Eurasian water-milfoil

Myriophyllum spicatum can easily be confused with native milfoil species that also may have four deeply-dissected leaves per whorl (e.g., M. heterophyllum, M. sibiricum, M. verticillatum). As a general rule, Eurasian watermilfoil typically has more than 14(12-20) leaflet pairs per leaf and reduced bracts on inflorescences, in contrast to native milfoils which have fewer than 14(5-10) leaflet pairs, as in M. sibiricum, and bracts at least twice as long as the flowers, as in M. heterophyllum and M. verticillatum (Aiken 1981; Gerber and Les 1994; Patten 1956). Bud production distinguishes between the exotic M. spicatum and the native M. sibiricum and M. verticillatum, as the native species produce winter buds, while the exotic does not (Patten 1954).

• Alabama - Alabama, Florida Panhandle Coastal (University of Alabama Biodiversity and Systematics 2007), Black Warrior-Tombigbee (Anderson 2009), Middle Tennessee-Elk (Smith 1971), and Mobile Bay-Tombigbee (Zolczynski and Eubanks 1990) drainages
• Arizona - Little Colorado, Santa Cruz, Upper Gila (University of Arizona Herbarium 2008), Lower Colorado, Lower Gila-Agua Fria, Rio De La Concepcion, San Pedro-Willcox (Arizona State University 2003), Rio Sonoyta, Salt (Couch and Nelson 1985), and Verde (Anonymous 2015) drainages
• Arkansas - Boeuf-Tensas, Red-Little (Anonymous 2015), and Upper Ouachita (Wilde et al. 2013) drainages
• California - Central California Coastal (Consortium of California Herbaria 2014), Klamath (Nyman 1978), Laguna-San Diego Coastal (Rebman et al. 2002), Lower Colorado (Aurand 1983), Lower Sacramento (California Department of Fish and Game 2009), North Lahontan (Thorne and Tilforth 1969), Northern California Coastal, San Joaquin (Couch and Nelson 1985), Northern Mojave (Raven 1961), Salton Sea (Legner and  Fisher 1980), San Francisco Bay, Santa Ana (Anonymous 2015), Truckee (Anonymous 1996), Tulare-Buena Vista Lakes (Dunnicliff 1979), Upper Sacramento (Klunk 2006), and Ventura-San Gabriel Coastal (White 1997) drainages
• Colorado - Rio Grande Headwaters, Upper Arkansas (Colorado Parks and Wildlife 2014), South Platte, and White-Yampa (Anonymous 2015) drainages
• Connecticut - Connecticut Coastal, Lower Connecticut (University of Connecticut 2011), and Lower Hudson (Lyman and Betke 1997) drainages
• Delaware - a pond along the C & D canal, near the town of Kirkwood in Lower Delaware drainage (Cathy Martin, DE DNR, pers. comm.)
• District of Columbia - Belch Spring pond in Potomac drainage (Cooke et al. 1990)
• Florida - Apalachicola, Florida Panhandle Coastal (Anderson 2009), Aucilla-Waccasassa, Peace, Southern Florida (Wunderlin and Hansen 2008), Escambia, Ochlockonee, St. Johns, Suwannee (Robert Kipker, FL DEP, pers. comm.), Kissimmee (Center for Invasive Species and Ecosystem Health 2015), and Tampa Bay (Schardt and Schmitz 1991) drainages
• Georgia - Savannah (Aurand 1982), Altamaha (many 1997), Apalachicola (Gholson 1968), and Ogeechee (Center for Invasive Species and Ecosystem Health 2015) drainages
• Idaho - Kootenai (Center for Invasive Species and Ecosystem Health 2015), Middle Snake-Boise (Anonymous 2006), Middle Snake-Powder, Upper Snake (Tom Woolf, ID Dept of Ag, pers. comm.), Pend Oreille, Spokane (Dickinson 1991), and Salmon (Anonymous 2015) drainages
• Illinois - Kaskaskia, Lower Illinois, Rock, Upper Illinois, Upper Mississippi-Skunk-Wapsipinicon, Wabash (Anonymous 2015), Lower Ohio, Southwestern Lake Michigan (Center for Invasive Species and Ecosystem Health 2015), Upper Mississippi-Maquoketa-Plum, Upper Mississippi-Meramec (Loyola University Chicago 2013), and Upper Mississippi-Salt (Hilty 2015) drainages
• Indiana - Great Miami, Southeastern Lake Michigan, Upper Illinois, Western Lake Erie (Indiana Department of Natural Resources 1997), Lower Ohio, Lower Ohio-Salt, Southwestern Lake Michigan (Anonymous 2015), Patoka-White (Landers and Frey 1980), and Wabash (University of Connecticut 2011) drainages
