Eurasian Water-milfoil (EWM)

From Stephanie Boismenue
Squash Lake Association Aquatic Invasive Species Coordinator
and Water Quality and Habitat Committee Member

Eurasian Water-milfoil (EWM) will never be completely eradicated from Squash Lake, but it can be managed and the process of managing it will be continuous – for years. The Squash Lake Association’s (SLA) immediate goal for managing the EWM infestation is to: swiftly eradicate as much of the EWM as possible, manage any remaining or new EWM populations to reduce the chances of further spread, protect Squash Lakes healthy and unique ecosystem, and take preventative measures to keep further EWM or other invasive species from entering the lake. In addition, property owners will need to assist with ongoing monitoring efforts and the SLA will need to create a long term management plan.

The Squash Lake Association’s Board of Directors would like your thoughts about how to best manage the EWM in Squash Lake during the 2010 season. After much research and many discussions with Kevin Gauthier, Lakes Management Coordinator of the WDNR and with SLA’s lake management consultant, Tim Hoyman, Aquatic Ecologist with Onterra, LLC, the board of directors have narrowed down the treatment options to physical control vs. chemical control vs. biological control. However, all options come with a significant price tag.

Who is going to pay for getting rid of the Eurasian Water-milfoil in Squash Lake?
Even though Squash Lake qualifies for the State of Wisconsin’s Aquatic Invasive Species, Early Detection and Rapid Response Grant, both the physical and chemical control methods are going to be extremely costly to the SLA. The grant has a cap up to $20,000.00 and operates on a reimbursement basis. The State of WI pays for 75% of the cost of the project and the SLA pays for the remaining 25%, (in the form of cash, time, services or “in-kind” items). Any expenses above $20,000.00 will be the responsibility of the SLA and must be paid in cash.

If the SLA is awarded the full $20,000 then:
The State of Wisconsin pays: 75% = $15,000.00
The Squash Lake Association pays: 25% = $5,000.00 plus any expenses above the $20,000 limit

However, this is not the end of the road for SLA’s expenses for managing the EWM and, as I mentioned above, managing the EWM will be an ongoing process – for years – and maybe forever. The SLA will need money, that currently does not exist, to fund this management plan and other necessary projects such as:
• Development and implementation of a long term EWM management plan,
• Development of a proactive and reactive management plan so the SLA will be prepared to take action immediately if other aquatic invasive species enter and infest the lake,
• Implementation of the proactive and reactive management plans,
• Contractor expenses,
• Continuous monitoring of EWM,
• Permit fees,
• Education expenses

What is Eurasian Water-milfoil?

EWM is a submerged invasive aquatic plant from Europe and Asia, that has adapted at reproducing and spreading rapidly and can literally “take over” a lake’s environment. It grows very quickly, up to two inches a day in ideal conditions, grows 6 feet or more in length and in water depths of 3-20 feet. EWM is a very opportunistic species that is adapted for rapid growth early in spring and starts growing when water temperatures reach 45-50 degrees F, before other native plants emerge. It’s roots and rhizomes produce many long spaghetti like stems that grow up to the water’s surface and each stem may branch multiple times forming incredibly dense mats of vegetation at the water’s surface. The dense mats of vegetation makes it an aggressive competitor towards the native aquatic plants by shading them out to the point of totally displacing the native plants, which in turns impacts the fish, wildlife, and ecosystem of the lake. In addition these dense mats entangle everything that it comes in contact with, thus making it impossible to swim, boat, and fish. EWM has four methods of reproducing: by seed, fragmentation, stem runners, and rhizomes. Unlike many other plants, EWM does not rely on seed for reproduction because its seeds germinate poorly under natural conditions. The primary mode of reproduction is via fragmentation – plant pieces that are broken off and settle in the bottom of the lake. A two-inch fragment is all it takes to start a new EWM colony. The fragments may be readily dispersed by water currents or inadvertently picked up by boaters and transported in their boats, motors, trailers, bilge’s, live wells, or bait buckets, and can stay alive for weeks if kept moist.

To determine how to best manage the EWM in Squash Lake, many factors have to be taken into consideration such as:
• The results of the WDNR and Onterra’s surveys and their recommendations,
• Researching the subjects in depth and many discussions with contractors, divers, other lake associations who are dealing with EWM, and individuals with knowledge of the subject
• Size of the EWM infestations,
• Squash Lake’s unique aquatic ecosystem and its physical and chemical characteristics,
• Recreational use on the lake,
• The narrow window of time that the plant infestation remains at low levels,
• Time of year that the plant is growing in relations to the time of the year for managing it,
• How might the lake’s ecosystem health be affected by physical, chemical, or biological control,
• How might human health be affected by physical, chemical, or biological control,
• Community opinion, and
• Financing.

