Hydrilla

Hydrilla verticillata

Management Options

Mechanical/Physical Control Options

Hydrilla can be removed by raking or 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. Aquashade, Blue Springs, and Crystal Blue are examples of non-toxic dye and other products are available. However, dyes do not enhance the natural food chain and may suppress the natural food chain of the pond.

Many types of mechanical removal devices are available that cut or chop up aquatic weeds. It is important to remember that many submerged plants regrow from fragments, so removal of cut fragments many be necessary to keep from spreading the unwanted plant. Companies that make cutters and rakes include but are not limited to Cutting Edge, Jenson Lake Mower, Midwest Aqua Care, and WeedRoller.

Physical barriers are also used to eliminate plants by shading the bottom. These work well for swimming areas, docks, etc. but must be kept clean of any buildup of sediment and debris. Lake Mat and Lake Bottom Blanket are examples of companies that makes these mats.

Biological Control Options

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 Control Options

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

Reward is a liquid diquat formulation that has been effective on hydrilla and is very effective if mixed with a copper compound. It is a contact herbicide. Contact herbicides act quickly and kill all plants cells that they contact.

Aquathol K, and Aquathol Super K are dipotassium salts of endothall and comes in both liquid and granular formulations. These endothall products have been effective on hydrilla and can be mixed with copper compounds for additional effectiveness. Contact herbicides act quickly and kill all plants cells that they contact.

Hydrothol 191 is an alkylamine salt of endothall and comes in both liquid and granular formulations. It is a contact herbicide and has been effective on hydrilla. Contact herbicides act quickly and kill all plants cells that they contact. Hydrothol can be toxic to fish.

Sonar,  Avast , and  Whitecap are floridone compounds and comes in both liquid and granular formulations, and have 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.

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

Nautique is a copper compound registered for use on hydrilla. (9.1% active) It is a contact herbicide. Contact herbicides act quickly and kill all plants cells that they contact.

Clearcast is a liquid imazamox formulation. 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. An aquatically registered surfactant (see the label) is needed for application.

Galleon is a liquid penoxsulam formulation. 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. Galleon may be sprayed directly onto emergent plants or applied directly into the water. Galleon should not be applied in areas where it will be diluted rapidly. Galleon will take 60-120 or longer to completely kill the target plants. Galleon will need a surfactant for foliar and exposed sediment applications.

Clipper is a flumioxazin product and comes in a water dispersible granule which must be mixed in water first and then either sprayed or injected.  It is a broad spectrum, contact herbicide.  Contact herbicides act quickly.  Flumioxazin should be applied to actively growing plants and a surfactant will be needed if the herbicide is applied foliage of floating or emergent plants.  Water pH needs to be below 8.5 or flumioxazin will rapidly degrade and lose effectiveness.

Tradewind is a bispyribac-sodium product and comes in a water soluble power formulated in packets.  Each packet should be mixed in water first then sprayed or injected. It is a selective, 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.  A surfactant will be needed if the herbicide is applied foliage of floating or emergent plants.

One danger with any chemical control method is the chance of an oxygen depletion after the treatment caused by the decomposition of the dead plant material. Oxygen depletions can kill fish in the pond. If the pond is heavily infested with weeds it may be possible (depending on the herbicide chosen) to treat the pond in sections and let each section decompose for about two weeks before treating another section. Aeration, particularly at night, for several days after treatment may help control the oxygen depletion.

One common problem in using aquatic herbicides is determining area and/or volume of the pond or area to be treated. To assist you with these determinations see SRAC #103 Calculating Area and Volume of Ponds and Tanks.

Many aquatically registered herbicides have water use restrictions (See General Water Use Restrictions).

To see the labels for these products click on the name. Always read and follow all label directions. Check label for specific water use restrictions.

Cultivation Options

It is against Texas law to possess hydrilla. It is a non-native, invasive plant and should not be propagated.