• Iowa - Des Moines, Grand, Iowa, Missouri-Little Sioux, Missouri-Nishnabotna, Upper Mississippi-Maquoketa-Plum, and Upper Mississippi-Skunk-Wapsipinicon (Anonymous 2015) drainages
• Kansas - Big Blue (Jessica Howell, KS DWPT, pers. comm.), Kansas, Upper Cimarron (Jason Goeckler, KS DWPT, pers. comm.), Missouri-Nishnabotna, Smoky Hill (University of Kansas Biodiversity Institute 2008), Neosho, and Osage (Anonymous 2006) drainages
• Kentucky - Lower Cumberland, Lower Ohio-Salt, Middle Ohio-Little Miami (Beal and Thieret 1986), Big Sandy, Kentucky (Jeff Herod, US FWS, pers. comm.), Licking, Middle Ohio-Raccoon, Upper Cumberland (Anonymous 2015), and Lower Tennessee (Shearer 1994) drainages
• Louisiana - Lake Pontchartrain (Montz 1980), Atchafalaya-Vermillion, Big Cypress-Sulphur, Calcasieu-Mermentau, Central Louisiana Coastal, Lower Grand, Lower Mississippi-New Orleans, Red-Saline, Sabine (Anonymous 2015), and Lake Maurepas (Louisiana State University Herbarium 2010) drainages
• Maine - Salmon Lake (consists of Ellis Pond and McGrath Pond) in Kennebec drainage (Elliott 2008), and Lake Arrowhead in Saco drainage (Anonymous 2015)
• Maryland - Lower Susquehanna (Orth et al. 1993), Potomac, and Upper Chesapeake (Smithsonian Institution 2014) drainages
• Massachusetts - Connecticut Coastal (University of Alabama Biodiversity and Systematics 2007), Lower Connecticut (Lyman 1995), Massachusetts-Rhode Island Coastal, Merrimack (Crow and Hellquist 1983), and Saco (Hendricks 2010) drainages
• Michigan - Northeastern Lake Michigan, Northwestern Lake Huron, Northwestern Lake Michigan, Southeastern Lake Superior, St. Clair-Detroit, Wisconsin (Anonymous 2015), Lake Superior, Southcentral Lake Superior (Great Lakes Indian Fish and Wildlife Commission 2008), Saginaw (University of Connecticut 2011), Southeastern Lake Michigan (Nichols 1994), Southwestern Lake Huron (Trudeau 1982), and Western Lake Erie (Reznicek et al. 2011) drainages
• Minnesota - Lake Superior, Lower Red, Southwestern Lake Superior, Upper Red (Anonymous 2015), Minnesota, Mississippi Headwaters, St. Croix, St. Louis, Upper Mississippi-Black-Root (Minnesota DNR Exotic Species Program 2002), Rainy (University of Alabama Biodiversity and Systematics 2007), and Upper Mississippi-Crow-Rum (Lindstrom and Sandstrom 1939) drainages
• Mississippi - Davis Lake, Tombigbee National Forest in Black Warrior-Tombigbee drainage (Aurand 1982), and Lower Pascagoula River in Pascagoula drainage (Center for Invasive Species and Ecosystem Health 2015)
• Missouri - Gasconade, Osage, Upper Mississippi-Meramec, Upper White (Padgett 2001), Lower Missouri-Blackwater, St. Francis, and Upper Mississippi-Salt (Anonymous 2015) drainages
• Montana - Fort Peck Lake, Marias, Pend Oreille (Anonymous 2015), Milk, Missouri-Poplar (Parkinson et al. 2011), Missouri Headwaters (Center for Invasive Species and Ecosystem Health 2015), and Upper Missouri (Byron 2010) drainages
• Nebraska - Elkhorn (Martin 2015), Lower Platte (Anonymous 2015), and Middle Platte (Rolfsmeier et al. 1999) drainages
• Nevada - Black Rock Desert (Utah State University 2007), Carson (Center for Invasive Species and Ecosystem Health 2015), and Truckee (Gill and Unsicker 1996) drainages
• New Hampshire - Merrimack (Brooks 2013), Saco (Padgett and Crow 1993), and Upper Connecticut (Vermont Department of Environmental Conservation  Water Management Division 2011) drainages
• New Jersey - Lower Delaware, Lower Hudson, Mid Atlantic Coastal (Huckins 1955), and Upper Delaware (Schuyler 1989) drainages
• New Mexico - Rio Grande Closed Basins, Rio Grande-Elephant Butte, Upper Canadian, Upper Gila (Anonymous 2015), Upper Rio Grande (Charles Ashton, USACE, pers. comm.), and Upper San Juan (Colorado Parks and Wildlife 2014) drainages
• New York - Eastern Lake Erie, Long Island, Northeastern Lake Ontario, St. Lawrence, Upper Delaware (Scott Kishbaugh, NY DEC, pers. comm.), Allegheny (Eaton and Schrot 1987), Connecticut Coastal (University of Connecticut 2011), Lake Champlain-Richelieu River (Madsen et al. 1988), Lower Hudson (Titus 1994), Oswego (Mississippi Herbarium Consortium 2013), Southeastern Lake Ontario, Southwestern Lake Ontario (Mills et al. 1993), Upper Hudson (Trudeau 1982), and Upper Susquehanna (Darring Freshwater Institute 1999) drainages
