Hydrilla and Hygrophila Frequently Asked Questions (FAQ’s)

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What is hydrilla?  Hygrophila?

Hydrilla is a submersed plant native to Southeast Asia and is a major aquatic weed in Florida and much of the United States.  Its stems can be up to 25 feet long and when they reach the surface they can form dense mats.  Hydrilla can be found in all types of water bodies.  For more information, see http://plants.ifas.ufl.edu/node/183   

Hygrophila is a mostly submersed plant although sometimes the tops of the plants can be above water.  Its stems are square and can grow up to 6 feet long.  It is mostly found in streams and in slow moving waters.  For more information, see http://plants.ifas.ufl.edu/node/191

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Are hydrilla and hygrophila native?

No.  Both hydrilla and hygrophila are exotic, or non-native, plants in the United States.  Hydrilla originates in Southeast Asia and hygrophila (aka East Indian Hygrophila) originates in the East Indies.

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What are some of the benefits of aquatic plants?

Plants form the base of the food pyramid upon which all living things depend on. 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.
  • A natural water purification system.
  • Aesthetically pleasing wild flowers.
  • Nesting sites for birds.

For more about native aquatic plants, see http://plants.ifas.ufl.edu/guide/natplant.html

(From http://www.myfwc.com/WILDLIFEHABITATS/InvasivePlants_faq.htm#130 )

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Are all aquatic plants weeds?

A weed is a plant growing where it's 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 affects 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 Florida's waterways are non-native plants (exotic), like water-hyacinth and hydrilla, and were introduced from foreign lands. In the absence of natural enemies, these non-native weeds grow uncontrolled and rapidly invade new areas. Most native plants have biological restraints that limit their abundance. Uncontrolled growth of non-native plants disrupts 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 into Florida during the early 1950's, can infest and cover an entire water body in as little as three years. By 1991, hydrilla infested more than 40 percent of Florida's public lakes and rivers.

A native of South America, the floating water hyacinth was first introduced into 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.
(From http://www.myfwc.com/WILDLIFEHABITATS/InvasivePlants_faq.htm#130 )

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Why is hydrilla a problem in Florida lakes and other waters?

Hydrilla verticillata is an invisible menace, invisible that is until it fills the lake or river that it infests, "topping out" at the surface. Hydrilla can grow an inch a day. When hydrilla invades, ecologically-important native submersed plants such as pondweeds (Potamogeton spp.), tapegrass (Vallisneria americana) and coontail (Ceratophyllum demersum) are shaded out by hydrilla's thick mats, or are simply outcompeted, and eliminated (van Dijk 1985).

Millions of dollars are spent each year on herbicides and mechanical harvesters in Florida alone in an effort to place hydrilla under "maintenance control."

Hydrilla verticillata greatly slows water flow and clogs irrigation and flood-control canals; in Florida, large mats of fragments collect at culverts and clog essential water control pumping stations.

Hydrilla seriously interferes with boating, both recreational and commercial, and prevents swimming and fishing; major infestations limit sportfish weight and size (Colle & Shireman 1980).

Dense hydrilla infestations can alter water chemistry and oxygen levels (Pesacreta 1988).
(from http://plants.ifas.ufl.edu/node/183)

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Why is hygrophila a problem?

Hygrophila polysperma is a fast-growing and fast-spreading invasive that can outshade and therefore outcompete other submersed plants; it can occupy the entire water column; many adventitious roots at stem nodes means that fragments can easily grow.
Hygrophila polysperma clogs irrigation and flood-control canals; in south Florida, large mats of fragments collect at culverts and interfere with essential water control pumping stations; it interferes with navigation; and it's even able to compete with another aggressive non-native invasive plant, hydrilla, and is replacing hydrilla in some Florida locations.

Hygrophila reportedly grew on Lake Tohopekaliga (Florida) from 0.1 acre in 1979 to 10 acres in 1980 (MITRE).
(From http://plants.ifas.ufl.edu/node/191 )

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What do hydrilla and hygrophila look like?

Hydrilla is a submersed plant with slender stems, branched and up to 25 feet long. Hydrilla's small leaves are strap-like and pointed. They grow in whorls of four to eight around the stem. The leaf margins are distinctly saw-toothed. Hydrilla often has one or more sharp teeth along the length of the leaf mid-rib. Hydrilla produces tiny white flowers on long stalks. It also produces 1/4 inch turions at the leaf axils and potato-like tubers attached to the roots in the mud. 
(From http://plants.ifas.ufl.edu/node/183)

Hygrophila stems are square. The submersed stems grow to six feet long. Its leaves are opposite on the stem. Leaves are 1 1/2 inch long and 1/2 inch wide. East Indian hygrophila flowers are bluish-white to white, and have two lips. They grow from the axils where the leaves meet the stems.
 (From http://plants.ifas.ufl.edu/node/191)

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True or False?  I can collect hydrilla and hygrophila and put them in my fish tank.

