Diquat, or diquat dibromide, is the common name of the chemical 6,7-dihydrodipyrido (1,2-a:2',1'-c) pyrazinediium dibromide. Originally registered by the EPA in 1986, diquat was reregistered in 1995 and is currently being reviewed again. It is sold for agricultural and household uses as well as for use on certain floating-leaf and submersed aquatic plants and some algae. The aquatic formulations are liquids: two of the more commonly used are Reward™ and Weedtrine-D™

Aquatic Use and Considerations

Diquat is a fast-acting herbicide that works by disrupting cell membranes and interfering with photosynthesis. It is a non-selective herbicide and will kill a wide variety of plants on contact. It does not move throughout the plants, so will only kill parts of the plants that it contacts. Following treatment, plants will die within a week.

Diquat will not be effective in lakes or ponds with muddy water or where plants are covered with silt because it is strongly attracted to silt and clay particles in the water. Therefore, bottom sediments must not be disturbed during treatment, such as may occur with an outboard motor. Only partial treatments of ponds or bays should be conducted (1/2 to 1/3 of the water body). If the entire pond were to be treated, the decomposing vegetation may result in very low oxygen levels in the water. This can be lethal to fish and other aquatic organisms. Untreated areas can be treated 10-14 days after the first treatment.

Diquat is used to treat duckweed Lemna spp.), which are tiny native plants. They are a food source for waterfowl but can grow thickly and become a nuisance. Navigation lanes through cattails ( Typha spp.) are also maintained with diquat. Diquat is labeled for use on the invasive Eurasian watermilfoil Myriophyllum spicatum) but in practice is not frequently used to control it because other herbicide options are more selective.

Industrial Vegetation Management Knowledge Base 

Biology and Control of Aquatic Plants  
Diquat Chemical Fact Sheet

Note: Products may not be registered for use in your state or locale. Check to be sure a specific use pattern is approved in your area before use. Check product labeling or your local state agency for more information. Most current product labels are available by visiting the product manufacturers website or at https://www.cdms.net

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