Hydrilla is a perennial plant that forms dense colonies and can grow to the surface in water over 20 feet deep. Hydrilla branches profusely and after reaching the surface it extends across it forming thick mats. Hydrilla can reproduce by fragmentation, from seeds, from turions (axilary buds), and from tubers. Leaves are blade-like about 1/8 inch and 3/8 inch long with small tooth margins and spines on the underside of the midrib which make them feel rough. Leaves are usually 4 to 8 in a whorl.
Hydrilla is native to Europe and Asia and was probably brought to the U.S. for the aquarium industry. It is considered a noxious pest because it grows so rapidly, out competing and eliminating native species, and forming surface mats that hinder recreation, navigation, and water intakes.
Hydrilla is often confused with the native Elodea or the non-native Egeria. Hydrilla has one or more teeth on the underside of the midrib, neither Elodea nor Egeria have these midrib teeth. The teeth make Hydrilla feel rough when drawn through your hand from base to tip. Flowers of Hydrilla are much smaller (1/4 inch in diameter) than Egeria. Submerged portions of all aquatic plants provide habitats for many micro and macro invertebrates. These invertebrates in turn are used as food by fish and other wildlife species (e.g. amphibians, reptiles, ducks, etc.). After aquatic plants die, their decomposition by bacteria and fungi provides food (called "detritus") for many aquatic invertebrates. Hydrilla turions and tubers are consumed by some ducks but generally it is not considered a good wildlife food.
Herbicide Management Options:
Reward: is a liquid diquat formulation that has been effective on Hydrilla. It is a contact herbicide. Contact herbicides act quickly and kill all [plant cells that they contact. A non-ionic aquatically registered surfactant (see the label) will have to be added to the Reward solution for good results.
Sonar AS: is a florid one compound and comes in a liquid formulation, and has been effective on hydrilla. These are broad spectrum, systemic herbicides. Systemic herbicides are absorbed and move within the plant to the site of action. Systemic herbicides tend to act more slowly than contact herbicides.
Aquthol K: Aquathol's active ingredent is endothal and comes in a liquid and grandular formulation.
Biological Management Options:
Grass carp: Grass Carp stocking rates to control Hydrilla are 20 fish per surface acre of plant biomass. In South Carolina, only Triploid Grass Carp are legal and requires a permit from the South Carolina Department of Natural Resources. AMS is licensed to provide these permits for you.