2008 Statewide Strategic Plan for Eurasian Watermilfoil in Idaho

I. Introduction
In April 2006 the Idaho State Legislature and the Governor approved $4 million for
the purpose of eradication of Eurasian watermilfoil (Myriophyllum spicatum) from
water bodies in the state of Idaho. In 2007, an additional $4 million was
appropriated for this program, which is administered by the Idaho State
Department of Agriculture (ISDA). Although Idaho is a leader in the field of
terrestrial plant management, pioneering the Cooperative Weed Management
Area (CWMA) strategy, the state had never before administered a major aquatic
plant control program.
This document is intended to provide a framework and strategy for the State of
Idaho and its cooperators. Information included herein is considered “the state of
knowledge” in Eurasian watermilfoil management. It will be updated annually
through the Idaho Invasive Species Council (IISC). Much of the information
included was taken directly from professional organizations such as the Western
Aquatic Plant Management Society (WAPMS) and the Aquatic Ecosystem
Restoration Foundation (AERF), and is noted as such.
II. Problem Statement
Eurasian watermilfoil is a
submersed perennial aquatic
plant. It adversely impacts
aquatic ecosystems by filling the
water column and forming
dense canopies that shade out
native aquatic vegetation
(Figure 1). Eurasian watermilfoil
is adaptable, able to survive in a
variety of environmental
conditions. It grows in still to
flowing waters, can tolerate
relatively high salinities, can
tolerate a wide range of pH
Figure 1. Eurasian watermilfoil infestation levels, grows rooted in water
depths from 1 to 10 meters, and
can survive under ice. This species regenerates readily from plant fragments
which are easily transported to uninfested water bodies on boats and boat trailers.
Pure stands of Eurasian watermilfoil provide poor habitat for waterfowl, fish, and
other wildlife. Significant plant sloughing, leaf turnover, and decomposition of large
amounts of plant material at the end of the growing season increase phosphorus
and nitrogen in the water column. Dense Eurasian watermilfoil mats alter water
quality by raising the pH, decreasing oxygen under the mats, and increasing
temperature.
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