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  • Author or Editor: Linsey A. Newton x
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Phalaenopsis orchids require a day temperature of 26 °C or less to initiate inflorescences, whereas the night temperature has little or no effect on inflorescence initiation. We determined the duration of high temperature required each day to prevent inflorescence initiation of four Phalaenopsis and Doritaenopsis clones. In Years 1 and 2, mature potted plants were grown in separate greenhouse sections with five daily durations at 29 °C: 0, 4, 8, 12, or 24 h. The high temperature was centered in the 16-h photoperiod (0600 hr to 2200 hr) and the remainder of the day was at 20 °C. Exposure to 29 °C for 8 h or longer inhibited inflorescence initiation of Phalaenopsis Miva Smartissimo × Canberra ‘Mosella’ and Phalaenopsis Brother Pink Mask × Brother Success ‘Explosion’, but Phalaenopsis Baldan's Kaleidoscope ‘Golden Treasure’ and Doritaenopsis ‘Newberry Parfait’ required exposure to 29 °C for 12 h or longer to inhibit inflorescence initiation. Flowering was completely suppressed only when high-temperature exposure time was continual for Doritaenopsis ‘Newberry Parfait’ and Phalaenopsis Baldan's Kaleidoscope ‘Golden Treasure’ and 12 h for Phalaenopsis ‘Mosella’. Plant leaf span generally increased as duration of exposure to 29 °C increased, but high-temperature exposure had few or no significant effects on flowering characteristics of flowering plants. These studies indicate that as few as 8 h of high temperature can prevent flowering of some Phalaenopsis hybrids, whereas others require greater than 12 h of high-temperature exposure.

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Inflorescences of some moth orchid (Phalaenopsis and Doritaenopsis) hybrids can become very tall, which can pose shipping challenges for commercial producers and be unwieldy for consumers. We determined the efficacy of paclobutrazol as a foliar spray to inhibit inflorescence elongation of these genera and intergeneric hybrids. A single application of 15, 30, or 45 mg·L−1 palcobutrazol at a volume of 0.2 L·m−2 was applied to Doritaenopsis Miss Saigon, Doritaenopsis Andrew, and Phalaenopsis ‘Smart Thing’ grown at 23 °C to induce flowering. Applications were made after inflorescence emergence but before flower initiation (inflorescences were 1 to 2 cm long) or after flower initiation (inflorescences were 10 to 18 cm long). None of the paclobutrazol applications inhibited total inflorescence elongation of ‘Smart Thing’ or Miss Saigon. However, paclobutrazol inhibited inflorescence elongation from treatment until first flowering of Andrew by 19% to 23% when plants were treated with 15 or 45 mg·L−1 before flower initiation and 30 or 45 mg·L−1 after flower initiation. One or more concentrations of paclobutrazol applied after flower initiation reduced the length of the internode between the first and second flower on all three orchid clones. Paclobutrazol delayed flowering only on Miss Saigon (by 2 days) and only when applied after flower initiation. Paclobutrazol application did not affect the number of inflorescences or flowers, diameter of the first flower, number of new leaves formed, or increase in leaf span. Growers are advised to perform small-scale trials with paclobutrazol solutions starting at 30 to 45 mg·L−1 within 1 week of inflorescence emergence, although higher concentrations may be appropriate for the most vigorous varieties. Furthermore, a late spray application can cause unwanted crowding of the flowers.

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