So, what is the best treatment option available for Squash Lake’s unique situation?
Option #1 Physical Control: Scuba Divers -Hand Harvesting
Hand pulling by certified Scuba divers can be an effective way to remove small stands or scattered growth of EWM. It would require at least two divers, who are familiar with EWM, working together at all times. Hand pulling can be a single treatment or as a follow up to chemical treatments.

Key elements of the technique are:
• Two to 3 divers will be working together at all times.
• In addition, SLA will need volunteers to work with the divers by assisting in the following capacity: 1 –2 volunteers scouting out and retrieving fragments, 1 volunteer to handle the boat, 1-2 volunteers collecting the plants from the divers.
• If done with care, hand harvesting is the ultimate “species selective” technique that causes minimal impact to other native species in the vicinity of the work area and allows for the removal of individual plants – one plant at a time.
• Removal of the entire plant, by hand and early in the season, can take away the plants competitive advantages and greatly reduces the amount of plants that would auto- fragment in late summer and fall.
• Divers are able to pull the entire plant, roots, and rhizomes with the utmost care and produce fewer fragments.
• Divers can visually inspect the extent of the EWM and thus allowing them to keep EWM colonies or small stands in check
• Hand harvesting removes plant biomass from the lake, where as the chemically treated plant mass remains in the water and decompose adding threat of low dissolved oxygen and increased nutrient load.

• Scuba diving to hand harvest EWM can be labor intensive, cumbersome, tiring, and weather dependent.
• There are equipment limitations and divers need up to 3 full tanks a day to be able to dive 6 hours a day.
• The best time to harvest EWM is early in the season, before native plants emerge – which means working in cold water temperatures.
• Despite the level of care taken during hand harvesting, it is nearly impossible to see and remove every stem and root fragment in the area. For this reason, ongoing monitoring of the sites is necessary and routine control activity is essential.
• SLA volunteers will need to assist the divers and possibly provide the divers with an old pontoon or flat bottom boat.
• The SLA is already having a difficult time getting volunteers to help with the aquatic invasive species PROACTIVE measures (lack of help monitoring the boats at the boat landing). This leads me to believe that there will also be a lack of volunteers to help with the aquatic invasive species REACTIVE measures ( helping the divers).
• Unfortunately, hand harvesting is not an effective means of getting rid of large colonies of EWM that are more then an acre, but is most effective on small stands and individual plants.
• Hand harvesting stirs-up the loose sediment at the bottom of the lake, creating zero visibility until the sediment settles down – handicapping the divers efficiency of doing their work.
• No one is exactly sure how long it will take to make a dent in the EWM during the 2010 season, but it’s estimated 400-500 hours of diving will be necessary.

Estimated Cost: $20.00 per hour – per scuba diver and allow up to 400-500 hours of diving (to be split between the divers) for the 2010 season. Other cost that the SLA will need to budge for, but are not limited to, are: purchase the required WDNR permit; possible equipment rental (air tanks run about $15.00 per day); possible equipment repair; $10.00 per day per diver for equipment depreciation; air tank refills; mileage to and from getting the air tanks refilled, possible insurance, and gasoline for the boat.

Option #2 Chemical Herbicide: Granular 2,4- D
2,4-D is 27.6% Butoxyethyl ester of 2,4-Dichlorophenoxyacetic acid and is sold under the trade name of Navigate. 2,4-D is a systemic herbicide that inhibits normal plant growth by interfering with the process of cellular divisions. It’s used for control of targeted invasive species such as EWM. The essence of the approach is to take away the plant’s competitive advantages which are: early emergence and growth that shades out and “out competes” native plants for photosynthesis. It is always hopeful that the need for chemical management is reduced over time and in fact it is possible to use the treatment for only one season.

The key elements of the technique are:
• The contractor must be licensed to apply chemical herbicides in Wisconsin’s public waters. The contractor must have a current license and respect the permit conditions set forth by the WDNR,
• EWM is the first aquatic plant to emerge in the spring – it starts growing when the water temp is 45 degree F. The 2,4-D would be applied early in the EWM’s growing season, and before native plants start growing (60 degree F).
• Pre and post treatment assessments must be completed to confirm the targeted treatment areas, check for changes in the distribution and density of EWM, and to guide the herbicide applicators. The assessments will also evaluate the effectiveness of the treatment, ensure that consistent methods are being implemented, detect residual chemicals in the water, and determine the success or failure of the project.
• To effectively treat the EWM, the 2,4-D must remain on the plant, at a specific concentration level, for several days. The 2,4-D then rapidly declines and within 14 days it should be broken down by microbial organisms. Water samples are taken at several intervals during the season to check for residual chemicals.

