Smartweed, Water Pepper

Polygonum hydropiperoides

Management Options

Mechanical/Physical Control Options

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

Biological Control Options

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

Chemical Control Options

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

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

Rodeo, Aquamaster, Eraser AQ, Touchdown Pro, and AquaNeat are liquid glyphosate formulations and have been effective on smartweed. 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.

Renovate is a liquid triclopyr formulation that is effective on smartweed. It is a selective broadleaf, 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) will improve the effectiveness of triclopyr.

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

Smartweed can be propagated by planting seeds into moist soils or transplanting whole plants during the winter.