An Integrated Pest Management strategy for aquatic invasive plants involves Biological Control, Mechanical Control, and Herbicidal Control methods, in addition to prevention, monitoring, and educational outreach.

Biological control involves the use of natural enemies of the plant, such as, insects, pathogens, and parasites. The use of natural enemies usually achieves some degree of control rather than eradication.  This is primarily due to the interaction between host and predator populations.
                    

        Alligatorweed Flea Beetle                            Megamelus Planthopper                            

Mechanical or physical control involves the use of machines, devices, or other methods, such as hand pulling, mechanical harvesters and barriers. These methods are usually non-selective and short-term.

                  
Grapple                                                            Harvester                       

Herbicidal control involves the use of herbicides to control or eradicate aquatic invasive plants. This method is usually the fastest, sometimes the only available, or the most cost effective measure.

      
Foliar Application                                    Cut & Spray

Photos: courtesy of Waterways Experiment Station, Noxious and Nuisance Plant Management Information System (PMIS) software.

Alligatorweed (Alternanthera philoxeroides) is an emersed, perennial invasive nonnative plant which thrives in both aquatic and wetland habitats. The plants become structurally adapted to their habitat type, giving alligatorweed a considerable advantage over indigenous species. Native to South America, alligatorweed was first introduced into the United States in the late 1890's, most probably from the ballast of ships. The problems caused by this invasive plant became so serious that a major effort was initiated to develop management methods to supplement costly chemical operations. Explorations undertaken in the native range of alligatorweed yielded three insects suitable for introduction into the U.S.

Agasicles hygrophila (alligatorweed flea beetle)

Amynothrips andersonii (alligatorweed thrips)

Arcola (Vogtia) malloi (alligatorweed  stem borer)

After exhaustive quarantine studies conducted to ensure host specificity, the insects were released in Florida and California in the 1960's. The hearty appetites of these very effective biocontrol agents has significantly decreased the use of chemicals to control alligatorweed. As an example, within three years after the release of the alligatorweed flea beetle in Florida, the U.S. Army Corps of Engineers had cancelled all herbicide spraying of alligatorweed. Populations of these three biocontrol species have become established throughout Florida and several other southern states. The Jacksonville District of the U.S. Army Corps of Engineers undertakes a yearly collection of alligatorweed flea beetles from local waters for shipment to locations where alligatorweed is becoming a problem. These shipments take place in late spring (May or June) and are commonly sent to government agencies or organizations in Alabama, Mississippi, South Carolina, North Carolina, Louisiana, Georgia, Tennessee, Texas, Virginia, Arkansas, Oklahoma and Puerto Rico to assist them in the control of this nuisance invasive plant. Shipments cannot be made to individuals unless they are representatives of a state or federal agency. The interstate shipment of biological control species is regulated by the U.S. Department of Agriculture.

Additional information on the control of alligatorweed can be found at the following site:

• University of Florida - Biological Controls: Alligatorweed

In addition to the above listed web sites, the U.S. Army Corps of Engineer Engineer Research and Development Center in Vicksburg, Mississippi has published Instruction Report A-81-1 titled, "The Use of Insects to Manage Alligatorweed". This manual was published in November of 1981.

State, local and federal agencies which are interested in receiving flea beetles can contact us via e-mail. For further information on the alligatorweed flea beetle collection and shipments, please contact Invasive Species Management Branch, (904)-232-2263 or email: Chelsea.A.Bohaty@usace.army.mil                   

Hydrilla (Hydrilla verticillata) is a submersed, freshwater invasive nonnative herb which is widespread in tropical areas of the world. The route of introduction into Florida was through the aquarium trade. First discovered in Crystal River and a Miami canal in the 1950's, hydrilla has spread rapidly throughout the state. This weed grows very rapidly. Under ideal conditions it may grow as much as 10 inches per day, and can reproduce vegetatively as well as by seeds and tubers. This invasive weed expanded its range from 50,000 acres to 100,000 acres between 1993 and 1995. Inconsistent funding for large scale herbicide treatments has impacted efforts to eliminate mature plants and stored reproductive structures.

