Mechanical/Physical Control Options
Blue flag can be cut and the rhizomes can be dug up but physical control is difficult.
Biological Control Options
There is no known biological control for blue flag, although goats are known to forage on many types of emergent vegetation.
Chemical Control Options
The active ingredients that have been successful in treating blue flag include diquat (G) and glyphosate (E). E = excellent, G = good
Reward is a liquid diquat formulation that has been effective on blue flag and is more effective if mixed with a copper compound. It is a contact herbicide. Contact herbicides act quickly and kill all plant 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 blue flag. 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.
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.
Blue flag can be propagated by transplanting whole plants with rhizomes into moist soils.