HERBICIDES-->ETHOFUMESATE

Mol. wt. 286.3 M.f. C₁₃H₁₈O₅S Form White, crystalline solid; (tech. is a light brown crystalline solid; mild aromatic odour). M.p. 70-72 ºC; tech., 69-71 °C V.p. 0.12 to 0.65 mPa (25 °C) K_OW logP = 2.7 (pH 6.5-7.6, 25 °C) Henry 3.7 ´ 10^-3 to 6.8 ´ 10^-3 Pa m³ mol^-1 S.g./density 1.29 (20 °C, tech.) Solubility In water 50 mg/l (25 ºC). In acetone, dichloromethane, dimethyl sulfoxide, ethyl acetate >600, toluene, p-xylene 300-600, methanol 120-150, ethanol 60-75, isopropanol 25-30, hexane 4.67 (all in g/l, 25 ºC). Stability Stable to hydrolysis in water at pH 7 and 9. At pH 5.0, DT₅₀ 940 d, forming the hydroxy analogue. Phototransformed in water, DT₅₀ 31 h. Degraded in air, DT₅₀ 4.1 h.

APPLICATIONS

Biochemistry Inhibits lipid synthesis (not ACCase inhibition). Mode of action Selective systemic herbicide, absorbed by the emerging shoots (grasses) and roots (broad-leaved plants), with translocation to the foliage. Not readily absorbed by leaves after the plant has generated a mature cuticle. Inhibits the growth of meristems, retards cellular division, and limits formation of waxy cuticle. Uses Used pre- and/or post-emergence in sugar and other beet crops, turf, ryegrass and the other pasture grasses, at 0.3-2.0 kg a.i./ha. It is effective in controlling a wide range of important grasses and broad-leaved weeds, with a good persistence of activity in the soil. In beet crops, 1.0-2.0 kg/ha can be used, but ethofumesate is normally recommended at 0.2-2.0 kg/ha in tank-mixtures or co-formulations with other residual or contact herbicides for use in beet. A high degree of tolerance is also shown by strawberries, sunflowers, Phaseolus beans and tobacco, depending on the time of application. Phytotoxicity Onions, peas, beans, carrots, and cotton are tolerant to some extent. Formulation types EC; SC.

ANALYSIS

Product and residue analysis by glc with FPD (R. J. Whiteoak et al., Anal. Methods Pestic. Plant Growth Regul., 1978, 10, 353). Details available from Aventis.

MAMMALIAN TOXICOLOGY

Oral Acute oral LD₅₀ for rats and mice >5000 mg/kg. Skin and eye Acute percutaneous LD₅₀ for rats >2000 mg/kg. Not a skin or eye irritant. Not a skin sensitiser. Inhalation LC₅₀ (4 h) for rats >3.97 mg/l air. NOEL (2 y) for rats >1000 mg/kg diet (37.6 mg/kg b.w. daily). ADI 0.4 mg/kg. Toxicity class WHO (a.i.) III (Table 5); EPA (formulation) IV

ECOTOXICOLOGY

Birds Acute oral LD₅₀ for mallard ducks >3552, bobwhite quail >8743 mg/kg. Dietary LC₅₀ (8 d) for mallard ducks >1082, bobwhite quail >839 mg/kg b.w. daily. Fish LC₅₀ (96 h) for rainbow trout 11.91-20.2, bluegill sunfish 12.37-21.2, mirror carp 10.92 mg/l. Daphnia EC₅₀ (48 h) 13.52-22.0 mg/l. Algae EC₅₀ 3.9 mg/l. Other aquatic spp. EC₅₀ (growth) (96 h) for Crassostrea virginica (Eastern oyster) 1.7 mg/l; LC₅₀ (96 h) Mysidopsis bahia (mysid shrimp) 5.4 mg/l. Bees LC₅₀ (contact and oral) >50 mg/bee. Worms LC₅₀ 134 mg/kg soil. Other beneficial spp. LD₅₀ for Aleochara bilineata >1250, for Poecilus cupreus and Chrysoperla carnea >2000 g/ha.

ENVIRONMENTAL FATE

Animals Major metabolite is the lactone or free acid form of the respective 2-oxo compound. Plants In plants, ethofumesate is metabolised to the 2-hydroxy and 2-oxo derivatives, methanesulfonic acid, and CO₂. Soil/Environment Ethofumesate is biologically degraded in soil to transient degradates which are rapidly converted to soil-bound residues and mineralised to CO₂. Photodegradation also occurs. DT₅₀ ranges from 10-122 d (lab.) and 84-407 d (field). It has been demonstrated under field conditions that ethofumesate does not accumulate in soil and that uptake by succeeding crops is negligible. It is weakly/moderately adsorbed to soil (mean K_oc 203), but field lysimeter studies have demonstrated only low mobility, most residues being located in the top 30 cm. It does not leach into groundwater.

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