Research has found four species of insects which feed on hydrilla to be candidates for introduction into the United States. Bagous affinis, the hydrilla tuber weevil and Bagous hydrillae, the hydrilla stem borer, were first introduced into Florida in 1987 and 1991 respectively; however no permanent populations have been established. Both the adults and larvae of Bagous affinis damage the tubers of hydrilla to reduce their reproductive success. A drawback with Bagous affinis as a biological control species is that it cannot withstand submergence for more than a few days. Therefore the success of this species in hydrilla control is maximized in water bodies which experience periodic drawdowns. Bagous hydrillae shows a potential for greater success in the control of hydrilla. The adults feed on the stems and leaves of the plant and lay their eggs within the stems. When the larvae hatch they chew through the stem and float to shore in the stem. This gives the hydrilla a mowed look by removing the top 100 cm of the plant.

Several species of hydrilla leaf mining fly have been utilized in the control of hydrilla. The larvae of these flies are aquatic and consume various parts of the hydrilla plant, while the adults are not aquatic. Hydrellia balciunasi, the Australian hydrilla leaf mining fly, was released in 1989. Currently, established populations occur only near Houston, Texas. Hydrellia pakistanae, the Asian hydrilla leaf mining fly, was released in 1987. This species is frequently found in association with hydrilla in the southeastern U.S.

Other types of insects also help to control the spread of this plant. A small aquatic moth, Parapoynx diminutalis, was accidentally introduced into the United States from Southeast Asia. This moth is now widespread in Florida. Its larvae can be found feeding on hydrilla but are slow to control the growth of the plant. In addition to the introduced species, there are several native species which are being utilized to control the growth of hydrilla. One of the most promising of the native species is the native leaf mining fly, Hydrellia bilobifera. The larvae of this fly feeds on the leaves of hydrilla and may damage as many as 20 leaves during its development.

In addition to these insects, many locations, such as Georgia and North Carolina, have shown success in the control of hydrilla by introducing the triploid grass carp or white amur. White amur are voracious grazers and will control even severe outbreaks of hydrilla. The use of grass carp is generally practiced in smaller lakes and ponds since the carp are not hydrilla specific when they feed and may damage fisheries habitat if the population is not controlled. Permits for the stocking of grass carp in Florida are issued by the Florida Fish and Wildlife Conservation Commission.

Additional information on the control of hydrilla can be found at the following sites

• University of Florida - Biological Control of Hydrilla
• Grass Carp Publication

Melaleuca (Melaleuca quinquenervia) or Australian paperbark tree was introduced into Florida early in the 1900's as an ornamental and lumber crop, and has been cultivated to increase evapotranspiration in wet areas. Due to rapid expansion over the past three decades, this exotic pest now infests almost half a million acres in southern Florida. Searches for biological control agents have been underway in Australia since the late 1980's. By the end of 1993, 450 species of herbivorous insects had been found feeding on melaleuca.

Two of the most promising of these insects for introduction into the U.S. are: Oxyops vitiosa, the melaleuca leaf weevil, and Lophyrotoma zonalis, the melaleuca defoliating sawfly. Adults and larvae of these two insect species are being shipped regularly to the Gainesville quarantine facility for testing. Two other species, Boreioglycaspis melaleucae, the melaleuca psyllid, and Eucerocoris suspectus, the melaleuca leaf-blotching bug, are awaiting approval for shipment into quarantine.

Oxyops vitiosa

Lophyrotoma zonalis

 Oxyops vitiosa was released on test plots of melaleuca in Ft. Lauderdale, Florida, on April 26, 1997. Since then, additional releases have taken place and it appears that the weevils are causing significant damage to the trees. This species feeds on new growth including leaves, stems, and buds of the melaleuca tree.

