GIBBERELLIC-ACID REVERSES EFFECTS OF EXCESS PACLOBUTRAZOL ON GERANIUM

Paclobutrazol (PBZ) was applied to 'Mustang' geranium (Pelargonium x hortorum L.H. Bailey) as a single growth-medium drench at 0.06 mg a.i./pot or as a single foliar spray at 100 mg.liter-1 when the plants had three to four expanded true leaves (34 days after sowing). At these rates, PBZ caused excessive growth suppression but plants flowered earlier than untreated controls. A single foliar spray of gibberellic acid (GA3) at 100 mg.liter-1 applied 0 (same day), 7, 14, or 21 days after PBZ reversed the growth suppression caused by PBZ. Plants treated with GA3 0 or 7 days after PBZ were as tall or taller and flowered at the same time as or later than the untreated (no PBZ, no GA3) controls. Plants treated with GA3 14 or 21 days after PBZ were shorter and flowered earlier than untreated controls but were taller than plants treated with PBZ alone. Response to GA3 was similar whether PBZ was applied as a drench or as a spray. Chemical name used: (+)-(R*,R*)-beta([4-chlorophenyl]methyl)-alpha-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol).