Download Management of Aquatıc Plants

Management of
Aquatıc Plants
College of Agricultural Sciences
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Under ideal conditions, limited amounts of aquatic vegetation add to the aesthetic beauty of the pond and the ecosystem balance among the
pond’s aquatic life.
Introduction
If you build it, they will come. That can be said of ponds and aquatic plants. Just as grass
and weeds will grow quickly on exposed soil, aquatic plants and algae will colonize new
ponds in short order. While these plants and algae can grow abundantly and interfere
with various pond uses, they also provide many benefits to the pond if their growth is
limited.
The first step in assessing the importance of aquatic plants to your pond is to
determine your intended primary use(s) for the pond. Ponds are frequently used in
several ways to satisfy more than one objective. For example, having water available in
the pond for fire protection may satisfy one objective without interfering or conflicting
with other objectives such as swimming or fishing. Multiple-use ponds are fine as long as
the uses are compatible. When conflicting or incompatible uses are desired, it is necessary
to assign priorities to the owner’s objectives. For example, the objective of providing an
If you build
it, they will
come.
area for swimming may conflict directly with the objective of having water available for
irrigation. Irrigation needs may lower the water level to a point where swimming is not
possible at a time when swimming is most wanted. For this reason, you should list and
prioritize specific objectives for your pond.
This publication is intended to help pond owners understand the importance and
benefits of aquatic plants and algae. When plant and algae growth reach nuisance levels,
pond owners have many options to restore balance to the pond ecosystem. Too often,
pond owners reach for quick fixes like aquatic herbicides. If not used properly, herbicides
may eliminate too much vegetation or beneficial plants along with the targeted weeds.
Herbicides are just one method of controlling unwanted plants and algae. Nonchemical
methods may provide longer and more permanent control and should be considered
when developing a pond vegetation management strategy. Information in this publication
will help pond owners properly identify aquatic plants, understand their benefits, and
choose appropriate control strategies (where necessary) to minimize damage to the pond
ecosystem.
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The Role of Aquatic Plants
in Natural Pond Ecology
Ponds are most healthy when there is a
balanced ecosystem of insects, plants, fish,
and animals otherwise known as a “food
web.” A balanced food web includes some
planktonic algae and aquatic plants at the
top, which serve as a food source for small
zooplankton and aquatic insects. The zooplankton and insects in turn provide food
for the smallest fish in the pond. These then
become prey for larger fish, which finally
may be taken by raccoons, bears, or fishermen.
Under ideal conditions, pond plants
also provide oxygen to the water during
the day as a result of photosynthesis. Some
of this oxygen is then used to support the
same plants during nighttime respiration.
In the winter, water temperatures get much
colder and ice may cover the top of the
pond for an extended period of time. Most
aquatic plants become dormant or produce seeds and die before winter, but a few
plants are capable of remaining green and
growing all winter long. These plants are
usually able to get enough light through
Aquatic plants serve as important habitat for insects and other pond life.
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the ice to cause some photosynthesis and
help support pond life during the harsh
winter conditions.
The optimum amount of aquatic vegetation for a given pond is difficult to identify because it depends on the preferred use
of the pond. Generally, aquatic vegetation
should cover 20 to 40 percent of the pond
area (bottom and top) to provide a healthy
pond ecosystem. The smaller percentage
is preferable for boating, irrigation, and
swimming, while the larger percentages are
best for ponds intended primarily for fishing recreation.
Benefits of Plants and Algae
A recent survey of Pennsylvania pond
owners found that nearly two-thirds felt
that aesthetic beauty was the main reason
for building a pond on their property. Part
of the picturesque view of a pond includes
at least some aquatic vegetation and the
beauty it can impart. The aesthetic beauty
of water features with aquatic plants is one
of the main reasons backyard ponds have
become so popular in the last decade.
Besides their aesthetic beauty, plants
and algae provide many benefits to the
pond ecosystem. Both the roots and leaves
of aquatic plants can reduce muddy water
conditions. The roots of submerged and
floating plants stabilize the bottom sediments while the dense leaves of submerged
plants trap floating debris and sediment.
The plants also remove nutrients from the
water column, thereby reducing the availability of nutrients to cause nuisance algae
blooms. The nutrients are stored in the
plants until fall when much of the nutrient load falls to the pond sediments as the
plants die. Around the edge of the pond,
the roots of emergent plants also stabilize
the pond banks and reduce erosion.
Under the water surface, the dense
stems, roots, and leaves of aquatic plants
serve as excellent habitat for insects and
invertebrates including snails, leeches, and
crayfish. The plant structure traps organic
material and promotes the growth of periphyton (attached algae) and attracts zooplankton (barely visible aquatic animals)
that serve as important food sources for
Overabundant Aquatic Plant Growth
Many of the same benefits provided to
ponds by optimum levels of plant growth
can be taken away by overabundant plant
growth. Nuisance plant and algae growth
can ruin the aesthetic appeal of the pond,
degrade water quality, and even kill aquatic
life. Unfortunately, nuisance plant growth is
a common complaint among pond owners
in Pennsylvania (Figure 1).
Healthy pond fish populations
depend on aquatic vegetation for food, cover,
and reproduction.
60
Pond Owners (Percent)
these scavengers. Aquatic insects also perch
on aquatic plants and filter the surrounding
water for food.
The benefit of aquatic algae and plants
to the pond fishery cannot be overestimated, especially since more than 50 percent
of pond owners in Pennsylvania consider
fishing recreation a major use of their
ponds. A healthy and well-balanced fish
population is more attainable if significant
aquatic plant beds exist in the pond. Many
pond fish use weed areas as nesting beds to
provide cover for their young. Some feed
directly on the plant leaves or the insects
resting on the leaves. All fish use the cover
provided by vegetation to stalk prey. Small
fish hide from larger fish in underwater
plants to prevent predation. As a result, the
amount and type of vegetation will affect
the fish population structures. Too much
vegetation will allow many young fish to
survive, making it difficult for larger fish to
grow. Too little vegetation allows predator
fish to easily capture smaller fish. In this
case, fish may grow quickly until they consume all the smaller fish in the pond.
In addition to fish, other types of wildlife thrive in the pond environment. In
fact, pond owners are often surprised at
the number and diversity of wildlife that is
attracted to a pond, especially if the pond
is constructed in an area that is otherwise
lacking water resources. Part of this attraction is the type of aquatic plants present in
the pond.Various aquatic plants are a vital
component in the diet of ducks and geese.
They not only eat the plants themselves
but also devour the insects that live on the
plant surfaces. Emergent plants around the
pond edge also serve as important nesting
areas that provide dense cover for waterfowl.Various mammals also use aquatic
plants. For example, muskrats prefer ponds
with cattail beds for food and cover. Many
pond owners are also surprised to see
whitetail deer occasionally feeding on various pondweed species in and around the
pond. Last but not least, amphibians and
reptiles such as turtles, salamanders, and
snakes rely on pond plants for food and
shelter.
40
20
0
Plants/Nuisance Leaks
algaewildlife
WaterFish
quality
kills
Figure 1. The prevalence of various pond problems based on a survey of Pennsylvania
pond owners.
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Overabundant plant and algae growth ruin
the aesthetic beauty of the pond.
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Aquatic plants and algae grow abundantly in certain settings for many reasons.
The simplest explanation is an overabundance of nutrients, primarily phosphorus
and nitrogen. A pond begins with mostly
water, few nutrients, and little aquatic life.
As a result, a newly created, deep, springfed pond may have little life of any kind
because of the lack of nutrients available
to support pond life. Over time, the pond
accumulates nutrients in a process known
as “eutrophication.” The addition of nutrients stimulates increased growth of algae,
plankton, and aquatic plants, which grow,
mature, and die. Their remains decay and
the nutrients are released back into the
water of the pond to keep the cycle going.
A shallow, nutrient-rich pond exposed to
sunlight with little water flowing through
it will be teeming with algae and aquatic
plants. Eventually, though, material that
resists decay will accumulate and the pond
will fill up and become a bog or wetland.
This process of conversion to a bog or
wetland can happen in a decade or may
take centuries. Humans greatly accelerate
the eutrophication process through landuse activities. Nearby fertilizer applications, septic systems, urban runoff, animal
manure, erosion, and waterfowl can all add
significant amounts of nutrients to a pond.
Too many plants are discouraging to
the pond owner and are also detrimental
to the pond ecosystem. For example, a
pond completely covered with water lilies will shade the pond enough to prevent
other vegetation from growing under the
water. The shade will also be sufficient to
reduce the growth of planktonic algae that
serve as the base of the pond food web.
The resulting situation is a pond that is
very unproductive for anything besides
water lilies. Similarly, a pond covered with
duckweed or watermeal will also shade out
any life beneath the surface. In some cases,
duckweed and watermeal may grow so
quickly that they cause submerged plants to
die prematurely due to shading. The decay
of the dead submerged plants can result in
reduced dissolved oxygen and the death of
fish and other pond life. Complete coverage of the pond by floating plants can also
eliminate oxygenation of the water and kill
pond life by maintaining a complete separation of the water surface from the atmosphere.
Important Pond Measures and
Features Related to Aquatic
Plants
Strategies to manage aquatic plants and
algae require an understanding of several
features related to the pond structure.
Some of these are basic measurements or
observations that are rarely done by pond
owners but can be easily accomplished.You
might be surprised what you learn about
your pond in the process.