The melaleuca psyllid (Boreioglycaspis melaleucae) was the second biocontrol insect to the be released. It was released in 2002 and quickly established, causing significant damage to melaleuca trees. A third insect, the melaleuca bud-gall fly (Fergosonina turneri) was released in 2005, but it did not successfully establish.

Additional information on the control of melaleuca can be found at the following sites:

University of Florida - Biological Controls: Melaleuca
 TAME Melaleuca 
 Cornell University - Biological Controls: Melaleuca

Waterhyacinth (Eichhornia crassipes) was first brought to Florida by a visitor to the 1884 Louisiana Cotton Exposition, who placed the plants in an ornamental pond adjacent to the St. Johns River near Palatka. After the hyacinths took over the pond, the land owner threw them into the St. Johns River. Hyacinths were further spread by cattle owners who viewed it as a cheap source of feed. By 1896, this invasive exotic had become a serious obstruction to navigation. Surveys in the 1960's detailed waterhyacinth infestations of 3,000 acres in Lake Okeechobee, 3,700 acres in the Ocklawaha River, 9,500 acres in the St. Johns River and 38,500 acres in the Kissimmee River. By 1972, the infestation in Florida was estimated to be 200,000 acres. Overseas surveys, conducted in Central and South America, to find organisms that feed on waterhyacinth produced three biological control agents. Neochetina eichorniae, the mottled waterhyacinth weevil, and Neochetina bruchi, the chevroned waterhyacinth weevil, were released in Florida in 1972 and 1974 respectively; releases were also made in Alabama, California, Louisiana and Texas a few years later. These weevils are now distributed throughout most of the U.S. range of waterhyacinth. Niphograpta albiguttalis, the waterhyacinth moth, was released as a biocontrol agent in Florida in 1977. It is the larval stage of this species that damages the plant.

Neochetina bruchi  & N. eichorniae

Niphograpta albiguttalis - water hyacinth moth

The most recent biocontrol agent for water hyacinth is the planthopper, Megamelus scutellaris. After several years of testing, it was released in May of 2010, near the original site where water hyacinth was introduced on the St. Johns River. The larvae of the Megamelus feed on the base of the leaves, cutting off the resources to the rest of the leaf. More releases are planned throughout the State of Florida. The release sites will be monitored to evaluate the success of this biocontrol agent.

Additional information on the control of waterhyacinth can be found at the following sites:

•   Cornell University - Biological Controls: Waterhyacinth
•   Waterhyacinth Biological Control Publication 

•   University of Florida - Biological Controls: Waterhyacinth

Waterlettuce (Pistia stratiotes) is a floating plant native to South America, which may have been introduced to the U.S. as early as the 1700's. The high reproductive rate, allows the formation of large, floating mats of vegetation. Problems associated with waterlettuce are: impacts to navigation and water uptake, reduced recreational access, and increased mosquito breeding habitat. The waterlettuce weevil, Neohydronomous affinis, is currently being used as a biocontrol agent for waterlettuce in Florida, Louisiana and Texas. The waterlettuce weevil is native to Central and South America, and was first released in Florida in 1987 at Torry Island and Kreamer Island in Lake Okeechobee. It is now widely distributed throughout the State, but it is having little effect on waterlettuce populations. Spodoptera pectinicornis, the waterlettuce moth, is native to Asia, the caterpillar of this species was first released in Florida in 1990, but it failed to establish.

Additional information on the control of waterlettuce can be found at the following sites:

• University of Florida - Biological Controls: Waterlettuce

• Waterlettuce - Biological Control of Invasive Plants in the Eastern United States

Mechanical control of exotic plants may include methods such as hand pulling, manual cutting, harvesting, rolling, rotovating, dredging, and the placement of barriers to inhibit growth. Several of these techniques, such as hand pulling, manual cutting, and rolling are used in small scale projects or individual waterfront lots. Harvesting, rotovating and dredging are used in larger scale aquatic weed removal.

