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  • 1 Department of Horticulture, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061.

Control of plant height and flowering are two major problems associated with the production of Hypoestes phyllostachya Bak. (polka-dot plant). In seed-propagated cultivars, sprays of ancymidol (A-Rest), chlormequat (Cycocel), paclobutrazol (Bonzi), and uniconazole (Sumagic) were effective in inhibiting shoot growth and internode elongation at 100, 1000, 33, and 10 mg·l-1, respectively. Daminozide (B-Nine), even at 6000 mg·l-1, was ineffective compared to untreated controls. Ethephon (Florel) was effective in retarding plant growth at 500 mg·l-1, but at 1500 mg·l-1 resulted in leaf distortion and horizontal shoot growth.

H. phyllostachya was determined to be a quantitative (facultative) short day plant. Seed-propagated plants with 16 or more nodes flowered regardless of photoperiod, but flowering was more rapid under short days (SD) than under long days (LD). Application of ethephon significantly inhibited shoot elongatioo and number of flower buds formed and also increased the incidence of flower bud abortion. In seed-propagated plants, 500 mg·l-1 ethephon did not adversely affect flowering when applied at any time during the first seven weeks after the start of SD. At 1500 or 2500 mg·l-1, ethephon applied at any time during the first five weeks after the start of SD maximized the number of vegetative buds and minimized the number of viable flower buds. When applied more than six weeks after SD began, ethephon did not promote the formation of vegetative axillary buds but did promote flower bud abortion.