Watershed and Water Source
The pond “watershed” is an important
concept that must be understood to determine the sources of nutrients that may be
causing excessive plant growth. The watershed includes the area of land surrounding
the pond that contributes water to it. Identifying the pond watershed is important
because anything that occurs within this
area can impact the pond. Locating a pond
in an undisturbed area and minimizing disturbance and land-use changes within the
pond watershed are important components
of protecting a pond.
A pond’s watershed is determined by
the source of water feeding the pond.
Ponds that collect surface drainage will
have a simple watershed boundary that
includes all the land that drains surface
water toward the pond. Ponds that collect stream or spring water will have more
complex and larger watershed boundaries
that include all the area that drains into the
respective stream or spring that feeds the
pond.
The source of water feeding the pond
can be important to the resulting growth
of plants and algae in the pond. A pond
with a continuous supply of water is almost
always going to be a more satisfactory pond
than one with an intermittent water supply.
The nutrient conditions in a pond with a
continuous overflow are likely to be better
because excess nutrients will leave with the
overflow water. In contrast, a pond having
intermittent flows only has a chance to
purge excess nutrients during storm events.
Such ponds are prone to accumulate nutrients—resulting in excessive plant growth—
much more rapidly than their overflowing
cousins. Pond water can be tested for nutrients like nitrate and phosphate to determine if excessive levels are accumulating in
the pond.
Land-use activities that occur near the
pond or within the watershed of the pond
source (spring, stream, etc.) will largely determine the amount of nutrients that enter
the pond and the resulting amount of plant
and algae growth. Identify and protect the
land areas directly adjacent to the pond and
the land areas surrounding the water sources that feed the pond. Special care should
be taken to avoid polluting activities such
as applying fertilizers and animal manures
or placing septic systems around the pond
and its water sources.
Pond Surface Area
The importance of getting an accurate
measurement of your pond surface area
cannot be overestimated. The majority of
pond owners visually estimate their pond
area, which usually results in an overestimate of the true pond surface area. Rather,
the pond area should be calculated based
on some simple measurements. The effort
necessary to estimate pond surface area is
directly related to your pond’s shape and
uniformity. The simplest method—using
basic equations for common shapes—can
be applied if your pond closely resembles a
circle, square, or rectangle in shape.
The area of a circular pond can be estimated by measuring the distance around
the pond shoreline in feet. Square the
shoreline distance and divide by 547,390
to get the pond area in acres. For example,
a pond that is 450 feet around the shoreline would have an area of 0.37 acres [(450
feet)2 ÷ 547,390 = 0.37 acres].
The area of a rectangular or square
pond is estimated by simply measuring the
length and width of the pond sides in feet.
Multiply the length by the width to get
the square feet of surface area. This value
can be converted to acres by dividing by
43,560 square feet per acre. So, a pond that
measures 150 feet long and 100 feet wide
would have an area of 0.34 acres (150 feet
x 100 feet = 15,000 ft2 or 0.34 acres).
Most ponds have an irregular shape for
which the surface area cannot be adequately estimated using the formulas for common geometric shapes. Three methods can
be used in this case depending on the degree of accuracy you desire. Keep in mind
that the accuracy of your pond surface area
estimate may be very important, especially
for the safe use of aquatic herbicides. The
three methods are described in order from
least to most accurate.You should strive to
use the most accurate method that you can
reasonably accomplish.
Nutrient levels in pond water can be easily
determined using test kits available at most
pet stores.
Land uses near the pond and within the
pond watershed can cause excessive aquatic
plant growth.
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20'
46'
48'
80'
70'
43'
42'
88'
108'
134'
163'
137'
Figure 2. An irregular-shaped pond broken
into six trapezoids for estimation of pond
surface area.
Handheld GPS units are one method to
measure pond area.
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159'
Average Length and Width Method
Take numerous measurements to determine the average length and width. Make
certain you get both the longest and shortest distances in calculating the average
length, as well as the widest and narrowest distances for determining the average
width. The more measurements you make,
the more accurate your result will be. The
area is then calculated by multiplying the
average width by the average length. If
you do your measurements in feet, your
result will be in square feet.You can convert square feet into acres by dividing it by
43,560 square feet per acre. Depending on
the number of width and length measurements you make, the final area will probably be within about ±20 percent of the
actual pond surface area.
“waypoints,” can be stored in the GPS unit
for use with mapping software that either
accompanies the unit or can be purchased
separately. The software can connect the
waypoints and calculate the area inside the
resulting shape.
You can estimate pond surface area by
walking the perimeter of the pond and
stopping at various waypoint locations
along the pond shoreline. If waypoints are
stored at each location where the pond
shape changes, the resulting area will be extremely accurate, probably within 1 percent
of the actual pond area. Even if you do not
own a GPS system, friends or family members that enjoy outdoor recreation may
own a unit that you can use to estimate
your pond surface area.
Multiple Trapezoids Method
A more accurate method to determine the
area of an odd-shaped pond is to divide the
pond into multiple trapezoid shapes. A new
trapezoid is defined anywhere the shoreline
makes a rapid change in direction. Figure 2
shows an irregular pond shape divided into
six trapezoids (shown in dotted lines). Note
that instead of horizontal transects, this
method requires measuring the distance
between each vertical transect. This is most
easily done during winter when the pond
is frozen and the transects can be easily laid
out and measured. This method requires
more measurement and effort, but the final
area estimate will probably be within about
±5 to 10 percent of the actual pond area.
For the pond in Figure 2, multiplying the
length and width of each trapezoid and
then summing the area for all six trapezoids
results in a pond area of 34,792 square feet,
or about 0.80 acres.
The volume of water in ponds is often expressed in units called “acre-feet.” An acrefoot represents one surface acre that is one
foot deep. To calculate the acre-feet of water in a pond, you’ll need the surface area
in acres as calculated above and an average
depth of water in the pond. For a typical
bowl-shaped pond, the average depth can
be estimated as 0.4 times the maximum
depth. So, a pond with a maximum depth
of 12 feet would have an average depth of
about 4.8 feet.
A more accurate method for calculating
average depth is to make many measurements and calculate an average. This is most
often done by measuring the pond depth
along two transects—one along the width
and one along the length. Make sure to
pick transects that represent the shallow
and deep portions of the pond. Depths can
be measured easily from a canoe or boat
using a weight and a string marked in feet.
The more depth measures you make, the
more accurate your final average will be.
An even better way to calculate an average pond depth is to divide the pond into
numerous (at least four) subareas (much as
we did in the trapezoid method). Take at
least one depth within each of the subareas
and use these to calculate the overall average pond depth. This method is especially
good if the pond bottom is irregular rather
than bowl shaped. For the pond example
Global Positioning Systems (GPS)
Handheld GPS systems have become quite
common over the past five years as they
have become more affordable. They are
now routinely used for outdoor recreation
(hunting, hiking, camping, etc.) and navigation. GPS units allow you to determine
your exact location on Earth using multiple satellites in space.Various locations, or
Pond Volume
given in Figure 2, water depths measured
in each of the six trapezoids resulted in an
average pond depth of 4.5 feet. Multiplying
this depth by the area of the pond in acres
provides the pond water volume in acrefeet (4.5 feet x 0.80 acres = 3.6 acre-feet).
Residence Time
The residence time of a pond measures the
average length of time it takes for a molecule of water to pass through the pond
from its entry to the overflow pipe. Knowing this characteristic of your pond may
be critical, especially for the use of some
herbicides. In some cases, herbicides will
not be effective unless they are present in
the pond water for some period of time.
For example, some herbicides suggest thirty
days of contact time with the targeted plant
to achieve effective control. If the residence
time of a pond is only seven days, using
this herbicide would not be successful in
achieving control.
The residence time is easy to calculate.
Simply calculate the pond volume in acrefeet as described above and measure the rate
that water leaves the pond in gallons per
minute (gpm). The outflow can be estimated using a simple bucket and stopwatch to
catch water leaving the pond through the
outlet of the overflow pipe. The residence
time in days can be calculated as follows:
residence time = 226 x [pond volume] ÷
overflow rate
For example, a one-acre pond with an average depth of 5 feet and an overflow rate
of 10 gallons per minute would have a residence time of 113 days [226 x (5 acre-feet)
÷ 10 gpm = 113 days].
Other Pond Characteristics That Affect
Plant Growth
Numerous physical features of the pond
are important in affecting the amount and
diversity of aquatic plant and algae growth.
You should inspect each of these pond
features annually to determine if changes
are needed before resorting to other plantcontrol strategies.
Pond Depth and Slope
Most plant and algae growth begins in
less than 3 feet of water. This water depth
allows sufficient sunlight to penetrate to
the pond bottom to allow plant growth
to begin from the sediment. This is true of
all kinds of aquatic plants, including submerged, emergent, floating, and algae.
Minimizing the area of the pond that
has less than 3 feet of water will minimize
the area that can be colonized by plants
and algae. This is most easily done during
pond construction by shaping pond banks
to have a 1:3 bank slope or greater (i.e., a
water depth of at least 3 feet at a point 9
feet from the shoreline). As the pond fills in
over time, pond depths will decrease, leading to greater plant growth. Dredging can
be used to restore deeper water and reduce
plant growth.
