Hydrilla (Hydrilla verticillata)

Hydrilla  (Hydrilla verticillata)

Hydrilla is a submerged aquatic plant that roots in the bed of a waterbody.It is native to Africa, Australia, and parts of Asia. It is considered the most problematic aquatic plant in the US. there are two varieties of hydrilla in the US; one produces only female flowers making it dioecious, while the other is monoecious and produces both male and female flowers. The plants in New York are monoecious and produce both female and male flowers. It is believed that hydrilla was introduced in the US via the aquarium trade. Hydrilla is a federally listed noxious weed, listed as a Class A weed on Washington’s Noxious Weed List, and is on the Washington State Department of Agriculture’s Quarantine list

Impacts

Hydrilla invades deep, dark waters where most native plants can’t grow; it is more efficient at taking up nutrients than native species, and has the ability to produce turions and tubers which  can easily  generate new plants–these characteristic give hydrilla a competitive edge against native aquatic vegetation.  Furthermore, hydrilla populations block out sunlight and suppress native vegetation. Major hydrilla colonies can alter the physical and chemical characteristics of lakes and deter recreational activities and reduce lakeshore property values.

Habitat/Distribution

Hydrilla can be found in slow moving aquatic habitats such as reservoirs, lakes, ponds, springs, rivers, and tidal zones. It can tolerate varying hydrological conditions such as salinity as high as 7% and a wide range of acidity (although optimum growth is seen at a pH of 7).Hydrilla is well established throughout southern portions of the US.

Current U.S. range map of Hydrilla verticillata

Identification

Hydrilla stems  are long (up to 25 feet in length) that branch at the surface where growth becomes horizontal and forms dense mats.

Leaves are small (2 – 4 mm wide, 6 – 20 mm long); they are pointed and appear in whorls of 4 to 8. Leaf margins are serrated and have 11 to 39 sharp teeth per centimeter and a red midrib.

hydrilla, Hydrilla verticillata (Hydrocharitales: Hydrocharitaceae) - 5396751

Tubers are pea-like structures buried in the sediment; they are 0.2 to 0.4 inch long and off-white to yellowish in color.

Hydrilla can be distinguished from its native look alikes elodea (Egeria densa) and American waterweed (Elodea canadensis) by observing a few characteristics: First, hydrilla will have tubers, whereas, elodea and waterweed don’t have tubers.

Other Characteristics to look for are in the abundance of leaves and leaf appearance.

Hydrilla has serrated leaflets that grow in whorls of 4 or more around the stem
Hydrilla has serrated leaflets that grow in whorls of 4 or more around the stem
Elodea has no leaf serrations and grows in whorls of 3 around the stem
Elodea has no leaf serrations and grows in whorls of 3 around the stem

Control

Prevention:Hydrilla can easily sprout new plants from root and stem fragments and is easily spread by boat propellers and other aquatic recreational equipment. Therefore, to prevent its’ spread it is important for boaters to Clean, Drain, Dry their boats and equipment before leaving/entering a body of water.

Physical control: Hydrilla can be controlled physically by hand removal via snorkelers and divers. It is important to remove tubers from plants to be successful with this control method.

Drawdowns can be used for small bodies of water such as ponds. This requires removal of all water and is not selective in the aquatic vegetation it will destroy. Drawdowns are most effective between fall and spring (before tubers form). However, tubers may remain viable in soil after draining, so drawdowns are limited in effectiveness.

Chemical control: Aquatic herbicides can be used but type and regulations depend on state. Contact local DEC office for information.

Photo Credits:

Introduction photo: AquariusSystems.com. Habitat/Distrubution map, Columbia.edu. Identification photos of stem, leaves and tubers,Washington State Noxious Weed Control Board and Robert Vidéki, Doronicum Kft., Bugwood.org.

Resources: 

Hydrilla Risk Assessment for the Great Lakes Basin

Video:  Biology, Impacts and Management of an Invasive Aquatic Plant

Aquatic Invasive Species: Hydrilla. N.p., 2010. Web. 22 Oct. 2015. <http://www.aquarius-systems.com/Entries/View/408/aquatic_invasive_species_hydrilla.aspx>.

“General Information About Hydrilla .” Non-native Invasive Freshwater Plants. N.p., n.d. Web. 22 Oct. 2015. <http://www.ecy.wa.gov/programs/wq/plants/weeds/hydrilla.html>.

“Hydrilla.” Noxious Weed Control Board (NWCB). N.p., 2010. Web. 22 Oct. 2015. <http://www.nwcb.wa.gov/detail.asp?weed=73>.

 

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