Aquatic Plant Control

Lake Mitchell has three major tributaries including Mitchell Creek, Brandy Creek, and Gyttja Creek. These were monitored in May 2009 for water quality parameters such as total phosphorus, pH, water temperature, conductivity, salinity, oxidative reduction potential, dissolved oxygen, and total dissolved solids. Recent surveys indicate that the lake is eutrophic, with low (5 feet from Secchi Disk reading) water clarity, elevated nutrients levels for phosphorus, and excessive aquatic plant (macrophyte) growth.

Brandy Brook in Little Cove contributed the highest total phosphorus concentration, followed by Gyttja Creek, and Mitchell Creek. The higher flow rate of Mitchell Creek allows that creek to contribute the highest phosphorus loads to the lake.

Eurasian Watermilfoil was introduced to the Untied States in the 1950s and currently exists in 33 states. Eurasian milfoil is among the first species to germinate in lakes after the ice melts and quickly forms a dense surface canopy that impedes the necessary light for more favorable aquatic plant species. Eurasian Watermilfoil reproduces by seed and fragmentation and may even hybridize with native milfoil species. At present, there appears to be hybrid milfoil in certain areas. The use of systemic herbicides such as 2-4-D and triclopyr (Renovate) in early June 2009 to control approximately 380 acres of the plant were successful. Systemic herbicides kill the entire plant including roots. The acreage was determined through a 990-point GPS aquatic plant survey during May 28-31. The survey detected 24 native aquatic plants, which consisted of 14 submerged, 4 floating-leaved, and 6 emergent (growing in wetlands) species. Four exotic species were found including Eurasian Watermilfoil found in 22% of grid points and Purple Loosestrife found around the shoreline of Big and Little Coves. The Giant Common Reed (Phragmites) and Yellow Iris were found during an August 12 post-treatment survey.

Mechanical harvesting allowed for the removal of nuisance native aquatic plants (approximately 49 acres of pondweeds and some lily pads) in all of the coves and along the northeast shore near Hiawatha Park. Harvesting began nearly four weeks after the Eurasian Watermilfoil was successfully treated and the dying milfoil was no longer a threat to spread by fragmentation.

Ten thousand milfoil-eating weevils were planted near the mouth of Mitchell Creek in early July. Samples of milfoil were taken in the fall to determine how effective the weevils have been. Preliminary results were encouraging and tests will continue in 2010.

The exotic Banded Mystery Snail experienced a large die-off in May 2009, which is a natural occurrence for snails when a rapid warming of the water occurs. Since the primary food source of snails is organic matter, it is not surprising that a large population exists in Lake Mitchell, which has high quantities of dissolved and particulate organic matter.

1) Treatment of milfoil areas determined by 990-point GPS survey in late spring with systemic herbicides.

2) Mechanical harvesting of coves and specific areas of the main lake as determined by Harvesting Guidelines developed by a committee of Lake Association members and approved by the Improvement Board in November 2009.

3) Removal of nuisance Cladophora algae in the Camp Torenta Canal with either the use of algaecides and/or a mechanical harvester.

4) The application of the Galerucella beetle to areas infested with Purple Loosestrife in Big and Little Coves.

5) The application of systemic herbicides to the Phragmites located at the southern portion of the Camp Torenta Canal in the wetlands.

6) The continued monitoring of water quality.

7) Oversight of herbicides and harvesting treatments by the Consultant.

8) Continued distribution of newsletter, as well as maintaining the www.lakemitchell.org website and correspondence with the lake association members’ email list.

9) Conduct Public Hearings in January of 2010 to determine the future of the Lake Mitchell Improvement Board.

10) Continuation of roadside pickup program from May 24 through September

Mechanical harvesting/cutting is generally preferred over herbicide use when submerged weeds cover large areas because vast quantities of decaying vegetation matter contribute significant organic matter to the lake bottom. Mechanical harvesting rarely removes the plants from the roots; however it does remove the majority of the plant biomass if conducted properly. Because Eurasian Watermilfoil spreads by fragmentation, harvesting is not recommended near this plant when it is living. Chemical treatments are applied to Eurasian Watermilfoil about two weeks before it is harvested. The majority of harvesting is conducted in water that is less than five feet deep. Approximately 49 acres of nuisance plants were harvested in 2009.

