:Metalaxyl

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| ImageFile = Metalaxyl.svg

| ImageSize =200px

| ImageFile2 = Metalaxyl 3D BS.png

| ImageSize2 = 200px

| IUPACName = Methyl 2-[N-(2,6-dimethylphenyl)(methoxy)acetamido]propanoate

| OtherNames = Methyl N-(2,6-dimethylphenyl)-N-(2-methoxyacetyl)alaninate

|Section1={{Chembox Identifiers

| CASNo_Ref = {{cascite|correct|CAS}}

| CASNo =57837-19-1

| UNII_Ref = {{fdacite|correct|FDA}}

| UNII = 16K4M187IF

| PubChem =42586

| ChEMBL_Ref = {{ebicite|correct|EBI}}

| ChEMBL = 105809

| SMILES = COCC(=O)N(c1c(C)cccc1C)C(C)C(=O)OC

| EINECS = 260-979-7

| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}

| ChemSpiderID = 38839

| StdInChI_Ref = {{stdinchicite|correct|chemspider}}

| StdInChI = 1S/C15H21NO4/c1-10-7-6-8-11(2)14(10)16(13(17)9-19-4)12(3)15(18)20-5/h6-8,12H,9H2,1-5H3

| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}

| StdInChIKey = ZQEIXNIJLIKNTD-UHFFFAOYSA-N

| RTECS =

| MeSHName =

| ChEBI_Ref = {{ebicite|correct|EBI}}

| ChEBI = 6790

| KEGG_Ref = {{keggcite|correct|kegg}}

| KEGG = C10947

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|Section2={{Chembox Properties

| Formula =C₁₅H₂₁NO₄

| MolarMass =279.33 g/mol

| Appearance =Fine white powder

| Density =1.20g/cm³ at 20 °C

| MeltingPtC = 71 to 72

| MeltingPt_ref = O'Neil, M.J. (ed.). The Merck Index - An Encyclopedia of Chemicals, Drugs, and Biologicals. 13th Edition, Whitehouse Station, NJ: Merck and Co., Inc., 2001., p. 1058

| BoilingPtC = 295.9

| BoilingPt_notes = at 760 mm Hg

| Solubility = 8,400 mg/L at 22 °C

| LogP =1.65 (octanol/water)Hansch, C., Leo, A., D. Hoekman. Exploring QSAR - Hydrophobic, Electronic, and Steric Constants. Washington, DC: American Chemical Society., 1995., p. 134

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|Section3={{Chembox Hazards

| MainHazards =

| FlashPt =

| AutoignitionPt =

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Metalaxyl is an acylalanine fungicide with systemic function.{{cite journal|last1=Sukul|first1=P|last2=Spiteller|first2=M|title=Metalaxyl: persistence, degradation, metabolism, and analytical methods.|journal=Reviews of Environmental Contamination and Toxicology|date=2000|volume=164|pages=1–26|pmid=12587832}} Its chemical name is methyl N-(methoxyacetyl)-N-(2,6-xylyl)-DL-alaninate. It can be used to control Pythium in a number of vegetable crops, and Phytophthora in peas. Metalaxyl-M is the ISO common name{{cite web |url=https://pesticidecompendium.bcpc.org/metalaxyl.html |title=Compendium of Pesticide Common Names: metalaxyl |publisher=BCPC}} and Ridomil Gold is the trade name for the optically pure (-) / D / R active stereoisomer, which is also known as mefenoxam.{{cite journal|last1=Monkiedje|first1=Adolphe|last2=Spiteller|first2=Michael|title=Effects of the phenylamide fungicides, mefenoxam and metalaxyl, on the microbiological properties of a sandy loam and a sandy clay soil|journal=Biology and Fertility of Soils|date=2002|volume=35|issue=6|pages=393–398|doi=10.1007/s00374-002-0485-1|s2cid=22642870}}

It is the active ingredient in the seed treatment agent Apron XL LS.{{cite web|url-status=dead|url=https://www.gov.mb.ca/agriculture/crops/vegetablecrops/pdf/bmz10s02.pdf|title=bmz10s02.pdf|publisher=Government of Manitoba|archiveurl=https://web.archive.org/web/20070930171045/http://www.gov.mb.ca/agriculture/crops/vegetablecrops/pdf/bmz10s02.pdf|archivedate=2007-09-30}}

The fungicide has suffered severe {{ Visible anchor | Resistance | text=resistance }} problems. The fungicide was marketed for use against Phytophthora infestans. However, in the summer of 1980, in the Republic of Ireland, the crop was devastated by a potato blight epidemic after a resistant race of the oomycete appeared.[http://www.bspp.org.uk/bsppnews/bsppnews32/bsppnews32-3.htm Working on potato blight in Northern Ireland] Irish farmers later successfully sued the company for their losses.{{Citation needed|date=February 2007}}

Maximum pesticide residue limits for the EU/UK are set at 0.5 mg/kg for oranges and 1.0 mg/kg for apples.{{citation needed|date=November 2020}} As early as 1998 Pythium was known to be widely developing resistance to metalaxyl{{cite web | title=Survey of Pythium Isolates for Resistance to Subdue (metalaxyl) | website=UMass Amherst | url=http://ag.umass.edu/sites/ag.umass.edu/files/fact-sheets/pdf/PYTHIU_2.pdf | access-date=2020-11-23}} which was the most effective control at the time. Various Pythium populations have been known to have resistance to mefenoxam since the 1980s and metalaxyl since 1984.{{cite journal | last=Sanders | first=P. L. | title=Failure of Metalaxyl to Control Pythium Blight on Turfgrass in Pennsylvania | journal=Plant Disease | publisher=American Phytopathological Society | volume=68 | issue=1 | year=1984 | issn=0191-2917 | doi=10.1094/pd-68-776 | page=776}} There is wide variability in resistance/sensitivity between Pythium species, with some populations showing complete ineffectiveness.