Common name: Pendimethalin

Other name: pendimethalin (BSI, E-ISO, ANSI, WSSA); pendimethaline ((f) F-ISO); penoxalin* (former WSSA name)

Iupac name: N-(1-ethylpropyl)-2,6-dinitro-3,4-xylidine

Chemical abstracts name:     N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine

Type: Herbicide

CAS RN: [40487-42-1]

M.F.: C₁₃H₁₉N₃O₄

Mol Wt: 281.3

 

Form (appearance): Orange yellow crystals.

Composition: Tech. grade is 90% pure.

M.P.: 54-58℃

B.P.: 4.0 mPa (25℃)

S.G.: 1.19 at 25℃

Solubility.: In water 0.3 mg/l (20℃). In acetone 700, xylene 628, corn oil 148, heptane 138, isopropanol 77 (all in g/l, 26℃). Readily soluble in benzene, toluene, chloroform and dichloromethane. Slightly soluble in petroleum ether and petrol.

Stability: Very stable in storage; store above 5℃ and below 130℃. Stable to acids and alkalis. Slowly decomposed by light. DT₅₀ in water <21 d.

K_owlogP: 5.18

 

Formulation types: EC; GR; WG.

Biochemistry: Microtubule assembly inhibition.

Mode of action: Selective herbicide, absorbed by the roots and leaves. Affected plants die shortly after germination or following emergence from the soil.

Uses: Control of most annual grasses and many annual broad-leaved weeds, at 0.6-2.4 kg a.i./ha, in cereals, onions, leeks, garlic, fennel, maize, sorghum, rice, soya beans, peanuts, brassicas, carrots, celery, black salsify, peas, field beans, lupins, evening primrose, tulips, potatoes, cotton, hops, pome fruit, stone fruit, berry fruit (including strawberries), citrus fruit, lettuce, aubergines, capsicums, established turf, and in transplanted tomatoes, sunflowers, and tobacco. Applied pre-plant incorporated, pre emergence, pre-transplanting, or early post-emergence. Also used for control of suckers in tobacco.

Phytotoxicity: njury to maize may occur if used as a pre-plant, soil-incorporated treatment.

 

Oral: Acute oral LD₅₀ for male rats 1250, female rats 1050, male mice 1620, female mice 1340, rabbits >5000, beagle dogs >5000 mg/kg.

Skin and eye: Acute percutaneous LD₅₀ for rabbits >5000 mg/kg. Non-irritating to skin and eyes (rabbits).

Noel: In 2 y feeding trials, rats receiving 100 mg/kg diet showed no ill-effects.
Water GV 20 μg/l (TDI 5 μg/kg b.w.).

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

EC hazard: Xn; R22

 

Birds: Dietary LC₅₀ (8 d) for bobwhite quail 4187, mallard ducks 10388 mg/kg diet.

Fish: LC₅₀ (96 h) for rainbow trout 0.14, bluegill sunfish 0.2, channel catfish 0.42 mg/l.

Worms: Bees LD₅₀ (topical) >50 μg/bee.

 

Plant: In plants, the 4-methyl group on the benzene ring is oxidised to the carboxylic acid via the alcohol. The amino nitrogen is also oxidised. At harvest time, residues in crops are below the validated sensitivity of the analytical method (0.05 ppm).

Animals: In rats, the major metabolic routes for pendimethalin involve hydroxylation of the 4 methyl and N-1-ethyl groups, oxidation of these alkyl groups to carboxylic acids, nitro-reduction, cyclisation and conjugation (J. Zulian, J. Agric. Food Chem., 1990, 38, 1743).

Soil/Environment: In soil, the 4-methyl group on the benzene ring is oxidised to the carboxylic acid via the alcohol; the amino nitrogen is also oxidised. DT₅₀ in soil is 3-4 mo (A. Walker & W. Bond, Pestic. Sci., 1977, 8, 359). K_d ranges from 2.23 (0.01% o.m., pH 6.6) to 1638 (16.9% o.m., pH 6.8) (H. J. Pedersen et at., Pestic. Sci.,1995, 44, 131).