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(Myriophyllum spicatum) is an exotic species most likely introduced
in the United Sates by the aquarium industry. It is considered one
of the most aggressive and problematic plants in the U.S. because
of the dense colonies which it forms. Eurasian Water Milfoil is a
major nuisance aquatic plant in the US and southern Canada.
Dense stands of Eurasian water milfoil
inhibit recreational uses like swimming, boating, and fishing. Some
stands have been dense enough to obstruct industrial and power
generation water intakes. Eurasian water milfoil competes
aggressively to displace and reduce the diversity of native aquatic
The visual impact that greets
the lake user on milfoil-dominated lakes is the flat yellow-green
of matted vegetation, often prompting the perception that the lake
is "infested" or "dead".
Cycling of nutrients from sediments to the water column by
Eurasian water milfoil may lead to deteriorating water quality and
Eurasian watermilfoil has less value as a food source for
waterfowl than the native plants it replaces (Aiken et al. 1979).
Dense cover allows high survival rates of young fish; however,
larger predator fish lose foraging space and are less efficient at
obtaining their prey thereby reducing the growth and vigor of
Eurasian watermilfoil is recognized primarily by its
whorls of four (number can vary from 3 - 5) feather-like leaves
around the stems.
Each leaf is divided into many thread-like leaflets
extending from a central rib (see leaf detail). Each leaf is finely
divided into paired thread-like leaflets of about the same
length. There are typically 12 to 21 pairs of leaflets per
The stems of Eurasian Water Milfoil plants are weak,
appearing limp when removed from the water. Each stem can grow to
7' or more. The number of stems per plant increases as the plant
ages. Each individual stem branches several times as it nears the
water surface, creating a dense floating mat over the surface of
Reddish flowers on leafless spikes form in mid to late
season and may extend above the water surface. Dense Eurasian
watermilfoil beds usually occur in water between 3 and 20 feet
deep. The tops of the milfoil plants, both stems and leaves,
often turn red in color. Eurasian water milfoil can
spread by seeds and fragmentation.
Eurasian watermilfoil typically has 12 to 21 pairs of leaflets.
The native northern watermilfoil, with which it is often confused,
usually has 5 to 9 pairs.
A. Once water temperatures are
around sixty degrees or warmer and the plants are viable.
Unfortunately, EWM arrives sooner in the spring and stays longer
than our native plants thus the control window is longer.
A. This varies with EWM depending
upon adjacent influences and control products. On average, two
applications per season. Your treatment site results will
establish their own history and hence the future
predictability. Keeping good records of your application will
expedite any tailoring that need to be done. Remember, we are here
A. Generally within ten to sixteen days things will be cleared
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