• North Carolina - Albemarle-Chowan (Carter and Rybicki 1994), Pamlico (Anonymous 2015), and Roanoke (North Carolina Division of Water Resources 1996) drainages
• North Dakota - Leeds in Devils Lake-Sheyenne drainage (Anonymous 2015)
• Ohio - Great Miami, Middle Ohio-Raccoon, Muskingum, Southern Lake Erie, Upper Ohio-Beaver, Upper Ohio-Little Kanawha (Anonymous 2015), Middle Ohio-Little Miami, Scioto, and Western Lake Erie (Couch and Nelson 1985) drainages
• Oklahoma - Robert S. Kerr Reservoir, Upper Cimarron (Aurand 1983), Lower Canadian, Red-Little, Upper Beaver, Verdigris (Ellmore et al. 2015), Lower Cimarron, Lower North Canadian (Nelson and Couch 1985), Red-Lake Texoma, and Washita (Anonymous 2015) drainages
• Oregon - Deschutes (Many 2005), John Day, Southern Oregon Coastal (iMapInvasives 2012), Klamath, Middle Columbia, Northern Oregon Coastal, Willamette (Anonymous 2015), Lower Columbia, Lower Snake (Many 2007), and Middle Snake-Boise (WeedMapper Team Department of Rangeland Ecology & Managment 2005) drainages
• Pennsylvania - Allegheny, Eastern Lake Erie, Lower Delaware, Lower Susquehanna, Monongahela, Upper Ohio-Beaver, West Branch Susquehanna (Pennsylvania Flora Database 2011), Upper Delaware (Schuyler 1988), and Upper Susquehanna (Anderson 2009) drainages
• Rhode Island - Barney Pond in Massachusetts-Rhode Island Coastal drainage (State of Rhode Island Department of Environmental Management Office of Water Resources 2015)
• South Carolina - Lake Murray in Santee drainage (Steve de Kozlowski, SC DNR, pers. comm.), and Par Pond, Savannah River Site in Savannah drainage (Hill and Horn 1997)
• South Dakota - Big Sioux, Minnesota (Anonymous 2015), and Fort Randall Reservoir (many 2009) drainages
• Tennessee - French Broad-Holston (Anderson 2009), Lower Cumberland, Lower Tennessee, Upper Tennessee (Bates and Smith 1994), Middle Tennessee-Elk (David Webb, TVA Muscle Shoals, pers. comm.), Middle Tennessee-Hiwassee (Smith 1971), and Upper Cumberland (Simpson 1990) drainages
• Texas - Big Cypress-Sulphur, Brazos Headwaters, Lower Colorado, Middle Colorado-Concho (Anonymous 2015), Galveston Bay-Sabine Lake, Neches, San Bernard Coastal, Upper Trinity (Helton and Hartmann 1996), Guadalupe (Lemke 1989), Middle Colorado-Llano (Anderson 2009), Nueces (Missouri Botanical Garden 2007), Red-Little (Johnson et al. 1991), and Sabine (Couch and Nelson 1985) drainages
• Utah - Escalante Desert-Sevier Lake, Lower Colorado-Lake Mead (Utah State University 2007), Lower Bear, Weber (Utah Division of Wildlife Resources 2009), and Upper Colorado-Dirty Devil (Anonymous 2015) drainages
• Vermont - Lake Champlain-Richelieu River (Crow and Hellquist 1983), Lower Connecticut (Rosen 2006), St. Francois River, Upper Connecticut, and Upper Hudson (Crosson 1990) drainages
• Virginia - Albemarle-Chowan (Carter and Rybicki 1994), James, Roanoke (Wieboldt et al. 2015), Lower Chesapeake (Stevenson and Confer 1978), and Potomac (Mills et al. 1993) drainages
• Washington - Lower Snake (Hong-Wa 2000), Lower Columbia (Weinmann et al. 1984), Middle Columbia, Washington Coastal (Parsons 1996), Pend Oreille (WATER Environmental Services Inc 1987), Puget Sound (Walton 1996), Spokane, Willamette, Yakima (Anonymous 2015), and Upper Columbia (Falter et al. 1974) drainages
• West Virginia - Buffalo Creek Reservoir in Monongahela drainage (Anonymous 2015), and South Fork South Branch Potomac River in Potomac drainage (Center for Invasive Species and Ecosystem Health 2015)
• Wisconsin - Oswego, Upper Mississippi-Black-Root (Wisconsin Dept of Natural Resources 2008), Chippewa, Fox, Lake Superior, Northwestern Lake Michigan, Rock, Southcentral Lake Superior, Southwestern Lake Michigan, Southwestern Lake Superior, St. Croix, St. Louis, Upper Illinois (Anonymous 2015), Upper Mississippi-Maquoketa-Plum (Great Lakes Indian Fish and Wildlife Commission 2008), and Wisconsin (Anonymous 2007) drainages