B. Aquatic Herbicides and Algaecides

The Natural Resources and Environmental Act of 1994 mandates that a permit be acquired from the MDEQ prior to all aquatic herbicide treatments. There are two category of herbicides; Contact and Systemic. Systemic herbicides kill the entire plant and Contact herbicides kill only the shoot portion of the plant. Algaecides kill algae. The use of systemic herbicides such 2-4-D and Triclopyr (Renovate) is recommended to maintain control of Eurasian Watermilfoil. Algal blooms were prominent in 2009 and BMP’s to reduce nutrient loads to the lake will be investigated in 2010.

The introduction of 10,000 weevils into a 2½ acre area (marked with orange buoys) of Big Cove near Mitchell Creek in July was largely paid for by a $10,000 grant from the National Forest Service. The weevil lays its eggs in the stem portion of a milfoil plant then burrows into the stem and eats plant tissue. The milfoil stems lose their support and fall to the bottom of the lake. Future stockings in Lake Mitchell will depend on the success of the 2009 planting.

D. Aquatic Vegetation Surveys

The Lakeshore Environmental, Inc. staff will conduct spring and fall 990 point GPS point surveys in order to assure that Lake Mitchell retains a balance and diversity within its native aquatic plant system as well as controls exotic plants such as Eurasian Watermilfoil, Purple Loosestrife, Yellow Iris and phragmites.

E. Watershed Monitoring

The Lake Mitchell watershed is approximately 23,315 acres, which is nine times larger than the size of the lake (2,580 acres). Water entering from its three major tributaries contributes significant nutrient loads to the lake. These tributaries were monitored and will continue to be tested to note changes in nutrient loading.

At several points in the lake water, quality tests were conducted and these will be continued in 2010. This will yield information that will allow trends in water quality to be noted and, if needed, aquatic management practices can be adjusted.

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A Plan for Aquatic Vegetation Control in 2009

What is the problem?

More than 70% of Lake Mitchell’s 2580 acres supports aquatic vegetation. The problem is that Eurasian Watermilfoil (EWM), an invasive plant which first appeared in the late 1980s, now covers 300-500 acres. This plant chokes out native vegetation and when it grows near the water surface, impedes boat navigation. Studies show that in 2006 more than 400 of Michigan’s lakes were infested with EWM.

Adding to Lake Mitchell boater frustration in 2008 was the long brown strands of flat stem pond weed, a native plant, which lay across many surface acres of the lake.

Although the spread of EWM is problematic in the main lake, heavy growth of EWM and native plants in the coves and selected shoreline areas greatly impedes off motorized boat traffic during the summer months.

How will the Lake Mitchell Improvement Board deal with the problem?

The Lake Mitchell Improvement Board will continue to deal with Eurasian Watermilfoil and nuisance weeds in 2009 by following the Board’s stated objectives for aquatic weed control. In order of priority, these objectives are stated as follows:

1. Control Eurasian Watermilfoil in the main part of the lake.
2. Remove vegetation that hinders boaters’ access to the lake.
3. Clear thick weeds away from ends of docks.
4. Provide roadside pick up for weeds.

To meet these objectives, Lakeshore Environmental Inc (LEI) has been hired as the Board’s environmental consultant replacing Progressive Engineering. At the February 23^rd Lake Mitchell Improvement Board meeting, Jennifer Jermalowicz-Jones, the consultant from Lakeshore Environmental Inc. who will be working with us on Lake Mitchell outlined the following program for aquatic plant management in 2009:

