Appendix
B - A Citizen's
Manual for Developing Integrated Aquatic Vegetation Management Plans
INVASIVE, NON-NATIVE
AQUATIC PLANT FACT SHEETS
Introduction: Correct identification of aquatic plants is important.
Control strategies that are effective on one may not be effective on another. The
following fact sheets will help in identifying the most common nuisance aquatic plants.
Only
a few aquatic plants create nuisance conditions in Washington. Usually there are key
features that easily differentiate aquatic plant species, but in some cases plants require
careful scrutiny for correct identification. Hydrilla, Brazilian elodea, and common
elodea, which are plants of concern in Washington State, are perhaps the most difficult
species to correctly identify. The importance of accurate identification is aptly
illustrated by this trio of plants. Hydrilla is one of the most damaging of the aquatic
plants. It is present in only one lake system in Washington, so early detection is
important. Care must be taken not to mistake Hydrilla for one of the other plants in the
trio because it requires special, rapid action to control its spread. Brazilian elodea is
a common nuisance aquatic weed in Washington, while common elodea is a native species. If
in doubt–call an expert!
Myriophyllum
(milfoil) species may also require careful observation for correct identification. There
are two weedy milfoils in Washington: Eurasian watermilfoil and Parrotfeather.
Parrotfeather has distinctive emergent leaves, while Eurasian watermilfoil and the native
milfoils are mostly submersed (except for the flower stalks). In addition to the native
milfoils, several other aquatic plants are commonly mistaken for Eurasian watermilfoil.
Plants are amazingly
adaptable organisms. Since they are usually rooted and can't move around to search out
hospitable environments like animals do, plants adjust their growth to match the
environment that they find themselves in. The form of an aquatic plant, like all plants,
is determined by an intricate interaction between its environment and biology. Photos and
drawings cannot convey the rich variation possible as individual plants respond to their
unique environment. The illustrations shown here represent the general features of the
plant. The plants you find in your lake should be compared to the illustrations with
special consideration of the key features mentioned in the text. If identification is in
doubt contact an expert (see Appendix F for a list of people who can answer your questions).
Eurasian watermilfoil (Myriophyllum spicatum L. )
Description: Milfoil has finely dissected leaves that form in whorls of four on
the stem. Milfoil leaves fall off as they age, so occasionally you may find less than four
leaves in a whorl, especially near the bottom of the plant. Leaves near the surface are
often a reddish or brown color. Eurasian watermilfoil generally has 12-16 pairs of
leaflets on each leaf. It's often difficult to separate Eurasian watermilfoil from its
native cousins: northern watermilfoil and whorled watermilfoil. Calling an expert at
Ecology may be the best way to positively identify your milfoil.
Growth Habit:
Eurasian watermilfoil is the culprit in many nuisance aquatic plant cases in Washington.
It has been the subject of much research, and its growth habits are well known. Milfoil
overwinters as short bright green stems from a few inches to a few feet long - rooted in
the sediments. Milfoil stores energy and nutrients in its roots over the winter. In early
spring, plants grow rapidly to the surface where they can form a mat or canopy of
branches. Rapid spring growth and canopy formation allows milfoil to outgrow and shade out
other, more desirable native plants.
Propagation: Milfoil
is spread primarily by stem fragments. Fragments are formed when pieces of the plant are
cut off of the main plant body, such as by a boat propeller or during harvesting
operations. These stems fragments can root and produce new plants. Milfoil also fragments
naturally. In the late summer, the stems of milfoil become quite brittle and roots begin
to form on the stem. Wave action or a duck paddling though a milfoil bed can cause stems
to break.
Control: Prevention of Eurasian watermilfoil invasion requires control of fragment
spread. Some management techniques, harvesting for example, can create fragments and
contribute to the spread of milfoil. Milfoil is susceptible to several herbicides,
including endothall and fluridone. With the proper herbicide and application rate, milfoil
can be selectively removed from an
aquatic system, leaving more desirable aquatic plant species. Other intensive methods,
such as bottom barrier placement and diver-dredging are effective against small-scale
infestations of milfoil. Milfoil is relatively unpalatable and is low on the grass carp
preference scale. Other biological controls of milfoil are under intensive investigation.
Key
features:
12 to 16 leaflets on
each leaf
Emergent flower
stalks sometimes are present during the summer
Milfoil
leaflets look like feathers
No emergent
leaves
Leaves near
surface may be reddish or brown
Parrotfeather (Myriophyllum
aquaticum (Vell.) Verdc.)
Description: Parrotfeather
has both emergent and submersed leaves. The submersed leaves are finely-dissected, and
feathery, often with a reddish color. The submersed growth form of parrotfeather is easily
mistaken for Eurasian watermilfoil (Myriophyllum spicatum L.). The emergent stems
can be from a few inches to over a foot high and are the most distinctive feature of
parrotfeather. Emergent leaves form in whorls on the stem. Leaves are bright green and
finely divided. In spring, very small, white, tuft-like flowers form where the emergent
leaves attach to the stem.