M. spicatum is a perennial that flowers twice a year, typically mid-June and late-July, followed by autofragmentation of the plant after each flowering (Nichols 1975; Patten 1956). Myriophyllum spicatum dies back in the fall, but the root system can survive the winter (Perkins and Sytsma 1987; Titus and Adams 1979). These root crowns begin growing the following spring once water temperatures reach about 60°F (Smith and Barko 1990).

Unlike many aquatic plants, this species does not produce turions (dormant vegetative structures that survive the winter) (Patten 1954). Each plant is able to produce approximately 100 seeds per season, but this species is much more successful at vegetative reproduction via fragments and runners (Patten 1956). After flowering, this species can undergo auto-fragmentation; new roots at nodes along the stem, and then the plant will break of at these nodes (Gustafson and Adams 1973; Nichols 1975). Plant fragments can be transported via wind, waves, or by human activity (Kimbel 1982).

Stem fragments are important for the colonization of new habitats while local colony expansion occurs mainly by stolons (Aiken et al. 1979; Madsen et al. 1988). Water currents disseminate vegetative propagules through drainage areas, while motorboat traffic contributes to natural seasonal fragmentation and the distribution of fragments throughout lakes.

Transport on boating equipment plays the largest role in introducing fragments to new waterbodies. Road checks in Minnesota have found aquatic vegetation on 23% of all trailered watercraft inspected (Bratager 1996).

Summary of species impacts derived from literature review. Click on an icon to find out more...

