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Diane M. Camberato, James J. Camberato and Roberto G. Lopez

Chemical plant growth regulators (PGRs) are important tools in greenhouse ornamental crop production because growers must increasingly meet specifications for plant shipping and marketability. However, the role of water quality parameters such as pH or alkalinity (bicarbonate in this study) on final PGR solution pH is not well documented and could impact efficacy. We assessed the interaction of PGR type and concentration on the final spray solution pH when combined with carrier water of varying pH and bicarbonate concentration. Eleven PGRs commonly used in floriculture (ancymidol, benzyladenine, chlormequat chloride, daminozide, dikegulac-sodium, ethephon, flurprimidol, gibberellic acid, gibberellic acid/benzyladenine, paclobutrazol, and uniconazole) at three concentrations (low, medium, and high recommended rates for each product) were added to reverse osmosis (RO) carrier water adjusted to four pH (5.3, 6.2, 7.2, 8.2) levels or added to tap carrier water adjusted to four bicarbonate concentrations (40, 86, 142, 293 mg·L−1 of CaCO3). Resultant solution pH levels were measured. Plant growth regulators were categorized as acidic, neutral, or basic in reaction based on the change of the carrier water pH on their addition. Benzyladenine, chlormequat chloride, gibberellic acid, and gibberellic acid/benzyladenine acted as weak acids when added to RO water, whereas daminozide, ethephon, and uniconazole reduced final solution pH from 1.25 to 5.75 pH units. Flurprimidol and paclobutrazol were neutral in reaction with final solution pH being similar to that of the RO carrier water before their addition. Ancymidol and dikegulac-sodium were basic in reaction, increasing final solution pH in RO carrier water up to 2.3 units. There was an interaction between chlormequat chloride concentration and RO carrier water pH on change in pH. When added to tap carrier water, final solution pH increased for all except the stronger acids, daminozide, ethephon, and uniconazole, where it decreased up to 3.5 units, and benzyladenine, where it decreased 0.35 units at 40 mg·L−1 bicarbonate. There was an interaction between PGR concentration and bicarbonate concentration in tap carrier water for daminozide and ethephon. The magnitude of change in pH (final solution pH minus initial carrier water pH) with the addition of each PGR was greater for RO than for tap water containing 40 to 293 mg·L−1 bicarbonate for all 11 PGRs tested.

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Diane M. Camberato, James J. Camberato and Roberto G. Lopez

Four complete water-soluble fertilizer (WSF) formulations including micronutrients applied at 200 mg·L−1 nitrogen (N) at each irrigation [Peters Excel (21N–2.2P–16.5K), Daniels (10N–1.8P–2.5K), Peters Professional (15N–1.3P–20.8K), and Jack’s Professional (20N–1.3P–15.7K)] were compared with two controlled-release fertilizer (CRF) products (also containing micronutrients) substrate incorporated at transplant at a rate of 3000 g·m−3 of substrate [Osmocote Plus (15N–4P–9.9K, 90 to 120 days longevity at 21 °C) and Osmocote Bloom (12N–3.1P–15K, 60 to 90 days longevity at 21 °C)] in the greenhouse production of four commonly produced bedding plant species with high alkalinity irrigation water (pH 7.1, 280 mg·L−1 CaCO3 equivalent). Species included Argyranthemum frutescens (L.) Sch. Bip. ‘Madeira Cherry Red’ and iron-inefficient Calibrachoa Cerv. hybrid ‘Cabaret Pink Hot’, Diascia barberae Hook. f. ‘Wink Coral’, and Sutera cordata Roth ‘Abunda Giant White’. Additional treatments included a combination of 100 mg·L−1 Excel and 2100 g·m−3 Osmocote Plus and an Osmocote Plus treatment irrigated with reduced alkalinity water (acidified to pH 6.3, 92 mg·L−1 CaCO3 equivalent). Bedding plants were evaluated at the end of a finish or market stage (3 or 5 weeks depending on species) for shoot dry mass (SDM) and root dry mass (RDM), tissue nutrient concentrations, and visual quality rating (0 to 4). At 3 weeks, there were no significant differences in SDM and RDM between fertilizer treatments for any of the four species. Shoot dry mass significantly increased at 5 weeks in the WSF and combination treatments over the three CRF only treatments for Argyranthemum and over the non-acidified Osmocote Plus treatment only for Calibrachoa. At finish, 3 weeks for Sutera and Diascia and 5 weeks for Argyranthemum and Calibrachoa, visual quality rating for all species was lowest when using Osmocote Plus with or without acidified irrigation water compared with the WSF treatments, except the Daniels treatment in Argyranthemum, which also resulted in a low visual quality rating. Leaf tissue N for all species and phosphorus (P) for all except Diascia were below the recommended range for bedding plant crops in the CRF treatments, which was reflected by the lower substrate electrical conductivity (EC) for the CRF alone and combination treatments. Leaf tissue N and P were related to visual quality rating for all species, leaf tissue potassium (K) for Argyranthemum and Calibrachoa only, and leaf tissue iron (Fe) for Diascia only.

