Water Pennywort

Hydrocotyle spp.

Management Options

Mechanical/Physical Control Options

Water pennywort can be cut and the roots can be dug up but physical control is difficult because it can reestablish from seeds or remaining roots.

Biological Control Options

There is no known biological control for water pennywort, although goats are known to forage on many types of emergent vegetation.

Chemical Control Options

The active ingredients that have been successful in treating water pennywort include 2,4-D (G), diquat (G), triclopyr (G), glyphosate (G), imazamox (E), and imazapyr (E). E = excellent, G = good

Navigate and Weedar 64 are 2,4-D compounds that have been effective on water pennywort. 2,4-D compounds are 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.

Reward is a liquid diquat formulation that has been effective on water pennywort. It is a contact herbicide. Contact herbicides act quickly and kill all plants 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.

Rodeo, Aquamaster, Eraser AQ, Touchdown Pro, and AquaNeat are liquid glyphosate formulations and have been effective on water pennywort. 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. An aquatically registered surfactant (see the label) will have to be added to the glyphosate solution for good results.

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.

Habitat contains the active ingredient, imazapyr, which inhibits the plant enzyme AHAS (acetohydroxyaced synthase). Habitat is a systemic herbicide that is effective on post-emergent floating and emergent aquatic vegetation. Imazapyr is effective at low-volume rates and does not contain heavy metals, organochlorides or phosphates, making it safe to humans and livestock. Habitat requires the use of a spray adjuvant when applying on post-emergent vegetation.

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

Water pennywort can be propagated by transplanting whole plants into moist soils that dry periodically.