1. In May when the first immature Eurasian Watermilfoil can be detected, Lake Mitchell will be surveyed with plant samples being taken where they are found in a GPS survey of at least 800 points. (In past years, 350 grid points were used in the survey.) This more comprehensive survey will ensure that a greater percentage of the lake’s milfoil will be detected.
2. Soon after the water reaches 55 degrees, (the minimum temperature for effective 2-4-D treatment) systemic aquatic herbicide will be applied. This likely will occur the second or third week of May. (In past years treatment was done the second week of June.) Early treatment kills plants before they have a chance to seed and the dying smaller plants create less decaying plant matter on the bottom of the lake.
3. On the day Aquatic Services Inc, (the applicator company hired this year replacing Professional Lake Management which has done the treatment in previous years) treats the lake, staff from Lakeshore Environmental Inc. will be on the treatment boats to supervise. The LEI staff will make sure that the areas treated correspond to the GPS surveyed grid points where EWM was found. The LEI staff will also ensure that boats are using GPS and depth finder equipment properly to insure accurate distribution of herbicide. The herbicide applied will be metered to make sure that the right dosage is applied.
4. It is estimated that we will harvest about 40 acres w/o Franke Cove and 43 acres if we include Franke Cove. Projecting the amount of EWM needing treatment is more difficult but it is likely we will locate 350-450 acres. This year contact herbicides (which only kill parts of the plant that comes in contact with herbicide) will not be used. Systemic herbicides will be used since they kill the entire plant including roots. The Board accepted Jennifer’s recommendation that West Michigan Weed Removal be hired as our harvester this year, replacing Professional Lake Management which has provided this service in the past. The Board approved her recommendation.
5. Several weeks after the herbicide treatment, LEI will return to survey the lake and if healthy milfoil is found, then it will be marked for retreatment and soon receive a dose of herbicide. A final survey will be conducted in September to evaluate the effectiveness of the program.

The herbicides used for treatment will be the same as have been applied in previous years and include the following:

1. 2-4-D, which kills milfoil, is a systemic chemical which means that it kills the entire plant, roots and all. Because of the presence of shallow wells this herbicide must be used no closer than 250 feet from the shore.
2. Triclopyr, with a brand name of Renovate, is also a systemic chemical, and is used near shorelines. Lawns may be watered within 24 hours of application, but ornamental plants should not be hydrated until the water has been tested.

All chemicals have a 24-hour restriction on swimming.

Weevils will be planted this year

Lakeshore Environmental plans to stock 10,000 weevils at a 50 acre site on Lake Mitchell early in the summer. Tentative plans will have weevils introduced near the mouth of Big Cove. A $10,000 grant from the United States Forest Service will pay for much of the weevil planting.

How weevils control milfoil

Weevils feed exclusively on Eurasian Watermilfoil by consuming stem tissue and causing it to die and fall to the lake bottom.

Although there have been some dramatic successes, introducing weevils does not guarantee that milfoil will be controlled. Areas where weevils are introduced cannot be chemically treated or harvested for several years until it can be determined if the trial was successful.

Plantings of weevils can fail for several reasons. These insects must fly to shore where they burrow into brush or ground littered with leaves for the winter. Well kept lawns provide poor habitat for overwintering weevils. Panfish, especially bluegills, eat this insect’s larva which can cause weevil plantings to be unsuccessful. Heavy boat traffic in a plant area can also be detrimental.

If Lake Mitchell’s weevil planting proves successful, the program will be expanded reducing the lake’s reliance on chemicals for weed control.

Weed Harvesting to continue in 2009

West Michigan Weed Removal will conduct harvesting in coves and shoreline areas where vegetation is inhibiting boat traffic. In 2008 harvesting was delayed because the record rains that fell on June 12 and 13^th raised water levels causing concerns about the effectiveness of harvesting during June. (Pictures of the aftermath of the June 12-13 rains are on our website.) This year the harvesters will begin cutting in late June in order to finish before the 4^th of July holiday.

The Nature of Harvesting

Because milfoil spreads by fragmentation, aquatic herbicide treatment is the primary means of controlling that plant. Once the plant has been killed, then harvesters can collect the dead milfoil and other nuisance vegetation. Harvesting is used where native plants are so dense as to cause problems for boating. This means that a lane will be cut so people can get their boats from their docks to open water. Because harvesters are too big to maneuver between docks and need 18" to 2’ of water to operate, not all weeds will be cut. In addition DEQ regulations forbid the cutting blades from digging into the bottom muck because according to the DEQ, would be dredging. The DEQ also stipulates that at least 20% to 40% of the littoral zone (meaning along the shore) be left vegetated to provide habitat for fish.

Without harvesters to cut and remove plants, shallow areas would be rendered unusable for recreation. However harvesting does not eliminate weeds permanently. During peak growing season, mature plants may appear in harvested areas within a few weeks after a cutting.

