June 2, 2023 - When you break up pond questions into different management questions, how to clear out excess vegetation is at the top of that list.
Before we start, please understand that some vegetation is good and even needed in most ponds. Vegetation provides cover for fish and helps add oxygen. But as we can imagine, too much vegetation can lead to problems as well.
There are four kinds of aquatic vegetation: submersed, emergent, floating, and algae or other plankton. Submerged plants are rooted plants with most of their vegetative mass below the water surface. Emergent plants are rooted plants often along the shoreline that stand above the surface of the water (cattails for example). True floating plants are not attached to the bottom. Algae are very primitive plants. Some algae are microscopic (planktonic algae). Others are thin and stringy or hair-like (filamentous algae).
Herbicides approved for aquatic weeds, when applied according to the label, are an effective, safe, and environmentally responsible method of eliminating excess vegetation.
Timing is important when applying aquatic herbicides. Pond owners will find a poor response to any treatment that is made in the dead of winter when vegetation is not actively growing. Fall is too late to do much good and summer may find aquatic weeds that are already causing too many problems to solve.
That leaves late spring and early summer as the ideal time to stay ahead of excessive pond weed growth. True, you can treat weeds later in the summer months, but you will have more total vegetation to contend with and you could run into a low oxygen problem if you try and treat too much of your pond’s weeds at once.
How do we have an oxygen problem that kills fish after killing weeds in the summer? First, warm water holds less oxygen than cold water. There is some hard science behind this fact. Specifically, “The solubility of oxygen decreases as the water temperature increases.” This means that colder water can hold more dissolved oxygen available to fish than warmer waters.
Additionally, when something is killed and begins to rot, the decomposition process consumes oxygen. A dead squirrel on the side of the road will not cause any serious lack of oxygen, but the drop in oxygen in a pond full of decomposing vegetation is not easily replenished.
So, if you combine warmer pond water in the summer with a large mass of decomposing vegetation, you certainly can have fish die from lack of oxygen. But do not blame the product used. The blame is all on the timing and actions of the applicator.
You may ask how to avoid any fish die-off in the summer months or during any other time of the year. The solution is to treat no more than a third of the pond at a time so that fish have oxygen available.
With the large number of products available, there is not enough room in this article to cover them all. Proper identification is a must for any success. Don’t hesitate to bring in samples of weeds and I will help with weed identification and treatment.
Let me say it again, herbicides approved for use in ponds will not kill fish. If they did kill fish, then I cannot imagine how they would ever have been approved.
It is also important to state that there are products commonly used in ponds that have no business being applied. If the label does not state that it can be used in a pond with specific instructions on how to apply it, then it is not legal to use in a pond. No, I don’t care what your neighbor said, if it is not labeled, then it is out of bounds.
Lane Dunn is the County Extension Agent for agriculture and natural resources for Shelby County. His email address is firstname.lastname@example.org .
Educational programs of the Texas A&M AgriLife Extension Service are open to all people without regard to race, color, sex, disability, religion, age, national origin, genetic information or veteran status. The Texas A&M University System, U.S. Department of Agriculture, and the County Commissioners Courts of Texas Cooperating.