Aquatic weed control is a management plan that incorporates preventive methods such as proper pond construction and maintenance, biological methods such as the grass carp (Ctenopharyngodon idella)and the use of labeled aquatic herbicides.
The development of an aquatic weed management plan is dependent upon correctly identifying the problem weed(s) and selecting control methods that are compatible with efficient fish culture procedures.
Basic methods used to control weeds include preventive, mechanical, biological and chemical techniques. Determining which of these techniques to use involves consideration of the target weed species, fish production objectives for the pond, secondary water uses and the cost of treatment options.
Preventive methods:
It is easier and less costly to prevent weed problems than it is to control them once they develop. Careful pond site selection and proper pond construction practices are the first steps in preventing aquatic weed problems.
Rooted aquatic weeds and algae usually begin growing in shallow water ( < 2 feet). Edges of new and existing ponds should be deepened so shallow water areas are minimized. The USDA Soil Conservation Service provides technical assistance for pond construction and renovation.
Farm ponds are commonly fertilized t. increase the fish production . capacity of the pond. Fertilization is also an effective and economical way to prevent the growth of many aquatic weeds. Fertilization stimulates the growth of plankton algae.
This algal growth is known as a bloom. The bloom blocks sunlight from reaching the pond bottom which limits the establishment of rooted aquatic weeds. The key to successful control of aquatic weeds with fertilization is to establish and maintain a bloom before rooted weeds begin spring growth.
Decreasing the pond water level exposes shallow areas to freezing temperatures and drying and can effectively limit certain types of submersed weeds. For a drawdown to be effective, the water level should be lowered in the late fall and not allowed to refill until the early spring.
Some weeds, such as hydrilla and cattail (Typhaspp.), are tolerant to drawdown and cannot be controlled by this method.
Biological control:
The grass carp is a practical and economical way to control certain types of pond weeds. Grass carp effectively control weeds with tender succulent vegetation such as filamentous algae and duckweed, but are ineffective in controlling weeds that have tough, woody vegetation such as waterlily and cattail.
Many states regulate the use of grass carp. Contact your Department of Natural Resources representative for state regulations on the use of grass carp.
Mechanical methods:
Various types of aquatic weed cutters and harvesters have been developed for canals and large reservoirs. Use of these machines is not practical in fish ponds. Early manual removal of weeds by seining or raking can prevent some weed problems.
Chemical control:
Herbicides may be used to control weeds in commercial fish ponds. The first step in successful chemical control is accurate identification of the problem weed. Weed identification assistance is available through county Extension and Department of Natural Resources offices. After the weed has been identified, a herbicide that is labeled for commercial fish ponds may be selected. The herbicide label must be read and fully understood by the user prior to application to the pond.
Integrated weed management:
Herbicides should be considered as a temporary control method. Depending upon the herbicide selection and the weed species, duration of control can range from a few weeks to several months. Long-term weed control can be achieved by using a combination of recommended aquatic weed methods.
For example, use of the proper herbicides followed by grass carp stocking will effectively control and prevent the reoccurrence of most submersed weed problems.
Authors:
JamesL. Sheltonand Tim R. Murphy
