Common name:Dicamba

Other name: dicamba (BSI, E-ISO, (m) F-ISO, ANSI, WSSA); dianat* (former exception, USSR); MDBA (JMAF)

Iupac name: 3,6-dichloro-o-anisic acid

Chemical abstracts name:     3,6-dichloro-2-methoxybenzoic acid

Type: Herbicide

CAS RN: [1918-00-9]; 5-hydroxy derivative [7600-50-2]

M.F.: C₈H₆Cl₂O₃

Mol Wt: 221.0

 

Form (appearance): /Colourless crystals; (tech. is a buff crystalline solid. ).

Composition: Tech. grade purity is 85% w/w, remainder being mainly 3,5-dichloro-O-anisic acid.

M.P.: 114-116℃

B.P.: >200℃

V.P.: 1.67 mPa (25℃, calc.)

S.G.: 1.488 (25℃)

Solubility.: In water 6.1 g/l (25℃). In ethanol 922, cyclohexanone 916, acetone 810, dichloromethane 260, dioxane 1180, toluene 130, xylene 78 (all in g/l, 25℃).

Stability: Resistant to oxidation and hydrolysis under normal conditions. Stable in acids and alkalis. Decomposes at c. 200℃.

Henry: 6.1 × 10^-5 Pa m³ mol^-1

K_owlogP: -0.55 (pH 5.0), -1.88 (pH 6.8), -1.9 (pH 8.9) (OECD 105)

Pka:1.97

 

Formulation types: GR; SL.

Biochemistry: Synthetic auxin (acting like indolylacetic acid).

Mode of action: Selective systemic herbicide, absorbed by the leaves and roots, with ready translocation throughout the plant via both the symplastic and apoplastic systems. Acts as an auxin-like growth regulator.

Uses: Control of annual and perennial broad-leaved weeds and brush species in cereals, maize, sorghum, sugar cane, asparagus, perennial seed grasses, turf, pastures, rangeland, and non-crop land. Used in combinations with many other herbicides. Dosage varies with specific use and ranges from 0.1 to 0.4 kg/ha for crop use, higher rates in pasture.

Phytotoxicity: Most legumes are sensitive.

 

Oral: Acute oral LD₅₀ for rats 1707 mg/kg.

Skin and eye: Acute percutaneous LD₅₀ for rabbits >2000 mg/kg. Extremely irritating and corrosive to eyes; moderately irritating to skin (rabbits).

Inhalation: LC₅₀ (4 h) for rats >9.6 mg/l.

Noel: (2 y) for rats 110 mg/kg b.w. daily; (1 y) for dogs 52 mg/kg b.w. daily. Developmental NOEL for rabbits 30 mg/kg b.w. daily, rats 160 mg/kg b.w. daily. Reproduction NOEL for rats 50 mg/kg b.w. daily. Not mutagenic.

Toxicity: WHO (a.i.) III (Table 5); EPA (formulation) III

EC hazard: Xn; R22|Xi; R41| R52, R53

 

Birds: Acute oral LD₅₀ for mallard ducks 2000 mg/kg. Dietary LC₅₀ (8 d) for mallard ducks and bobwhite quail >10000 mg/kg diet.

Fish: LC₅₀ (96 h) for rainbow trout and bluegill sunfish 135 mg/l.

Daphnia: LC₅₀ (48 h) 110 mg/l.

Algae: LC₅₀ 41 to >250 mg/l (depending on species).

Worms: Bee: Not toxic to bees; LD₅₀ >100μg/bee.

 

Plant: The degradation rate in plants varies greatly with species. In wheat, the major metabolite is 5-hydroxy-2-methoxy-3,6-dichlorobenzoic acid, whilst- 3,6-dichlorosalicylic acid is also a metabolite. Soil/Environment In soil, microbial degradation occurs, the principal metabolite being 3,6-dichlorosalicylic acid. Under conditions amenable to rapid metabolism, DT₅₀ <14 d. K_oc 2.

Animals: In mammals, following oral administration, dicamba is rapidly eliminated in the urine, partly as a glycine conjugate.