• Do not assume that the use of any chemical herbicide is safe or without risk. There are still many unknowns and uncertainties regarding long term effectiveness and unintended impacts to humans health and the health of the lakes ecosystem by the use of 2, 4-D.
• Chemical treated plants remain in the water and decompose adding threat of low dissolved oxygen and increased nutrient load.
• Raises concern over the immediate effect of the application on non-targeted species.
• Treatments may need to be repeated for several years
• There is a specific number of days, post treatment, that the lake water cannot be used for irrigation or drinking (I believe 21 days). All riparian owners will be notified of the necessary information prior to application.
• Mid- to late- summer chemical treatments have the least effective and lasting control on EWM.
• Unknown impact of applying a herbicide in the spring – during a time when every aquatic organism, invertebrates, amphibians and vegetation in and around the lake are in an incredibly vulnerable state as they are just emerging from their long winters naps and are mating, spawning, hatching, and growing.

Estimated Cost: $6,100.00. Other cost that the SLA will need to budge for, but are not limited to, are : purchase the required WDNR permit; purchase ads in the local newspapers and send announcements to residents announcing the application of 2,4-D (as required by the WDNR); equipment fees and possibly insurance.

Option #3 Biological Control: Milfoil Weevils
The milfoil weevils (Euhrychiopsis lecontei) are native to Wisconsin lakes and feed on both native and EWM. Weevils have been found to suppress some EWM populations, but it’s a very slow process.

Key elements to the technique are:
• Adults weevils spend the majority of their time clinging to the top of the plants in the water as they feed on the milfoil leaves, mate and lay eggs.
• The eggs are deposited on the actively growing tips of the EWM.
• When the eggs hatch into larvae, the larvae burrow in and out of the plant, feeding on the tips of the plant and vascular tissue as they working their way down the stem.
• Damage caused by eating the plant and burrowing in and out of the stem causes the stems to be less buoyant, collapse and eventually die. It also prevents the plant from flowering.
• The adult weevil over-winters in organic matter (leaves and debris) on the shore and if they survive the winter they fly or swim back to the water in the spring.

• Suppression of EWM is achieved over a very long period of time.
• Cold water temperatures, fish perdition, calcium carbonate deposits, chemicals, and the lack of natural shoreline negatively affect weevils.
• The weevils are easily knocked off the plant and washed away by waves and wake action. The use of weevils would be ideal in an area that was protected from the elements such as a small-protected bay, but not in a large open area.
• Some lake associations have had success suing the weevils over a long period of time. Other lake associations have had the weevils completely disappear just after being applied to the milfoil – a big investment wasted.
• Weevils over-wintering habitat must be on natural, undisturbed, and undeveloped shorelines.
• The WDNR feels that, at this time, the use of the weevils does not appear to be an effective-enough treatment for EWM, therefore use of the weevils is NOT covered under the grant.

Estimated Cost: $1.25 to $1.50 per weevil and the minimal amount of weevils that can be purchased is 1,000. Other cost that the SLA will need to budge for, but not limited to, are: purchase the required WDNR permit.

Combining options to managing the EWM during the 2010 season.
A. The SLA can opt to use the hand harvesting method with scuba divers and continue to monitor and evaluate the EWM areas. If hand harvesting does not keep the EWM in check, then use the herbicide in the spring of 2011.
B. Use the herbicide 2,4-D early this spring and follow-up with scuba divers in the late spring/early summer.

Following this article are the survey results, recommendation, and mapping of EWM locations from the SLA contractor Tim Hoyman of Onterra.

Please remember that these treatment methods are not free to the SLA, as I have outline above and that there in not a guarantee that any one method will work. In addition, even though another lake in the area may have had great success with one treatment method, that doesn’t mean that that method is suitable for our Squash Lake.

The Squash Lake Board of Directors would like your thoughts about how to best manage the Eurasian Water-milfoil in Squash
Lake for the 2010 season.

Please submit them by February 20th to:
Pat Dugan, President of the Squash Lake Association
7306 Squash Lake Road, Rhinelander WI 54501
Or email to

My Final Thoughts
Each lake has its own unique aquatic ecosystem, function, and recreational use. To determine what management method is suitable for Squash Lake, we, the Squash Lake community, must think about the uniqueness of Squash Lake and factor in the lakes already healthy, diverse, and well balanced ecosystem and how we recreate on the lake. Follow your heart and be passionate about it.

Please be an Ambassador to every living organism in Squash Lake, as they are frail and at the mercy of human hands. Stephanie Boismenue