Aquatic Weeds found in North Carolina

Giant salvinia (Salvinia molesta)Picture of Giant Salvinia (Salvinia molesta)

Giant salvinia (Salvinia molesta) is an extremely invasive free-floating fern indigenous to South America. The USDA listed this plant as a noxious weed in 1983. The first discovery of salvinia in the U.S. occurred in a small pond in South Carolina in 1995. The infestation was identified quickly and the pond was treated successfully with herbicides. Infestations currently exist in Texas, Louisiana, Mississippi, Alabama, Georgia, Florida, Arizona, California, and since 2000, North Carolina has been added to this list.

Description - Salvinia varies in color from green to gold. The leaves of this plant are about the size and shape of fingernails. Leaves of young plants tend to lie flat upon the water. The largest leaves may grow to about two inches. Giant salvinia can grow very rapidly. Under favorable conditions, infestations will double biomass in 4-10 days. Imagine if the tree in your yard doubled it's size every week!!

Spread - Boats and other recreational watercraft transport salvinia from one water body to another. Some plants will get pushed by wind or carried by water flow to new areas. Unintentional introductions from flooded aquatic plant nurseries, ornamental ponds, and water gardens are a threat. Small salvinia plants will often "hitchhike" on other ornamental aquatics. Always inspect for hitchhikers when purchasing aquatic plants. Sometimes it is even for sale under disguising common names. Remember, salvinia is a controlled organism, and is illegal to sell or transport.

Damage - Salvinia molesta can greatly alter aquatic ecosystems. Mature plants create a dense floating mat. In places where salvinia has not been controlled, mats have grown to be two feet deep. Vegetation beneath these thick mats suffers from lack of light. The level of dissolved oxygen (DO) will drop, forcing fish to move to other areas. Reptiles, amphibians, and other aquatic animals will be burdened by the change of habitat. Wading birds and other waterfowl will have difficulty finding food and will likely relocate. Swimming, boating, and other recreation will be inhibited. Drinking water and agricultural water intakes, hydroelectric and other industrial water intakes will all be faced with fouling problems.

Control - Salvinia in Brazil is naturally controlled by an indigenous weevil (Cyrtobagous salviniae). This weevil is host specific, and doesn't feed on other vegetation. This particular characteristic makes C. salviniae an excellent candidate as a biological control agent for use outside of its native environment. USDA-APHIS scientists have experimented with the use of this bug and observed exciting results. Trial releases in North Carolina began in 2004.

The creation of the multi-agency Giant Salvinia Task Force has played a major role in monitoring and controlling the infestations in NC. The Task Force is praised as a model example of the Early Detection Rapid Response (EDRR) concept.

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Hydrilla (Hydrilla verticillata)
Picture of hydrilla (Hydrilla verticillata) plant under water

Hydrilla (Hydrilla verticillata) is a particularly aggressive aquatic plant.   Importation into the U.S. is banned as it is regulated by the USDA.  Two biotypes exist, monoecious and dioecious.  Monoecious hydrilla currently infests many aquatic systems throughout North Carolina from ponds to lakes and even some rivers.   It is native to Korea.  Hydrilla was first identified in a few lakes within Wake County around 1980.  Since its introduction to Wake County hydrilla has spread across the state in all directions.  The people of North Carolina have spent millions of dollars managing hydrilla infested waters.  The State of North Carolina recognizes hydrilla as a noxious aquatic weed; it is illegal to culture, transport, and sell this plant.

Description - Hydrilla grows in long strands as a submersed plant.   Rooted into the bottom it will grow vertically to the surface and then horizontally just beneath the surface of the water.  Mature stands tend to fill the entire water column in shallow water.  Established hydrilla colonies will creep into deeper water to depths of 10 feet, sometimes deeper.  Leaves are short (~1/2") and form whorls along the stems.  Mature plants will produce pea-sized structures in the hydro-soil called "tubers".  These propagative structures sprout in the spring after the water warms up; however some tubers can lay dormant for many years.   For more details read Hydrilla verticillata "The Perfect Aquatic Weed".

Damage - The loss of recreational use of waters, intake fouling, and habitat alterations are the major concerns.  Watercrafts get hung-up in dense stands of hydrilla to the point where docks and slips become unusable.   Heavy infestations discourage or even inhibit swimming and fishing activities.   Advanced infestations alter habitat and drive ecological shifts like changes in fish population dynamics.  For example, largemouth bass populations shift to an increased number of small fish and decreased number of large fish as the hydrilla infestation advances.