Do harvested weeds float away to the shore around Lake Mitchell?

As harvesters cut weeds they are fed onto a conveyer belt that carries them to a collection bin. When the bin’s capacity is reached, the harvester returns to shore and off loads the weeds onto a dump truck which carries the weeds to an area farmer who uses them for mulch. Every effort is made to ensure that weeds cut by the harvester do not escape and float to other parts of the lake. Most floating vegetation has been cut by motor props, dropped by anglers, and is the result of the natural or chemically induced die-off of plants.

Harvesting usually occurs during the last week of June. Property owners are encouraged to visit Big, Little, and the Franke Coves to observe the harvesting.

Integrated Lake Management

The Lake Mitchell Improvement Board will be following an integrated management program. To give you an understanding of what this means, the following information was provided by Lakeshore Environmental Inc:

Integrated lake management involves the combined use of chemical, biological, mechanical, aeration, or other control methods for aquatic plant control or the combination of various methods for the management of nutrients, erosion, or other lake issues. Integrated lake management is becoming increasingly common since aquatic ecosystems are multi-dimensional and have different problems at various spatio-temporal scales in certain lake areas and thus may show variable responses to specific solutions. The recommended use of systemic chemical herbicides for the Eurasian water milfoil (M. spicatum) present within Lake Mitchell and the use of biological control (i.e. the weevils), along with mechanical harvesting of nuisance aquatic vegetation is indicative of an integrated management plan. Care must be taken to assure that the weevils are stocked during a period when chemical herbicide residues may not be detected in the water column and have been assimilated by treated M. spicatum plants.

What can we expect from our efforts to control the weed problem?

Nothing can be done to return Lake Mitchell to what it was in the 1980s.The sewer system that was installed in the 1978 greatly reduced the leakage from septic systems into the lake which improved the water quality but also increased water clarity. The clearer water allowed light to penetrate farther into the lake stimulating plant growth in deeper water. In the late 1980s Eurasian Watermilfoil was introduced to Lake Mitchell. The clearer water and the appearance of EWM greatly increased plant growth.

Each year plants, whether killed through herbicide treatment or because of their natural seasonal die-off, fall to the lake bottom and decompose. This creates a fertile base which encourages an ever expanding area for plant growth.

The Lake Mitchell Improvement Board working in concert, with Lakeshore Environmental, Aquatic Services, and West Michigan Weed Removal will administer a program of chemical treatment and harvesting to clear plants away from the water’s surface so boaters and fishermen can utilize more of the lake. It is hoped that by detecting and treating more EWM in 2009, that there will be a significant reduction of this plant in future years.

The problem with native plants in the main lake

While invasive plants such as Eurasian water milfoil can be treated wherever they are found, according to regulations set forth by the Michigan Department of Environmental Quality, chemicals cannot be used to treat native plants that are more than 300 feet away from shore. In a situation such as 2008 when a bumper crop of flat stem pondweed covered parts of Lake Mitchell, herbicide treatment of that plant cannot be undertaken.

Fluridone (Sonar) – a solution to Mitchell’s weed problem?

Fluridone is an aquatic herbicide, known by the trade name Sonar, which was used in 2002 to treat Houghton Lake’s Eurasian Watermilfoil problem. At that time 54%, more then 11,000 acres of Houghton Lake, was infested with EWM. The treatment virtually eliminated the plant although EWM has gradually returned and in 2008 covered about 1310 acres.

Last fall the Lake Mitchell Improvement Board considered a fluridone treatment for this year. Representatives from SePro and Progressive Engineering conducted preliminary studies and felt Lake Mitchell was a candidate for this treatment. Officials from the DNR and MDEQ opposed the treatment pointing out that only 16% of the vegetation in the lake was milfoil.

The Improvement Board voted to forego using a fluridone treatment at this time feeling that the program proposed by Lakeshore Environmental Inc involving more detailed surveys of the lake, and then coordinating a control plan using 2-4-D, trichlopyr, harvesting, and weevils might be best for Lake Mitchell.

