Cattails, plants belonging to the genus Typha, are a common sight in wetlands, ponds, and slow-moving waters across North America. These emergent aquatic plants are characterized by their tall, slender stalks and distinctive brown, cylindrical seed heads. While they are a natural part of the ecosystem, their aggressive growth habit allows them to quickly colonize shallow areas. Homeowners and pond managers often seek effective control methods that eliminate these plants without introducing substances toxic to fish populations.
Why Cattail Management Is Essential
Unchecked cattail growth can severely compromise the health and usability of an aquatic ecosystem. The plants spread rapidly through wind-dispersed seeds and an extensive network of underground stems called rhizomes, quickly forming dense, single-species stands, or monocultures. This growth restricts the natural flow of water, leading to stagnant conditions that can reduce water quality and increase water temperature. A dense cattail border reduces the amount of open water surface, limiting recreational activities like fishing or boating. Furthermore, this habitat homogenization decreases biodiversity by crowding out native plants and reducing spawning areas for fish.
Non-Chemical Removal Techniques
For smaller infestations or where chemical use is a concern, mechanical removal offers a fish-safe alternative to control cattails. One effective non-chemical method is cutting the stems well below the water line, ideally six inches or more. This technique prevents oxygen from reaching the rhizome system, effectively “drowning” the plant. Repeated cutting throughout the growing season or in late summer is necessary to deplete the plant’s stored energy reserves. Physical barriers, such as specialized benthic mats, can also be placed over cut areas to permanently block sunlight and prevent regrowth.
Aquatic Herbicides Safe for Fish
When mechanical removal is impractical, targeted application of specific aquatic herbicides offers an efficient solution to eliminate the entire plant, including the rhizomes. The active ingredients glyphosate and diquat are commonly used and are considered non-toxic to fish when applied correctly in their aquatic-labeled formulations.
Glyphosate
Glyphosate is a systemic herbicide absorbed through the foliage and translocated down to the root system. It targets a biochemical pathway unique to plants, giving it a low toxicity profile for aquatic life. Effective treatment requires the addition of an aquatic-approved, non-ionic surfactant to help the herbicide penetrate the cattail’s waxy leaf coating. Application is best timed for late summer or early fall when the plant is moving nutrients down to its root structure for winter storage.
Diquat
Diquat is a contact herbicide that works much faster than systemic options, quickly destroying the plant tissue it touches. Unlike glyphosate, diquat does not travel to the roots, making it less effective for permanent control of mature stands. Once applied, diquat binds rapidly and strongly to suspended particles and bottom sediment, minimizing its presence in the water column and reducing the risk to fish.
Essential Safety Protocols to Protect Fish
While the herbicides are safe for fish, the resulting decomposition of a large amount of dead plant matter can inadvertently cause a fish kill. When decaying, the organic material consumes large amounts of Dissolved Oxygen (DO) from the water, a process known as biological oxygen demand. This DO depletion is the primary threat to fish after a successful herbicide treatment.
To mitigate this risk, treat only a small portion of the total cattail infestation at one time. A common guideline is to treat no more than one-third of the total aquatic vegetation area during a single application. A waiting period of ten to fourteen days between sectional treatments is necessary to allow the treated biomass to decompose and for the water body’s oxygen levels to recover and stabilize.
Monitoring the fish closely for signs of stress, such as gasping at the surface, is prudent, especially during the first week after treatment. Avoiding herbicide application during periods of high water temperature is advised because warm water naturally holds less dissolved oxygen. Supplemental aeration devices, such as fountains or diffusers, can be used to inject oxygen into the water, providing a crucial safety buffer during the decomposition phase.