TEBUCONAZOLE
NOMENCLATURE
Common name tebuconazole (BSI, draft E-ISO)
IUPAC name (RS)-1-p-chlorophenyl-4,4-dimethyl-3-(1H-1,2,4-triazol-1-ylmethyl)pentan-3-ol
Chemical Abstracts name (?-a-[2-(4-chlorophenyl)ethyl]-a-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol
Other names fenetrazole*; terbuconazole*; terbutrazole*; ethyltrianol* CAS RN [107534-96-3] EEC no. ELINCS: 403-640-2 Development codes HWG 1608 (Bayer)
PHYSICAL CHEMISTRY
Composition Racemate. Mol. wt. 307.8 M.f. C16H22ClN3O Form Colourless crystals; (tech., colourless to light brown powder). M.p. 105 oC V.p. 1.7 X 10-3 mPa (20 oC) (OECD 104) KOW logP = 3.7 (20 °C) Henry 1 X 10-5 Pa m3 mol-1 (20 °C) S.g./density 1.25 (26 °C) Solubility In water 36 mg/l (pH 5-9, 20 oC). In dichloromethane >200, isopropanol, toluene 50-100, hexane <0.1 (all in g/l, 20 oC). Stability Stable to elevated temperatures, and to photolysis and hydrolysis in pure water, under sterile conditions; hydrolysis DT50 >1 y (pH 4-9, 22 °C). See also Environmental Fate.
COMMERCIALISATION
History Fungicide reported by Kuck & Berg (Mitt. Biol. Bundesanstalt. Land.-Forstwirtsch. Berlin-Dahlem, 1986, 232, 196). Introduced by Bayer AG in South Africa in 1988. Patents EP 40345; US 4723984
APPLICATIONS
Biochemistry Steroid demethylation (ergosterol biosynthesis) inhibitor. Mode of action Systemic fungicide with protective, curative, and eradicant action. Rapidly absorbed into the vegetative parts of the plant, with translocation principally acropetally. Uses As a seed dressing, tebuconazole is effective against various smut and bunt diseases of cereals such as Tilletia spp., Ustilago spp., and Urocystis spp., also against Septoria nodorum (seed-borne), at 1-3 g/dt seed; and Sphacelotheca reiliana in maize, at 7.5 g/dt seed. As a spray, tebuconazole controls numerous pathogens in various crops including: rust species (Puccinia spp.) at 125-250 g/ha, powdery mildew (Erysiphe graminis) at 200-250 g/ha, scald (Rhynchosporium secalis) at 200-312 g/ha, Septoria spp. at 200-250 g/ha, Pyrenophora spp. at 200-312 g/ha, Cochliobolus sativus at 150-200 g/ha, and head scab (Fusarium spp.) at 188-250 g/ha, in cereals; leaf spots (Mycosphaerella spp.) at 125-250 g/ha, leaf rust (Puccinia arachidis) at 125 g/ha, and Sclerotium rolfsii at 200-250 g/ha, in peanuts; black leaf streak (Mycosphaerella fijiensis) at 100 g/ha, in bananas; stem rot (Sclerotinia sclerotiorum) at 250-375 g/ha, Alternaria spp. at 150-250 g/ha, stem canker (Leptosphaeria maculans) at 250 g/ha, and Pyrenopeziza brassicae at 125-250 g/ha, in oilseed rape; blister blight (Exobasidium vexans) at 25 g/ha, in tea; Phakopsora pachyrhizi at 100-150 g/ha, in soya beans; Monilinia spp. at 12.5-18.8 g/100 l, powdery mildew (Podosphaera leucotricha) at 10.0-12.5 g/100 l, Sphaerotheca pannosa at 12.5-18.8 g/100 l, scab (Venturia spp.) at 7.5-10.0 g/100 l, white rot in apples (Botryosphaeria dothidea) at 25 g/100 l, in pome and stone fruit; powdery mildew (Uncinula necator) at 100 g/ha, in grapevines; rust (Hemileia vastatrix) at 125-250 g/ha, berry spot disease (Cercospora coffeicola) at 188-250 g/ha, and American leaf disease (Mycena citricolor) at 125-188 g/ha, in coffee; white rot (Sclerotium cepivorum) at 250-375 g/ha, and purple blotch (Alternaria porri) at 125-250 g/ha, in bulb vegetables; leaf spot (Phaeoisariopsis griseola) at 250 g/ha, in beans; early blight (Alternaria solani) at 150-200 g/ha, in tomatoes and potatoes. Phytotoxicity Good plant compatibility in most crops with any formulation, and achieved in more sensitive crops by appropriate formulations, e.g. WP, WG or SC. Formulation types DS; EC; ES; EW; FS; GF; SC; SE; WG; WP; WS.
