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Douglas A. Cox

Paclobutrazol (PBZ) was applied to `Mustang' geranium (Pelargonium × 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-l 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 (GA) at 100 mg·liter-l applied 0 (same day), 7, 14, or 21 days after PBZ reversed the growth suppression caused by PBZ. Plants treated with GA30 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 GA, 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*)-β([4-chlorophenyl]methyl)-α-(1,1-dimethylethyl)-1 H -1,2,4-triazole-1-ethanol (paclobutrazol).

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David M. Hunter and John T.A. Proctor

A system was developed to evaluate the response of grapes (Vitis spp. `Seyval') to soil-applied paclobutrazol. The youngest fully expanded leaf, and its axillary bud, on single shoots 6 to 9 nodes long developing on rooted softwood cuttings, were retained for use in a bioassay. The shoot that developed from the axillary bud exhibited a dosage-dependent growth inhibition following soil applications of paclobutrazol at 4 dosages between 1 and 1000 μg·g-1 soil. Other aerial components showed no response to paclobutrazol. This test plant system has potential for use in physiological studies with soil-applied plant growth regulators. Chemical name used: β -[(4-chlorophenyl)methyl]- α -(1,1-dimethylethyl)1H-1,2,4-triazole-1-ethanol (paclobutrazol).

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Laura J. Lehman, C.R. Unrath, and Eric Young

Mature spur-type `Delicious'/seedling apple trees (Malus domestica Borkh.) were examined for 2 years after paclobutrazol (PB) foliar sprays with or without a soil cover to direct spray runoff away from the root zone, soil sprays, or a trunk drench. Foliar sprays with runoff reduced shoot number and fruit pedicel length in the year of treatment, but had no effect on shoot length. Trees that received foliar sprays with no runoff had fewer and shorter shoots and shorter pedicels the year after treatment. Soil sprays or a trunk drench reduced shoot number and pedicel length for 2 years after application, while only soil sprays reduced fruit weight, diameter, and length. Chemical name used: β- [(4-chlorophenyl)methyl]- α -(1,1-dimethylethyl)-1 H -1,2,4,-triazol-1-ethanol (paclobutrazol).

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Laura J. Lehman, Eric Young, and C.R. Unrath

Spur-type or nonspur `Delicious' apple scions on either Malus domestica Borkh. (seedling) or M.26 rootstocks received paclobutrazol foliar sprays in one or two `consecutive years or a soil drench in the year of planting. For each scion, total shoot, root shank, and tree dry weights measured in the 3rd year after planting were suppressed by all treatments. Trees on M.26 put less dry weight into rootstock wood after foliar sprays, but trees on seedling were not similarly affected. No treatment influenced fibrous root dry weight of the spur-type scion on seedling, while all treatments suppressed dry-weight gain of the same scion on M.26. All trees had higher root: shoot ratios and blossom densities 3 years after the soil drench and several had higher ratios after foliar sprays. Chemical name used: ß-[(4-chlorophenyl)methyl] (l,l-dimethylethyl)-l-H-1,2,4-triazole-l-ethanol (paclobutrazol, PB).

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Fouad M. Basiouny and Floyde M. Woods

Applications of paclobutrazol (PP333), Daminozide (DZ), and Nutri-cal to rabbiteye blueberry (Vaccinium ashi Reade) was studied. The application of these chemicals at different concentrations was made in the fall and throughout the growing season. PP333, DZ and Nutri-cal induced variable effects on yield, inte rnal and external fruit qualities. Shelf-life of hand-harvested fruits responded favorably to each of these chemicals.

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David M. Hunter and John T.A. Proctor

Paclobutrazol applied as a soil drench at 0, 1, 10, 100, or 1000 μg a.i./g soil reduced vegetative growth of `Seyval blanc' grapevines (Vitis spp.). At all rates, there was a reduction in internode length, while at rates higher than 10 μg a.i/g soil, there was also a reduction in node count. Leaf area produced following treatment declined in response to increasing rates, but specific leaf weight increased. Treatment with paclobutrazol delayed senescence and increased the retention of basal leaves that were nearly fully expanded at the time of treatment. Paclobutrazol application had no effect on fruit set or berry size, but the reduction in vegetative growth following treatment decreased the ability of the vine to supply sufficient photoassimilates for fruit maturation. Chemical name used: ß[(4-chlorophenyl)-methyl]-a-(1,1-dimethylethyl)1H-1,2,4-triazole-1-ethanol (paclobutrazol).

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David M. Hunter and John T.A. Proctor

Paclobutrazol applied as a soil drench at 0, 1, 10, 100, or 1000 μg a.i./g soil reduced photosynthetic CO2 uptake rate of leaves formed before paclobutrazol treatment within 3 to 5 days of treatment and the reductions were maintained for 15 days after treatment. The percentage of recently assimilated 14C exported from the source leaf was reduced only at the highest paclobutrazol dose, and there was little effect of treatment on the partitioning of exported 14C between the various sinks. In response to increasing doses of paclobutrazol, particularly at the higher doses, an increasing proportion of recent photoassimilates was maintained in a soluble form in all plant components. Reduced demand for photoassimilates as a result of the inhibition of vegetative growth may have contributed to a reduction in photosynthetic CO2 uptake rate, but this reduction in photosynthesis rate could not be attributed to a feedback inhibition caused by a buildup of starch in the leaves. Paclobutrazol had only a minor effect, if any, on photosynthetic electron transport. Chemical name used: β-[(4-chlorophenyl) methyl]-α-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol).

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Gary J. Keever and William J. Foster

`Redwings' and `Gloria' azaleas (Rhododendron × `Redwings' and `Gloria') were treated with foliar sprays of uniconazole, paclobutrazol, or daminozide to suppress bypass shoot development and promote flower initiation and development. Uniconazole at 5 and 25 mg·liter-1 suppressed bypass shoot development of `Redwings' and `Gloria', respectively. Flowering of `Gloria', but not `Redwings', was delayed slightly with uniconazole sprays up to 25 mg·liter-1 ; with the highest uniconazole concentration, 200 mg·liter-1, flowering was delayed as much as 18 days. Flower count of `Gloria' was not affected by lower concentrations of uniconazole, but it was greatly reduced in both cultivars with concentrations above 75 mg·liter-1. Uniconazole was more active than paclobutrazol sprays of similar concentrations or than two daminozide sprays of 3000 mg·liter–1 . Chemical names used: (E)-1-(p-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-1-penten-3-ol (uniconazole); (2RS,3RS)-1-(4-chlorophenyl)-2-(1,1-dimethylethyl)-(1H-1,2,4,-triazol-l-yl-)pentan-3-ol (paclobutrazol); butanedioic acid mono(2,2-dimethylhydrazide (daminozide),

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R.I. Wilkinson and B. Hanger

Miniature flowering potted Hydrangea macrophylla Thunb. cv. Merritt's Supreme plants (multistem, 15 to 20 cm tall) were grown in a modified hydroponic system. High-quality plants were produced by pulsing plants with paclobutrazol (0.2 mg·liter-1) for 4 weeks. Flower initiation was advanced in the terminal buds of treated plants by 12 days, and this earlier flower development was maintained through to flower maturity, without loss of inflorescence diameter. Chemical name used: β -[(4-chlorophenyl) methyl] -α-(1,1-dimethylethyl)-1 H -1,2,4-triazole-1-ethanol (paclobutrazol, ICI-PP333).