Invasive Weeds in Georgia

Evans, C.W., C.T. Bargeron, D.J. Moorhead & G.K. Douce. 2005. The Bugwood Network, The University of Georgia.

Hydrilla

Hydrilla verticillata (L. f.) Royle

Hydrilla is a submersed, rooted aquatic plant that can grow from depths of 20 feet. Leaves are whorled in bunches of 3-8. The midribs of the leaves are reddish in color and the margins are slightly toothed. Tiny, translucent to white flowers can be found on the upper branches. Winter buds (called turions) are produced in the leaf axils. Hydrilla can be recognized by the dense mats it can form at the surface of the water.

Hydrilla is believed to be native to Asia or Africa, although it is widely spread across the globe. It was first introduced into America as an aquarium plant in the 1950s. The first reported instance of hydrilla escaping cultivation was in Florida in 1960. Since then it has spread throughout the southeastern United States and can also be found in both the Atlantic and Pacific coastal states. Several infestations have been found in Georgia.

Hydrilla can cause significant amounts of ecological and economic damage, which led to its inclusion on the federal noxious weed list in 1979. It forms thick mats of vegetation in waterways, restricting native vegetation growth, irrigation practices, recreation, hydroelectric production, and water flow. Hydrilla can reproduce via turions and root tubers as well as by plant fragments. This trait allows it to spread between waterways on boating equipment, in live wells, and by waterfowl.

Hydrilla is a federal noxious weed; any occurrence should be promptly reported.

Control:
A variety of control measures, such as biological, chemical, and mechanical, has been attempted with varying results.

Recommended herbicides for control:
Fluridone

Photo by Tim Murphy, The University of Georgia