Overflow and Drain Pipes
Most ponds have a vertical overflow drain
pipe that controls the level of the pond
water. This L-shaped pipe moves water and
associated nutrients under the dam and
out of the pond to a receiving stream. The
overflow pipe is sized based on the pond’s
drainage area, inflow, and water-storage
characteristics. It is especially important to
inspect the overflow pipe and remove debris
in or near the pipe. Obstructions of this pipe
may result in increased retention of water in
the pond and greater sediment buildup on
the pond bottom. Blockage of the overflow
pipe may also cause increased erosion and
sedimentation from bank sediments.
Depending on the construction, a
drainpipe may also be installed in the pond
to allow for easy manipulation of the pond
water level (called “drawdown”), which
can be helpful in controlling plant growth
around the edges of the pond.
Steep slopes along pond banks will prevent
most aquatic plant growth.
An annual pond inspection might reveal
structural problems (such as a clogged overflow pipe in this picture) that can be quickly
fixed before they cause serious problems.
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Types of Aquatic Plants and
Algae
Plankton algae
Successful control of aquatic plants and
algae always begins with accurate identification of the plants that exist in the pond
or lake. Dozens of aquatic plant and algae
species occur in Pennsylvania—some are
unique and easy to identify, while others are very difficult to accurately identify.
They may change their appearance at different times of the year and many do not
have conspicuous flowers or seeds to assist
with identification. All aquatic plants can
be separated into one of four categories:
algae, submerged aquatic vegetation, floating plants, and emergent plants.
Algae
Filamentous algae
Chara
Nitella
Leafy pondweed
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Algae occur in all ponds and frequently
grow to nuisance levels due to excessive
amounts of phosphorus and nitrogen in the
pond water. In fact, surveys of pond and
lake owners in Pennsylvania have found
that algae are the most common nuisance
aquatic plant. Algae are important to the
pond ecosystem, providing food for insects that are fed upon by fish and other
pond wildlife. However, excessive growth
of algae can ruin the aesthetic appeal of
the pond and also have devastating effects
on pond life when it dies in the fall of the
year. Algae occur in three different types—
plankton, filamentous, and an attached
branched form.
Plankton algae (phytoplankton) are the
minute, single-celled suspended types that
usually make the water pea-soup green,
reddish, or brown. Ponds with excessive
plankton algae will usually have clear water
during the cold, winter months, but the
water will quickly cloud up during spring
and summer as plankton algae grow in response to warm water. The exact species of
plankton algae in a pond can only be identified using a microscope.
Filamentous algae are the most common algae complaint among pond and lake
owners. These algae begin to grow on the
bottom of the pond, usually in shallow water less than 3 feet deep. As the algae grow,
they produce oxygen, which becomes
trapped in the filaments, causing the algae
to float toward the pond surface. Once
enough oxygen becomes trapped in the algae, a large mat will break loose and spread
across the surface. Although all filamentous
algae begin to grow in shallow water, they
can quickly cover the entire pond surface
as mats break loose and become free floating. Filamentous algae are easily distinguished from all other plants and algae, but
a microscope is usually necessary to identify the exact species.
Attached branched algae look very
much like a plant. They are anchored to
the bottom just like a submerged plant, but
they have no true root system. Two common attached branched algae are Chara and
Nitella. Chara usually grows in ponds and
lakes with hard water in areas underlain
by limestone. It is gritty to touch and has
a skunklike odor when crushed. Nitella is
soft and usually found in higher elevation
ponds and lakes with soft water. It is difficult to distinguish from several rooted,
submerged aquatic plants.
Submerged Aquatic Vegetation
Submerged plants are the most diverse
group of aquatic plants with many special
features. They generally have submerged
leaves that are flexible and small to reduce
drag from underwater currents. The leaves
tend to be buoyant with air vacuoles that
allow them to capture the maximum light
in the water column. The leaf surface is
usually thin and without a waxy surface
to allow for gas exchange from the surrounding water. Many submerged plants
have multiple types and shapes of leaves
(submersed and floating) to maximize their
ability to capture energy from sunlight,
making them difficult to identify. The stems
of these plants are flexible and buoyant
to allow the plant to float well within the
water column. Stems also often contain
chlorophyll to assist the plant in capturing
the limited sunlight under the water. Most
submerged aquatic plants grow in shallow
water less than 3 feet deep where sunlight
penetrates to the bottom of the pond. A
few plants have the ability to grow in dimmer light conditions in very deep water.
Submerged plants have very diverse
roots that allow them to grow among other
aquatic plants, maximizing diversity. Some
submerged plants prefer thick muck layers, while others prefer a sandy or gravel
bottom. They also have a wide variety of
reproduction methods. Some are annuals
that die each year and regrow by seeds the
following year, but most rely on continual,
spreading growth from rhizomes or roots.
A few even remain green all year long in
a reduced growth state. In most cases, the
flowers and seeds of submerged plants
reach the surface of the pond or even grow
on stems above the pond surface. Pictured
on these pages are some of the most common submerged plants found in Pennsylvania ponds and lakes. See the invasive plants
section on page 10 for information on
other submerged plants that are not native
to Pennsylvania.
Naiad
Also known as bushy pondweed, naiad
has fine leaves that are arranged in whorls
around the stem. The leaves are brittle and
will often fall from the stem if the plant is
handled. This plant usually prefers sandy or
gravel substrate and can grow in very deep
water. Naiad produces seeds and dies each
fall with growth the following year coming
entirely from the deposited seeds. During
the summer, naiad can spread quickly from
stem fragments.
Pondweeds
There are more than two dozen species
of pondweeds in Pennsylvania. Most are
native aquatic plants that are beneficial to
the pond ecosystem, especially serving as
habitat for fish and other aquatic life. A few,
such as leafy pondweed (left), can grow
abundantly and interfere with pond uses.
Floating Aquatic Plants
Elodea
This common aquarium plant is usually
dark green and grows densely with whorls
of two or three leaves that become more
crowded near the tips of the stems. This
plant prefers to grow in clear, spring-fed
ponds with fine, organic sediment. It is one
of the few aquatic plants that remain green
during the winter. Elodea spreads primarily
through stem fragments.
Coontail
Named because of its similarity to a raccoon’s tail, coontail has whorls of many
fine leaves. It often grows to nuisance levels
because it can tolerate low light levels in
deeper portions of the pond. It does not
have true roots, so it is often free floating
or loosely attached to bottom sediments.
As does elodea, coontail can also overwinter as a green plant and reproduces mostly
through stem fragments.
Bladderwort
This dense-growing plant has fine leaves
arranged around stems that end with a
small bladder, which makes this plant easy
to identify. Bladderwort is most common
in northeast Pennsylvania in acidic ponds
and lakes, where it often occurs as a freefloating plant.
As the name implies, floating aquatic plants
have most or all their leaves floating freely
on the pond surface. Some floating plants
(such as water lilies) get their nutrients
through stems that extend to roots in the
pond bottom. Other free-floating plants
(such as duckweed) get all their nutrients
from the water itself through roots that
extend into the water beneath the floating
leaf. All floating aquatic plants prefer quiescent water.
Water lilies
The classic pond plant, native water lilies
have leathery leaves with air spaces that
allow it to float. Water lilies are slow growing and usually grow in relatively shallow
water less than 5 feet deep. The leaf stalks
and stems are often flexible to allow leaves
to move up and down with the water level.
They use stored energy in their extensive
roots to grow leaves rapidly to the surface
in the spring. Native water lilies have large,
white flowers, while nonnative tropical varieties have different-colored flowers. Water
lilies provide excellent habitat for fish and
other aquatic life.
Elodea
Coontail
Naiad
Bladderwort
Water lily
9
Duckweed
Duckweed
This plant is easy to identify by its small,
floating leaf with a tiny root extending
from the bottom of the leaf. In the fall,
duckweed produces winter buds that sink
to the pond bottom. As the water warms in
the spring, these buds float to the surface
to start another colony of duckweed plants.
Duckweed is spread between ponds by
waterfowl and can grow very quickly, ultimately covering the entire water surface in
stagnant ponds.
Watermeal
With very small, round leaves that are pale
green or yellowish without any obvious
root, watermeal appears more like grass
seed than an actual plant. Watermeal often
occurs with duckweed on stagnant ponds.
Watermeal
Watershield
Watershield
This plant has a 2- to 4-inch elliptical or
football-shaped floating leaf that is purple
underneath. The underside of the leaves
and elastic stems are covered with a characteristic gelatinous coating. Purple flowers
are produced on stems above the water
surface during summer. Watershield prefers
clear, acidic ponds with a thick, organic
muck layer on the bottom.
Emergent Plants
Cattail
Bulrush
10
Emergent plants often look very much like
terrestrial plants because most of the plant
is above the water line. These plants like
to have their “feet” (roots) wet but like to
have their stems and leaves dry. Emergent
plants can withstand changing water levels
in the pond and some even thrive under
these conditions. Their leaves are spongy
with numerous air spaces and most have
extensive roots that grow horizontal in
pond sediments providing stability and preventing erosion along the pond edge. Most
emergent plants grow slowly and provide
excellent fish and wildlife habitat. Many
pond insects, including beautiful dragonflies and damselflies, will use stems of
emergent plants for perching areas. Emergent plants tend to cause fewer problems
for pond owners than other aquatic plants.
Cattail
The most common of the emergent plants,
cattails often colonize shallow water areas,
especially in older ponds. Cattails are slow
growing and limited to shallow water, so
their growth rarely reaches nuisance levels.
