kayaks & canoes is extremely helpful to catch and scoop any fragments that do break away.
*A permit for D.A.S.H. is required by the VT DEC.
​
PRO’S:
-
Chemical free
-
No impact on other aquatic plants or organisms.
-
Immediate removal of plants to clear clogged waterways
-
Long lasting
CON’S:
-
Labor intensive, although less so than Hand harvesting alone
-
Costly
-
Typically needs to be done multiple times a year
-
Risk of fragmentation (pieces of plant breaking off and re-rooting elsewhere). Incidence however is far less than with hand harvesting alone.
​
(3) Benthic Blankets
A benthic blanket is a heavy synthetic material that lays on the Benthos layer (bottom) of a lake or pond. They prevent growth by blocking out sunlight and basically smothering out the plants. Gases from the decomposition of plants under the material can cause unwanted movement of the blanket and so they must be weighted down. The lake Eden Association has purchased Benthic blankets that are designed to allow for escape of these gases to reduce chance of unwanted movement.
*A permit, for Benthic blankets, is required through the VT. DEC.
​
PRO’S:
-
Effective in areas of dense growth of EWM and where there are no to minimal native species affected.
-
Can be moved, roughly every 60 days, to other infested areas
-
Spread via Fragmentation is not a concern as entire plant is covered
-
Specifically Targeted: Effect only area covered
-
Highly effective; will kill 100% of the weeds it covers.
-
Non- Chemical and Reusable; if maintained they can last for years.
CON’S:
-
They are heavy and cumbersome to work
-
Can kill beneficial native plants that might also be trapped under the blanket. Therefore not ideal for use in areas with a lot of beneficial native plants mixed in with the milfoil.
-
VT state requires benthic blankets be placed no earlier than May 1 and removed by Oct 1 each year to minimize any negative impacts. This can be labor intensive & costly as divers are needed to place & remove.
-
High cost per square foot in comparison to herbicides
-
Need to be inspected monthly to make sure they are still anchored, haven’t move and there are no plants growing on top.
​
(4) Herbicide Treatments
Herbicide treatment options for EWM have been vastly improved in recent years. As of 2018, there is now a highly targeted herbicide, ProcellaCOR that is effectively used to target and kill Eurasian Water Milfoil with minimal to no affect on other aquatic species or heath concerns for humans. It has been shown to have an overall benefit for aquatic ecosystems. It has been approved by the State of VT (permit required) as spot treatments only and at the lowest levels of concentration needed to be effective. The herbicide dissipates quickly and Water use (household & recreational) can resume 24 hours after a treatment. It is currently being used in 12 Vermont lakes.
​
Due to public concern and the reporting of misinformation around the use of ProcellaCOR, the Vermont Department of Environmental Conservation (DEC), Watershed Management Division, Lakes and Ponds Management and Protection Program published a document in October of 2022 entitled “Permitting Aquatic Herbicide In Vermont”
DEC Report Summary
“Permitting Aquatic Herbicides In Vermont”
​
-
After application of a ProcellarCOR treatment, there was a statistically significant reduction of Eurasian watermilfoil (target aquatic invasive species) and Coontail (non-target native species) lake wide. The impact on Coontail was anticipated as the ProcellaCOR label listed it as being susceptible to the herbicide. This impact was determined to be an acceptable risk
-
There was a statistically significant increase in numbers of other beneficial native plant species. With the exception of Coontail, other aquatic native species showed no observable impact from the herbicide treatment. The overall result was from the herb viewed as” a positive impact on the overall biological integrity of the native aquatic plant community.”
-
These results of studies demonstrated that “targeted Eurasian watermilfoil control projects are not resulting in the suppression of all aquatic plant species lake wide, that native plant species can reestablish in areas once dominated by Eurasian watermilfoil, and that the benefits of the structural habitat provided by aquatic plants remain.
-
“ProcellaCOR rapidly degrades in the environment. Using a minimum concentration detection limit of 1 part per billion (ppb), nearly 100% of post treatment sampling found that ProcellaCOR is undetectable in the water 48 hours after treatment.”
-
“The potential for acute and chronic risks to fish, aquatic invertebrates, amphibians, and other aquatic animals is considered low. Any potential chronic toxicity of concern would be short lived due to dissipation in the environment.”