Hand pulling aquatic weeds is similar to weeding your garden. The individual attempts to remove the entire plant, including roots, while leaving the beneficial species intact. This technique works best in softer sediments, with shallow rooted species and for smaller infestation areas. But, as with garden weeding, this process must be repeated often to control regrowth. Additionally, the disturbance of the sediment may result in murky water, thus making it difficult to see the remaining plants. When hand pulling nuisance species, the individual should take care to remove the entire root system and collect all of the plant fragments since even small root or stem fragments could result in additional growth of the species. One point to keep in mind is that aquatic plants act to retain sediment around their roots and lower stems. The removal of these plants may result in increased erosion along the shoreline since there would no longer be any roots holding the sediment in place. It is suggested that native species be replanted in place of the exotics which have been removed. This will not only act to stabilize the shoreline, but also inhibits the regrowth of some exotic species.

Manual cutting, of exotic weeds, is similar to mowing your yard. Weed cutters are commercially available. These tools consist of two blades in a "V"-shape with a rope tied to them. Home-made weed cutters can be constructed from a sturdy rake head, such as an asphalt rake, tied to a rope in a similar manner. It is thrown into the weeds and pulled to shore. The plants are cut and float to the surface. The individual must then collect the plant fragments and remove them to an upland site to insure that they do not recolonize adjacent areas. Like lawn mowing, this method will not remove the plants from an area, it is only meant to reduce the extent of their growth. Mechanical harvesters are large machines which cut and collect aquatic plants. These machines can cut the plants from five to ten feet below the water surface and may cut a swath between 6 and 20 feet wide. The weeds are cut and collected by the harvester and may be retained or deposited in a barge. The vegetation is then transferred to an upland disposal site. The advantage of this type of aquatic weed control is that it immediately opens an area such as boat lanes. It also removes the upper portion of the plant while leaving the lower portion for habitat enhancement.

Due to the large size of the equipment, mechanical harvesting is limited to water areas of sufficient size and depth. Mechanical harvesting results in fragments of the plant which, if not captured by the harvester, must be hand collected to eliminate the possibility of spreading the plant to new areas. Additionally, harvesters may impact fish and insect populations in the area by including them in the harvested material. The use of harvesters is fairly expensive and has to be performed several times per growing season to maintain control of the nuisance weed. The price per acre may range from $500-$800 dollars, excluding mobilization, and the cost for the equipment could exceed $100,000.

Weed Rollers are a fairly new method to control nuisance weed populations. This type of equipment works on the principle that if you roll over an area frequently enough the plants will die, similar to trails produced in yards by human and pet traffic. The roller, which can be up to 30-feet long, is powered by an electric motor and is anchored in place. It travels forward and reverse in a 270 degree arc around its anchor position and compresses the plants and soil in the area. This type of equipment is low effort on the operators part and can be left in place and used as the plants begin to grow. Frequent use of the roller should maintain a low amount of weed growth in the area being rolled. The use of rollers may disturb bottom dwelling organisms and spawning fish. Additionally, fragmentation of the nuisance plant may occur. Also, the equipment should not be used when people are swimming or wading in the area due to the potential for injury.

A rotovator is similar to under-water rototiller. The equipment has rototiller-like blades which turn seven to nine inches below the bottom to dislodge and remove roots. The plants and roots can then be removed either manually or with a rake attachment. This method of plant removal works best when the plants are shorter since longer plants tend to wrap around the spinning blades and may damage the equipment. Due to the size of the equipment and high costs, this method is best suited for larger waterbodies. Since the rotovator greatly disturbs the sediment, there are several environmental considerations to look at; will the rotovator resuspend contaminated sediments, release nutrients locked-up in the soil, adversely impact benthic (bottom dwelling) organisms, and will it impact fish spawning areas. This method is useable year-round and has been shown to be very effective in rapidly clearing areas and maintaining low levels of weed growth for several seasons. However, similar to rototillers, rotovating should be used in waterbodies with few obstructions since encountering rocks, logs, or other debris could damage the equipment.

