IDENTIFICATION
Common name: Paclobutrazol
Iupac name: (2RS,3RS)-l-(4-chlorophenyl)-4,4-dimethyl-2-(1H-1,2,4- triazol-1-yl)pentan-3-ol
Chemical abstracts name: (R*,R*)-(±)-β-[(4-chlorophenyl)methyl]-α-(1,l-dimethylethyl)-1H-1,2,4-triazole-1-ethanol
Type: Plant growth regulator
CAS RN: [76738-62-0] stated stereoisomers
M.F.: C15H20ClN3O
Mol Wt: 293.8
PHYSICAL CHEMISTRY
Form (appearance): White. crystalline solid.
Composition: Tech. material is 90% pure.
M.P.: 165-166℃
V.P.: 0.001 mPa (20℃)
S.G.: 1.22 g/ml
Solubility.: In water 26 mg/l (20℃). In acetone 110, cyclohexanone 180, dichloromethane 100, hexane 10, xylene 60, methanol 150, propylene glycol 50 (all in g/l, 20℃).
Stability: Stable for more than 2 years at 20℃, and more than 6 months at 50℃. Stable to hydrolysis (pH 4-9). and not degraded by u.v. light (pH 7, 10 days).
Henry: 1.13 × 10-5 Pa m3 mol-1 (calc.)
KowlogP: 3.2
APPLICATION
Formulation types: GR; SC; WP
Biochemistry: Inhibits gibberellin and sterol biosynthesis, and hence the rate of cell division.
Mode of action: Plant growth regulator taken up into the xylem through the leaves, stems, or roots, and translocated to growing sub-apical meristems. Produces more compact plants and enhances flowering and fruiting.
Uses: Used on fruit trees to inhibit vegetative growth and to improve fruit set; on pot grown ornamentals and flower crops (e.g. chrysanthemums, begonias, freesias, poinsettias and bulbs) to inhibit growth; on rice to increase dllering, reduce lodging, and increase yield: on turf to retard growth; and on grass seed crops to reduce height and prevent lodging. To be applied as a foliar spray, as a soil drench, or by trunk injection. Has some fungicidal activity against mildew and rusts.
Phytotoxicity: Non-phytotoxic, though it intensifies greening. Some spotting has been noted on periwinkle foliage at higher temperatures.
MAMMALIAN TOXICOLOGY
Oral: Acute oral LD50 for male rats 2000, female rats 1300, male mice 490, female mice 1200, guinea pigs 400- 600, male rabbits 840, female rabbits 940 mg/kg.
Skin and eye: Acute percutaneous LD50 for rats and rabbits >1000 mg/kg. Mild skin irritant; moderate eye irritant (rabbits). Not a skin sensidser (guinea pigs).
Inhalation: LC50 (4 h) for male rats 4.79, female rats 3.13 mg/l air.
Noel: (1 y) for dogs 75 mg/kg daily; (2 y) for rats 250 mg/kg diet.
ADI: (JMPR) 0.1 mg/kg b.w. [1988]. /Other Not mutagenic.
Toxicity: WHO (a.i.) Ⅲ; EPA (formulation) IV
EC hazard: (Xn: R20/22| R36| N; R51, R53)
ECOTOXICOLOGY
Birds: Acute oral LD50 for mallard ducks >7900 mg/kg.
Fish: LC50 (96 h) for rainbow trout 27.8 mg/l. NOEC 3.3 mg/l.
Daphnia: LC50 (48 h) 33.2 mg/l.
Algae: EC50 (cell volume) for Chloretfa fusca 180 μmol/l (Pestic. Sci., 47, 337 (1996))
Worms: Bees: Acute oral NOEL >0.002 mg/bee; acute percutaneous NOEL >0.040 mg/bee.
ENVIRONMENTAL FATE
Soil/Environment: Soil DT50 0.5-1.0 y in general; in calcareous clay loam (pH 8.8, 14% o.m.), DT50 <42 d; in coarse sandy loam (pH 6.8, 4% o.m.), DT50 >140 d.
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