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Cyhalofop-butyl

Cyhalofop-butyl 97%TC
Cyhalofop-butyl 18.5%EC
Cyhalofop-butyl 18%EC
Cyhalofop-butyl 10%EC

Herbicide
HRAC A WSSA 1; aryloxyphenoxypropionate

Cyhalofop-butyl NOMENCLATURE
Common name cyhalofop-butyl (pa ISO, ANSI)
IUPAC name butyl (R)-2-[4-(4-cyano-2-fluorophenoxy)phenoxy]propionate
Chemical Abstracts name butyl (R)-2-[4-(4-cyano-2-fluorophenoxy)phenoxy]propanoate
CAS RN [122008-85-9]; [122008-78-0] (for acid) Development codes DE-537; XDE-537; XRD-537; DEH112; EF 1218; NAF-541

PHYSICAL CHEMISTRY
Composition Purity 96.5% nominal. Material is the resolved (R)- isomer. Mol. wt. 357.4 M.f. C20H20FNO4 Form White crystalline solid. M.p. 49.5 °C B.p. decomp. >270 °C V.p. 5.3 10-2 mPa (25 ºC) KOW logP = 3.31 (25 °C) Henry 9.51  10-4 Pa m3 mol-1 (calc.) S.g./density 1.172 (20 °C) Solubility In water 0.44 (unbuffered), 0.46 (pH 5), 0.44 (pH 7.0) (all mg/l, 20 °C). In acetonitrile >250, n-heptane 6.06, n-octanol 16.0, dichloroethane >250, methanol >250, acetone >250, ethyl acetate >250 (all in g/l, 20 °C). Stability Stable at pH 4, hydrolysed slowly at pH 7. At pH 1.2 or pH 9, decomposition is rapid.

COMMERCIALISATION
History Discovered in the mid-1980s by The Dow Chemical Company (now Dow AgroSciences) and reported by P. G. Ray et al. (Proc. 10th Australian & 14th Asian-Pacific Weed Conference, Brisbane, Australia, September 1993, p. 41). Introduced in Asia in 1995; now marketed in rice-growing territories worldwide. Patents US 4894085 (1990); US 4897481 (1990); EP 302203 (1989) Manufacturers Dow AgroSciences

Cyhalofop-butyl APPLICATIONS
Biochemistry Fatty acid synthesis inhibitor, by inhibition of acetyl CoA carboxylase (ACCase). Selectivity between susceptible grasses and dicotyledonous plants is attributed to the forms of ACCase present and their compartmentalisation within plant cells. Susceptible grasses contain the susceptible eukaryotic form of ACCase; dicotyledonous plants contain both susceptible eukaryotic and herbicide-resistant prokaryotic forms of ACCase, rendering them resistant to cyhalofop-butyl. Rice tolerance to cyhalofop-butyl is due to rapid metabolism to the herbicidally inactive diacid (t1/2 <10 hr), whereas susceptible grasses metabolise cyhalofop-butyl to the herbicidally active monoacid. Mode of action Post-emergence herbicide with foliar uptake only and no soil activity. A systemic herbicide that is readily absorbed by plant tissue, is moderately phloem-mobile and accumulates in meristematic regions. Grass weeds cease growth immediately after treatment, with yellow patches appearing within 2-3 days to one week, leading to necrosis and death of the whole plant within 2 to 3 weeks. Uses For post-emergence control of grass weeds in rice. Applied at 75-100 g/ha in tropical rice and 180-310 g/ha in temperate rice. For selectivity in Poaceae species, see M. Ito et al., J. Weed Sci. & Tech. 43(2) 122-128 (1998). Phytotoxicity Rice is completely tolerant to due to rapid metabolism to the inactive diacid. Formulation types EC; EW; GR. Compatibility Not compatible with most broadleaf and sedge herbicide products. Selected products: 'Cleaner' (Dow AgroSciences); 'Clincher' (Dow AgroSciences); mixtures: 'Clincher Bas' (+ bentazone-sodium) (Dow AgroSciences)