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William B. Miller

drenches. Therefore, it was concluded that “reduced immersion times or rates should result in simple and inexpensive” height control for freesia Gianfagna and Wulster (1986) . Wulster et al. (1989) showed that an average daily temperature (ADT) of 20 °C

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Teresa A. Cerny, Nihal C. Rajapakse, and Ryu Oi

A research collaboration between Clemson Univ. and Mitsui Chemicals, Japan, has been established to develop and test photoselective greenhouse covers that can filter out far-red (FR) light and control plant height with minimal use of chemicals. The effects of polymethyl methacylate (PMMA) filters containing FR-intercepting dyes were evaluated on watermelon, pepper, chrysanthemum, and tomato to select an optimum dye concentration. As the dye concentration increased, FR interception increased, photosynthetic photon flux (PPF) decreased, and phytochrome photoequilibrium increased from 0.72 to 0.82. Light transmitted through photoselective filters reduced plant height effectively in all species tested. However, watermelon was the most responsive (50% height reduction) and chrysanthemum was the least responsive (20% height reduction) to filtered light. Tomato and peppers had an intermediate response. In watermelons, total shoot dry weight was reduced over 25% compared to the control plants, with a progressive decrease in shoot weight as the dye concentration increased. The specific stem dry weight was gradually reduced as the dye concentration increased. Specific leaf dry weight was slightly reduced under filters, suggesting that smaller plants as opposed to a reduction in dry matter production primarily caused total dry weight reduction. Light transmitted through filters reduced percentage dry matter accumulation into stems from 27% to 18% and increased dry matter accumulation into leaves from 73% to 82%. Photoselective filters are effective in controlling height similarly to chemical growth regulators. Considering the PAR reduction by increase in dye concentration, a dye concentration that gives a light reduction of 25% or 35% may be optimum for commercial development of photoselective films.

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Shawn D. Lyons, William B. Miller, H. Christian Wien, and Neil S. Mattson

unlikely to result in sufficient height control overall. Anti-gibberellin PGRs are used to restrict stem elongation in a wide variety of floriculture crops. Flurprimidol and paclobutrazol reduce stem and scape elongation in tulip ( Tulipa gesneriana

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William B. Miller

For a number of flower bulb crops, pre-plant dips or soaks into antigibberellin PGRs are an effective method of height control ( Krug et al., 2006a , 2006b ; Larson et al., 1987 ; Ranwala et al., 2005 ). Previous research has shown that a given

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Shinsuke Agehara and Daniel I. Leskovar

primarily for height control and must be applied during early development, no later than 14 d after two to four true leaf stage. ABA is a plant hormone, which biosynthesis increases under water stress to induce adaptive stress responses ( Davies and Jones

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Kenneth C. Sanderson

Cuttings (3 per 1.5-liter pot) of `Annette Hegg Lady' and `V-14 Glory' poinsettias were directly rooted under mist and subsequently grown for treatment with various growth regulator sprays. Sprays of 40 ppm and 61 ppm paclobutrazol, 2,500 ppm daminozide plus 1,500 chlormequat, 20 ppm and 40 ppm ethephon, 150 ppm ancymidol, 5,000 ppm daminozide, 20 ppm and 40 ppm uniconazole, and 25 ppm and 50 ppm flurprimidol were applied to the plants with a low pressure, high volume sprayer on October 23. Sprays of 40 ppm uniconezole caused the most height retardation with both cultivers, however 4000 ppm ethephon, 20 ppm uniconazole and 61 ppm paclobutrazol often gave comparable height retardation. Bract area of both cultivars was most severely retarded by 40 ppm uniconazole and 4,000 ppm ethephon.

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Brian E. Whipker, Robert T. Eddy, and P. Allen Hammer

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Brian E. Whipker, Robert T. Eddy, Farah Heraux, and P. Allen Hammer

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Brian Whipker and P. Allen Hammer

Mini-poinsettias are a popular form of potted plant, but there is a need to control plant height because tall growing cultivars are used. A study was conducted to determine the suitability of paclobutrazol to control height of mini-poinsettias. Cuttings of poinsettia cultivars Freedom and Red Sails were taken on 10 Sept. 1993 and rooted under mist. On 11 Oct. when short days began, plant height was measured and 4 plant growth regulator (PGR) treatments were applied as foliar sprays using a volume of 204 ml·m-2: paclobutrazol at 15, 30, 45 and 60 mg·liter-1, plus an untreated control. At anthesis, plant height (pot rim to top of plant) and bract diameter (measured in 2 directions and averaged) were measured. Data for plant height gain (PHG), the difference between plant height at anthesis and when PGRs were applied, and bract diameter were analyzed statistically.

PHG was significantly different at the cultivar × treatment interaction. For `Red Sails' all paclobutrazol treatments significantly retarded PHG, but there were no significant differences in PHG with increased rates of application. For `Freedom' only paclobuuazol rates at 30 and 45 mg·liter-1 significantly retarded PHG. Bract diameter was significantly different at paclobunazol rates 30 mg·liter-1 or greater, with diameter decreasing as the rate of PGR applied increased

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P.M. Shaw, K.A. Schekel, and V.I. Lohr