Growth Habit: Parrotfeather
grows best when rooted in shallow water. In nutrient-enriched lakes parrotfeather can grow
as a floating plant in deep water. The emergent stems can survive on wet banks of rivers
and lake shores, so it is well adapted to moderate water level fluctuations. Parrotfeather
invasion of lakes and streams severely changes the physical and chemical characteristics
of the aquatic ecosystem. The emergent stems shade the water column eliminating algae
growth, which is the basis of the aquatic food web. Parrotfeather is also excellent
habitat for mosquito larvae.
Propagation: Parrotfeather
spreads only by plant fragments. All the parrotfeather plants in Washington are female. In
fact, there are no male plants anywhere outside of its native range in South America.
Consequently, there is no sexual reproduction and no seeds are formed. Parrotfeather
rhizomes are quite tough and can be transported long distances on boat trailers.
Parrotfeather's attractive green foliage make it a popular aquascaping plant, which has
contributed to its spread.
Control: Parrotfeather has a
high tannin content, which makes it unpalatable for most grazers, including grass carp.
Parrotfeather is sensitive to many herbicides, but a thick cuticle, which forms a waxy
cover on the emergent leaves, hampers aerial application of herbicides. Research has shown
that parrotfeather growing in water deeper than about 20 inches may be particularly
sensitive to reduction in phosphorus concentrations in the water column.
Key features:
- Bright green, christmas-tree like emergent
stems
- Dense mat of intertwined rhizomes in
the water with abundant, long roots
- Reddish feathery-leaved, very limp
submersed leaves may be present
Brazilian elodea (Egeria
densa Planch. )
Description:
Brazilian elodea is often confused with Hydrilla and Common elodea. Since Common elodea is
a native species and Hydrilla an extremely aggressive invader, it is important that the
plants be correctly identified. Common elodea has three leaves per whorl, Brazilian elodea
four (sometimes eight) leaves per whorl, and Hydrilla five leaves per whorl. Common elodea
leaves are usually less than 1/2 inch long and about 1/4 inch wide.
Brazilian elodea leaves are greater than 1/2 inch long and less than 1/4
inch wide. Hydrilla has small "prickle hairs" on the leaf edges and spines on
the midvein of the leaf that gives the plants a rough feeling. Hydrilla also forms small (1/4
to 1/2 inch long) tubers in the sediment, which are not formed by the other two
species. Brazilian elodea has three-petaled, white flowers, less than an inch in diameter,
that float on the water surface.
Growth Habit:
Brazilian elodea is rooted in the sediment and grows rapidly in the spring, forming a
canopy of intertwined stems at the surface that shades out native aquatic plants. It is a
popular aquarium plant, once commonly sold in tropical fish stores, but no longer legally
for sale in Washington. The characteristics that make Brazilian elodea a popular aquarium
plant: rapid growth under low light levels, easy propagation, and tolerance of a wide
range of water and sediment types, also makes it a nuisance aquatic plant. when it escapes
and grows in lakes and streams.
Propagation: Plant
fragments are the primary mode of spread of Brazilian elodea. Fragments are formed when
pieces of the plant are cut off of the main plant body, such as by a boat propeller or
during harvesting operations. These stems fragments can root and produce new plants.
Control: As with
other aquatic plants that are spread by stem fragments, prevention of Brazilian elodea
fragment spread is critical to preventing the invasion of new lakes. Some management
techniques, harvesting for example, can create fragments and contribute to the spread of
Brazilian elodea. Once established, Brazilian elodea can be controlled by several
herbicides and appears to be a preferred species grazed by grass carp. Other methods, such
as bottom barrier placement and diver-dredging are effective against small-scale
infestations of Brazilian elodea.
 Key features:
Submersed, sometimes
with white floating flowers
Leaves in whorls of
four or eight
Leaves greater than
one-half inch long and less than one-quarter inch wide
No tubers attached to
roots in sediment
Hydrilla (Hydrilla
verticillata (L.F.) Royle)
Description:
Hydrilla closely resembles its cousins Brazilian elodea (Egeria densa) and common
elodea (Elodea canadensis), both widespread in Washington. The primary
distinguishing feature of Hydrilla is the presence of tubers that form on the roots.
Tubers are small potato-like structures 1/4 to 1/2 inch long. Hydrilla also has small prickles on its leaves that give the
plant a rough feel. Hydrilla typically has 3 to 8 leaves in a whorl around the stem that
are 1/10 to to
1/8 inch wide and inch wide and
1/4 to
to 3/4 inches long. Hydrilla also forms turions
(small, hard buds) on the stem and has small (1/2 inch diameter) white, floating flowers. inch diameter) white, floating flowers.
Growth Habit:
Hydrilla is a submersed plant that is rooted in the sediment. Hydrilla is probably the
most troublesome submersed aquatic plant in North America. It grows rapidly under very low
light levels, in a variety of aquatic habitats from static to flowing water and at depths
from an inch to 50 feet. The stem branches in the upper parts of the water column, forming
a canopy that inhibits growth of native species and interferes with recreational use of
lakes.
