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 simplified, 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 with
hairlike roots. Duckweed is the most common floating plant, seldom
creating problems.
Submerged plants
These plants usually 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
Two methods of reducing or eliminating nuisance aquatic vegetation
are: mechanical 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.
Chemical
No single all-purpose chemical that controls all aquatic weeds exists.
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 60 degrees F. Regrowth or belated appearance of dormant weed species require 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 insure 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 by green plants disappears or is greatly reduced. Oxygen levels may be reduced to levels 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 to prevent failures 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. Rodeo works well on cattails, which is the most common emergent aquatic plant. 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, use of water for livestock and irrigation.