Reward Herbicide – Diquat Data

Diquat Dibromide

Overview


Diquat dibromide is a nonselective, fast-acting desiccant herbicide, which damages only the parts of a plant to which it is applied. It is used agriculturally and also has a number of outdoor residential weed control applications.

Diquat dibromide binds strongly with soil, and has a low mobility in the environment.

Diquat dibromide may be sold under names such as Aquacide, Aquakill, Dextrone, Diquat, Reglone, Reglox, Reward, Tag, Torpedo, Vegetrole, and Weedtrine-D (#EXTOXNET).

Chemical Description


Diquat dibromide is a colorless to yellow crystal that is red in solution. It is odorless. It is highly soluble in water and has a high affinity for soil (#CEPA).

Because highly concentrated forms of diquat chemicals are corrosive, they often contain corrosion inhibitors (#CEPA).

Uses


Diquat dibromide is registered for weed control on several food crops including potato, carrot, cucumber, melons, pepper, radish, squash, and turnip. In addition, it is also used on some feed crops, most notably alfalfa. It may also be used to defoliate the tops of some seed or root crops. Diquat dibromide can be used to treat irrigation systems and agricultural drainage systems (#EPA).

Residentially, diquat dibromide may be used to control weeds around ornamental plants and trees, as well as in lawns. It can also be used on paved areas, patios, fencerows, or hedgerows (#EPA).

Diquat dibromide targets a variety of plants such as algae: pithophora, spirogyra; and weeds: bladderwort, crabgrass, elodea, jimsonweed, leafy spurge, naiad, poison ivy, salvinia, shepherdspurse, and waterlettuce (#EPA).

Human Health Effects


Diquat dibromide has a moderate acute toxicity. The oral LD50 is 120 mg/kg for rats, 233 mg/kg in mice, and 188 mg/kg in rabbits. Repeated dermal doses of diquat dibromide caused redness, thickening, and scabbing to the skin of rabbits. Workers handling highly concentrated diquat dibromide have reported color change, softening, and shedding of the fingernails (#EXTOXNET).

A study in which rats were fed diquat dibromide for 104 weeks found that cataracts occurred in nearly all test animals. Kidney functions were also disrupted. Another study in which dogs were fed diquat dibromide for one year found chronic intestinal inflammatory lesions and kidney weight increases in addition to a clouding of the eyes (#CEPA).

Inhalation of diquat dibromide may cause coughing and sore throat. Exposing the skin and eyes may cause redness and pain. Ingesting diquat dibromide may cause abdominal pain, diarrhea, nausea, vomiting, and ulcerations in the mouth (#PANNA). Extreme exposures can cause kidney failure or liver damage (#EXTOXNET).

Environmental Health Effects


Plants absorb diquat dibromide rapidly through the leaves. There, the chemical interferes with plant growth, and quickly destroys tissue necessary for translocation before it can move to other parts of the plant. The plant dies after diquat dibromide interrupts normal plant respiration (#EXTOXNET).

Diquat dibromide has a moderate acute toxicity to birds. The oral LD50 is 564 mg/kg for mallard, and 200 to 400 mg/kg in hens (#EXTOXNET). It has a slight to moderate toxicity to fish. The 8-hour LC50 is 12.3 mg/L for rainbow trout and 28.5 mg/L for Chinook salmon (#EXTOXNET). Diquat dibromide is not expected to bioaccumulate in fish. It is practically nontoxic to bees (#EPA).

Diquat dibromide binds strongly with soil, and has a low mobility in the environment. The half-life of diquat dibromide could not be calculated, since no noticeable deterioration of the chemical occurred in three year intervals. This suggests that diquat may accumulate in soil (#CEPA). Diquat dibromide is an unlikely water contaminant (#EPA).

Regulation


Diquat dibromide is a General Use Pesticide.

Precautionary Notes


Heating diquat dibromide may cause the release of toxic fumes (#NIOSH).

References



California Environmental Protection Agency. Public Health Goal for Diquat in Drinking Water. (August 2000). http://oehha.ca.gov/water/phg/pdf/diquat.pdf [Accessed 8-31-10].


Environmental Protection Agency. Reregistration Eligibility Decision- Diquat Dibromide. (July 1995). http://www.epa.gov/oppsrrd1/reregistration/REDs/0288.pdf [Accessed 8-31-10].


Extension Toxicology Network. Diquat Dibromide. (1996). http://extoxnet.orst.edu/pips/diquatdi.htm [Accessed 8-31-10].