Propagation:
Hydrilla has three primary means of spread: Stem fragments, tubers, and turions. Stem
fragments are formed by harvesting operations and by boat props. Each stem piece can root
and form a new plant. Tubers form on the roots in the sediment, and turions form on the
stem in the water column. Tubers are produced in the sediment by the thousands, and sprout
in the spring. Turions are smaller and are easily carried by water currents, providing a
mechanism for long distance transport. Some strains of Hydrilla can set very small seeds.
Control: Hydrilla is
found in one lake system in western Washington where an eradication program has been
underway since 1995. Tubers and turions complicate control strategies. There is currently
no technique, short of dredging, to remove tubers from the sediment once they are formed.
Herbicide treatm ents can kill vegetative parts of the plant but do not affect the tubers.
Therefore repeated herbicide treatments are needed to eradicate hydrilla from a lake.
Grass carp will readily eat leaves and stems of Hydrilla, but do not eat the tubers. No biocontrol agent has been found that can
effectively attack tubers in areas with even mild winters.
Key
features:
Fanwort (Cabomba
caroliniana Gray)
Description: Fanwort
has distinctive fan-shaped submersed leaves arranged in pairs on the stem. In the water,
fanwort has a "tubular" look because leaves are quite dense on the stem and
there is little branching. Submersed leaves resemble those of water buttercup (Ranunculus
aquatilus). Buttercup leaves, however, are arranged alternately (one per node) on the
stem. Distinctive, but small, floating leaves may also be present. Floating leaves are
long (less than one-half inch) and narrow (less than one-quarter inch). The stem attaches
to the floating leaf blade at the center where there is a slight constriction. Small (less
than one-half inch diameter), white flowers float on the water surface.
Growth Habit:
Fanwort is a rooted aquatic plant with a limited distribution in the Northwest. In
Washington it is restricted to side-channels of the Columbia River near Longview. In
contrast to other rooted aquatic plants, fanwort is reported to obtain nutrients important
for growth from the water column rather than the sediment. Fanwort has been in Cullaby
Lake, on the north coast of Oregon, for at least 10 years where it creates severe nuisance
conditions. Fanwort is a serious aquatic weed as far north as upstate New York and
Michigan. It clearly has the ability to grow and create serious weed
problems in Washington.
Propagation: Like
many problem aquatic plants, fanwort can regenerate from small stem fragments. Fanwort
stems become brittle in late summer, which causes the plant to break apart, facilitating
distribution and invasion of new water bodies. Fanwort is self-pollinating in the South
and seeds readily germinate. Yet, seeds collected in New Jersey failed to germinate. There
is no information on seed viability in the Northwest.
Control: There has been little
research on fanwort biology or management. There are reports that fanwort is less
sensitive to the herbicides available for management in Washington than other aquatic
plants. Drawdown has been used to reduce fanwort growth in the South, however, extreme
drying is necessary to prevent regrowth from seeds. Grass carp eat fanwort but there has
been no research on other biocontrol agents. Because it may obtain most of its important nutrients from the water, fanwort may be sensitive to
reduction in nutrients in the water. The fanwort invasion in Washington is in a pioneering
stage. Prompt action and vigilant monitoring of our lakes, may prevent further spread and
increased management costs in the future.
Key features:
- Fan-shaped leaves in pairs on the
submersed stem
- Submersed stems have a
"tubular" appearance
- Small (less than one inch long), oval
floating leaves with stem attached in the center
Water hyacinth (Eichhornia
crassipes (Mart.) Solms)
Description:
Water hyacinth is a floating plant with round to oval leaves up to 10 inches in diameter,
although smaller leaves are common. Leaves are bright green and shiny and held upright so
they act like sails, which facilitates distribution of the plant. The leaf stalk is spongy
and thick and helps to keep the plant bouyant. A mass of fine roots hang in the water
column. Flowers are large (2-3 inches) and attractive. They are blue-ish purple or lilac
colored with a yellow spot.
Growth Habit: Water
hyacinth can form impenetrable mats of floating vegetation. Water hyacinth has not been
found in the wild in Washington but it is sold as an ornamental plant in garden stores in
the state. Although it is thought that water hyacinth cannot survive Washington's winters,
its presence as an ornamental makes it possible for escape and growth in the wild under
the right conditions.
Propagation: Water
hyacinth reproduces by seeds and vegetatively. Daughter plants form on rhizomes forming
dense beds of water hyacinth. In one study, two plants produced 1200 daughter plants in
four months. Individual plants break off of the mat and are dispersed by water currents.
As many as 5000 seeds can be produced by a single plant. Seeds are eaten and transported
by water fowl. The seeds sink to the bottom and may remain viable for 15 years.
Seedlings are common on mud banks exposed by low water levels.
Control: The best
way to manage water hyacinth is to keep it from becoming established in Washington. Grass
carp will eat water hyacinth and the plant can be managed with herbicides. All management
options are very expensive and require an ongoing commitment. Be aware of the threat of
water hyacinth and report any sitings to your local weed board and/or the Department of
Ecology! Never delibrately introduce water hyacinth into a lake, stream or other waterbody in Washington.
Key
features:
Floating bunches of
oval leaves that form a dense surface mat
Long roots dangling
in the water
Attractive
hyacinth-colored (purplish) flowers
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Contact Kathy Hamel by e-mail at kham461@ecy.wa.gov
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