Environmental	Socioeconomic	Beneficial

This species is tolerant of low water temperatures and begins to photosynthesize and grow early in the spring (IISCTC 2007, MISIN and MNFI 2013). This growth habit allows M. spicatum to reach the water’s surface before native plants and create a dense canopy to out-compete for sunlight and space (IL DNR 2009, Madsen et al. 1991, MISIN and MNFI 2013). This advantage allows Eurasian milfoil to form dense beds with stem densities in excess of 300/m2 in shallow water; essentially excluding other plant species (Aiken et al 1979). Although in small tank experiments the native northern watermilfoil (Myriophyllum sibiricum) appears competitively superior, in the field, however, M. spicatum has replaced M. sibiricum over much of the temperate range of this species in North America (Valley and Newman 1998). Suppression of native plant communities in the field can happen in only a few years (GLIFWC 2006).

Myriophyllum spicatum is capable of hybridizing with the native M. sibiricum to produce M. sibricum X spicatum which has an intermediate number of leaf segments between the two parent species (Reznicek et al. 2011). These hybrids have been found in Wisconsin (Moody and Les 2002, Ortenblad et al. 2006). Any hybrid of M. spicatum and a native milfoil could create a more aggressive species of invasive plant (Lui et al. 2010).

Keast (1984) found that stands of Eurasian watermilfoil in lakes in Ontario had reduced abundance and diversity of aquatic insects and other benthic macroinvertebrates compared to native communities. Keast (1984) also found that there were 3-4 times as many fish feeding in native plant communities than in beds of M. spicatum. Dense cover allows high survival rates of young fish; however, larger piscivorous fish lose foraging space and are less efficient at obtaining their prey (Lillie and Budd 1992). Madsen et al. (1995) found growth and vigor of a warm-water fishery reduced by dense Eurasian watermilfoil cover. Myriophyllum spicatum also has less value as a food source for waterfowl than the native plants it replaces (Aiken et al. 1979).

Large infestations of M. spicatum can also alter the hydrology of waterbodies and even create stagnant waters conditions (OISAP 2013). Altered hydrology can result in decreased dissolved oxygen levels and it can alter temperature and pH of the surrounding water (Engel 1995, GLIFWC 2006, Jacobs and Margold 2009). Myriophyllum spicatum communities also impact nutrient cycling by uptaking phosphorus from the sediments and releasing them during fall senescence; which could contribute to eutrophication of ponds and lakes (GLIFWC 2006, Jacobs and Margold 2009).

Myriophyllum spicatum populations and stagnant water also create habitat for the parasites that cause swimmer’s itch and mosquitoes (Jacobs and Margold 2009, OISAP 2013).

Potential:
In lab experiments, polyphenolic allelochemicals taken from M. spicatum, inhibited the growth of green algae and cyanobacteria; such as Microcystis aeruginosa (Leu et al. 2002, Nakai et al. 2012). In studies in Finland, chemicals secreted by M. spicatum caused high mortality (73% to 89%) of the mysids Neomysis integer and Praunus flexuosus (Lindén and Lethiniemi 2005).

Myriophyllum spicatum has a high socio-economic impact in the Great Lakes.
Realized
Property owners, lake associations, and local governments incur costs to keep boat channels clear and the disposal of M. spicatum (Bowen 2010). Waterfront property owners in Michigan spend an estimate $20 million annually to control aquatic invasive plants—primarily Eurasian watermilfoil and curly lead pondweed ( Michigan Sea Grant Coastal Program 2007). In New York, annual costs of control of Eurasian watermilfoil are estimated at $500,000 (Johnson and Blossey 2003).

Even with control efforts, large infestations of M. spicatum can severely limit recreational activities such as boating, fishing, swimming, and/or waterfowl hunting (IL DNR 2009, Jensen 2010). Long stems can get tangled around boat propellers and may cause damage (IL EPA 1996). Large populations of Eurasian watermilfoil are often found to be aesthetically unpleasant (IL DNR 2009). Diminished recreational uses can lead to lost tourism revenue. It is estimated that Eurasian watermilfoil costs Michigan millions of dollars annually in lost tourism revenue (Michigan Sea Grant 2012).

Dense mats of M. spicatum can reduce water flow or clog agricultural, residential, industrial, and/or power plant water intakes; removal from these structures can be expensive (IL DNR 2009, Jacobs and Margold 2009).

