Hydrilla: A Rapidly Spreading Aquatic Weed in North Carolina

NC Cooperative Extension Resources

Intoduction

Hydrilla (Hydrilla verticillata) is a submersed aquatic plant that forms nearly impenetrable mats of stems and leaves at the surface of the water. Originally called Florida elodea, this plant causes many problems in ponds, lakes, and rivers.

Hydrilla:

• crowds out beneficial native vegetation,
• blocks irrigation and drainage canals,
• increases sedimentation in flood control reservoirs,
• interferes with public water supplies,
• harbors the vectors of human and animal diseases,
• impedes commercial fishing and navigation,
• blocks docks, marinas, and boat launching sites,
• makes recreational activities such as swimming, boating, skiing, and sport fishing difficult and dangerous if not impossible.

Origin and Distribution of Hydrilla

Hydrilla is native to central Africa and possibly Australia but now is found in temperate and tropical regions around the world. It apparently entered the United States as an aquarium plant, and it was sold to retail aquarium dealers across the country. In 1960 it was discovered growing wild in Florida.

Hydrilla was initially misidentified because of its close resemblance to two native species of American elodea (Elodea canadensis and Elodea nutallii) as well as another exotic aquarium plant, Brazilian elodea (Egeria densa). It is a close relative of both Brazilian and American elodea. Hydrilla was well established by 1967 in several lakes in northern and central Florida and in the St. Johns River. Since that time it has spread throughout the state. Aquatic weed managers have found this new weed very difficult to control. Since its introduction in Florida, hydrilla has spread across the southern United States from the Atlantic Coast as far north as Washington, DC, across the Gulf Coast into Texas, and west into Arizona and California. Hydrilla also overwintered and grew well for several years in a pond in Iowa. It thus has the capability of becoming a serious problem in inland waters throughout most of the United States and possibly Canada.

Hydrilla was first identified in North Carolina in Umstead Park (Wake County) in 1980. A survey conducted by the North Carolina Department of Agriculture in 1981 found hydrilla in 11 locations, primarily in Wake County. A multiagency survey initiated in 1989 revealed that hydrilla had spread to approximately 48 locations since 1981, and 51 locations were known by the end of 1990. About 80 percent of the confirmed infestations are in the Neuse River Basin in the vicinity of Raleigh (in Wake and surrounding counties). However, outlying infestations of hydrilla are present in Burnt Mill Creek in Wilmington, as far north as Lake Gaston on the Virginia state line, and as far west as Asheville in a small pond adjacent to the French Broad River. The explosive growth rate of this weed and its competitiveness with native vegetation makes hydrilla the most serious weed threat in North Carolina’s inland waters.

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