Muskrats like to eat cattails and are often
attracted to ponds with significant cattail
growth.
Bulrush
This plant has unique stems that are triangular in shape when cross-sectioned. They
usually grow 2 to 3 feet tall with flowers
on spikes near the tip. They may form very
dense stands after being established for several years and can grow in water up to 3 feet
in depth. Bulrush sprouts each spring from
buds on rhizomes in the pond sediment.
Invasive Aquatic Plants—Watch Out
for These!
Nonnative aquatic plants are increasingly
becoming a problem in private ponds and
lakes throughout Pennsylvania. Some of
these plants have occurred in the state for
many years and are slowly spreading, while
others have only recently appeared and are
spreading rapidly. Listed below are some
of the most troublesome invasive plants in
Pennsylvania ponds.
Hydrilla
A submerged aquatic plant that resembles
native elodea, hydrilla has finely toothed
leaves coming off stems in whorls of three
to eight. This aggressive plant roots in the
bottom of ponds, lakes, and canals and outcompetes native aquatic plants. Stems grow
to the surface, where they can branch and
extend horizontally. This nonnative plant is
extremely prolific in the warmer ponds of
southern Pennsylvania. Hydrilla can also be
spread into ponds as a hitchhiker on some
potted aquatic plants.
Curly Leaf Pondweed
Curly leaf pondweed is a European plant
that is quite common in ponds throughout
Pennsylvania, especially those with fertile
and hard water. It has a very distinctive
appearance with crinkled, finely toothed
leaves that occur alternately along the stem.
The flower spikes often stick up above the
water surface during spring. It can tolerate low light and may grow in deep water.
Curly leaf pondweed grows abundantly
until late summer when it dies back to
form winter foliage that remains green
throughout the winter.
Eurasian Milfoil
Unlike native watermilfoil, which is usually
found in acidic ponds and lakes in northern
Pennsylvania, Eurasian watermilfoil is an
invasive nonnative plant that quickly grows
to nuisance levels. The leaves are green
with a fine, feather-like appearance growing on long, reddish-colored stems (native
milfoil species look very similar but usually
have more delicate leaf structures). Flowers
develop on a terminal spike with very short
leaves surrounding them; however, it usually reproduces through fragmentation. It
entered Pennsylvania from the Great Lakes
drainage and quickly spread into all major
watersheds in the state. It grows in a variety
of conditions and often outcompetes and
replaces native pond plants.
Parrot Feather
This is another submerged, rooted plant
closely related to Eurasian milfoil. Parrot
feather is popular among backyard pond
owners, leading to its spread into larger
ponds throughout the state. It has green,
featherlike leaves that often grow above the
water surface for up to 12 inches. It reproduces mostly through stem fragments and
can quickly take over a pond.
Purple Loosestrife
An exotic, emergent plant from Europe
and Asia that quickly spreads and outcompetes native plants. It should be removed as
soon as it first appears. It has long, square
stems with opposite leaves in whorls of
about three. The narrow leaves are about
1 to 4 inches long and end in a point. It
produces clusters of purple flowers on a
terminal spike. Purple loosestrife often first
appears in disturbed areas around the pond
from seed germination. Many pond owners
have been tempted by the beautiful purple
flowers on this plant and have unknowingly planted loosestrife around their pond
only to regret this decision in a few years
when the plant takes over the entire pond
edge.
Yellow Floating Heart
A relative newcomer to Pennsylvania, this
floating plant is becoming widespread due
to its popularity among backyard pond enthusiasts. This plant has a similar appearance
to water lily, but its leaves are slightly more
heart shaped and the flowers are yellow.
This plant will grow more quickly than
water lily and can reach nuisance levels.
Hydrilla
Curly leaf pondweed
Eurasian milfoil
Additional Sources of Help for Aquatic
Plant Identification
The following Web sites provide pictures
and descriptions of aquatic plants:
Aquaplant from Texas A&M University: aquaplant.tamu.edu
Center for Aquatic and Invasive Plants from the
University of Florida:
plants.ifas.ufl.edu
Penn State Cooperative Extension Water
Resources:
water.cas.psu.edu/ponds.htm
Other Web sites can be found by typing
“aquatic plant identification” into any Web
search engine. Several excellent field guides
and books on aquatic plant identification
are available through the North American
Lake Management Society (phone 608233-2836; www.nalms.org). For more
help with identifying aquatic plants, e-mail
digital photos of aquatic plants to Bryan
Swistock at [email protected].
Parrot feather
Purple loosestrife
Floating heart
11
Aquatic Plant Growth
Prevention and Control
Preventing Aquatic Plant and Algae
Growth
The old saying “an ounce of prevention
is worth a pound of cure” also applies to
controlling aquatic plants and algae in
ponds and lakes. Reacting to overabundant
growth, once it has occurred, is simply a
band-aid approach that often involves perpetual treatment to control the plant. But
several strategies can be used to prevent
plant and algae growth before it occurs.
Pond Construction Features
Most plant and algae growth begins in
shallow water less than 3 feet deep where
sunlight can reach the pond bottom.
Therefore, limiting the amount of shallow
water in the pond will control the amount
of plants and algae that can grow. As was
mentioned earlier, this can be achieved by
constructing the pond so the water is at
least 3 feet deep at a point 9 feet from the
shoreline (a 1:3 bank slope). If the pond
will be used for swimming, you may wish
to construct a small area with a gentler
slope to allow for easy and safe entry into
the pond.
For existing ponds with gentle bank
slopes and extensive shallow water, dredg-
A simple strip of unmowed grass around the pond edge, like this buffer around a golf course
pond, can reduce aquatic plant and algae growth in the pond by reducing nutrients delivered to
the pond.
12
ing can be used to deepen the pond edges
and prevent future plant and algae growth
(see “Dredging” section later in this publication).
Nutrient Control Strategies
As was previously discussed, aquatic plants
and algae grow to nuisance levels in response to excess levels of phosphorus and
nitrogen in the pond water. Thus, strategies
that reduce nutrient entry into the pond
will have the benefit of preventing future
plant and algae growth. Nutrient control
strategies are rarely employed by pond
owners because they are often perceived as
too difficult and expensive, and they also
do not provide an immediate reduction in
plant growth. Rather, nutrient reductions
will lead to a gradual and long-term reduction in plant and algae growth. In an era of
quick fixes for all problems, pond owners
are unfortunately more likely to choose
other approaches, such as herbicides, to
control plants and algae.
Buffer Strips
Perhaps the easiest method to control
nutrients entering a pond is to establish a
buffer strip of vegetation. Maintaining a
strip of vegetation around the pond and
also around streams and springs that feed
the pond is very beneficial for capturing nutrients before they enter the water.
Buffer strips act to slow water down and
encourage infiltration of the water into the
soil where the plant roots can capture and
utilize nitrogen and phosphorus. Buffers
also act to remove sediment from the water
by slowing water velocity.
The composition of a buffer does not
need to be fancy. A simple, 30-foot wide
strip of taller grass will often suffice on
gentle slopes around the pond. A wider
buffer with more diverse vegetation is better, especially on steeper slopes that provide
runoff to the pond. Buffer strips planted
with native vegetation and wildflowers can
also attract wildlife to the pond area.
A buffer area that includes larger vegetation capable of shading some of the pond
water will also help reduce plant growth by
limiting direct sun and cooling the water
temperature.
Erosion and Sediment Control
Most phosphorus enters a pond attached
to soil particles that are suspended in water
entering the pond. Practices that reduce
erosion near the pond and sediment delivery to the pond through the water supply
can be effective in reducing aquatic plant
and algae growth. Reducing sediment
delivery also prevents the pond from becoming shallower and thus reduces aquatic
plant growth.
Erosion control around the pond involves the creation and maintenance of the
vegetated buffer strip as described above.
Reducing sediment delivery to the pond
through surface runoff or surface streams
is more difficult. The processes that cause
sediment delivery to streams and springs
are often large-scale land-use activities that
are out of the pond owner’s control (e.g.,
stormwater runoff from housing developments and shopping centers upstream).
Assuming that sediment cannot be reduced
in the incoming runoff water, the pond
owner can reduce the impact of sediment
on the pond by creating a small sediment
pond or shallow pool at the inlet of the
main pond. Water passing through this
sediment pond or pool on its way to the
pond will have an opportunity to drop its
sediment load in the pool. This pool should
be of such dimensions that it can be easily
cleaned with a backhoe. A sedimentation
pool helps the pond in the same way that
sediment is removed by buffer strips.
Limit Fertilizer and Manure Applications
Fertilizers and manures applied to lawns,
golf courses, and farm fields may run off
into adjacent ponds and lakes. Some of the
nutrients contained in these products may
run off from the land where they are applied because plants are never able to utilize
100 percent of the nutrients. Heavy rain
immediately after application of fertilizers
and manures is especially likely to cause
runoff of nutrients into nearby ponds and
lakes. Just as these fertilizers are intended
to stimulate growth of grass and crops,
they also act to stimulate growth of aquatic
plants and algae in receiving waters. Reducing fertilizer and manure application
rates on lands near ponds and prohibiting
use of these products within the buffer area
around the pond will reduce nutrients entering the pond.
Limit Other Nutrient Sources
Other sources of nutrients to ponds can
often be controlled or diverted. Barnyards,
feedlots, and pastures may contain high
amounts of animal wastes rich in nutrients.
