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Claudio C. Pasian and Daniel K. Struve

The effectiveness of a paclobutrazol/paint mix in controlling growth of poinsettia plants (Euphorbia pulcherrima) cultivars Freedom Red and Angelica Red was evaluated. Plants were grown in containers whose interior walls were coated with a flat latex impregnated with varying concentrations of paclobutrazol: 0, 5, 20, 80, 100, 150, 200, and 300 mg·L–1 (0. 0.032, 0.128. 0.512, 0.64, 0.96, 1.28, and 1.92 mg a.i. per container, respectively). As a comparison, one treatment consisted of plants drenched with 118 ml/container of a paclobutrazol solution at 3 mg·L–1.

Plants grown in containers with the paint–paclobutrazol mix were shorter than the control plants. Treatments involving concentrations of 100 mg·L–1 or more (even as much as doubled or tripled) did not produce proportionately shorter plants. Root dry weights of plants in all treatments were not significantly different. However, the length of roots touching the internal surface of the container decreased with increasing growth regulator concentrations. This may help explain why doubling concentrations of growth regulator-in-paint does not produce proportionately shorter plants: roots start absorbing the growth regulator as soon as they touch the wall of the container. As a consequence, all root elongation is reduced, resulting in less root-growth regulator contact and less growth regulator uptake. More measurements of root length and root area are required in order to proof this hypothesis. When paclobutrazol concentrations were higher than 100 mg·L–1, some bracts showed evidence of “crinkling.”

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Claudio C. Pasian and Daniel K. Struve

The effectiveness of two application methods of the growth regulator paclobutrazol on the growth of Chrysanthemum plants, Dendranthema ×grandiflora (Ramat) (cv. `Fina' and `Cream Dana') were compared. Plants were grown in containers with their interior covered by a mixture of flat latex paint and several concentrations of paclobutrazol (0, 5, 10, 20, 40, 80, 100, 150, 160, and 200 mg·L–1) or were treated with a soil drench of the growth regulator according to label recommendations (59 ml/container of paclobutrazol solution at 4 mg·L–1). Plants grown in containers with the paint–paclobutrazol mix at concentrations >80 mg·L–1 were shorter than plants given the control and paint only treatments but taller than plants given the drench treatment. Increasing paclobutrazol concentrations in paint from 100 to 150 and 200 mg·L–1 did not produce proportionately shorter plants. Paint alone had no effect on growth and development. Plants subject to growth regulator treatments appeared greener than the control plants. None of the plants given treatments with paint with or without paclobutrazol showed any sign of phytotoxicity. These results suggest the possibility of a new application method for systemic chemicals with the potential of reducing or eliminating worker protection standard restricted entry intervals and reducing the release of chemicals to the environment. Chemical name used: beta-[(4-chlorophenyl)methyl]-α-(1,1-dimethyl)-1H-1,2,4,-triazole-1-ethanol (paclobutrazol).

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Claudio C. Pasian and J. Heinrich Lieth

Nondestructive dry-weight (DW) estimates of plant parts are important for analyzing production and partitioning patterns of horticultural crops, particularly when repeated measurements of the same plant must be made without affecting growth. Equations were developed for estimating leaf, stem, and flower bud DW (LDW, SDW, and FDW, respectively) from linear measurements of the flowering shoot parts of Rosa hybrida L. `Cara Mia'. We used a stepwise forward polynomial regression to develop a set of equations that represented the data well; from these, we chose equations to make data collection as simple as possible. LDW was computed from leaf length. LDW of the whole shoot was calculated by adding the computed LDW of each leaf on a shoot. Each stem was divided into 30-mm segments and the DW of each segment was correlated with its diameter. SDW was calculated by adding all of the stem segments' DWs. FDW was directly correlated with flower bud diameter. The selected models can be used for rose shoot DW prediction; although in some cases, errors were encountered. Despite these errors, this approach may represent the only feasible method for DW estimation when destructive methods cannot be used.

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Claudio C. Pasian, Daniel K. Struve and Richard Lindquist

