Metalaxyl-M

Composition (R)- enantiomer of metalaxyl. Mol. wt. 279.3 M.f. C₁₅H₂₁NO₄ Form Pale yellow to light brown, viscous liquid. M.p. -38.7 °C (glass transition temperature) B.p. Decomp. c. 270 °C V.p. 3.3 mPa (25 °C) K_OW logP = 1.71 (25 °C) Henry 3.5 ´ 10^-5 Pa m³ mol^-1 (calc.) S.g./density 1.125 (20 °C) Solubility In water 26 g/l (25 °C). 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 °C). Specific rotation Negative F.p. 179 °C (EEC A10)

APPLICATIONS Metalaxyl-M

Biochemistry Inhibits protein synthesis in fungi, by interference with the synthesis of ribosomal RNA. The (R)- (metalaxyl-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 metalaxyl-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 metalaxyl-M/ha. Soil applications of metalaxyl-M alone are used to control soil-borne pathogens causing root and lower stem rots on avocado and citrus, Phytophthora 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. Formulation types DS; EC; FS; GR; SC; WG; WP. Selected tradenames: 'Apron XL' (Syngenta); 'Ridomil Gold' (Syngenta); mixtures: 'Maxim XL' (+ fludioxonil) (seed treatment) (Syngenta)

MAMMALIAN TOXICOLOGY Metalaxyl-M

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 oncogenic, not mutagenic, not teratogenic. Toxicity class WHO (a.i.) II EC hazard (Xn; R22, R41)

ECOTOXICOLOGY Metalaxyl-M

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 E_rC₅₀ (72 h) for Scenedesmus subspicatus 103 mg/l. Other aquatic spp. EC₅₀ (96 h) for Eastern oyster (Crassostrea virginica) 9.7 mg/l. Bees LD₅₀ (48 h, contact) 25 mg/bee. Worms LC₅₀ (14 d) for Eisenia foetida 830 mg/kg soil. Other beneficial spp. EC formulation (480 g/l ) harmless to Poecilus cupreus and Orius insidiosus (IOBC).

ENVIRONMENTAL FATE Metalaxyl-M

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 low and there was no evidence for accumulation or retention of metalaxyl-M or its metabolites. Plants 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 II, most of the metabolites are sugar conjugated. Soil/Environment DT₅₀ in soil 21 d (realistic range 5-30 d). K_oc 70 ml/g (realistic range 30-300 ml/g). Stable to photolysis.

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