IDENTIFICATION
Common name: Metalaxyl-M
Other name: Metalaxyl-M (BSI, E-ISO, (m) F-ISO)
R-metalaxyl; CGA 76539; mefenoxam
Iupac name: methyl N-(methoxyacetyl)-N-(2,6-xylyl)-D-alaninate; methyl (R)-2-{[(2,6-dimethylphenyl)methoxyacetyl]amino}propionate
Chemical abstracts name: methyl N-(2,6-dimethylphenyl)-N-(methoxyacetyl)-D- alaninate
Type: Fungicide
CAS RN: [70630-17-0]
M.F.: C15H21NO4
Mol Wt: 279.3
PHYSICAL CHEMISTRY
Form (appearance): Pale yellow to light brown, viscous liquid.
Composition: (R)- enantiomer of metalaxyl.
M.P.: -38.7%℃ (glass transition temperature)
B.P.: Decomp. c. 270℃
V.P.: 3.3 mPa (25℃)
F.P.: 179℃ (EEC A.10)
S.G.: 1.125 (20℃)
Solubility: In water 26 g/l (25℃).In n-hexane 59 g/l; miscible with acetone, ethyl acetate, methanol, dichloromethane, toluene, n-octanol.
Stability: Hydrolytically stable under acidic and neutral conditions (DT50 >200 d). Under alkaline conditions, DT50 116 d (pH 9, 25℃).
Specific rotation Negative
Henry: 3.5 × 10-5 Pa m3 mol-1 (calc.)
KowlogP: 1.71 (25℃)
APPLICATION
Formulation types: DS; EC; FS; GR; SC; WG; WP.
Biochemistry: Inhibits protein synthesis in fungi, by interference with the synthesis of ribosomal RNA. The (R)- (metalaxyi-M) and (S)- isomers have the same mode of action, but differ considerably in effectiveness.
Mode of action: Systemic fungicide with protective and curative action, absorbed through the leaves, stems, and roots.
Uses: To control diseases caused by air- and soil-borne Peronosporales on a wide range of temperate, subtropical and tropical crops. Foliar sprays with mixtures of metalaxyI-M and protectant fungicides are recommended to control air-borne diseases caused by Pseudoperonospora humuli on hops, Phytophthora infestans on potatoes and tomatoes, Peronospora tabacina on tobacco, Plasmopara viticola on vines, downy mildews of vegetables, and Bremia lactucae on lettuce, at 100-140 g metalaxyI-M/ha. Soil applications of metalaxyI-M alone are used to control soil-borne pathogens causing root and lower stern rots on avocado and citrus, Phythophthora nicotianae on tobacco, Phytophthora spp. on peppers, and Pythium spp. on many different crops, including ornamentals, at 250-1000 g/ha. Seed treatments control systemic Peronosporaceae on maize, peas, sorghum and sunflowers, at 35-300 g/100 kg seed, as well as damping-off (Pythium spp.) of various crops, at 8.25-17.5 g/100 kg seed.
MAMMALIAN TOXICOLOGY
Oral: Acute oral LD50 for rats 667 mg/kg.
Skin and eye: Acute percutaneous LD50 for rats >2000 mg/kg. Not a skin irritant (rabbits); risk of serious damage to eyes (rabbits). Not a skin sensitiser (guinea pigs).
Inhalation: LC50 (4 h) for rats >2290 mg/m3.
Noel: for rats 2.5, mice 35.7, dogs 8.0 mg/kg b.w. daily.
ADI: 0.025 mg/kg b.w.
Other Not 0ncogenic, not mutagenic, not teratogenic.
Toxicity: WHO (a.i.) Ⅱ EC hazard (Xn; R22,R41)
ECOTOXICOLOGY
Birds: LD50 (14 d) for bobwhite quail 981-1419 mg/kg. LC50 (8 d) for bobwhite quail >5620 mg/kg.
Fish: LC50 (96 h) for rainbow trout >100 mg/l.
Daphnia: LC50 (48 h) >100 mg/l.
Algae: ErC50 (72 h) for Scenedesmus subspicatus 103 mg/l.
Other aquatic spp. EC50 (96 h) for Eastern oyster (Crassostrea virginica) 9.7 mg/l.
Worms: LC50 (14 d) for Eisenio foetido 830 mg/kg soil.
Other beneficial spp. EC formulation (480 g/l ) harmless to Poecilus cupreus and Orius insidiosus (IOBC).
Bees LD50 (48 h, contact) 25 μg/bee.
ENVIRONMENTAL FATE
Plant: Metabolised by more than 4 types of phase I reaction (oxidation of the phenyl ring, oxidation of the methyl group, cleavage of the methyl ester and N-dealkylation) to form eight metabolites; at phase Il, most of the metabolites are sugar conjugated.
Animals: In mammals, following oral administration, rapidly absorbed and also rapidly and almost completely eliminated in urine and faeces. Metabolism proceeds via hydrolysis of the ester bond, oxidation of the 2-(6)-methyl group and of the phenyl ring and N-dealkylation. Residues in tissues were generally Iow and there was no evidence for accumulation or retention of metalaxyI-M or its metabolites.
Soil/Environment: DT50 in soil 21 d (realistic range 5-30 d). Koc 70 ml/g (realistic range 30-300 ml/g). Stable to photolysis.
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