Dredging of weed infested areas is usually not practical unless it is in conjunction with boat channels or canals. Hydraulic or clam shell dredges will remove a large amount of sediment along with the vegetation and therefore a suitable disposal site must be present nearby. Dredging results in similar problems with suspended sediment and habitat impacts as explained above with rotovating and harvesters.

The placement of barriers has not been demonstrated to be as effective in aquatic weed control as other methods. This method consists of the placement of sheets of plastic or other material on the bottom over the plants. By eliminating the sunlight from the area the plants cannot photosynthesize and therefore die. This control method will also result in the loss of habitat for benthic organisms due to the loss of bottom areas. Additionally, as sediment builds up on the sheet or tears are created, the nuisance plant may recolonize the area.

Research and Development Aquatic Plant Information System (APIS) Engineer Center USACE APIS Home Page.

The following is a guide to the use of various mechanical control methods for the management of aquatic and wetland vegetation. Please click on the appropriate underlined topic heading listed below (please note that you may also search by plant type):

The Jacksonville District Corps of Engineers and their contractors use a variety of herbicides in their continuing effort to control exotic aquatic and wetland plants in Florida.

The first step in controlling plant problems is to identify the Target Species. To identify a plant you can contact one of our field offices in Palatka (386) 328-2737 or Clewiston (863) 983-8101.

Aquatic Herbicide Safety Considerations

Aquatic herbicides have been extensively tested and approved for use in aquatic environments by the United States Environmental Protection Agency (USEPA). Please click this link from the University of Florida IFAS to view a table of herbicide toxicities and EPA testing requirements.

Aquatic Herbicide Use Guide

To view a complete list of aquatic/wetland herbicides (local restrictions may apply) and the plants that they control, please see the links below. This information is courtesy of Engineer Research and Development Center USACE (ERDC). Please note that this information regarding herbicide products should be used as a general guide only. Use and regulations regarding registered pesticide products are always being updated. Please consult the product label for complete information.

Advantages of Chemical Weed Control

•   Aquatic herbicide application can be less expensive than other aquatic plant control methods.
•   Aquatic herbicides are easily applied around underwater obstructions and structures, such as docks.
•   Aquatic herbicides can be applied directly to problem areas of all size scales.
•   Aquatic herbicides are deemed safe by USEPA for intended use when used as directed.  

Disadvantages of Chemical Weed Control

•   Some herbicides have swimming, drinking, and water use restrictions.
•   Herbicide use may have unwanted impacts to people who use the water and to the environment.

•   Non-targeted plants as well as nuisance plants may be adversely impacted by some herbicides. 

•   Depending on the herbicide used, it may take several days to weeks or several treatments during a growing season before the herbicide controls or kills treated plants. 

•   Rapid-acting herbicides like Aquathol may cause low oxygen conditions to develop as plants decompose. Low oxygen conditions may result in fish kills.

• To be most effective, herbicides must be applied to specific stages of the plants, (i.e. young shoots, flowering stages).

• Some expertise in using herbicides is necessary in order to be successful and to avoid unwanted impacts. Therefore, permits are required for certain types of herbicides.

• Many people have strong feelings against using herbicides in water. Having the public involved and educated in the treatment process is beneficial.

• Some local jurisdictions have policies forbidding or discouraging the use of aquatic herbicides. As policies change, control practices must adjust.