False.  Hydrilla and hygrophila are classified as Class 1 and 2 Prohibited Aquatic Plants and it is illegal to possess them. 

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How much money does the state spend per year on Hydrilla control in Florida?

The Invasive Plant Management Section of the Florida Fish and Wildlife Conservation Commission (FFWCC; formerly the Department of Environmental Protection’s Bureau of Invasive Plant Management) is responsible for managing aquatic plants on state waters.  In the 2007/2008 fiscal year, approximately $10 million was spent by FFWCC to manage hydrilla in Florida.  Almost $5 million of this was spent in Osceola County alone.

For more information see http://myfwc.com/WILDLIFEHABITATS/InvasivePlants_AquaticPlantManagement.htm

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Why is it important to manage exotic aquatic plants like hydrilla and hygrophila?

Scientific studies strongly indicate that invasive non-native plants harm Florida's natural environment and lead to a loss of biodiversity. Many of Florida's unique native plant and animal communities are found nowhere else in North America. Invasive non-native plants disrupt Florida's natural environment by forming novel habitats and by altering ecological processes that permit native plant and animals to survive.
(From http://www.myfwc.com/WILDLIFEHABITATS/InvasivePlants_faq.htm#110 )

If aquatic weeds are not kept in check, they can create serious navigation blockages, cause major flooding, and interfere with boating, swimming, and fishing. Native desirable plants can be displaced and the overall health of the ecosystem can suffer.

For more information, see http://plants.ifas.ufl.edu/guide/whymanag.html

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How are invasive aquatic plants, including hydrilla and hygrophila, managed?

Many people become quite concerned when they see aquatic plants being sprayed with herbicides in Florida waters. 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 non-native species 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 non-native aquatic plants under control would be devastating to the environment.
The Invasive Plant Management section, within the Florida Fish and Wildlife Conservation Commission, administers a program involving state, federal, and local governments that is designed to ensure statewide management of noxious aquatic weeds and to protect our valuable natural ecosystems. This program recognizes the important role native aquatic plants play in aquatic ecosystems, and these native plants are not the target of control activities except in those rare instances when they have become noxious and create problems for navigation, flood control, or other public welfare considerations.
This program is focused on bringing invasive, non-native aquatic weeds under what is called maintenance control. Noxious aquatic plants are those that have the potential to hinder the growth of beneficial aquatic plants, to interfere with irrigation or navigation, or to adversely affect the public welfare or the natural resources of this state.
(From http://www.myfwc.com/WILDLIFEHABITATS/InvasivePlants_faq.htm#130 )

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What does maintenance control mean?

This concept is not new or unusual. Anyone who maintains a car, or a lawn, practices the maintenance control concept. Preventive maintenance on a car is when one frequently spends small amounts of time and money to prevent major breakdowns or repairs that can cost much more or perhaps even the loss of the use of the car. For example with a lawn, one would not allow the grass to become too tall or allow weeds or some other lawn pest to kill all the grass before taking some corrective action. Maintenance control prevents damage to a lawn and limits the time, effort and money necessary to keep it attractive and in good health.

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 or rivers 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.

What then is maintenance control? 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 systematic, planned approach for controlling noxious aquatic weeds. The specific goals and objectives of each management plan are developed through interagency coordination and public input.
For more information, see http://plants.ifas.ufl.edu/guide/sup1herb.html
(From http://www.myfwc.com/WILDLIFEHABITATS/InvasivePlants_faq.htm#130)

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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.

To learn more about aquatic herbicides, see "Why Aquatic Herbicides Affect Aquatic Plants and Not You!" PowerPoint and the EPA (Environmental Protection Agency) web site.  Also, see http://plants.ifas.ufl.edu/guide/sup7herb.html .

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

The FWC and the University of Florida have done studies on Florida waterbodies which indicate that spraying does not affect the catchability 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, then it may adversely affect the dissolved oxygen levels. It is to avoid fish kills that the department requires that the dissolved oxygen in the water to be treated be measured beforehand. These activities are also sometimes spread out over a five or six week period to assure no adverse affects on the dissolved oxygen levels.

(From http://plants.ifas.ufl.edu/guide/whymanag.html )

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How long has hydrilla been a problem in Florida lakes?

Hydrilla was first discovered in 1960 in two Florida locations, a canal near Miami and in Crystal River.  By the early 1970s it was established in major water bodies of all the drainage basins in Florida.  In the 1980s over 20,000 hectares of water in Florida contained hydrilla and in the 1990s it had increased to over 40,000 hectares.

