Quick Facts...
- In moderate amounts, aquatic vegetation is beneficial to the
natural ecosystem of most lakes and ponds.
- Reduce aquatic vegetation if it interferes with fishing,
boating or swimming.
- Proper plant identification is necessary when considering
aquatic vegetation control.
- Aquatic plant classification is based on growth form and
location in the pond.
- Three methods of vegetation control are: mechanical,
biological and chemical.
Aquatic vegetation is found in most lakes and ponds and is
beneficial to the natural ecosystem in moderate amounts.
Vegetation is needed for food production and cover for fish.
Aquatic plants produce oxygen, stabilize bottom sediment, protect
the shoreline from wave erosion, and serve as feeding and nesting
habitat for waterfowl.
Aquatic vegetation can become so abundant it interferes with
recreational use. When fishing, boating or swimming is seriously
impeded, aquatic vegetation should be reduced. Periodic die-offs
of dense vegetation also occur after periods of cloudy weather,
long winter ice and snow cover, or the end of their growing
season. Oxygen is consumed by bacteria that decompose dead
plants. Microscopic bacteria can be so abundant that they can
lower oxygen levels, inhibit fish from feeding and growing, and
possibly cause death.
Identification
Probably the most essential thing to know in aquatic
vegetation control is the type of plant causing the problem.
Aquatic plants are classified into general categories
based on their growth form and location.
Algae
Algae are primitive plants with no true leaves or flowers.
They have three classifications: planktonic, filamentous, and
attached-erect forms.
Planktonic algae (often called phytoplankton) gives the
water a green to greenish-brown tint, but individual plants
cannot be seen without a microscope. Filamentous algae, often
referred to as "moss," float freely and form greenish mats on the
surface. The attached, erect forms often are mistaken for higher
plants. The best way to identify these advanced algae is by the
musky odor and gritty feel. Common examples of algae are
spirogyra, cladophora and chara.
Floating Plants
This group includes plants that have leaves floating on the
surface and roots hanging down into the water not connected to
the bottom. Their leaves usually are smaller than the end of a
wooden match stick, and they have hairlike roots. Duckweed is the most
common floating plant, seldom creating problems.
Submerged Plants
These plants are rooted to the pond bottom and grow
to the surface. Submerged weeds usually consist of long flexible
stems with clumps of narrow leaves around the stem. Flowers, if
present, may extend above the surface. Common examples of
submerged plants are potamogeton, coontail and elodea.
Emergent Plants
This type of plant is rooted in the pond bottom with
extensions above the water's surface. Shoreline plants are
included in this group. Many are not truly aquatic, but can live
in saturated soils or submerged in water for considerable time.
Common examples of emergent plants are cattails, bulrush,
smartweed and arrowhead.
Control
Three methods of reducing or eliminating nuisance aquatic
vegetation are mechanical, biological and chemical.
Mechanical
Mechanical control involves physically removing plants from
the pond. Hand-pulling is effective to control cattails, willow
trees and cottonwood trees while they are small. Rake to remove
algae and submerged vegetation from the pond, especially around a
swimming area. Submerged vegetation also can be removed by
pulling a chain or cable through the pond between two tractors.
Mechanical control is temporary and normally affects a
portion of the pond's vegetation. It is the least effective
method and may aggravate the problem because some aquatic plants
spread through broken fragments and become new plants.
Biological
Biological control includes the most effective control for Colorado warmwater ponds: the grass carp, an herbivorous fish. The grass carp requires large rivers for spawning and does not reproduce in ponds. The Colorado Division of Wildlife requires notification of stocking. Only triploid grass carp are permitted on the West Slope. Grass carp stocked on the West Slope must also meet the stocking criteria of the Upper Colorado River fish recovery program.
Grass carp are expensive but can provide many summers of vegetation control with one stocking. Little evidence of control will be seen the first summer but change will appear the second. Stock fingerling grass carp (3 to 4 inches) at the rate of 10 to 25 fish per acre of vegetation. If adult bass are present, stock grass carp of at least 8 inches to avoid predation. After several years, additional grass carp will have to be stocked when consumption of vegetation by large grass carp declines.
Ducks, geese and crayfish are used to control aquatic
plants. They produce inconsistent results, and some pond owners
object to the mess waterfowl can make.
Fertilization can be used to discourage other types of aquatic vegetation and promote phytoplankton. This method has produced inconsistent results, can cause oxygen depletion, and is not recommended for Colorado ponds.
Chemical
No single, all-purpose chemical exists to control all aquatic weeds. Proper plant identification is important for
selecting the best chemical for a specific vegetation problem.
Generally, chemical applications are most effective when
weeds grow rapidly and have not yet gone to seed. One to two
treatments usually are sufficient to control submerged
vegetation, whereas one to four treatments may be needed to
control algae for a season. Do not apply chemicals in strong
winds where drift might occur. Apply chemicals early in the day
under sunny conditions and water temperature above 60 degrees F.
Regrowth or belated appearance of dormant weed species requires
re-treatment.
After the nuisance plant is identified, choose the proper
chemical and read the label carefully. Next determine the area to
be treated. Application of the chemical can be done by hand,
pressure tank sprayer, or by ladling the chemical from a bucket.
Dilute the chemical tenfold with water to ensure uniform coverage
over the area to be treated. Mix only as much chemical as is
needed for the job.
Usually plants begin to show signs of weakness,
discoloration or drooping within two weeks; plants may even die.
Filamentous algae often turn a pale green or yellow. When large
masses of plant materials decay, nutrients are released and can
lead to plankton or filamentous algae growth. Bacteria that
multiply to take advantage of the rotting vegetation consume
oxygen. At the same time demand for oxygen increases, production
of oxygen by green plants disappears or is greatly reduced.
Oxygen levels may be so reduced that fish die. Reduction
of plants in the spring or early summer before large growth
occurs usually prevents oxygen depletion. If treatment is not
done until heavy growth occurs, treat the pond in sections with
at least two weeks between treatments.
Failures may be due to one or more of the following reasons: - not reading and following directions on the label;
- misidentification of the weed; or
- miscalculation of treatment volume.
Other things to consider prior to treatment are adverse weather conditions or high water exchange in the pond.
Chemicals are registered for specific uses and few are
cleared for aquatic use. Cutrine is effective on algae. Control
submerged plants with Aquathol; the potassium formulation is more
effective in Colorado than the sodium formulation. Rodeo works
well on cattails, which is the most common emergent aquatic plant
in Colorado. Many chemicals have restrictions on the use of water
for a period of time after application. Follow the directions on
the label and read restrictions on fishing, swimming, and use of
water for livestock, and irrigation.
To obtain names and addresses of most major herbicide
manufacturers and distributors in Colorado, contact your Colorado
State University Extension county office.
References
- How to Identify and Control Water Weeds and Algae. Applied
Biochemists, Inc. 5300 West County Line Road, Mequon, WI 53092.
Fee required.
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