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Ecology and Management of Eurasian Watermilfoil (Myriophyllum spicatum L.)
Invasive Species Technical Note Number MT-23
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Invasive Species Technical Note Number MT-23
(PDF; 117 KB)
February 2009By Jim Jacobs, Plant Materials Specialist, NRCS, Bozeman, Montana
Jane Mangold, Montana State University Extension Invasive Plant Specialist
Abstract
Eurasian watermilfoil is a submersed aquatic forb with branching stems
growing two to 21 feet (0.5 - 7 meters) long and supporting whorls of featherlike
leaves (see Figure 1). The pink inflorescence is a terminal spike two to eight
inches long. Watermilfoil reproduces by seed and vegetative fragments, but
colonization of new sites is mainly by vegetative fragments. It flourishes in
eutrophic (low levels of dissolved oxygen, high levels of organic matter) lakes
and waterways. Plants commonly grow in water three to 12 feet (0.5 - 3 meters) deep
and form tangled weed beds that can competitively displace submerged plant
communities in two to three years. Dense beds reduce recreational qualities of
water bodies, reduce water flow, create favorable habitat for mosquitoes, and
clog industrial, agricultural, and drinking water supplies. Eurasian watermilfoil was first reported in Montana in Noxon Reservoir (Sanders County)
in 2007. It is a Category 3 noxious weed. Water recreationalists are the
predominant vector of long distance spread of Eurasian watermilfoil. However,
waterfowl can also carry vegetative fragments from one lake to another.
Figure 1. Eurasian watermilfoil stems and leaves. Photo by Alison Fox,
University of Florida, available from Bugwood.org.
Early detection and immediate action to contain and eradicate infestations
are the most important management actions for Eurasian watermilfoil in Montana.
If you find a new infestation, you should save a specimen and report the
infestation as soon as possible to your county Extension Agent or the
Montana
Department of Fish, Wildlife and Parks.
It is highly susceptible to 2, 4-D. Repeated mechanical harvests may reduce stem
densities. In reservoirs, water drawdowns during cold weather have reduced
infestations. Larvae of the European moth Acentria ephemerella, and the native
weevil Euhrychiopsis lecontei, are associated with plant declines.
Plant Biology
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Technical Notes
Last Modified:
02/13/2009
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