Fencing ponds and streams to limit animal
access will help reduce nutrient runoff and
soil erosion into ponds and the streams that
feed them.
Just as domestic animals may contribute
nutrients to ponds, excessive amounts of
wildlife can also be problematic. The most
likely cause for concern is large flocks of
Canada geese. A recent study in the northeastern United States found that Canada
geese can be a large contributor to phosphorus additions to ponds. A flock of 200
geese were found to produce about 100
grams of phosphorus each day, enough
to stimulate large quantities of algae. Approaches to limit the numbers of geese and
the length of time that they visit the pond
will reduce the nutrient load to the pond. Finally, human wastes can be a significant source of nutrients to some ponds and
lakes. Care should be taken to locate septic
systems as far from the pond or lake shore
as possible. Homeowners with septic systems need to properly maintain the system
to ensure that malfunctions don’t occur
that could cause nutrient pollution into
nearby ponds.
In the absence of strategies to control
nutrients entering ponds, many pond owners are limited to reacting to excessive
growth after it has started. It is important to
realize that acting to reduce plant and algae
growth without addressing the underlying
cause may simply create alternate problems.
For example, reducing submerged and
floating aquatic plants may lead to increased
algae growth by releasing nutrients formerly bound up in living plant material. A truly
integrated approach is usually necessary that
incorporates water quality measurements,
pond construction features, and physical,
biological, and chemical controls to create a
balanced aquatic plant management plan.
Sediment and nutrient levels in farm ponds
can be greatly reduced by fencing the pond
and piping drinking water to troughs.
Canada geese can increase aquatic plant and
algae growth through their wastes.
13
Physical Control Strategies
Physical control strategies are akin to pulling weeds from your flower beds. Many
of these processes are time consuming and
labor intensive, but they often have longerterm benefits than chemical control. That’s
because removal of plants and algae from
the pond also removes the nutrients associated with the plants, which makes fewer
nutrients available for future plant growth.
Raking and other physical removal of plants
can be advantageous because they also remove nutrients from the pond.
Harvesting
Physical harvesting of aquatic plants and
algae can be very effective, especially for
small quantities of plants near the shorelines. Also, unlike many other aquatic plant
control strategies, hand or mechanized removal of aquatic plants and algae does not
require a state permit.
Many pond owners have developed
innovative tools and techniques to accomplish aquatic plant harvesting. All these
methods involve some type of cutting,
mowing, raking, digging, skimming, or
pulling. Harvesting techniques must often
be repeated several times each growing season to eliminate new growth as it appears.
On larger lakes, consultants can be hired to mechanically remove large amounts of aquatic
plant growth with plant harvesters.
14
Many submerged aquatic plants can reproduce through fragmentation. As a result,
attempts to cut and harvest these plants can
result in increased growth due to sprouting from fragments left behind. Before
attempting to harvest submerged plants,
make sure you properly identify the plant
and determine if it can spread through
fragmentation. If the problem plant is
known to reproduce from fragments, avoid
attempting to harvest the plant and focus
on other physical, biological, or chemical
control techniques.
Plants and algae that are harvested from
the pond should be removed from the vicinity of the pond edge. This will prevent
the nutrients released from the decay of
the plants from being washed back into the
pond water.
In larger ponds and lakes, mechanized
harvesters may be used to remove aquatic
plants and algae. These mechanized harvesters can be expensive because of high maintenance costs. The most widely used type
of mechanized equipment is called a plant
harvester (weed cutter). Plant harvesters are
used mainly on large lakes and cut off the
underwater rooted vegetation 4 to 5 feet
below the water surface. As with hand removal of plants, mechanized removal offers
the advantages of removing much of the
nutrients associated with the aquatic vegetation, thus reducing future plant growth.
Mechanized weed cutters that do not
harvest or collect the weeds for transport
to shore are not recommended because
plant fragments can live for long periods
of time, develop root systems, and grow in
areas that previously were unaffected with a
weed problem.
Aeration
Aeration can be beneficial to the overall
health of some ponds and lakes, but it should
be viewed as part of an integrated management plan to reduce plant and algae growth
rather than a solution to the problem.
The most efficient type of aeration
involves introducing air bubbles at the bottom of the lake or pond through diffusers
or hoses with small holes. This type of aeration, called diffuse aeration, requires electric
power and some installation by a profes-
sional. The air bubbles rising from the diffusers on the bottom of the pond oxygenate the water and push the oxygen-poor
water to the surface where it is reaerated
through an exchange with atmospheric
oxygen. In addition, some oxygen is directly transferred from the air bubbles to
the surrounding water. The resulting aeration of the bottom pond water activates a
number of complex processes that can help
control algae by precipitating phosphorus
out of solution and keeping phosphorus
bound to the bottom sediments. Aeration
of the bottom water layers can also be beneficial to reduce the depth of the organic
muck layer that forms on the bottom of
the pond. Aerobic (oxygen-loving) bacteria
work much faster than anaerobic bacteria
in breaking down organic material on the
bottom of the pond.
The other type of pond aeration involves surface aeration through fountains.
Fountains generally only aerate a shallow
layer of water near the pond surface, so they
have little or no benefit to reduce phosphorus levels and control algae. The mechanical
agitation of the pond surface by the fountain will reduce the growth of some floating plants, such as water lily and duckweed,
that prefer to grow in stagnant water.
Drawdown
Most aquatic plants and algae begin growing in shallow water near the pond edge.
Partially draining the pond to expose
these shallow areas—called drawdown—
is another physical method to reduce the
growth of aquatic plants. Drawdown is
usually done during the fall to expose pond
sediments to freezing temperatures during the winter. The degree of plant control
from a drawdown depends on the plant
species present and the minimum winter
temperatures. A drawdown accompanied
by below-freezing temperatures provides
the greatest aquatic plant control.
Drawdown is often difficult for pond
owners to accomplish because they cannot easily draw the water level down and
keep it lower for an extended time over the
winter. More often, drawdown is done on
larger lakes and reservoirs that can easily
control the water level.
A permit for drawing down an impoundment is required for ponds larger
than one acre or for any pond drawdown
to conduct an activity that requires another state permit, such as a Pennsylvania
Department of Environmental Protection
Waterways Obstruction and Encroachment
Permit. Additional information is available
through your local office of the Pennsylvania Fish and Boat Commission and the
Pennsylvania Department of Environmental Protection.
Dredging
As sediment and organic debris enter the
pond, they will settle to the bottom and
reduce the water depth. This sedimentation process occurs quickly in ponds that
receive erosion and stormwater from disturbed areas and slowly in ponds that are
spring fed in undisturbed areas. Shallower
water from sedimentation allows sunlight
to reach more of the pond bottom, resulting in increased plant and algae growth.
Dredging sediment from the pond can
be a remedy to reduce plant growth, albeit
a time-consuming and expensive one. The
first steps in any dredging project should
be to locate where the sediment originates
and then determine how the sediment
delivery may be controlled. Restoration of
a pond to its original configuration usually
provides significant benefits, but they can
be short lived if the sedimentation is allowed to continue. Dredging is a regulated
activity that may require a drawdown permit and a dredging permit before proceeding. Pond owners should consult the local
office of the Department of Environmental
Protection before beginning any dredging
project.
Diffuse aeration
Fountain aeration
Biological Control Strategies
Many pond owners desire biological or
“natural” techniques to control unwanted
aquatic plants. These methods are less physically demanding than mechanical control
strategies described above and are usually
less damaging to the pond ecosystem when
compared to the chemical control strategies
described in the next section.
Drawdown of lakes and ponds will reduce
plant growth by freezing bottom sediments
during winter.
15
Triploid Grass Carp
Grass carp are a nonnative, plant-eating
fish that can be stocked in ponds and lakes
to provide control of some aquatic plants.
They have been used successfully on many
ponds and lakes throughout Pennsylvania
to control abundant aquatic plant growth.
When used improperly, however, they can
have negative impacts such as increased
growth of algae, muddying of water, or no
control of unwanted plants. Several steps
should be followed to maximize the success
of grass carp in your pond.
1. Plant identification is absolutely essential when considering the use of grass
carp. These fish will voraciously eat
some aquatic plants while ignoring others. Grass carp can be very effective at
controlling most varieties of submerged
aquatic vegetation. The table below lists
some of the common likes and dislikes
of grass carp.
Plants Preferred
by Grass Carp
Pondweeds (many
Potamogeton species)
Elodea
Coontail
Naiad
Duckweed
Muskgrass (Chara)
Water milfoil
Bladderwort
Water-stargrass
Plants Not Preferred
by Grass Carp
Filamentous algae
Planktonic algae
Cattail
Bulrush
Arrowhead
Watershield
Large-leaf pondweed
Water lily
Spatterdock
Grass carp can be very effective in controlling some rooted aquatic plants.
16
2. Acquire a state permit. Once you have
determined that the nuisance plant in
your pond is a species preferred by grass
carp, you must obtain a state permit
through the Pennsylvania Fish and Boat
Commission (PFBC) to purchase grass
carp. Grass carp stocked in Pennsylvania
waters must be triploid, or sterile, nonreproducing fish. This genetically altered
carp was created by exposing the fertilized eggs to heat shock, causing both
sexes of the fish to have three sets of
chromosomes (triploid) rather than the
normal two (diploid).
