Hydrilla (Hydrilla verticillata)

Hydrilla

Products to Control Hydrilla

Redwing is a liquid diquat formulation that has been effective on coontail. It is a contact algaecide and herbicide. Contact herbicides act quickly and kill all plants cells that they contact.

WhiteCap is a fluridone compound and has been effective on coontail. It is a broad spectrum, systemic herbicide. Systemic herbicides are absorbed and move within the plant to the site of action. Systemic herbicides tend to act more slowly than contact herbicides.

Current is a copper compound registered for use on elodea (8% active). It is a contact herbicide. Contact herbicides act quickly and kill all plants cells that they contact.

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 undersideof 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.

Hydrilla Control Options

Mechanical/Physical

Hydrilla can be removed by rakingor seining it from the pond but will reestablish from any remaining fragments, roots, tubers, and other vegetative structures.
Fertilization to produce a phytoplankton or algal "bloom" prevents the establishment of most bottom rooted aquatic weeds and produces a strong food chain to the pond fish.
Non-toxic dyes or colorants prevent or reduce aquatic plant growth by limiting sunlight penetration, similar to fertilization. However, dyes do not enhance the natural food chain and may suppress the natural food chain of the pond.

Biological

Grass carp will seldom control aquatic vegetation the first year they are stocked. They will readily consume hydrilla, in fact, it is one of their most preferred plants. Grass carp stocking rates to control hydrilla are usually in the range of 7 to 15 per surface acre. In Texas, only triploid grass carp are legal and a permit from the Texas Parks and Wildlife Department is required before they can be purchased from a certified dealer.

Chemical

The active ingredients that have been successful in treating hydrilla include copper complexes (G), diquat (G), copper with diquat (E), fluridone (E). E = excellent, G = good

Information and photos courtesy of:
Department of Wildlife and Fisheries Sciences, Texas A&M University
http://aquaplant.tamu.edu/