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Christopher J. Biai, José G. Garzon, Jason A. Osborne, Jonathan R. Schultheis, Ronald J. Gehl and Christopher C. Gunter

had significantly shorter plant heights ( Bir and Conner, 1999 ). The height control achieved with foliar exogenous applications of ABA may be an alternative to this commercial growth regulator, although limited work has been done investigating ABA use

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Sean C. Clifford, Erik S. Runkle, F. Allen Langton, Andrew Mead, Shirley A. Foster, Simon Pearson and Royal D. Heins

Most commercial markets require growers of poinsettia (Euphorbia pulcherrima Willd. ex Klotzsch.) to produce plants within strict height specifications. Plant growthretarding chemicals (PGRs) are commonly used to limit internode extension, but in some countries, growers are being pressured to reduce chemical use. Recently, a photoselective film was developed that specifically reduces the transmission of far-red light [(FR), 700 to 800 nm], offering an alternative strategy for height control. Two complementary trials, one in the United Kingdom and one in the United States, showed that plants grown under the FR film for 10 to 12 weeks were ≈20% shorter than control plants growing under neutral density (ND) films transmitting a similar photosynthetic photon flux as the FR film. In the United Kingdom trial, the FR filter delayed time to 50% bract color and first visible cyathia by 6.0 and 3.5 days, respectively, but did not influence time to final harvest. In the United States trial, plants under the FR film had an average of 25% more axillary branches than those under the ND film. In addition, the effects of reduced red [(R), 600 to 700 nm] and blue [(B), 400 to 500 nm] light on internode length, plant biomass, and axillary branching were determined using other photoselective plastics. Compared with plants under the ND film, internode length was 9% or 71% greater in plants grown under environments deficient in B or R, respectively. Our results indicate that poinsettia is highly sensitive to the R: FR ratio, and that spectral manipulation has potential for height control of commercial poinsettia crops.

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Kimberly R. Hilgers, Cynthia Haynes and William R. Graves

The objective of this study was to determine the efficacy of plant growth regulators applied as foliar sprays on height and branching of seashore mallow (Kosteletzkya virginica). Five chemical plant growth regulators were applied: ancymidol [15, 25, and 50 mg·L–1 (ppm)] (A-Rest; Elanco Products Co., Indianapolis), dikegulac sodium (500, 1000, and 1500 mg.L–1) (Atrimmec; PBI/Gordon Corp., Kansas City, Mo.), paclobutrazol (10, 20, and 60 mg·L–1) (Bonzi; Uniroyal Chemical Co., Middlebury, Conn.), chlormequat chloride (CCC) (750, 1000, and 1500 mg·L–1) (Cycocel; Olympic Horticultural Products, Mainland, Pa.), and CCC/daminozide mixes (1000/2500, 1000/5000, and 1500/5000 mg·L–1) (Cycocel and B-Nine; Uniroyal Chemical Co.). Ten replicate plants of each concentration were evaluated weekly for plant height and number of branches for 8 weeks. Plants that received CCC and CCC/daminozide treatments at all concentrations and paclobutrazol at 60 mg·L–1 were 60%, 60%, and 48% shorter than control plants and had 113%, 100%, and 75% more branches than control plants, respectively. All concentrations of ancymidol and dikegulac sodium-treated plants were similar to control plants. Paclobutrazol was applied twice, and only the highest concentration was effective for height control. Chlormequat chloride at the lowest concentration was as effective as all other concentrations of CCC and CCC/daminozide.

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James E. Barrett, Carolyn A. Bartuska and Terril A. Nell

Paclobutrazol drench treatments were evaluated for efficacy on Caladium ×hortulanum (Birdsey) cultivars Aaron, White Christmas, and Carolyn Wharton. Drenches at 2.0 mg/pot did not reduce height of `Aaron' and `White Christmas' plants when applied 1 week after planting, but 2.0 mg applied at 3 weeks after planting did result in shorter plants. The difference for time of application may be due to the amount of roots present to take up paclobutrazol when applied. In two factorial experiments, there were no interactions between cultivar and time of application or amount of chemical. Paclobutrazol at 0.5 mg/pot resulted in plants that were shorter than the controls. Higher amounts of paclobutrazol provided additional reductions in height, but there was variation between the experiments for degree of effect with amounts >1 mg. Generally, commercially acceptable height control was provided by paclobutrazol drench treatments at 0.5 and 1.0 mg/pot applied 3 weeks after planting. Chemical names used: (2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-1,2,4-triazol-1-yl-pentan-3-ol (paclobutrazol).