National Institute for Occupational Safety and Health. Diquat Dibromide. http://www.cdc.gov/niosh/ipcsneng/neng1363.html [Accessed 8-31-10].


Pesticide Action Network North America. Diquat Dibromide. http://www.pesticideinfo.org/Detail_Chemical.jsp?Rec_Id=PC33217 [Accessed 8-31-10].

Diquat Fact Sheet from the Wisconsin Department of Natural Resources

Wisconsin Department of Natural Resources

January 2012

Diquat Chemical Fact Sheet

Formulations

Diquat, or diquat dibromide, is the common name of the chemical 6,7-dihydrodipyrido (1,2­a: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 in Wisconsin are Reward™ and Weedtrine-D™ (product names are provided solely for your reference and should not be considered endorsements).

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.

Post-Treatment Water Use Restrictions

There are no restrictions on swimming or eating fish from water bodies treated with diquat.  Treated water should not be used for drinking water for one to three days, depending on the concentration used in the treatment.  Do not use treated water for pet or livestock drinking water for one day following treatment.  The irrigation restriction for food crops is five days, and for ornamental plants or lawn/turf, it varies from one to three days depending on the concentration used.

Herbicide Degradation, Persistence and Trace Contaminants

Diquat is not degraded by microbes.  When applied to a waterbody, diquat binds with the organic matter in the sediment indefinitely.  It does not degrade and will accumulate in the sediments.  Diquat is usually detectable in the water column for less than a day to ~35 days after treatment.  Diquat will remain in the water column longer when treating a waterbody with sandy soils due to the low organic matter and clay content.  Because of its persistence and very high affinity for the soil, diquat does not leach into groundwater.

Ethylene dibromide (EDB) is a trace contaminant in diquat products.  It originates from the manufacturing process.  EDB is a carcinogen, and the EPA has evaluated the health risk of its presence in formulated diquat products.  The maximum level of EDB in diquat dibromide is 10 ppb (parts per billion), it degrades over time, and it does not persist as an impurity.

The Wisconsin Department of Natural Resources provides equal opportunity in its employment, programs, services, and functions under an Affirmative Action Plan. If you have any questions, please write to Equal Opportunity Office, Department of Interior, Washington, D.C. 20240.  This publication is available in alternative format (large print, Braille, audio tape. etc.) upon request.  Please call (608) 267-7694 for more information.

Page 2 Diquat Chemical Fact Sheet

Wisconsin Department of Natural Resources
Wisconsin Department of Natural Resources

 

Impacts on Fish and Other Aquatic Organisms

At application rates, diquat does not have any apparent short-term effects on most of the aquatic organisms that have been tested.  However, certain species of important aquatic food chain organisms such as amphipods and Daphnia (water fleas) can be adversely affected at label application rates.  Direct toxicity and loss of habitat are believed to be the causes. Tests on snails have shown that reproductive success may be affected, as well.  These organisms only recolonize the treated area as vegetation becomes re-established.

Laboratory tests indicate walleye are the fish most sensitive to diquat, displaying toxic symptoms when confined in water treated with diquat at label application rates.  Other game and panfish (e.g. northern pike, bass, and bluegills) are apparently not affected at these application rates.  Limited field studies to date have not identified significant short or long-term impacts on fish and other aquatic organisms in lakes or ponds treated with diquat.

The bioconcentration factors measured for diquat in fish tissues is low.  Therefore, bioconcentration is not expected to be a concern with diquat.

Human Health

The risk of acute exposure to diquat would be primarily to chemical applicators.  Diquat causes severe skin and eye irritation and is toxic or fatal if absorbed through the skin, inhaled or swallowed.  Wearing skin and eye protection

(e.g. rubber gloves, apron, and goggles) to minimize eye and skin irritation is required when applying diquat.

The risk to water users of serious health impacts (e.g. birth defects and cancer) is not believed to be significant according to the EPA.  Some risk of allergic reactions or skin irritation is present for sensitive individuals.

For Additional Information

Environmental Protection Agency Office of Pesticide Programs

www.epa.gov/pesticides

Wisconsin Department of Agriculture, Trade, and Consumer Protection

http://datcp.wi.gov/Plants/Pesticides/

Wisconsin Department of Natural Resources 608-266-2621

http://dnr.wi.gov/lakes/plants/

Wisconsin Department of Health Services

http://www.dhs.wisconsin.gov/

National Pesticide Information Center 1-800-858-7378

http://npic.orst.edu/

 

Wisconsin Department of Natural Resources DNR PUB-WT-969 2012 Box 7921 Madison, WI 53707-7921