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Imazapic is an imidazolinone herbicide that targets broadleaf weeds and annual or perennial grasses (#WSDOT). It can be used as both a pre-emergent or post-emergent herbicide. It may also be formulated as an ammonium salt.

Imazapic is used mostly on commercial grasses and for nonselective residential weed control. Imazapic can be quickly transported throughout all regions of a plant, including edible portions such as seeds, leaves, and fruits, and it accumulates in actively growing tissues (#JPR). Thus, it is unsuitable for use on food crops. It has also been found to inhibit the growth of some crops.

Imazapic is marketed as Plateau, Plateau DG, and Cadre (#JPR).

Chemical Description

Imazapic is persistent in soil, with an average half-life of 232 days (#JPR). It is soluble in water (#USDE).


Commercially, imazapic is used on peanut crops and grasses such as rangeland and pastures (#JPR). It may be used on highway rights-of-way (#WSDOT).

Imazapic can also be found in residential weed treatment and prevention products.

Human Health Effects

Imazapic has a low acute toxicity to mammals. The oral LD50 in rats exceeds 5000 mg/kg (#USDE). Imazapic is excreted rapidly and does not accumulate in tissues (#WSDOT).

A study on chronic toxicity was conducted in which dogs were fed imazapic for one year. Researchers found deterioration of abdominal and thigh muscles, as well as some tissue death. Anemia or red blood cell deficiency, increased cholesterol, and increased liver size was also noted (#JPR).

Imazapic may cause irritation to the eyes (#JPR).

Environmental Health Effects

In plants, imazapic is absorbed through plant roots and shoots. It can then rapidly move to other parts of the plant. Imazapic inhibits the function of an enzyme, acetolactate synthase, which is essential in the production of specific amino acids. This interrupts protein synthesis and plant growth, and eventually causes the death of the plant (#JPR).

Imazapic is practically non-toxic to birds in acute exposures. The oral LD50 was greater than 15,000 mg/kg in bobwhite quail. It also has a low toxicity to bees, with an LD50 greater than 100 ug/bee. Imazapic is slightly toxic to fish. Both rainbow trout and bluegill sunfish have a 96 hour LC50 greater than 100 mg/L (#USDE).

Due to its persistence and mobility, imazapic has a moderate potential for ground water contamination (#WSDOT).

Imazapic may have significant adverse effects on some non-target plants. In tests performed by the manufacturer, the weights of cabbage seedlings were reduced by 25% by a dose of less than 1% of the recommended application. Onion, tomato, cucumber, and ryegrass seedlings were reduced by 25% in weight after doses of 2-3% of recommended applications were administered (#JPR).


Imazapic is a General Use Pesticide.

Precautionary Notes

Imazapic products are often formulated with unidentified ingredients listed as inert ingredients. Inert ingredients do not require testing for product registration, but may still be hazardous to health. In 2003, crystalline silica was identified as one of the inert ingredients in some imazapic products, a known carcinogen according to the International Agency for Research on Cancer (#JPR). Understand that there are risks when working with unknown substances. Imazapic can have synergistic effects with other pesticides, particularly organophosphate insecticides. Use caution near desirable plants and water sources.


Journal of Pesticide Reform. Herbicide Factsheet: Imazapic. (Fall 2003). [Accessed 8-29-10].

Pesticide Action Network North America. Imazapic. [Accessed 8-29-10].

US Department of Energy- Bonneville Power Administration. Imazapic: Herbicide Factsheet. [Accessed 8-29-10].

Washington State Department of Transportation. Imazapic: Roadside Vegetation Management Herbicide Fact Sheet.

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