Herbicide

HRAC  K3 WSSA  15; oxyacetamide

NOMENCLATURE

Common name mefenacet (BSI, draft E-ISO, (m) draft F-ISO)

IUPAC name 2-(1,3-benzothiazol-2-yloxy)-N-methylacetanilide; 2-benzothiazol-2-yloxy-N-methylacetanilide 

Chemical Abstracts name 2-(2-benzothiazolyloxy)-N-methyl-N-phenylacetamide 

CAS RN [73250-68-7]  EEC no. 277-328-8  Development codes FOE 1976 (Bayer); NTN 801 (Nihon Bayer) 

PHYSICAL CHEMISTRY

Mol. wt. 298.4  M.f. C16H14N2O2S  Form Colourless, odourless crystals.  M.p. 134.8 ºC  V.p. 6.4 ´ 10-4 mPa (20 °C); 11 mPa (100 ºC)  KOW logP = 3.23  Solubility In water 4 mg/l (20 ºC). In dichloromethane >200, hexane 0.1-1.0, toluene 20-50, isopropanol 5-10 (all in g/l, 20 ºC).  Stability Stable to light. In storage, 94.8% remains unchanged after 6 months at 30 ºC. Stable to hydrolysis at pH 4-9. 

COMMERCIALISATION

History Herbicide reported by R. R. Schmidt et al. (Meded. Fac. Landbouwwet. Rijksuniv. Gent, 1984, 49, 1075). Introduced in Japan (1987) by Nihon Bayer Agrochem K.K.  Patents DE 2822155; DE 2903966; DE 3038636; DE 3323334; DE 3344236; DE 3418167; DE 3422861  Manufacturers Bayer

APPLICATIONS

Biochemistry Inhibits cell division and growth.  Mode of action Selective herbicide.  Uses Used pre-emergence and early post-emergence, mainly in transplanted rice, at 1.0-1.6 kg/ha, to control grass weeds (with a specific action against Echinochloa crus-galli). Preferably used in mixtures with other herbicides.  Formulation types GR; SC; WP.  Selected tradenames: 'Hinochloa' (Bayer); 'Rancho' (Bayer); mixtures: 'Act' (+ pyrazosulfuron-ethyl) (Nihon Bayer, Nissan, Yashima); 'Wolf-Ace' (+ bensulfuron-methyl+ thiobencarb) (Kumiai); 'Zark' (+ bensulfuron-methyl) (Du Pont, Kumiai, Nihon Bayer, Sankyo)

OTHER TRADENAMES

Mixtures: 'Batl' (+ daimuron+ imazosulfuron) (Nihon Bayer, Takeda); 'Inegreen D' (+ bensulfuron-methyl+ cyhalofop-butyl+ daimuron) (Nihon Bayer); 'Inegreen' (+ bensulfuron-methyl+ cyhalofop-butyl) (Nihon Bayer); 'Revolver' (+ cyhalofop-butyl+ pyrazosulfuron-ethyl) (Nissan); 'Zark D' (+ bensulfuron-methyl+ daimuron) (Sankyo)

ANALYSIS

Product analysis by hplc. Details and methods for determination of residues available from Bayer. 

MAMMALIAN TOXICOLOGY

Oral Acute oral LD50 for rats, mice and dogs >5000 mg/kg.  Skin and eye Acute percutaneous LD50 for rats and mice >5000 mg/kg. Not irritating to skin and eyes (rabbits).  Inhalation LC50 (4 h) for rats >0.02 mg/l (dust).  NOEL (2 y) for rats 100, mice 300 mg/kg diet.  ADI 0.0036 mg/kg b.w.  Toxicity class WHO (a.i.) III (Table 5); EPA (formulation) IV  EC hazard N; R51, R53 

ECOTOXICOLOGY

Birds LC50 (5 d) for bobwhite quail >5000 mg/kg diet.  Fish LC50 (96 h) for carp 6.0, trout 6.8, golden orfe 11.5 mg/l.  Daphnia LC50 (48 h) 1.81 mg/l.  Algae EC50 (96 h) for Scenedesmus subspicatus 0.18 mg/l.  Worms LC50 (28 d) for Eisenia foetida >1000 mg/kg dry substrate. 

ENVIRONMENTAL FATE