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What was done in 2007: Grid survey completed and improved in 2008

To better locate Eurasian milfoil beds in Lake Mitchell, an 11-hour survey of the lake was conducted on June 5^th, during which time a lake grid of 267 points was checked for milfoil. A rake head attached to a rope was tossed in likely milfoil areas in an effort to find evidence of the weed. No milfoil was found at depths greater than twelve feet. At this time of year most plants are small and not-visible at depths greater than five feet so dragging a rake across the bottom is the only method of detecting deep water plants. Initially 239 acres of milfoil was found and subsequent surveys revealed more milfoil. By season’s end 305 acres was treated with 2-4-D. Areas where the plants resisted the first treatment were dosed again with 2-4-D at no charge.

The result was that there was less milfoil visible during the summer, but the lake board is still concerned about the amount of milfoil that could be seen in mid-summer. Visible milfoil beds were marked by GPS readings in the late summer and fall and will be treated in 2008. In addition the grid points will be recalibrated putting them closer together which will allow a more comprehensive examination during the early summer boat survey.

Lake Mitchell Herbicide Map.

Lake Cadillac has been treating Eurasian milfoil since 2006. To learn more about their program check out their website.

http://web1.msue.msu.edu/wexford/LC/index.html

Thirty-one acres, predominantly in the Franke and Little Cove area, were harvested in late June. Weed cutting is done where weeds grow so thick that normal boating is impaired as vegetation fouls propellers and is sucked into engine uptakes. The harvester blades are prohibited by law from digging into the bottom because that would legally be considered dredging. The harvesters cut rather than uproot weeds. Typically within a month to six weeks after a cutting has been made, the weeds grow back. It appears, in some cases, that they grow back thicker than the original crop. For this reason harvesting is only used in areas primarily near docks where boating has been made difficult because of the presence of vegetation.

The Lake Mitchell Improvement Board will continue to deal with Eurasian milfoil and nuisance weeds in 2008 by following the Board’s

stated objectives for aquatic weed control. In order of priority these objectives are stated as follows:

1) Control Eurasian milfoil in the main part of the lake.

2) Remove vegetation that hinders boaters’ access to the lake.

3) Clear thick weeds away from ends of docks.

4) Provide roadside pick up for weeds.

To meet these objectives the Board held a public hearing on January 13^th 2007 for the purpose of raising the property owners’ assessments and getting feedback from members of the Lake Mitchell Association.

Early June – comprehensive survey of lake conducted at 267 GPS grid points to locate Eurasian milfoil and determine harvesting needs

Mid-June - 2-4-D applied in all areas that are more than 250 feet from shore. (2-4-D cannot be used within 250 feet of any shallow wells.)

Milfoil and nuisance plants near the shore, will treated with Renovate and Reward chemicals. For more information see "Chemical Treatment and Harvesting Procedures."

Late June - In addition to chemically treating thick vegetation in coves, harvesting will be done in late June to remove the vegetation near docks and to provide navigation paths so boats can enter and exit the coves. As the harvesters cut the weeds, they will collect them so the weeds do not pile up and clog these waters. For more information see "Chemical Treatment and Harvesting Procedures."

July – Surveys done to determine effectiveness of chemical treatment and harvesting and where deficiencies are noted, corrections are made.

The roadside pickup program will continue to operate starting the week before Memorial Day and ending the week after Labor Day. For more information see "Roadside Pickup."

Barley straw? A solution for Lake Mitchell
Ponds and lagoons in waste water treatment plants often use barley straw to reduce the amount of suspended solids in their ponds. Although the process is not fully understood, it occurs as the barley decomposes and releases chemicals This process does not remove pond scum, sludge mats, or duckweed. To use barley, approximately 300 hundred pounds of barley per acre, are tied into sausage booms which then are floated in the effected water. The barely must be replaced every six to eight weeks. Mackinaw City is using barley in its waste water ponds. The algae and weed problems found in Lake Mitchell’s coves would not likely be solved by the use of barley straw.

Weeder’s Digest offers relief from invasive aquatic weeds.
This website, www.weedersdigest.com, offers several pages of information about products such as weed rakes, underwater weed cutters, and devices for removing muck and algae. In addition it presents ideas for lakeshore property owners on the best ecological practices. To contact them directly go to Info@WeedersDigest.com  or call 763-551-1441.

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