Water-willow (American Water-willow)

Justicia americana

Management Options

Mechanical/Physical Control Options

Water-willow can be cut or grazed but is difficult to control physically because it will propagate from seeds or the roots.

Biological Control Options

At this time there is no available biological control for water-willow, 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-willow include 2,4-D (E), and fluridone (G).  E = excellent, G = good

Weedar 64 is 2,4-D amine compound that has been effective on water-willow.  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.

Sonar, Avast, and Whitecap are fluridone compounds and come in both liquid and granular formulations.  Fluridone has been effective on water-willow in the water.  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.

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.  For General Water Use Restrictions click here.

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-willow can be propagated by seeds or by transplanting the rhizomes into shallow (less than 1 foot deep).