The permit application has a small fee
and must include a photo of the outflow
structure of the pond. In some cases, you
may be required to install a device over
the outflow to prevent the grass carp
from escaping. For lakes larger than 5
acres, a more detailed environmental assessment must be done before grass carp
can be stocked. The permit application
along with other grass carp information
can be downloaded from the Penn State
Water Resources Extension Web site at
water.cas.psu.edu or obtained from your
local PFBC office.
3. Purchase and stock the fish. Once you
have obtained the state permit, you can
purchase grass carp for stocking in your
pond. A limited number of hatcheries
sell grass carp (list available on the Web
site shown above) and you must show
the permit to purchase fish from the approved hatcheries. Grass carp are typically
sold as 10- to 12-inch fish to maximize
their chances of survival after stocking.
Up to fifteen grass carp may be stocked
for each acre of pond, but starting with
an initial stocking of just a few fish per
acre is usually best.
4. Monitor and alter management. Grass
carp will live for up to fifteen years after
stocking, although their ability to consume
aquatic plants declines markedly after ten
years. For that reason, large grass carp are
often removed and replaced with a restocking of smaller fish. Grass carp should
also be removed if they overcontrol aquatic
plants and muddy the water looking for
additional plants—a common problem if
too many are stocked in the pond.
Other Plant-Eating Fish
(Not Recommended)
Other fish species, including koi, common
carp, and Israeli carp, are sometimes marketed for control of aquatic plants and algae. While these fish do occasionally nibble
on plants and algae, they are not exclusive
plant eaters and may cause more problems
than they solve. As a result, they are not
recommended for aquatic plant control.
Biological Additives
Various pond additives have recently been
developed that may reduce plant and algae growth through biological processes.
These products normally contain various
microbes or enzymes that feed on or consume nutrients (nitrogen and phosphorus),
making them unavailable for plant growth.
In other words, they outcompete plants
and algae for available nutrients in the
pond. Currently, no permit requirements
exist to use these products in Pennsylvania
and success has been mixed. Some products
are expensive and may require multiple
applications during each year, and their
results may be affected by the water quality conditions in each pond. Still, as these
products are further developed, they appear
to be a promising alternative to the use of
chemicals in aquatic plant control.
Barley Straw
Barley straw has been used for many years
with some controversy to control filamentous algae. Some pond owners claim
remarkable control with barley straw while
others report no effect or increased algae
growth. The mechanism by which barley
straw inhibits algae growth is poorly understood, but it is thought to be related to
the release of hydrogen peroxide.
Barley straw should be applied to the
pond during the fall or winter prior to
the plants’ growing season. As it decays, it
may prevent algae growth in the following
spring and summer. It does not kill existing algae. Approximately three to five bales
of barley straw should be used per acre
of pond area. The bales should be broken
apart and submerged in cages, nets, or other
containers that will allow water to move
through the straw. The containers should be
placed where maximum water movement
is occurring in the pond (near the spring
or stream that feeds the pond, if possible).
Keep these three key points about barely
straw in mind:
• It is only used for prevention of filamentous algae (not for other aquatic
plants).
• It must be applied weeks before algae
growth begins.
• It doesn’t always work and should be
viewed as an inexpensive alternative that
might be worth a try.
Chemical Control Strategies
When aquatic plants and algae appear at
nuisance levels, pond owners often turn to
aquatic herbicides. Herbicides are effective and usually provide quick solutions to
aquatic plant problems. Aquatic herbicides
fall into two categories: contact and systemic. Systemic herbicides are absorbed
through leaves or roots and then transported within the treated plant. Contact
pesticides are not absorbed by the treated
plants; they must directly touch the plant to
be effective.
The use of aquatic herbicides has some
disadvantages. Aquatic plants often have
to be treated every year to keep them under control. Some chemicals can be quite
costly and, if used incorrectly, may be
hazardous to the applicator and the pond
environment. The preceding sections of this
publication have demonstrated the multitude of options that exist for aquatic plant
control in addition to aquatic herbicides.
The use of aquatic herbicides should only
be undertaken after these other options
have been investigated. Keep in mind that
effective control of aquatic plants and algae
usually integrates nutrient management
into the control plan. Carefully follow each
of the steps listed below if you are using an
aquatic herbicide.
Barley straw submerged in bags may help
prevent growth of some filamentous algae.
Aquatic herbicides can be effective, but they
must be used with extreme care.
1. Properly identify your aquatic
plant. No single aquatic herbicide will kill
every aquatic plant. In fact, most herbicides
have a relatively small number of plants that
they will effectively control. Therefore, it
is imperative that you accurately identify
the offending plant and choose the cor17
Trout are especially sensitive to aquatic
herbicides.
Careful measurement of pond area and
depth is critical to determine the proper
amount of aquatic herbicide to apply to your
pond.
18
rect herbicide that will control it. Use the
information and links provided above for
assistance with proper plant identification.
Example
A nearly rectangular pond measures 275
feet long and 110 feet wide.
2. Select appropriate herbicide. Once
the plant is properly identified, the next
step is to select an appropriate herbicide
for control. Several herbicides are available for any given aquatic plant found in
ponds. The selection of the “best” herbicide
should be based on a number of variables:
• effect on the target plant needing control
• effect on other nontarget plants in the
pond
• presence of sensitive fish (like trout) or
other aquatic life
• water use restrictions for the herbicide
• cost
Appendix 1 of this publication provides
a description of the most common aquatic
herbicides used in Pennsylvania and a table
showing which plants each will control
effectively. Water use restrictions should
be carefully evaluated before choosing an
herbicide. For example, a pond owner that
needs a pond for irrigation would not want
to choose an herbicide that has a thirty-day
irrigation restriction after application.
Pond area = 275 feet x 110 feet = 30,250
square feet (ft2). There are 43,560 square
feet in one acre, so this pond is 0.69 acres
(30,250 ft2 ÷ by 43,560ft2).
3. Calculate correct herbicide dose.
Earlier in this publication you learned how
to calculate the area and volume of a pond.
Now it’s time to use those calculations. All
aquatic herbicides are applied in dosages
that are based on either the surface area of
the pond (in acres) or the volume of pond
water (in acre-feet). It is imperative that
you carefully calculate these pond parameters to ensure that you apply the proper
amount of herbicide. Measurements should
be made immediately before you intend
to apply the herbicide since pond depth
can change dramatically in a short period
of time in some ponds. Overestimating the
pond size or volume will result in overapplying an herbicide that could kill pond
fish and other aquatic life. Underestimating the pond size or volume will result in
an underapplying an herbicide that may
result in little or no control of the target
plant. Do not estimate your pond area or
depth—calculate it carefully.
Now let’s assume the pond above has
nearly the entire pond bottom covered
with elodea. After consulting information
on the Penn State Pond Management Web
site (water.cas.psu.edu/ponds.htm), the
pond owner determines that diquat dibromide is the most effective active ingredient
to control elodea in a pond with a healthy
fish population.
The label for Reward® (one of the diquat
dibromide products) recommends 1 to 2 gallons per acre of pond area to be treated (for
typical application rates of commonly used
aquatic herbicides, see the information in
Appendix 1). Given the 1- to 2-gallon-peracre recommended dose, the pond owner
uses the average of 1.5 gallons per acre.The
total amount of herbicide that would be
needed in this case would be as follows:
1.5 gallons per acre x 0.69 acres of pond
area = about 1 gallon of Reward®
Given the heavy growth of elodea, the
herbicide should be applied in two separate
treatments—half of the pond each time—
to prevent a lethal loss of dissolved oxygen
from the pond due to the death of too
much aquatic vegetation. Splitting herbicide applications into two or three treatments separated by 7 to 10 days is always a
good idea when abundant plant and algae
growth is being treated.
4. Obtain state permit for herbicide
application. Many pond owners are unaware that a state permit is necessary before
making any herbicide application to a
private pond or lake. The permit, officially
known as the Application and Permit for
Use of an Algaecide, Herbicide, or Fish Control
Chemical in Waters of the Commonwealth, is a
simple, two-page permit that is jointly reviewed by the Pennsylvania Fish and Boat
Commission and the Pennsylvania Department of Environmental Protection. The
permit must be submitted and approved by
both agencies before the herbicide is used.
It is available online at water.cas.psu.edu or
from any local PFBC or DEP office. The
permit application requires the following
information:
• Name and location of the water body,
including a topographic map or latitude
and longitude of the pond
• Specific uses of the water body
• Types of fish present in the water body
• Total area of the water body and the
size of the area to be treated
• Average depth of the water body
• Name of plant to be controlled
• Commercial and manufacturer’s name
of the chemical to be applied (Note:
Only herbicides that are registered with
the U.S. Environmental Protection
Agency, registered with the Pennsylvania Department of Agriculture, and
labeled specifically for aquatic use can
be listed on the permit application.)
• Dosage of each chemical to be applied
• Number of treatments to be made
throughout the year
Effects of the chemical in and downstream from the pond are considered in the
approval process. The permit may be denied or limited if the pond overflows into a
stream where downstream aquatic life may
be affected. In an impoundment with a wet
weather discharge, avoid problems by treating when little or no overflow is occurring.
Keep in mind that herbicides are more
likely to be effective in ponds with little or
no outflow where the chemical stays in the
water for a longer period of time.
5. Apply herbicide. Once you have received the state permit to apply the aquatic
herbicide, you can purchase it at many local
farm and home supply stores or through
numerous online outlets. Simply type the
herbicide name into any Web search engine to find online suppliers. Make sure
you purchase the correct herbicide for your
problem—using the wrong herbicide will
result in failure to control the target plant
and may damage other nontarget plants or
aquatic life in the pond.
