Native to: Argentina, Brazil and Uruguay
Brazilian waterweed has been distributed globally as an aquarium plant and has become invasive in many places. It is present throughout much of the United States, with the exception of the upper Midwest, and occurs in a variety of freshwater habitats both flowering and still. Although present in Florida, it is not currently considered a problem species.
Habit: Rooted submersed perennial aquatic plant.
Leaves: Thin, small (1-1/2 inches long and 1/8 inches wide), and lance-shaped leaves with minute teeth along the edges are arranged in whorls around the stem.
Flowers: Egeria is dioecious and “Female” plants (with pistillate flowers) are not known to occur outside South America, “male” plants have staminate flowers.
Distribution in Florida: Vouchered from 18 counties scattered across the state.
Thought to primarily enter waterways from discarded aquaria water it then spreads vegetatively. The long stems from a single rooted plant commonly form a canopy near the water surface that can cover an area of six feet or more. Dense mats reduce recreational opportunities and crowd out native species. They also alter hydrology – plants release oxygen during the day; however, plants respire (take up oxygen) at night and cause the lowest oxygen levels to occur in the early morning. Fish kills can occur if plant density is high enough and dissolved oxygen levels become depleted overnight due to plant respiration.
Never dump aquarium water into waterways. Clean all boating equipment when moving to a new waterway.
Hand removal and the use of benthic barriers can be selective but are time and labor intensive. Water level drawdowns may be used where feasible.
Mechanical harvesters can clear large areas but may produce thousands of fragments and expand the population. Also, since they essentially mow the upper portions of the plant, the need to remove stem tips after harvesting is critical.
Sterile grass carp effectively control egeria in areas where low water temperature does not limit their feeding.
Herbicides commonly used to control egeria include the systemic herbicides fluridone and penoxsulam and the contact herbicides copper, endothall (mono(N,N-dimethylalkylamine salt) and diquat. Consult your local UF IFAS Extension Office for management recommendations.