Environmental & Extension Services - Pest Management

Aquatic Weeds - Frequently Asked Questions

What are some of the benefits of aquatic plants?

Plants form the base of the food pyramid upon which all living things depend. Aquatic plants turn sunlight into plant matter and forms the base of the food pyramid that nurtures all aquatic animals.

Benefits of aquatic plants include:

  • Nursery areas and shelter for small fish.
  • A buffer zone preventing bank erosion from waves and boat wakes.
  • A food source for fish, waterfowl, and manatees.
  • Aesthetically pleasing wild flowers.
  • Nesting sites for birds.

Are all aquatic plants weeds?

No. A weed is a plant growing where it is not wanted. By this definition, any aquatic plant has the potential to be a weed if it hinders navigation, water movement in irrigation and flood control canals, swimming, recreational boating or fishing, or if its abundant growth adversely effects fish populations and other wildlife.

The vast majority of plant species growing in Florida waters are considered beneficial and only rarely become a problem. The major weed species clogging our waterways are exotic plants (non-native), like water hyacinth and hydrilla, and were introduced from foreign lands. In the absence of natural enemies, these exotic weeds grow uncontrolled and rapidly invade new areas. Most native plants have biological restraints that limit their abundance. Uncontrolled growth of exotic plants disrupt the delicate ecological balance of Florida’s waterways by destroying native habitat for fish and wildlife, and by destroying the biodiversity.

Hydrilla, first introduced from Sri Lanka in Florida during the early 1950s, can infest and cover an entire water body in as little as three years. By 1991, hydrilla infested more than 40% of Florida’s public lakes and rivers.

A native of South America, the floating water hyacinth was first introduced to Florida during the late 1800s. It grows extremely fast, capable of doubling in area in as little as two weeks. Control programs in recent years have been successful in reducing water hyacinth to low levels in most of Florida’s public waterways.

Does our Department spray native plants as well as exotics?

Native plants are not targeted for control unless they have become noxious. Under the maintenance control program, even small patches of floating noxious weeds are sprayed. Sometimes they are mixed in with native plants which unintentionally get sprayed while trying to control the exotics. Herbicides formulations are used that will kill the exotics, but will only temporarily “brown” the natives.

Spray crews are directed to minimize, as much as possible, exposure of herbicides to native plants. However, weather and water conditions do sometimes change unexpectedly and lead to an adverse and unintended impact on some native plants. Also, the natural browning of plants due to seasonal change, and damage caused by insects or disease, is sometimes confused with the effect of the herbicides an aquatic plants.

Why are invasive plants managed?

Many people become quite concerned when they see aquatic plants being sprayed with herbicides. Their concerns seem to focus in two areas. First, they believe that all aquatic plants in Florida waters are beneficial to the environment, not realizing that many of these aquatic plants are not native to Florida, but are invasive exotics that are quite harmful. Second, they believe that the use of any herbicide in water must be extremely harmful to the environment. They fail to understand that not only are approved aquatic herbicides safe to use in water when properly applied, but failure to keep invasive, exotic, aquatic plants under control would be devastating to the environment.

What does maintenance control mean?

Maintenance control is the preferred method of managing noxious aquatic vegetation such as hydrilla, water hyacinth, and water lettuce. To understand what maintenance control is, it is best to first understand what it is not. First, it is not allowing our lakes, rivers, or canals to become completely covered with noxious aquatic weeds. Letting noxious aquatic weeds take over a water body may not only render that water body virtually unusable for recreation or fishing, but it may also displace desirable native plants, adversely affect fish and wildlife populations, interfere with flood control, irrigation, and potable water uses.

Maintenance control is not allowing certain aquatic plants to build up to levels that provide habitat for disease carriers such as some species of mosquitoes, or to present other health and safety dangers to the public. To allow such things to occur before any effort was made to manage these noxious plants would be considered crisis management. When workers are out managing noxious aquatic weeds, they are normally conducting maintenance control, not crisis management.

Florida law defines maintenance control as a method of control in which techniques are utilized in a coordinated manner on a continuous basis in order to maintain the plant population at the lowest feasible level as determined by the Department of Environmental Protection. In every day language, that means maintenance control is a systemic, planned approach for controlling noxious aquatic weeds. The specific goals and objectives of each management plan are developed through interagency coordination and public input.

What can I do to help stop the spread of aquatic weeds?

  • Boat trailers are one of the major sources of moving exotic aquatic weeds from one water body to the next. Before you leave a boat ramp, carefully inspect your trailer and boat for aquatic weeds. Many plant species can grow back from even tiny fragments, thereby infesting new water bodies.
  • Never transplant aquatic vegetation without first contacting a Department of Environmental Protection aquatic biologist. A permit (no fee) is required to transport and cultivate aquatic plants. This permitting procedure was instituted to help insure that an introduced plant will not become a weed problem and a taxpayer burden.
  • Never empty the contents of your home aquarium into the wild. Many aquarium plants are imported from around the world and could become a nuisance weed in Florida’s waters.
  • Report new infestations of pest species such as water hyacinth and hydrilla to the Department of Environmental Services.

Are aquatic herbicides safe to use?

In their concentrated form, all herbicides should be handled with great care. However, once diluted according to label instructions for application into an aquatic environment, herbicides labeled for aquatic use are considered safe by the U.S. Environmental Protection Agency, the Florida Department of Agriculture and Consumer Services, and the Florida Department of Environmental Protection. Aquatic herbicides meet the most stringent safety standards under federal and state regulations; and, these herbicides permitted for use in water are not restricted use herbicides, which means they are far less toxic than herbicides used in most agricultural operations or even those pesticides used in the home.

Why doesn’t the Department use mechanical harvesters exclusively to control floating plants such as water hyacinth and water lettuce?

Research conducted on Lake Okeechobee and other places throughout the state have consistently shown that harvesters alone are ineffective for large-scale control of these fast growing exotics. When harvesters replaced chemicals, on Lake Okeechobee the plants grew out of control. It is also far more cost effective to use herbicides than mechanical harvesters. One crew applying herbicide can cover approximately 10 acres a day, whereas a crew operating a harvester can clear only one-half acre a day.

Do herbicides kill fish or cause them to leave areas that have been sprayed?

Florida Fish and Wildlife Commission biologists and university researchers have conducted studies on Florida water bodies that indicate that spraying does not affect the catch-ability of fish, or adversely affect bedding fish. Isolated fish kills do sometimes naturally occur due to low levels of dissolved oxygen in the water. When dead plants begin to decay and the organisms that break down the plant material use the dissolved oxygen in the water, it may adversely affect the dissolved oxygen level. That is why the Department requires the amount of dissolved oxygen in the water be tested in the area to be sprayed before control activities are undertaken to avoid fish kills. These management activities are also sometimes spread out over a five or six week period to assure no adverse affects upon the dissolved oxygen levels.