-
VT Dept. of Health found that”… human exposure to the inert compounds contained in ProcellaCOR at the concentrations that would result under the conditions proposed by the applicants, is not likely to result in an increase in the level of concern for public health.”
-
“The DEC’s Drinking Water & Groundwater Protection Division (DWGWPD) acknowledges the presence of public and private drinking water systems that draw waters treated with ProcellaCOR as well as groundwater drinking water systems that may be adjacent to a treated. DWGWPD does not have concerns with the use of ProcellaCOR provided the conclusions from VDH have not changed and that treatment concentrations do not exceed 5 PDUs.”
​
PRO’S:
-
Highly effective
-
Rapid & selective control; used as a spot treatment
-
Lasts longer than harvesting methods
-
Does not affect other beneficial aquatic plant & organisms with a few exceptions (i.e. Coontail)
-
When using ProcellaCOR, minimal amounts of the herbicide are needed (100x or more less than older herbicides used in the past)
-
Short Exposure period
CON’S:
-
Re-applications are needed every 1-3 years and depending on degree of infestation.
-
Can be costly depending on size of treatment area
-
Takes 2-4 weeks for plants to die back
-
Avoid Water use 24-48 hours.
-
Can kill native Coontail if present in the targeted treatment area
(5) Water Weevils
The milfoil weevil (Euhrychiopsis lecontei) is a small, herbivorous aquatic beetle that is native to North America. It is a watermilfoil specialist, meaning that it feeds and develops only on plants in this genus. Milfoil weevil has shown the most promise as a potential bio-control agent for Eurasian watermilfoil and why it has been the subject of much research.
Milfoil weevils affect Eurasian watermilfoil mainly by boring through the stem and consuming the cortex. This results in reduced plant buoyancy and accumulated carbohydrate stores, which may ultimately decrease overwinter survival and competitive ability. The weevil however can also be a threat to the beneficial northern milfoil aquatic plant.
VTDEC has been studying the use of the watermilfoil weevil as a control for Eurasian Watermilfoil since 1989. Research thus far shows that weevil populations are unpredictable and that they are unreliable control agents. Research continues on this potential bio-control as it has shown promise in some situations. At this time, it is not a recommended effective control method in Vermont.
Eurasian Watermilfoil Control Methods Used by Lake Eden
Prevention Measures
​
Since 2006 Lake Eden has had a Greeter Program and VIP (Vermont invasive species patrol program) aimed at preventing and identifying any invasive species in the lake. We credit these programs for helping to keep EWM, and other invasive species, out of our lake until now (2022). It was an educated property owner/family that actually identified the presence of EWM (Thank you to James & Monica Wood’s family). EWM is so widespread and so easily transferred from one body of water to another that it was inevitable. As of 2022, it has been identified in over 100 bodies of water in VT.
While we do staff Greeters at the Public Boat & Fishing Access, it is not 24/7 and is seasonal (mid may-mid Oct) due to funding limitations. The lake is a public lake with many points of public and private access and so it is impossible to completely control.
Over the years, the Lake Association and other dedicated volunteers have made efforts to educate all property owners including residential property owners, the Boy scout camp, the private campground, and the Town of Eden. These efforts have included many discussions with the Select board, presentations at Town meetings, conversations with BSA, and Campground management. Over the years the Lake Association has had multiple speakers on the topic at the annual Lake Association meeting and has trained numerous volunteers on how to survey the lake and how to ID invasives. The Lake Association started an Invasive Species fund roughly 20 years ago in an effort to accumulate funds to manage future IS. This earmarked fund is expected to pay for no more than 2 years of anticipated control measures for the EWM in Lake Eden.
Control Measures (Initiated July 2022)
-
Hand harvesting (divers & snorkelers)
-
D.A.S.H. (Diver Assisted Suction Harvesting)
-
Benthic Blankets-12 blankets were purchased and laid in the area of largest and most dense growth (town beach & campground) in August 2022. These blankets will continue to be used and repositioned to other areas of infestation as needed.
-
Herbicide treatment - Permit was approved and first treatment was August 26, 2025 - See info page - link
Note: For more information on these methods click here.
​
Learn More:
​