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Amir Rezazadeh and Richard L. Harkess

leaves and attractive terminal or axillary lavender to purple spikes of flowers ( Riffle, 1998 ). However, without height control, firespike grows too tall exceeding the commercial requirements for potted plants. Thus, control of firespike stem elongation

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Shinsuke Agehara and Daniel I. Leskovar

field establishment can be slow and non-uniform, potentially delaying early harvest and limiting marketable yield. Height control is important for producing compact and high-quality vegetable transplants. Although several gibberellin inhibitors such as

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Royal D. Heins and Paul Fisher

Height control is a major challenge in the production of high quality poinsettia crops. Graphical tracking is a technique where growers make height control decisions by comparing actual measured plant height with a desired height. A computer decision support tool, the Poinsettia Care System, is being developed to combine graphical display of plant height with an expert system to provide height control advice. A simulation model is used to predict future growth of the crop based on greenhouse temperature, growth retardant applications, plant spacing, plant maturity, and light quality. Growth retardant and temperature recommendations are made based on a crop's deviation from the target height, expected future growth rate, and crop maturity. The program was beta tested by 8 Michigan growers over the 1991 poinsettia season. The test growers reacted positively to the program in a follow-up survey. Perceived benefits included improved height control, consistent crop recording, and a `second opinion' when making height control decisions. Improvements were suggested to combine the advice of different crops within the same greenhouse zone, to improve the predictive growth model, and to streamline data entry and output.

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Michael A. Schnelle, B. Dean McCraw and Timothy J. Schmoll

Height control for vegetable transplants has become challenging with the loss of the industry standard growth regulator, daminozide (Alar). One alternative to growth regulators—brushing—was conducted on two cultivars of Lycopersicon esculentum Mill. Five weeks of brushing twice daily resulted in height suppression for both tomato cultivars. Brushing treatments were performed successfully by use of a grower-designed apparatus constructed from readily available materials.

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Brian A. Krug, Brian E. Whipker and Ingram McCall

Eight experiments were conducted to develop height control protocols for greenhouse-forced hyacinth (Hyacinthus orientalis) bulbs. `Pink Pearl' hyacinth bulbs were treated with flurprimidol preplant bulb soaks to determine optimal timing of treatment, soak duration, quantity of bulbs that could be treated before the solution lost efficacy, bulb location of solution uptake, and if higher concentrations of flurprimidol can be used to overcome stretch that occurs with extended cold treatment. No difference in height control occurred when bulbs were soaked in flurprimidol the day of, 1 day before, or 7 days before potting; therefore, growers can treat bulbs up to 1 week before potting with no difference in height control. All preplant bulb soak durations of 1, 5, 10, 20, or 40 min controlled plant height. Any soak durations ≥1.3 min resulted in similar height control, which would provide growers with a flexible time frame of 2 to 40 min in which to soak the bulbs. When 1 L of 20 mg·L-1 flurprimidol solution was used repeatedly over 20 batches of five bulbs, solution efficacy was similar from the first batch to the last batch, indicating the soak solution of flurprimidol can be used repeatedly without loss of efficacy. Soak solution temperature was also tested to determine its effect on flurprimidol and paclobutrazol uptake. Temperature of the soak solution (8, 16, or 24 °C) had no effect on flurprimidol and only at a temperature of 8 °C was the efficacy of paclobutrazol lower. Postharvest heights of `Pink Pearl' hyacinths were similar whether only the top, bottom, or the entire bulb was soaked. Control provided by flurprimidol, paclobutrazol, or uniconazole preplant bulb soaks varied among the three hyacinth cultivars Delft Blue, Jan Bos, and Pink Pearl, so growers will have to conduct their own trials to determine optimal cultivar response to preplant bulb soaks. Also, `Pacino' sunflowers (Helianthus annuus) were treated with residual soak solution of flurprimidol to determine if substrate drenches could be used as a disposal method. Fresh and residual solutions of flurprimidol (1.18, 2.37, or 4.73 mg/pot a.i.) applied to `Pacino' sunflowers were similar in their efficacy of controlling height, which would enable growers to avoid disposal problems of residual soak solutions.

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Paul R. Fisher and Royal D. Heins

A methodology based on process-control approaches used in industrial production is introduced to control the height of poinsettia (Euphorbia pulcherrima L.). Graphical control charts of actual vs. target process data are intuitive and easy to use, rapidly identify trends, and provide a guideline to growers. Target reference values in the poinsettia height control chart accommodate the biological and industrial constraints of a stemelongation model and market specifications, respectively. A control algorithm (proportional-derivative control) provides a link between the control chart and a knowledge-based or expert computer system. A knowledge-based system can be used to encapsulate research information and production expertise and provide management recommendations to growers.