Additional Information

•   Plant identification
•  Specific plant species by common name:
•   Alligatorweed (Alternanthera philoxeroides (Mart.) Griseb.)
•   American Lotus (Nelumbo lutea Willd.)
•   American Pondweed (Potamogeton nodosus Poir.)
•   Bladderwort (Utricularia spp.)
•   Brazilian Elodea (Egeria densa Planch.)
•   Brazilian Peppertree (Schinus terebinthifolius Raddi)
•   Buttonbush (Cephalanthus occidentalis L.)
•   Cattails (Typha spp.)
•   Climbing Hempweed (Mikania scandens (L.) Willd.)
•   Common Reed (Phragmites australis (Cav.) Trin. ex Steud.)
•   Coontail (Ceratophyllum demersum L.)
•   Curlyleaf Pondweed (Potamogeton crispus L.)
•   Duckweed (Lemna spp.)
•   Eel-Grass (Vallisneria americana Michx.)
•   Elodea (Elodea canadensis Michx.)
•   Eurasian Watermilfoil (Myriophyllum spicatum L.)
•   Floating Primrose Willow (Ludwigia peploides (Kunth) Raven)
•   Fragrant Water-Lily (Nymphaea odorata Ait.)
•   Giant Duckweed (Spirodela polyrhiza (L.) Schleid.)
•   Giant Foxtail (Setaria magna Griseb.)
•   Giant Reed (Arundo donax L.)
•   Giant Salvinia (Salvinia molesta Mitchell)
•   Gray Fanwort (Cabomba caroliniana Gray)
•   Great or Soft-Stem Bulrush (Schoenoplectus tabernaemontani (K. C. Gmel.) Palla)

•   Horned Pondweed (Zannichellia palustris L.)

•   Hydrilla (Hydrilla verticillata (L.f.) Royle)
•   Illinois Pondweed (Potamogeton illinoensis Morong)
•   Maidencane (Panicum hemitomon Schult.)
•   Melaleuca (Melaleuca quinquenervia (Cav.) Blake)
•   Mosquito Fern (Azolla spp.)
•   Mud-Midget (Wolffiella gladiata (Hegelm.) Hegelm.)
•   Northern Watermilfoil (Myriophyllum sibiricum Komarov)
•   Para Grass (Urochloa mutica (Forsk.) T.Q. Nguyen)
•   Parrotfeather (Myriophyllum aquaticum (Vell.) Verdc.)
•   Pickerelweed (Pontederia spp.)
•   Purple Loosestrife (Lythrum salicaria L.)
•   Rice Cut-Grass (Leersia hexandra Sw.)
•   Sago Pondweed (Stuckenia pectinatus (L.) Boerner)
•   Saw-Grass (Cladium spp.)
•   Slender Naiad (Najas minor All.)
•   Small pondweed (Potamogeton pusillus L.)
•   Smartweed (Polygonum hydropiperoides Michx.)
•   Southern Naiad (Najas guadalupensis (Spreng.) Magnus)
•   Southern Watergrass (Luziola fluitans (Michx.) Terrell & H. Robins.)
•   Spatter-Dock (Nuphar lutea (L.) Sm.)
•   Spiny Naiad (Najas marina L.)
•   Tamarisk or Salt Cedar (Tamarix spp.)
•   Tearthumb (Polygonum arifolium L.)
•   Torpedo Grass (Panicum repens L.)
•   Uruguayan Primrose Willow (Ludwigia uruguayensis (Camb.) Hara)
•   Variable-Leaf Milfoil (Myriophyllum heterophyllum Michx.)
•   Water Buttercup (Ranunculus longirostris Godr.)
•   Water Chestnut (Trapa natans L.)
•   Water Millet (Zizaniopsis miliacea (Michx.) Doell and Aschers.)
•   Water Paspalum (Paspalum fluitans (Ell.) Kunth)
•   Water Pennywort (Hydrocotyle spp.)
•   Water Spangles (Salvinia minima Baker)
•   Waterhyacinth (Eichhornia crassipes (Mart.) Solms)
•   Waterlettuce (Pistia stratiotes L.)
•   Watermeal (Wolffia spp.)
•   Water-Shield (Brasenia schreberi J.F. Gmel.)
•   Waterwillow (Justicia americana (L.) Vahl)
•   Widgeon-Grass (Ruppia maritima L.)
•   Herbicide use guide by plant growth-form or other criteria
•   Information concerning the use and restrictions of various herbicides