After obtaining the herbicide, read and
follow the product label very carefully.
All aquatic herbicides are potentially dangerous and should be handled carefully. The
information on the label of the herbicide
comes from years of testing and research
required by the U.S. Environmental Protection Agency as part of the herbicide registration process. Keep in mind that the label
is the law. Applicators are legally obligated
to follow all label instructions, including
the following:
• Protective clothing. The label will
give specific information on the types
of protective clothing recommended for
each herbicide. Protective clothing such
as coveralls, boots, rubber gloves, eye
protection, and a mask or respirator are
often needed.
• Mixing instructions. Herbicides
should be mixed in an approved container or sprayer in a well-ventilated
area. If using a hose to provide water
for mixing, do not allow the hose to
be submerged in the container as this
might allow back-siphoning of the herbicide into the water line.
• Proper dosage. Herbicide doses will
usually be given in pounds or gallons of
herbicide per surface acre of pond or per
acre-foot of pond water. Double-check
your pond area or volume calculations
as described earlier in this publication to
make sure you are applying the proper
dosage. Overdosing the herbicide may
lead to damage to nontarget plants and
aquatic life, while underdosing may lead
to no control at all.
• Water use restrictions. Most aquatic
herbicides have restrictions on how the
pond water can be used for some time
period after the herbicide treatment.
These restrictions are summarized for
each herbicide in Appendix 1. Be careful not to use water in violation of these
restrictions.
• Timing of application. Applications
should be made on calm days to prevent
drifting of the chemical off site. Herbi-
Use protective clothing when applying an
aquatic herbicide. In this example, the pond
owner has eye protection, rubber gloves, long
sleeves, and leg protection as listed on the
herbicide label.
Remember! A state permit is
required to apply an aquatic
herbicide to your pond.
Aquatic herbicides should be applied when
plants are actively growing. To avoid impacts
to fish, avoid applying herbicides during fish
spawning and incubation periods.
19
Always read and follow the label of the
aquatic herbicide very carefully. Failure to do
so may cause personal injury or damage to
aquatic life.
Professional herbicide applicators can be
hired to apply herbicides to ponds or lakes.
20
cides should also be applied when the
target plant is actively growing but not
when the plant has already reached a
nuisance level (see the “Cautions about
Using Aquatic Herbicides” section below). Most aquatic herbicides work best
when applied to warmer water above
60ºF. Avoid applying herbicides when
fish are spawning in the pond (usually
during May and early June).
• Application method. The method
used to apply an herbicide varies between liquid and granular products.
They range from use of a backpack
sprayer to hand application of granules
from the shoreline. In general, when
applying herbicides along shorelines or
spot-treating weed beds, start applications along the shoreline or in the shallowest area and apply out to the deeper
water. This will enable fish to move into
deeper water to escape the chemical.
• Cleanup. Once the herbicide application is complete, all equipment should
be cleaned. The wastewater produced
from cleaning the spraying container can
be added to the pond as long as it does
not exceed the dosage allowed for the
herbicide. Other wastes from the cleanup
should be disposed of according to the
herbicide label. Be sure to wash hands
and any other exposed body areas after
completing the herbicide application.
• Storage. Unused herbicide should be
stored in the original container with the
label intact in a cool, dry, and ventilated
location.
6. Make follow-up herbicide applications. Completely eradicating a nuisance
plant through the use of aquatic herbicides
is rarely accomplished and unrealistic. More
often, the herbicide treatment will reduce
the growth below a nuisance level. Aquatic
herbicides often must be reapplied every
year or every few years to keep a problem
plant under control. Multiple applications
during a year, however, should be done
with great caution. This can be damaging to both the pond ecosystem and the
pond owner’s wallet. Herbicide applications
that are made too frequently may result
in high concentrations of the chemical in
the water that result from one application
overlapping on the residual chemical from
a previous application. Frequent treatments
can also cause accumulation of chemicals
in the pond sediments and the possibility
of plants or algae becoming resistant to the
herbicide active ingredient. The problems
associated with frequent reapplications of
chemicals can best be avoided by treating
the plant or algae early in the growing season before it becomes a major problem or
through combining the nonchemical plant
control strategies discussed earlier in this
publication.
Professional Herbicide Applicators
Keep in mind that many professional consultants are available to apply herbicides to
a pond or lake. These consultants must be
state certified to make herbicide applications. They can take care of all aspects of
an herbicide application, including choice
of herbicide, permit acquisition, and application of the chemical. A complete list
of state-certified aquatic herbicide applicators is available at the Penn State Pond
Management Web site at water.cas.psu.
edu/ponds.htm.
Cautions about Using Aquatic
Herbicides
Each year many pond owners experience
problems when using aquatic herbicides for
plant control in ponds. These problems often can be traced to the following mistakes:
• Failure to acquire state permit. The
state permit is not only required by law
but also provides a valuable service to
prevent the use of incorrect or inappropriate aquatic herbicides. The permit
process allows an aquatic herbicide expert to review the target plant to ensure
that the correct herbicide and dose are
being used to minimize the chances of
an accidental fish kill.
• Overdose of herbicide. An overdose
of herbicide can cause direct toxicity to
fish and other aquatic life, along with
death of nontarget plants in the pond.
Herbicide overdoses may be caused by
inaccurate estimates of pond area or
volume or incorrect measurement of
the amount of herbicide.
• Failure to follow the herbicide label. Problems may arise if the herbicide
is not used according to the label. These
problems might include application at
the wrong time of year, incorrect herbicide for target plant, using water in
violation of the water use restrictions,
wrong application method, or incorrect
dose. In short, read the herbicide label carefully to avoid these problems.
• Treatment of too much vegetation.
A very common problem associated
with aquatic herbicide use is indirect
death of fish due to oxygen depletion.
This occurs when too many aquatic
plants are killed quickly. The resulting
decay of large amounts of plants or algae
will consume oxygen from the pond
water, causing fish mortality. To reduce
this danger, treat only one-third to onehalf of the pond at a time when controlling abundant plant or algae growth.
Summary and Sources of More
Information
Nuisance growth of aquatic algae and
plants is the most common problem reported by pond owners in Pennsylvania.
Excessive addition of nutrients into the
pond through natural processes and landuse activities around the pond are usually
to blame for this growth. Pond owners
frequently rely on aquatic herbicides for
a quick fix—sometimes with disastrous
results.
Proper management of aquatic plants
and algae usually requires a comprehensive
plan that includes reduction in nutrient
loads and a combination of physical, biological, and/or chemical control strategies. Explore all the control options before taking
action. Where aquatic herbicides are found
to be a suitable part of the management
plan, be sure to obtain the proper state permit, choose the least damaging chemical
possible, and follow the label carefully to
maximize the chance of success and minimize the chance of detrimental impacts.
For more information on
all aspects of pond management, consult the Penn
State Cooperative Extension
Water Resources Web site
(water.cas.psu.edu) and
choose “Pond Management”
from the menu.
Improper use of aquatic herbicides may result in fish kills.
21
Appendix 1
Herbicide Descriptions
Aquashade
• Active ingredient: Various dyes (acid
blue dye, acid yellow dye, etc.)