Potential:
Given the reduction in recreational access and aesthetics associated with large, obstructive populations of M. spicatum, the values of nearby property could decline (Bowen 2010, IL DNR 2009). According to an economic study conducted in New Hampshire, the value of property adjacent to waterbodies with large submerged aquatic plants was reduced by 15% or more (Halstead et al. 2003 in RICRMC 2007).

Myriophyllum spicatum has a moderate beneficial effect in the Great Lakes.
Realized:
Myrophyllum spicatum is one of the few species that is capable of shading out the invasive curly pondweed, Potamogeton crispus (Aiken et al. 1979). Myriophyllum spicatum is also known to inhibit the growth of cyanobacteria; which are responsible for causing harmful algal blooms (Nakai et al 2012).

Freshwater crustaceans and bass can utilize stands of M. spicatum for habitat and cover (Jacobs and Mangold 2009). Dense mats of Eurasian watermilfoil can support the weight of frogs and wading birds (Aiken et al. 1979).

Eurasian watermilfoil can grow in adverse conditions (high nutrients/pollution or high traffic areas) that native submerged species cannot tolerate (Benson et al. 2004, GLIFWC 2006). 

Potential: 
If concentrations of nitrate are high, M. spicatum can absorb nitrogen from the sediments or the water (Best and Mantai 1978). This ability could help improve water quality for those waterbodies affected by fertilizer runoff. Myriophyllum spicatum is able to take up moderate amounts of cadmium, zinc, copper, lead, and selenium from its environment and store it in its leaves (Fawzy et al. 2012, Mechora et al. 2013). This species could be used in remediation efforts where the plants are grown in contaminated water and harvested before the leaves can break down and release the contaminants.

Myriophyllum spicatum is a prohibited species in Illinois and Michigan; its hybrids and variants are also prohibited in Minnesota and Wisconsin (GLPANS 2008). In Michigan, a person cannot knowingly possess a live organism (Latimore et al. 2011). In Minnesota, it is illegal to possess, import, purchase, sell, propagate, transport or introduce Eurasian watermilfoil (Invasive Species Program 2011).

The Great Lakes Indian Fish & Wildlife Commission listed this species as a “high priority” for control within their ceded territories (Falck et al. 2012).

Note: Check federal, state/provincial, and local regulations for the most up-to-date information.

Control
Due to decades of university, state and federal research and experience with Myriophyllum spicatum in the U.S. and Canada, several methods have been developed to help in its management.

The best way to minimize the spread of Myriophyllum spicatum is to remove any visible plant fragments and rinse all equipment; allow them to dry completely before using them in another waterbody (IL DNR 2009).

Biological
Since 1963, the grass carp, Ctenopharyngodon idella has been released to suppress Eurasian watermilfoil and other nuisance aquatic plants in numerous sites within North America (CEH 2004, Julien and Griffiths 1998). It has been found that grass carp may only eat Eurasian watermilfoil after native plants have been consumed (IL DNR 2009). To achieve control of Eurasian watermilfoil generally means the total removal of more palatable native aquatic species before the grass carp will consume Eurasian watermilfoil. In situations where Eurasian watermilfoil is the only aquatic plant species in the lake, this may be acceptable. However, generally grass carp are not recommended for Eurasian watermilfoil control (Washington State Department of Ecology 2013).

Laboratory research has shown that the fungus Mycoleptodiscus terrestris reduces the biomass of M. spicatum significantly and may be a possible biocontrol agent (IL DNR 2009).

A North American weevil, Euhrychiopsis lecotie, may be associated with natural declines at northern lakes (Creed Jr. and Sheldon 1995, Sheldon 1994). Euhrychiopsis lecotei feeds on the new growth of M. spicatum and can help keep populations under control; it is common for the populations of for E. lecotei and M. spicatum to exhibit the classic predator-prey cycles (Creed Jr. and Sheldon 1995, Michigan Sea Grant 2012). Studies have found the herbivorous weevil to cause significant damage to Eurasian water-milfoil while having little impact on native species, suggesting the insect as a potential biocontrol agent (Creed Jr. and Sheldon 1995). Female weevils have great fecundity when raised the on M. spicatum as opposed to native M. sibiricum (Sheldon and Jones 2001, TNC Vermont 1998, Creed 1998, Solarz and Newman 1996).