Spread - Hydrilla has multiple reproductive strategies; it fragments (small piece of separated plant grows into a whole new plant), produces turions and tubers, and develops seeds.  Boaters unintentionally spread hydrilla to new locations if they are not careful to remove fragments from their equipment and trailers at the boat ramp.  Bait buckets and live wells are other "carriers" that can keep fragments from drying out and become vectors of accidental releases.   Some people have intentionally spread hydrilla in the past with the notion that it would improve fishing areas.  We know now that the long-term negative impacts greatly outweigh any initial benefits that may be realized.

Control - The spread of hydrilla is best controlled through public awareness and good environmental stewardship.  Once hydrilla does infest an area it can be managed with herbicides and in some cases grass carp can be used.   The grass carp (a.k.a. White Amur) is an herbivorous cyprinid indigenous to Asia.   This fish has been used to control hydrilla and other aquatic weeds in the U.S. for decades.  Aquaculture farms provide sterile grass carp intended for aquatic weed control.  Only the sterile "triploid" grass carp can be legally released into waters of NC.  Contact your local extension agent or the Division of Water Resources' Aquatic Weed Control Program for guidance on stocking grass carp.

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Alligatorweed (Alternanthera philoxeroides)Picture of an Alligator Weed (Alternantherea philoxeroides) plant

Alligatorweed (Alternanthera philoxeroides) is native to South America. It was introduced inadvertantly to Southeast states in the late 1800's. The white clover-like flowers bloom throughout the summer. Alligatorweed typically grows in floating mats along the waters edge. Although it will also grow emersed and even terrestrially. The leaves are opposite, lance shaped, about 1-2 inches long, and have a distinct midrib. The midrib is a vein or crease that runs from the stem (alligatorweed has no petioles) to the tip of the leaf. The stems are hollow when growing aquatically, providing buoyancy.

Damage - There are several threats that Alligatorweed infestations impose.   Flooding and erosion; floating mats get hung-up around dams, structures, fallen trees and bottlenecks.  It can grow across an entire waterway and become a navigation hazard.  Infestations depreciate aesthetic value, impede recreational use, and pose a health problem by harboring mosquitoes.

Spread - Alligatorweed is found in 12 states and Puerto Rico.  It reproduces primarily by fragmentation.  Boaters must take caution when transporting their trailers and boats from waters infested with Alligatorweed, and be sure they are not inadvertently spreading this nuisance plant.  Alligatorweed tends to be common around boat ramps because it is often introduced at these sites by human activity.

Control - In North Carolina Alligatorweed is managed with the use of herbicides.   Even with annual herbicide applications Alligatorweed can be persistent.   Its ability to grow both aquatically and terrestrially complicates the management of infestations.  There are two insects that have been used as biological control agents, a beetle and a moth.  The release of Alligatorweed flea beetles in Florida has been a huge success and has greatly reduced the need for herbicide applications there.  Flea beetles have also been released in North Carolina but their ability to control Alligatorweed is limited because the insect doesn't over-winter well (temperatures get too low).  The best use of flea beetles occurs in the Coastal Plain when a combination of mild winters and multiple releases coincide.   The other biological control used for Alligatorweed management is the stem borer moth.   This insect is not very effective in North Carolina because it does not survive through our winter temperatures.

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Parrotfeather (Myriophyllum aquaticum)Picture of a Parrotfeather (Myriophyllum aquaticum)

Parrotfeather (Myriophyllum aquaticum) is a submersed aquatic perennial that pushes its feathery floral spike above the waters surface. A member of the watermilfoil family (haloragaceae), it is considered to be native to South America, possibly Brazil. It was introduced into the U.S. in the late 1800's as an aquarium plant. Water garden enthusiasts who culture this plant need to take precautions to avoid potential escapement.

Description - Growing in a variety of habitats ranging from lakes to wetlands, full sun to shade, parrotfeather can be spotted from a distance by its odd gray-green color. Stems are often a reddish hue when viewed up close. Although the plant is largely submersed, it is the stem tips portion (floral spike) that is readily seen and used to identify this species. The plant gets its name from the feathery appearance of the leaves tightly whorled along the floral spike.

