Texas has more than 800 thousand private ponds. Recreation is probably the most important reason for building a pond; and for good reason, with July 4th weekend behind us recreational water sources are being used extensively. Because of that, many folks have been expressing concerns over aquatic weeds. If too many weeds become established in a pond, too many small fish overpopulate the pond and predators become thin because they are not able to prey on the forage species hidden in the weeds. Large growths of weeds also remove nutrients needed for (algae) fish food production. Aquatic weeds can also become problematic for swimming, boating, and fishing. Aquatic weeds are difficult to control once they have become established in a pond. Therefore, the best way to control them is prevention. Preventive measures include: building the pond so that banks slope steeply to a depth of at least 2 1/2 feet; fertilizing to establish an algal bloom before weeds appear; and stocking triploid grass carp.
Fertilizing to establish a bloom and steep bank slopes both help keep the pond bottom shaded. Rooted plants cannot get started if the bottom is shaded. Stocking triploid grass carp is the best overall way to prevent and control aquatic weed growth. Grass carp eat almost all types of submerged aquatic plants. Compared to herbicide treatments, they are relatively inexpensive because they control submerged weeds effectively for many years (usually 5 to 7). Grass carp do not eat other fish or their eggs, do not muddy the water and cannot reproduce in ponds. Because they cannot reproduce, they must be restocked as they age and can no longer control weeds effectively. To keep grass carp in a pond during heavy rains, build a barrier across the pondís emergency spillway. Permits for stocking triploid grass carp must be obtained from the Texas Parks and Wildlife Department. Permits cost $15 plus $2 per carp. This does not include the cost of the fish, which can only be purchased from a licensed provider.
However, if aquatic weeds have established and taken over your favorite swimming hole or stock pond there is hope. Management practices that can help reduce aquatic weed problems include maintaining a good grass sod around the pond, keeping livestock and waterfowl out of the pond to prevent adding fertilizer to the pond, and examining the land area drainage into the pond to identify sources of fertilizer and pollution inputs. These practices will eliminate excess nutrients that increase the potential for excessive algae and weed growth.
If it becomes necessary to chemically treat the weed problem, the best time to treat most aquatic weeds is late spring or early summer when the plants are young and actively growing. Do not wait until late summer to treat a weed problem. Killing a lot of vegetation all at once can result in a fish kill. This is due to the lack of oxygen in the water not due to toxicity of the chemical to the fish. If it is necessary to treat in the summer, treat only small portions of the pond at a time. Algae can be controlled with copper sulfate or copper chelates. Control underwater flowering plants with endothall, diquat, or fluridone. Emergent plants such as cattails, willows and bulrush can be controlled with glyphosate plus surfactant. Pesticide applicators should always read and follow label directions and restrictions (swimming, fishing, drinking, etc.) before using any herbicide.
The key to selecting the proper herbicide needed to achieve control of a weed species is correctly identifying the problematic weed species. An excellent resource to help pond owners identify aquatic weeds and to make other pond management decisions can be found at http://aquaplant.tamu.edu/.
Individuals with disabilities, who require an auxiliary aid, service or accommodation in order to participate in any of the mentioned activities, are encouraged to contact the County Extension Office eight days before all programs for assistance. Extension programs serve people of all ages regardless of socioeconomic level, race, color, sex, religion, disability or national origin.