ANALYSIS
Product analysis by glc with FID (CIPAC Handbook, 1998, H, 261; AOAC Methods, 17th Ed., 997.01). Residues in soil, water and plant material determined by glc (W. Maasfeld, Pflanzenschutz-Nachr. Bayer (Engl. Edn.), 1987, 40, 29; H. Allmendinger, ibid., 1991, 44, 5). Details available from Bayer CropScience.
MAMMALIAN TOXICOLOGY
Reviews FAO/WHO 71, 73 (see part 2 of the Bibliography). Oral Acute oral LD50 for male rats 4000, female rats 1700, mice c. 3000 mg/kg. Skin and eye Acute percutaneous LD50 for rats >5000 mg/kg. Non-irritating to skin; mild irritant to eyes (rabbits). Inhalation LC50 (4 h) for rats 0.37 mg/l air (aerosol), >5.1 mg/l (dust). NOEL (2 y) for rats 300, dogs 100, mice 20 mg/kg diet. ADI (JMPR) 0.03 mg/kg b.w. [1994]. Toxicity class WHO (a.i.) III; EPA (formulation) II ('Elite' 45DF); III ('Folicur' 3.6F) EC classification (Xn; R22)
ECOTOXICOLOGY
Birds Acute oral LD50 for male Japanese quail 4438, female Japanese quail 2912, bobwhite quail 1988 mg/kg b.w. Dietary LC50 (5 d) for mallard ducks >4816, bobwhite quail >5000 mg/kg feed. Fish LC50 (96 h) for rainbow trout 4.4, bluegill sunfish 5.7 mg/l (flow through). Daphnia LC50 (48 h) 4.2 mg/l (flow through). Algae ErC50 (72 h, static) for Selenastrum capricornutum 3.80 mg/l. Other aquatic spp. No effect on Chironomus riparius at 0.1 mg/l (28 d). Bees LD50 (48 h, oral) 83 mg/bee; (contact) >200 mg/bee. Worms Acute LC50 (14 d) for Eisenia foetida 1381 mg/kg dry soil. Other beneficial spp. No adverse effects on ground dwellers, e.g. ground beetles (Poecilus cupreus) (adults and larvae) or on foliage dwellers, e.g. ladybirds (Coccinella septempunctata), up to 375 g/ha (EW 250 formulation).
ENVIRONMENTAL FATE
Animals After three days, elimination was almost complete (>99%). Tebuconazole was excreted with the urine and the faeces. Plants Metabolism studies on wheat, grapes and peanuts show that tebuconazole is the major terminal residue. The metabolites detected were mainly triazole-containing compounds of no toxicological relevance. In plant tissue, a mean half-life of 12 days could be derived (cereals). Soil/Environment The degradation of tebuconazole in soil was slow in laboratory studies. Under field conditions, the compound degraded much more rapidly, and did not accumulate in long-term studies (3-5 y). Since no residues could be detected in deeper soil layers of these and other studies, and adsorption/desorption studies indicated a low mobility in the soil, groundwater contamination through leaching can be excluded. In natural waters, hydrolysis and indirect photolysis occur; in a pond study, the compound dissipated from the water body with DT50 1-4 w. Low vapour pressure and strong adsorption result in low volatilis
