Metalaxyl-M

Description

Metalaxyl-M is the more active of the two enantiomers of the phenylamide fungicide metalaxyl; metalaxyl is currently registered in more than 80 countries with uses on more than 60 crops. 1996 Mefenoxam (metalaxyl-M) first registered for use in NYS. Metalaxyl-M is the first enantiomeric form of a fungicide introduced into the market. When used as seed-treatment, soil treatment or foliar application against fungi of the order Peronosporales, it provides the same excellent level of efficacy as metalaxyl but at half the application rate. Mefenoxam is more commonly used than metalaxyl in most pesticide products registered in NYS today.

The Uses of Metalaxyl-M

Metalaxyl-M is an isomer of Metalaxyl (M258740), an agricultural fungicide. Phenylamide fungicide or use in food crops, shrubs and turf.

Definition

ChEBI: Metalaxyl-M is a methyl N-(2,6-dimethylphenyl)-N-(methoxyacetyl)alaninate that is the more active R-enantiomer of metalaxyl. A systemic fungicide, it is active against phytopathogens of the order Peronosporales and is used to conrtrol Pythium in a number of vegetable crops. It has a role as an agrochemical. It is a methyl N-(2,6-dimethylphenyl)-N-(methoxyacetyl)alaninate, a D-alanine derivative, an acylamino acid fungicide and an anilide fungicide. It derives from a D-alanine. It is an enantiomer of a (S)-metalaxyl.

Toxicity evaluation

Metalaxyl-M is the R-enantiomer-enriched (97%) form of metalaxyl. This compound is a phenylamide that disrupts fungal RNA polymerase, and the R-enantiomer is much more active. The rat oral LD50 is 670 mg/kg for both formulations. Metalaxyl-M is a severe ocular irritant, but otherwise is toxicologically equivalent to metalaxyl. Both are non-irritating and non-sensitizing for skin. Rats in repeated-dose studies with metalaxyl-M developed centrilobular hepatocellular hypertrophy. In dogs treated daily for 2 years with up to 80 mg metalaxyl/kg, highdose dogs showed transient spasms and salivation, especially during the first year, and four high-dose dogs died between study weeks 20 and 52. Histopathological liver changes were not detected in the dogs despite increased liver weights as well as elevated serum alanine aminotransferase (ALT) and alkaline phosphatase (ALP) activities. Two-year rodent studies showed a small increase in hepatocellular fatty change and centrilobular hypertrophy, but no increase in neoplasia. Metalaxyl is also negative for reproductive and developmental effects, and the great majority of genotoxicity tests have been negative.

Mode of action

Metalaxyl-M controls all economically important diseases caused by fungi in the order Peronosporales. Thiamethoxam, metalaxyl-M and difenoconazole act systemically in seeds and young plants. They are taken up from the treated seed coat and translocated to all parts of the plant during germination.