• recreational waters used for fishing, boating, and aquatic sports,
• agricultural reservoirs and water distribution channels used for stock-watering, irrigation, and drainage,
• ornamental ponds,
• coastal bays, estuaries, and channels, and .drinking water reservoirs.

Effective management of aquatic pests requires the combination of all appropriate control methods,
including:

• mechanical
• biological
• chemical
• cultural

AQUATIC WEEDS:

The first step towards prevention or control of aquatic weeds is to identify them correctly. Most control methods are aimed at specific weeds or at groups of weeds with similar growth habits. Aquatic weeds can be grouped as follows:

• Emersed aquatic weeds-weeds that grow standing out of the water, or in water-saturated soils. Examples are cattails, bulrushes, and arrowheads.
• Submersed aquatic weeds-weeds that grow under the water surface. Examples are pondweeds, naiads, coon-tails, and water-milfoils.
• Floating aquatic weeds-weeds that float on the water surface. Examples are duckweeds, water-hyacinth, water-lettuce, water-fens, and water- lilies.
• Algae weeds without true stems, leaves, or vascular systems. Examples are watemet, pithophora, and chara.

Many of these plants may be pests in some situations and desirable plants in others, depending on:

• their abundance and
• the use of the water they inhabit.

POND AND DITCH DESIGN:

Proper design and construction of ponds is an important factor in preventive control of weeds. shallow water at the margins of ponds provides an ideal habitat for emersed weeds, such as cattail. Submersed weeds can easily become established there and then spread into deeper water. Banks should be sloped steeply so that there is very little water less than 2 or 3 feet deep.
Proper design and construction of ditches and channels makes weed control easier in the future. If the banks are leveled and smoothed, hard-to-reach places will be eliminated. Lining canals will help in alleviating water weed problems.
 

MECHANICAL CONTROL:

It may be necessary to use mechanical methods to control submersed weeds. Sources of water for drinking, for livestock, and for fish ponds often cannot be treated with chemicals.

• Chaining may be practical in some instances, particularly in canals,
• Drag lines are useful for cleaning canals and margins of lakes and ponds.
• Weed mowers are used in both canals and lakes for cutting weeds, Some mowers simply cut the weeds loose beneath the water surface. Others (aquatic weed harvesters)
  collect the weeds for removal from the water. Disposal of harvested weeds is often a problem.

 Most methods of mechanical control fragment the weeds. This may actually aid in the spread of most species of weeds, since they may reproduce from the pieces. Mechanical control is usually slower and more costly than control of the same weeds with chemicals.

DRAINING AND DRYING:

Some ponds, lakes, canals, and ditches may be drained so aquatic weeds will dry .The water levels in some large lakes and reservoirs may be lowered enough to expose weeds in shallow areas. Drying periods of several months may be needed to control weeds in some ponds and lakes. In canals, it may not be practical to interrupt water flow for longer than 3 or 4 days. The season of year and species of plant present may determine whether this method will be useful in a particular situation. Be sure to consider the resident fish species and their normal spawning times.
 

FERTILIZATION:

Fertilization with inorganic nutrients may be a convenient and inexpensive method for control of weeds in ponds and small lakes. Fertilization stimulates a dense bloom of microscopic algae. The algae shade the pond bottom and prevent or reduce the growth of submersed weeds. Unless the fertilization is done correctly, however, the weed problem may become even more severe. The fertilizer may be applied broadcast, applied from a boat, or dissolved in the water in other ways. Existing weeds either are not affected or their growth may be stimulated. You may need to remove them before fertilizing. Ponds that have a monthly water exchange greater than the capacity of the pond do not respond well to fertilization. Fertilizers are more effective in deep water than in shallow water.

BIOLOGICAL CONTROL:

Biological control is not often used. It has been successful in several situations. Biological control agents include:

• Tilapia-This plant-eating fish has only limited value. It will eat aquatic plants and reproduce
  rapidly, but it survives winter temperatures in only a very few areas of this country .
• White amur-The white amur is a large fish that eats la}:ge amounts of aquatic plants. It survives well in many areas of the United States. Because its environmental hazards are not fully known only a few States permit its use.
• Insects-Several insects have been brought into this country to control aquatic weeds. The most successful are a beetle arid a moth that are parasitic on alligatorweed. They have provided good control of this weed in large areas of the South. Other insects are under study for control of other species of weeds.

CONTROL WITH PESTICIDES:

Chemicals used in aquatic weed control are classified as herbicides. Herbicides used primarily for control of algae are called algicides, even though they may also kill other aquatic plants. Aquatic herbicides are available in several formulations:

SPRAYABLE FORMULATIONS-Most herbicides are formulated to be mixed with a water carrier and sprayed. Some perform best as aquatic herbicides when applied into static or flowing water so that they disperse evenly and contact underwater surfaces of weeds. Kinds available are:

• water-soluble powders or crystals that form true solutions in water,
• wettable powders that can be suspended in water and applied,
• water-soluble liquid concentrates that form true solutions in water,
• emulsifiable liquid concentrates that form ordinary "oil-in-water" emulsions in water, and
• special liquid concentrates that form "water-in oil" emulsions {called invert emulsions) when mixed with water and oil in the spray tank or when applied through special mixing nozzles.

GRANULAR FORMATIONS-Many aquatic herbicides are used as dry granules of various sizes. Kinds available are:

• granulated pure chemical, such as crystalline cop- per sulfate,
• granules or larger-size pellets of clay and other materials impregnated with active ingredient, and
• slow-release granules or pellets designed to re- lease the active ingredient in small amounts over an extended period of time in the water.
   

Spraying Water Hyacinths

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