Physical
Because this plant spreads readily through fragmentation, mechanical controls such as cutting, harvesting, and rotovation (underwater rototilling) should be used only when the extent of the infestation is such that all available niches have been filled. Using mechanical controls while the plant is still invading, will tend to enhance its rate of spread.

Mechanical harvesting has been widely used in the Midwest (RICRMC 2007). Small populations of Eurasian watermilfoil, such as those around docks or in swimming areas, can be removed by hand-pulling and/or the use of a sturdy handrake (Bargeron et al. 2003) Multiple harvests within the same growing season will yield the best results (Bargeron et al. 2003). If multiple harvests are not possible, the single harvest should happen before peak biomass, in early summer, otherwise regrowth will occur (Bargeron et al. 2003, WI DNR 2012). Large equipment exists to mechanically remove milfoil in larger areas (Bargeron et al. 2003). Dredging is also effective method of removal (CEH 2004). Care should be taken to remove all fragments to prevent regrowth or deoxygenation from plant decomposition (CEH 2004, MISIN and MNFI 2013). Plant fragments can be disposed of by burning, burying, composting (away from the water), or by trash disposal (IL DNR 2009). In Okanagan Lake, British Columbia, authorities have apparently successfully experimented with management by simultaneously rototilling plants and roots and underwater vacuuming (Newroth 1988).

Where possible, Eurasian watermilfoil can be drowned or dehydrated by water level manipulation (Bargeron et al. 2003, WI DNR 2012, Bates et al. 1985). Water drawdowns are most effective when the plants are exposed to several weeks of drying time and root crowns are exposed to sub-freezing temperatures (IL DNR 2009). This method could have serious effects on other aquatic life (IL DNR 2009).
Water level manipulation is often used conjunction with herbicides and/or shade barriers (Bargeron et al. 2003, Swearingen et al. 2002). Localized control (in swimming areas and around docks) can be achieved by covering the sediment with an opaque fabric which blocks light from the plants (bottom barriers or screens).
Myriophyllum spicatum is also susceptible to ultrasound pulses and this could prove to be a more selective physical method of control (USACE 2011c).

Chemical
Numerous chemicals will have an effect on M. spicatum: amine salts of endothall, and dipotassium salts of endothall, diquat dibromide, copper, and carfentrazone (RICRMC 2007, Water Bureau 2005).

The amine formulations of 2,4-D granules are effective on controlling Eurasian watermilfoil and will not damage grasses (IL DNR 2009, Lembi 2003, Water Bureau 2005). The liquid formulation of 2,4-D can be used in ponds and lakes at concentrations less than 2.0 parts per million (Bargeron et al. 2003). This herbicide method is not appropriate for large unmanageable areas of milfoil (Bargeron et al. 2003).

One lose-dose application (10 µg/ L) of fluridone applied in the early stages of growth can result in season long control of Eurasian watermilfoil (USACE 2011a, Water Bureau 2005,WI DNR 2012). This application rate resulted in >93% control for a year post-treatment in 7 out of 8 test lakes in Michigan (USACE 2011a). However, the Minnesota Department of Natural Resources found that the application rate of 10 parts per billions would cause unavoidable damage to native vegetation (Welling 2013).

Liquid triclopyr will provide effective control of Eurasian watermilfoil and is safe to use around grasses and cattails (IL DNR 2009, Lembi 2003). A concentration of 0.75 parts per million of triclopyr was used to control Eurasian watermilfoil in Loon Lake, New York (Miller 2013).

Note: Check state/provincial and local regulations for the most up-to-date information regarding permits for control methods. Follow all label instructions.

Hybridization was documented between M. spicatum and M. sibiricum [Myriophyllum spicatum X sibiricum] in Idaho, Michigan, Minnesota, Wisconsin, and Washington (Moody and Les 2002; Moody and Les 2007). The hybrid must be determined by molecular analysis, as morphology is indistinguishable from both parent species.

The occurrence of sixteen species including Potamogeton illinoensis and Potamogeton pectinatus may be indicaters of conditions suitable for Eurasian water-milfoil invasion. Searching areas colonized by these species may provide early detection, the best method for preventing new invasion (Nichols and Buchan 1997).