Damage - Dense growths of parrotfeather provide breeding areas for mosquitoes, and will degrade both water quality and habitat for fish and wildlife. It fouls intakes used to supply municipal drinking water and irrigation, and becomes a navigation hazard. Parrotfeather should never be introduced to open waters.

Spread - Parrotfeather has spread through most of the subtropical regions of the South and along the West Coast. Recently, populations have been reported in more temperate zones. The plant reproduces by fragmentation. Although flowers can be found, only pistillate plants (no males) occur in the U.S., and no seeds are produced. The spread of this invasive plant parallels its sale and distribution by wetland nurseries and water garden hobbyist across the country. Most of the complaints about parrotfeather in North Carolina can be traced back to water garden escapement or intentional plantings through "pond beautification" efforts.

Control - The best control method, as with all invasive species, is to avoid its introduction. Where infestations exist, herbicides are used to control or eradicate this nuisance plant.

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Creeping Water Primrose
(Ludwigia grandiflora) Also known as Uruguayan primrose-willow
Picture of a Creeping Water Primrose (Ludwigia grandiflora) plant

Creeping water primrose (Ludwigia grandiflora) is an emersed aquatic perennial. Native to South America, it was previously named Ludwigia uruguayensis. It grows along the margins of lakes, ponds, and rivers, forming floating mats at first. By summer it becomes slightly woody, forming stalks that will flower above the surface.

Description - Water primrose can be easily spotted due to its bright yellow flowers. There are several varieties of primrose, some are native, and all have similar yellow flowers. Leave appear in two distinct forms. Early in the season, leaves are obovate (rounded) and grow in rosettes (grouped), later in the season the plant will produce lanceolate leaves.

Damage - Dense growths of water primrose provide breeding areas for mosquitoes, and will degrade both water quality and habitat for fish and wildlife. It fouls intakes used to supply municipal drinking water and irrigation, and becomes a navigation hazard. Creeping water primrose should never be introduced to open waters. It has been placed on North Carolina's noxious weed list.

Spread - Water primrose was likely brought to the U.S. as an ornamental plant. It produces bright yellow flowers throughout much of the season. It ranges from New York to Florida, west to Texas, and along the west coast. Primrose produces abundant seeds that are very small. It will also reproduce by fragmentation; roots will readily grow from the nodes.

Control - Control methods are limited to herbicide use. No biological control agents have been found. Mechanical removal (except hand-removal of small infestations) is difficult and costly.

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Eurasian watermilfoil
(Myriophyllum spicatum)
Picture of a Eurasian Water Milfoil (Myriophyllum spicatum) plant

Eurasian watermilfoil (Myriophyllum spicatum) is a submersed aquatic perennial. It was introduced to the U.S. from Eurasia in the 1940's as an aquarium ornamental. It is now considered one of the worst aquatic weeds, occurring in nearly every state. Watermilfoil tolerates a wide range of water conditions, and often forms large infestations.

Description - This watermilfoil grows long stems through the water column. Relatively short, branched leaves resembling feathers develop at the uppermost parts. The plants typically grow into dense mats and may develop small floral spikes that will emerge from the water.

Damage - This aquatic weed is tolerant to cold temperatures and begins to grow early in spring, sooner than native submersed plants. It forms a dense canopy along the surface and shades out the vegetation below. It is considered to have less value as a food source for waterfowl compared to native plants. Water quality is degraded by the senescence of watermilfoil. Recreational activities are hindered. Water intakes get obstructed, and decaying mats can foul lakeside beaches.

Spread - Eurasian watermilfoil reproduces by fragmentation and also by seed. Human activities can spread this invasive weed if caution is not taken to remove fragments from boats, trailers, and equipment extracted from infested waters. NC Department of Agriculture & Consumer Services has listed this species as a Class B noxious weed. It is illegal to sell or transport Myriophyllum spicatum in North Carolina.

Control - Both biological and chemical control are used to prevent the further spread of watermilfoil infestations. Bio-control work began as early as the 1960's. Research continues the effort to find better control agents. Herbicides are moderately effective.

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Thanks to the Center For Aquatic & Invasive Plants, and NCSU's Aquatic non-cropland weed group, for additional plant images, and information.

If you think you have seen one of these plants, please contact one of the agencies below.

Rob Emens, NC DWR (919) 715-5452

Rick Iverson, NCDA (919) 733-6930 x246

Dr. Rob Richardson, NCSU (919) 515-5653

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