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Roberto G. Lopez and Diane M. Camberato

Biodegradable, compostable, and traditional plastic containers were evaluated for production of ‘Eckespoint Classic Red’ poinsettia (Euphorbia pulcherrima), a long-term greenhouse crop (12–16 weeks transplant to finish, depending on cultivar). Containers were rated for appearance and durability during the 14-week production period and plant quality parameters were measured at anthesis. Plastic, rice hull, wheat starch-derived bioresin, and molded fiber containers remained unchanged in appearance and integrity and received a rating of 5 (1–5 rating scale, where 1 = container integrity compromised substantially and 5 = container was intact, no visible changes in terms of color or construction). However, straw, coconut coir, composted cow manure, and Canadian sphagnum moss and wood pulp containers had an average rating of 2.9, 2.7, 1.4, and 1.6, respectively. Both shoot and root dry weights were greatest in plants produced in molded fiber and straw containers. The root to shoot dry weight ratio and days to anthesis was not significantly different among container types. Bract area index (a measurement derived to estimate bract area) was greatest for plants produced in molded fiber containers and lowest for those produced in the wheat starch containers. When adjusted for container height, final plant height was greatest in molded fiber containers and lowest in wheat starch containers. Plants produced in molded fiber containers, on average, exhibited the greatest height, bract area index, and total root and shoot weight, with no visible changes to container integrity. Based on these results, plant quality was not negatively impacted by any of the seven containers, though marketability of finished plants can be affected by container integrity.

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Diane M. Camberato, Roberto G. Lopez and Brian A. Krug

The holiday poinsettia (Euphorbia pulcherrima Willd. ex Klotzsch.) is the number two potted flowering crop sold in the United States with a reported wholesale value of $146 million in 2010. Profitability is increasingly threatened as the cost to heat greenhouses has increased by over 90% in the last 10 years. As energy costs continue to increase and poinsettia prices remain relatively constant, growers are seeking cultivars that can be finished under reduced temperatures. Our objectives were to quantify how reduced temperature finishing (RTF) 2 weeks after the start of short days influences height, bract area index, and time to anthesis of poinsettia. Eight red poinsettia cultivars were selected based on their early response attributes (initiate and finish within 6 to 8 weeks), moderate to high vigor, and naturally large bracts. Rooted cuttings were grown at day/night temperature set points (12 h/12 h) of 24/19 °C until 15 Oct. and under a 16-h photoperiod consisting of natural daylengths with day-extension lighting until 1 Oct. On 15 Oct., plants were transferred to day/night temperatures (12 h/12 h) of 20/14, 21/17, or 24/19 °C. Time to anthesis from the start of short days was 60 and 55 days at 24/19 °C and 76 and 68 days at a reduced finishing temperature of 20/14 °C for ‘Prestige Early Red’ and ‘Early Orion Red’, respectively. Final height was not significantly influenced by RTF in either cultivar. Our results indicate that RTF is a viable option that greenhouse growers can use to help reduce energy costs of carefully selected poinsettia cultivars.

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Christopher J. Currey, Diane M. Camberato, Ariana P. Torres and Roberto G. Lopez

Parboiled rice hulls have become a more common component of soilless growing substrates. While there have been reports that some organic substrate components reduce the efficacy of plant growth retardant (PGR) drenches, the influence of rice hulls on PGR drenches is unknown. ‘Callie Deep Yellow’ calibrachoa (Calibrachoa ×hybrid) and ‘Delta Orange Blotch’ pansy (Viola wittrockiana) were planted in containers filled with substrate containing (v/v) 80% peat and 20% perlite or parboiled rice hulls. After planting, 2.5-fl oz drenches containing deionized water or ancymidol, paclobutrazol, or uniconazole were applied to plants grown in each substrate. Plant growth retardants, but not substrate, affected growth rate, and final stem length of calibrachoa and plant height of pansy. There were no differences in regression model coefficients between substrates within PGR applications for plant height (pansy) or stem length (calibrachoa) over the course of the experiment. Paclobutrazol (2.0 or 4.0 ppm) and uniconazole (1.0 or 2.0 ppm), but not ancymidol (1.0 or 2.0 ppm) suppressed final stem length of calibrachoa. Final height of pansy was suppressed by each concentration of paclobutrazol and uniconazole and 2.0 ppm ancymidol, but not 1.0 ppm ancymidol. Based on these results, rice hulls did not reduce PGR drench efficacy when included as a substrate component comprising (v/v) 20% of a substrate.