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MYRIOPHYLLUM SPICATUM L.
Eurasian water-milfoil; spike water-milfoil
Haloragaceae/Water-milfoil Family

pronounced: mirio-file-um / spi-ka-tum
from: myrios (G.): numberless
phyllon (G.): leaf
spica (L.): spike
"a plant with many leaf divisions, and a spike of flowers"
How Eurasian Milfoil Got Here

There are about 40 species of Myriophyllum in the world. Some opinions believe that Myriophyllum spicatum, Eurasian water-milfoil, originated in Eurasia (Europe & west Asia) while others believe it came from northern Africa. Never-the-less, it is here in the upper Midwest, and likely your lake. More broadly, it occurs in Europe, Asia, India, Japan, Canada and the U.S.

Eurasian water-milfoil was probably intentionally introduced, possibly by federal authorities, into the U.S. and was first found in 1942 in Washington, D.C. (Couch & Nelson 1985); or the plant was introduced in the late 1800s, possibly in ship ballast, in the Chesapeake Bay area (Aiken et al. 1979). Its geographical spread may have enhanced as a packing material for worms sold to fishermen in Oklahoma (Couch & Nelson 1985). It was first observed in Ontario in the 1960s and found in Wisconsin in the late '60s. It is now found in thousands of lake across the U.S. Eurasian water-milfoil is not on the U.S. Federal Noxious Weed List; it continues to be sold through aquarium supply dealers and over the Internet.

--Couch R, Nelson E. 1985. Myriophyllum spicatum in North America. In: Anderson LWJ, ed., First International Symposium on Watermilfoil and Related Haloragaceae Species, 23-24 July 1985, Vancouver, BC. Aquatic Plant Management Society, Vicksburg, MS.
--Aiken SG, Newroth PR, Wile I. 1979. The biology of Canadian weeds. 34. Myriophyllum spicatum L. Canadian J. Plant Sci. 59:201-215.
Eurasian milfoil is one of the most invasive water plants known.
One reason for this is that Eurasian Milfoil can re-generate from small pieces of the parent plant. These fragments then re-root and worsen the spread to other areas.

To make matters worse, this Milfoil has an apical meristem (active growth zone that make the plant grow straight up) and when the meristem is cut off the plant gets more bushy. Thus, cutting (e.g., mechanical harvesting, boats) without removal can actually increase its density in the impacted area. Every
gardener understands that when a bush gets cut, it grows more bushy. Moreover, removal of Milfoil fragments after cutting is never complete or even close to complete. Anyone suggesting that mechanical harvesting and removal is effective should be questioned about their view. Cutting also removes natural predators of Eurasian Milfoil, like the Milfoil Weevil, which also exacerbates the problem. Weed harvesters are a short term solution. Experience acquired on many lakes has shown that the actual density of milfoil doesn’t decrease with this technique.

Registered aquatic herbicides such as endothall, 2,4-D and fluridone do provide temporary control of Eurasian milfoil, but efforts to eradicate the plant "are rarely, if ever, likely to succeed" (Smith CG, Barko JW. 1990. Ecology of Eurasian watermilfoil. Journal of Aquatic Plant Management 28:55-64). Chemical herbicides are highly controversial due to their potential ecosystem impact and human health issues.

Eurasian milfoil is a submersed, rooted, perennial herb. Consisting of long underwater stems that branch and produce many whorled, finely divided leaves upon nearing the surface. Leaflets are uniformly tapered so that the leaf shape is more like an equilateral triangle with a curved base. Leaflets stand at acute angles (less than 45 degrees) to the rachis and are parallel to each other (Ceska 1985). Leaves are divided in to threadlike leaflets, usually in pairs of more than 14 (Nichols 1975).

Other Species:
Myriophyllum spicatum might be confused with a number of other submersed plants, including other water-milfoils and other submersed plants.

Native northern milfoil (Myriophyllum sibiricum):  has fewer than 12 leaf segments on each side of the leaf axis, whereas Eurasian water-milfoil leaves have 14 or more leaf segments on each side of the leaf axis; and has somewhat stouter stems than does Eurasian milfoil. M. spicatum is distinguished from the native M. sibiricum primarily by the overall shape of the leaf and then by the number of leaflets.  Meanwhile, M. sibiricum has basal leaflets that are as long as the leaf. They curve over and extend almost to the top of the leaf, forming a more feathery shape.

Native coontail (Ceratophyllum demersum): leaves are toothed and the plant feels rough when pulled through the hand, whereas Eurasian milfoil leaves are not toothed and the plant does not feel rough. Its leaves are in whorls with each leaf having a distinct fork in it.

--Ceska, O. and A. Ceska. 1985. Myriophyllum Haloragaceae species in British Columbia: problems with identification. Pp. 39-50 in: L.W.J. Anderson [ed.] Proceedings of the First International Symposium on Watermilfoil (Myriophyllum spicatum and related Haloragaceae species. Aquatic Plant Management Society, Vicksburg, Mississippi.
--Nichols, S. A. 1975. Identification and management of Eurasian Water Milfoil in Wisconsin. Wisconsin Academy of Sciences, Arts and Letters 63:116-126.

Eurasian milfoil appears to prefer lakes, ponds and slow-moving rivers and to a lessor extent it can grow in fast-moving water. It tolerates a range of water conditions, including spring water and even estuary brackish water of tidal creeks and bays. Eurasian milfoil is winter-hardy, able to overwinter in frozen lakes and ponds in northern states and Canada.

Milfoil reproduces extremely rapidly and can infest an entire lake within two years of introduction to the system.  Milfoil also starts spring growth sooner than native aquatic plants and can shade out these beneficial plants. When milfoil invades new territory, typically the species diversity of aquatic plants declines.


Identification
Milfoil Growth

Eurasian milfoil exhibits an annual pattern of growth. In the spring, shoots begin to grow rapidly as water temperatures approach 15 degrees centigrade. When they near the surface, shoots branch profusely, forming a dense canopy. The leaves below 1 meter senesce in response to self-shading. Typically, plants flower upon reaching the surface (usually in mid to late July). After flowering, plant biomass declines as the result of the fragmentation of stems. Plant biomass may increase again later in the growing season and a second flowering may occur. During fall, plants die back to the root crowns, which sprout again in the spring. In some areas Eurasian watermilfoil overwinters in its leafy form.

Reproduction

Eurasian milfoil can potentially spread by both sexually and vegetatively (asexual). Vegetative spread is considered the major method of reproduction. In some lakes a young population of Eurasian milfoil can average around 100 seeds per stalk. Eurasian milfoil seeds readily germinate in the laboratory. Despite the high seed production, it is thought that germination of seed is not a significant factor in Eurasian milfoil reproduction. Colonization of new sites is mainly by vegetative fragments.

Fragments are produced by wind and wave action, boating activities, and mechanical harvesting -- with each fragment having the potential to develop into a new plant. For this reason, once introduced, Eurasian milfoil may spread rapidly. During the growing season, the plant also undergoes autofragmentation.
Myriophyllum spicatum
Eurasian milfoil, Myriophyllum spicatum
Myriophyllum spicatum
Eurasian Milfoil
Myriophyllum sibiricum
Northern Milfoil (native)
Ceratophyllum demersum
Coontail (native)