Hydrilla (Hydrilla Verticila) 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
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.
Hydrilla is found in freshwater bodies and is well established throughout southern portions of the US.
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), pointed, often serrated and arranged around the stem in whorls of 4 to 10.
Tubers are pea-like structures buried in the sediment; they are 0.2 to 0.4 inches 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
Elodea has no leaf serrations and grows in whorls of 3 around the stem
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.
Chemical control: Aquatic herbicides can be used but type and regulations depend on the state. Contact the local DEC office for information.
Introduction photo: AquariusSystems.com. Habitat/Distribution map, Columbia.edu. Identification photos of stem, leaves, and tubers, Washington State Noxious Weed Control Board and bugwood.org.
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>.