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Where do hydrilla and hygrophila grow?

Hydrilla can grow in almost any freshwater, including springs, lakes, marshes, ditches, rivers, and tidal zones. It can grow in just a few inches of water or in water more than 20 feet deep.  It tolerates a variety of nutrient conditions and can even tolerate some salt water.  Hydrilla is also able to withstand cold temperatures to some degree.  The hydrilla growing in the colder climates of the northern United States can overwinter and regrow from tubers.  It only needs 1% of full sunlight to grow which makes very competitive because it can start growing in low light before other plants do.
(adapted from http://plants.ifas.ufl.edu/node/183 )

Hygrophila grows in warm climates and prefers flowing water, but it may also be found in slow-moving water in lakes.  In Florida, it is found in scattered locations south of Orlando, most notably in canals.  It can tolerate a range of pH and water hardness conditions.  It is similar to hydrilla in that it can also grow in little sunlight which makes it competitive. 

(adapted from http://plants.ifas.ufl.edu/node/191 )

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How fast does hydrilla grow?

Hydrilla can grow an inch or more per day when conditions are favorable.

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Is hydrilla harmful to fish and wildlife?

Some sport fishermen consider hydrilla a benefit to largemouth bass habitat.  Some research supports this and other research suggests that largemouth bass are adversely affected when hydrilla coverage exceeds 30%.

Hydrilla may have deadly impacts on eagles and waterfowl because of a type of cyanobacterial algae (aka blue-green algae) that grow on top of the hydrilla.  These algae are potentially toxic to birds.  It is suspected that waterfowl consume the toxic algae when they eat hydrilla and become poisoned.  When eagles eat the infected waterfowl they succumb to the disease as well.  More than one hundred eagle deaths are believed to be a result of the disease.

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Are there any benefits to hydrilla and hygrophila?

Yes.  Hydrilla is eaten by waterfowl, and maintaining hydrilla populations is sometimes advocated by waterfowl scientists because it increases the feeding habitat for ducks.  In addition, large amounts hydrilla, hygrophila or other aquatic plants (excluding algae) can result in increased water clarity, which is often considered desirable.  In some artificial waterbodies (such as storm treatment areas) where there are little to no native plants, hydrilla can provide habitat that may be beneficial to fish populations in the absence of other plants.

Overall, detrimental impacts caused by hydrilla and hygrophila far outweigh beneficial impacts and they are usually more difficult to manage than native plant populations, which they displace.

(adapted from Dr. Langeland’s, “The Perfect Aquatic Weed” publication)

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What is Osceola County doing to find new control methods for hydrilla and hygrophila?

Osceola County, Florida was awarded a $2.881 million dollar grant by the Environmental Protection Agency (EPA) to conduct a project to find new and alternative ways to manage hydrilla and hygrophila (and other invasive exotic plants) in the Upper Kissimmee Chain of Lakes.  This project is deemed the Demonstration Project on Hydrilla and Hygrophila in the Upper Kissimmee Chain of Lakes (Demonstration Project for short).  For detailed information about the project, view the Workplan.  For current reports on the ongoing research for the project, view the Project Reports.

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Goal of the Demonstration Project:

To provide cost-effective and selective control of hydrilla and hygrophila (and other target invasive plants) while encouraging the establishment and growth of native plants.

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Project Components:

Evaluating new herbicides that are being developed for use on aquatic weeds.
Evaluating existing herbicides and different application methods to improve their effectiveness on controlling aquatic weeds.
Searching for biological control agents, such as insects, that control hydrilla and hygrophila in their native environment.
Developing outreach strategies and demonstrating the results of the project to the public, federal, state, and local government partners, and local herbicide applicators.

(from http://plants.ifas.ufl.edu/osceola/project_information.html )

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What can I do to help “Stop the Spread”?

Preventing the introduction and spread of non-native invasive plants in Florida is the most effective and least expensive way to protect Florida’s natural habitats. Here are a few things we can all do:
Learn to identify which plants are invasive, especially in your area.
Always remove plant matter from boats and trailers after use.
Practice good stewardship: never transport Florida’s aquatic or wetland plants to other areas, and never empty your aquarium into a body of water (not even a ditch).
Volunteer to help remove invasive plants in your area.
Avoid chopping aquatic plants with boat propellers as some plant fragments can grow into new infestations.
Get the word out! By telling others about invasive plants, we can help prevent their spread.
Read more about what you can do to prevent the spread of non-native and invasive plants

(From http://plants.ifas.ufl.edu/osceola/about.html#help)

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What plant species are found in Osceola County lakes?

Visit our Plant Species in Osceola County web page.

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Where can I go to find a map of the Kissimmee Chain of Lakes?

The South Florida Water Management District’s web site has links to maps at:

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