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. 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.