• Mode of action: Designed to shade
portions of the light spectrum required
by underwater aquatic plant and algae
growth
• Uses: Normally used to control planktonic algae, but also can inhibit photosynthesis in filamentous algae and
submerged aquatic vegetation if applied
early during the growing season
• Dose: Usually applied at a rate of 1
quart per acre-foot early in the growing season before plants or algae reach a
nuisance level
• Cautions: Dyes should not be used and
will not be permitted for ponds with a
significant outflow to a surface stream;
dyes should also be used early in the
season while algae and plants are confined to the bottom of the pond
• Approximate cost: $30 per acre-foot of
pond volume
• Water use restrictions: None
Aquathol-K
• Active ingredient: Dipotassium salt of
endothall
• Mode of action: Contact herbicide that
inhibits photosynthesis
• Uses: Effective on most submerged
pondweeds, milfoil, coontail, and naiad
• Dose: Normally applied at a rate of 0.6
to 1.9 gallons per acre-foot
• Cautions: Breaks down rapidly but still
very toxic to trout
• Approximate cost: $200 per acre-foot of
pond volume
• Water use restrictions: Irrigation and
watering livestock should be prohibited
for 7 to 25 days
22
Copper Sulfate
• Active ingredient: Copper sulfate
• Mode of action: Usually applied as a
blue crystal, it disrupts the cell membrane, which inhibits the cell growth
• Uses: Effective on all types of algae,
although the long-term use of this
product has led to algae that are now
resistant to it
• Dose: Normally applied at a rate of 0.68
to 1.36 pounds per acre-foot
• Cautions: Water hardness should be
measured in the pond prior to application because hardness directly affects the
dosage and toxicity of copper sulfate;
copper sulfate should not be used where
trout, grass carp, koi, channel catfish, or
other sensitive fish exist; slight overdoses
of coppers sulfate can kill even more
tolerant fish species; a state permit will
not be granted for the use of copper
sulfate if the pond overflows into a surface stream with fish
• Approximate cost: Less than $10 per
acre-foot of pond volume
• Water use restrictions: None
Cutrine Plus, Cutrine Ultra,
Earthtec, K-Tea
• Active ingredient: Various percentages
of elemental copper
• Mode of action: Similar to copper
sulfate except these are chelated copper compounds that prevent the copper from precipitating out of solution
in hard water; most are available as a
granular (for bottom-dwelling algae) or
liquid (for floating or suspended algae)
formulation; Cutrine Ultra was recently
developed for algae that are resistant to
other copper algaecides
• Uses: Effective on all types of algae
• Dose: Cutrine-Plus liquid = 0.6 to
1.2 gallons per acre-foot, Cutrine-Plus
granular = 60 pounds per acre, Cutrine
Ultra = 0.6 to 3.0 gallons per acre-foot,
Earthtec = 0.22 gallons per acre-foot,
K-Tea = 0.7 to 1.7 gallons per acrefoot for planktonic or filamentous algae
and 1.7 to 3.4 gallons per acre-foot for
branched algae
• Cautions: Similar to copper sulfate—
these products should not be used in
ponds with trout, carp, koi, channel catfish, or other sensitive fish species; treat
one-third to one-half of the pond at a
time
• Approximate costs: Less than $50 per
acre-foot for filamentous and planktonic
algae, $100 to $150 per acre-foot for
branched algae
• Water use restrictions: None
GreenClean
• Active ingredient: Sodium carbonate
peroxyhydrate
• Mode of action: Granular product first
sold in 2004 for algae control; works
rapidly through direct contact and oxidation
• Uses: Used on filamentous or planktonic algae, especially where copperresistant algae occur or where fish
species sensitive to copper are present
• Dose: Normal application rates are 3 to
17 pounds per acre-foot depending on
the amount of algae growth
• Cautions: None
• Approximate cost: $50 to $200 per acrefoot depending on severity of problem
• Water use restrictions: None
Komeen
• Active ingredient: Elemental copper
• Mode of action: See information above
for Cutrine Plus
• Uses: Although this is a copper-based
herbicide, it is not used to control algae;
instead, it provides broad control of submerged aquatic plants like pondweeds,
elodea, coontail, and milfoil
• Dose: 1.7 to 3.3 gallons per acre-foot
• Cautions: As with other copper herbicides, it should not be used in ponds
with sensitive fish species like trout,
grass carp, koi, or channel catfish; since
it is a chelated copper compound, it is
not affected by water hardness
• Approximate cost: $70 to $150 per acrefoot
• Water use restriction: Ponds used for
human drinking water should not contain more than 1 part per million of
copper after application
Navigate/AquaKleen/Aquacide
• Active ingredient: 2,4–D
• Mode of action: These are systemic
herbicides that cause the plant cells to
divide rapidly and respiration to increase
while photosynthesis decreases causing
exhaustion of the plants food supply
• Uses: Mostly used for floating plants like
water lily, spatterdock, and watershield;
some use for a few submerged plants
like milfoil and bladderwort
• Dose: 100 to 200 pounds per acre (lower dose for submerged plants, higher for
floating plants)
• Cautions: Not used frequently because
of water use restrictions listed below
• Approximate cost: $300 per acre (submerged plants) to $600 per acre (floating plants)
• Water use restrictions: Should not be
used on water bodies that are used for
irrigation, animal watering, or human
consumption
Reward/Weedtrine-D
• Active ingredient: Diquat dibromide
• Mode of action: Systemic herbicide that
is quickly absorbed by plant tissues and
interferes with photosynthesis
• Uses: Broad control of nearly all submerged aquatic plants
• Dose: Reward = 1 to 2 gallons per acre,
Weedtrine-D = 5 to 10 gallons per acre
• Cautions: Few because diquat decomposes in aquatic environments through
microbial degradation and exposure to
light
• Approximate cost: $150 to $400 per
acre
• Water use restriction: One to five days
(Reward); 14 days (Weedtrine) for irrigation and animal drinking water
Rodeo
• Active ingredient: Glyphosate
• Mode of action: Glyphosate is a systemic herbicide that moves through the
plant from the point of foliage contact
into the root system; this results in a cessation of growth, cellular disruption, and
eventually plant death
• Uses: Used for many emergent plants
like cattail, arrowhead, purple loosestrife,
and common reed; also can be used for
some floating plants like water lily, spatterdock, and watershield
• Dose: 0.75 gallons per acre for emergent
plants; 0.5 to 0.9 gallons per acre for
floating plants
• Cautions: Rodeo should be applied
during the active growing season until
later summer
• Approximate cost: $30 to $70 per acre
• Water use restrictions: None
Sonar SRP and Sonar A.S.
• Active ingredient: Fluridone
• Mode of action: A systemic herbicide
that is absorbed through leaves and
roots; absorbed fluridone inhibits carotene formation; the absence of carotene
pigment causes unprotected chlorophyll
to photodegrade, causing plant death
• Uses: Sonar SRP can be used on many
submerged aquatic plants; Sonar A.S. is
useful for many floating plants and a few
submerged plant species
• Dose: 3.2 to 5 pounds per acre-foot
(Sonar SRP), 0.16 to 1.5 quarts per
acre-foot (Sonar A.S.)
• Cautions: This product needs a long
contact time to work effectively; it is
best used on ponds with little or no
overflow; split treatments may be beneficial to maintain a more constant concentration
• Approximate cost: $500 to $1,000 per
acre
• Water use restriction: Seven to thirtyday restriction on irrigation use of water
23
Table 1. Effectiveness of various aquatic herbicides on common aquatic plants and algae in Pennsylvania ponds.1
Filamentous algae
Aquashade
Aquathol-K
Copper2
GreenClean
Komeen
Navigate/
AquaKleen/
Aquacide
+++
—
+++
+++
—
—
Reward/
Weedtrine-D
Rodeo
Sonar
+
—
—
Planktonic algae
++
—
+++
+++
—
—
++
—
—
Branched algae
(Chara, Nitella)
+++
—
+++
++
—
—
++
—
—
Bladderwort
—
—
+
—
—
+++
+++
—
+++
Coontail
++
+++
+
—
+++
++
+++
—
+++
Elodea
++
+
+
—
+++
++
+++
—
+++
Eurasian milfoil
++
+++
+
—
+++
+++
+++
—
+++
Hydrilla
++
++
++
—
++
—
++
—
+++
Naiad
++
+++
+
—
+++
—
+++
—
+++
Parrotfeather
++
+++
+
—
++
—
+++
—
+++
Pondweeds
++
+++
+
—
+++
—
+++
—
+++
Duckweed
—
—
—
—
—
—
++
—
+++
Spatterdock
—
—
—
—
—
+++
—
+++
+++
Water lily
—
—
—
—
—
+++
—
+++
+++
Watermeal
—
—
—
—
—
—
—
—
++
Watershield
—
—
—
—
—
+++
—
+++
+++
Yellow floating heart
—
—
—
—
—
++
—
+++
+++
Arrowhead
—
+
—
—
—
—
++
+++
—
Bulrush
—
—
—
—
—
++
—
+++
—
Cattail
—
—
—
—
—
—
+++3
+++
+
Common reed
—
—
—
—
—
—
—
++
—
Pickerelweed
—
—
—
—
—
—
++
++
—
Purple loosestrife
—
—
—
—
—
—
—
+++
—
+++ = excellent control; ++ = good control; + = some control; — = little or no control
1. All ratings assume that the product is used early in the growing season to suppress growth. Mid- to late-summer use not recommended.
2. Includes copper sulfate, Cutrine Plus, Cutrine Ultra, Earthtec, and K-Tea.
3. Surfactant use recommended.
24
3
Prepared by Bryan Swistock, senior
extension associate, School of Forest
Resources; and Mark Hartle, chief, Aquatic
Resources Section, Division of Environmental
Services, Pennsylvania Fish and Boat
Commission.
This publication was supported, in part,
with funding from the U.S. Environmental
Protection Agency, Region 3, Pesticide
Misuse Initiative, under Grant Agreement
97337101.
Based on Pond Management and Aquatic
Plant Control (The Pennsylvania State
University, 1998) by Daniel Angelo,
Penn State Pesticide Education Program;
Mark Hartle, Pennsylvania Fish and Boat
Commission; and Winand Hock, professor
of plant pathology and director of Pesticide
Education Program.
The authors wish to thank the following
individuals who served as reviewers for
versions of this publication:
Thomas McCarty, senior extension
educator, Penn State Cooperative
Extension, Cumberland County
Heather Smiles, fisheries biologist,
Pennsylvania Fish and Boat Commission
Ed Molesky, owner, Aqua Link, Inc. and
Hydro Logic Products, Doylestown,
Pennsylvania
Eric Lorenz, senior extension associate,
Pesticide Education Program, Penn State
Photo Credits
Cover; pages 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,
17, 18, 19, 20: Bryan Swistock
Inside cover; pages 4, 8, 15: Ed Molesky,
Aqua Link, Inc. and Hydro Logic Products
Page 3: Dr. Richard Soderberg, Mansfield
University of Pennsylvania
Page 5: Louis Cunfer
Pages 8, 10, 16, 21: Mark Hartle,
Pennsylvania Fish and Boat Commission
Page 9: Susan Boser, Penn State
Cooperative Extension, Beaver County
Pages 9, 11: Amy Smagula, New Hampshire
Department of Environmental Services
Page 11: Nadine Barrie Smith
Pages 14, 15: Heather Smiles, Pennsylvania
Fish and Boat Commission
Page 18: Adam Kaeser
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