The effectiveness of two methods of application of the insecticide imidacloprid in controlling 1) aphids (Brachycaudus helichrysi) on Chrysanthemum plants, Dendranthema ×grandiflora (Ramat) (cv. Nob Hill) and 2) whitefly (Bemisia argentifolii) on poinsettia, Euphorbia pulcherrima (Wild.) (cv. Freedom Red) were compared. Plants were grown in containers with their interior covered by a mixture of flat latex paint and several concentrations of imidacloprid (0, 10, 21, 42, and 88 mg·L–1), or treated with a granular application of the insecticide (1% a.i.) according to label recommendations. All imidacloprid treatments were effective in reducing aphid survival after 8 weeks. The two most effective treatments were: granular (1% a.i.) and 88 mg·L–1 with an average of 0.2 aphid per plant as opposed to 50.4 aphids per plant for the control. The 42-mg·L–1 treatment had an aphid survival rate 1.6 aphids per plant. All imidacloprid treatments were effective in reducing white fly larvae. The 42 and 88 mg·L–1 and the granular (1% a.i.) were equally effective in reducing larvae numbers in lower poinsettia leaves: 0.5, 1.9, 0.9 larvae/2.5 cm leaf disk, respectively, while the control treatment had 62.9. None of the plants given treatments with paint showed any sign of phytotoxicity. These results suggest the possibility of a new application method for systemic chemicals with the potential of reducing or eliminating Worker Protection Standard (WPS) Restricted Entry Intervals (REI) and reducing the release of chemicals to the environment. Chemical name used: 1-[(6-Chloro-3-pyrimidil)]-N-nitro-2-imidazolidinimine.

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Claudio C. Pasian, Daniel K. Struve and Richard K. Lindquist

The effectiveness of two application methods of the insecticide imidacloprid in controlling 1) melon aphids (Aphis gossypii Glover) on `Nob Hill' chrysanthemum (Dendranthema ×grandiflora Ramat) plants and 2) silverleaf whitefly (Bemisia argentifolii Bellows & Perring) on `Freedom Red' poinsettia (Euphorbia pulcherrima Wild.) were compared. Plants were grown in containers with their interior covered by a mixture of flat latex paint plus several concentrations of imidacloprid (0, 10, 21, 42, and 88 mg·L−1), or treated with a granular application of the insecticide (1% a.i.) according to label recommendations. All imidacloprid treatments effectively reduced aphid survival for at least 8 weeks. The two most effective treatments were the granular application (10 mg a.i.) and the 88-mg·L−1 treatment (0.26 mg a.i). All imidacloprid treatments effectively reduced whitefly nymph survival. The 42- and 88-mg·L−1 treatment and the granular application (1% a.i.) were equally effective in reducing nymph numbers in lower poinsettia leaves. None of the plants given treatments with paint exhibited any phytotoxicity symptoms. These results suggest the possibility of a new application method for systemic chemicals with the potential of reducing the release of chemicals to the environment. Paint and imidacloprid mixes are not described in any product label and cannot be legally used by growers. Chemical name used: 1-[(6-chloro-3-pyrimidil)-N-nitro-2-imidazolidinimine (imidacloprid)

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Stanislav V. Magnitskiy, Claudio C. Pasian, Mark A. Bennett and James D. Metzger

Determination of plant growth regulator accumulation in fruits and vegetables for human consumption is an important safety issue even when it is applied to seeds. Paclobutrazol accumulated preferentially in the seedcoats when soaking cucumber (Cucumis sativus L., cv. Poinsett 76SR) seeds in 1000 or 4000 mg·L–1 paclobutrazol. Cucumber plants grown from seeds soaked in 1000 mg·L–1 paclobutrazol had lower average fruit weights than the control plants. Individual fruit length in cucumber was reduced by 40% when seeds were soaked in 1000 mg·L–1 paclobutrazol solutions for 180 minutes. Soaking tomato (Solanum lycopersicum L., cv. Sun 6108) seeds in 0 to 1000 mg·L–1 paclobutrazol did not reduce average fruit weight or diameter per treatment. Paclobutrazol residue was not detected in cucumber and tomato fruits harvested from plants grown from seeds soaked in 1000 mg·L–1 paclobutrazol for 180 minutes. Soaking seeds in paclobutrazol solutions represents a promising method of applying plant growth regulators to tomato and cucumber without accumulation of paclobutrazol residue in fruits.

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Stanislav V. Magnitskiy, Claudio C. Pasian, Mark A. Bennett and James D. Metzger

Shoot stretching in plug production reduces quality and makes mechanized transplanting difficult. The objectives of this study were to measure seedling emergence and shoot height of plugs as affected by paclobutrazol application during seed soaking, priming, or coating on seedling emergence and height. Verbena (Verbena ×hybrida Voss. `Quartz White'), pansy (Viola wittrockiana L. `Bingo Yellow Blotch'), and celosia (Celosia cristata L. `New Look') seeds were soaked in water solutions of paclobutrazol and subsequently dried on filter paper at 20 °C for 24 h. Soaking seeds in paclobutrazol solutions before sowing reduced growth and percentage seedling emergence of verbena and pansy but had little effect on those of celosia. Verbena seeds soaked in 50, 200, or 500 mg paclobutrazol/L for 5, 45, or 180 min produced fewer and shorter seedlings than controls. Osmopriming verbena seeds with 10 to 500 mg paclobutrazol/L reduced seedling emergence. Seedling height and emergence percentage of pansy decreased with increasing paclobutrazol concentrations from 2 to 30 mg·L–1 and with soaking time from 1 to 5 min. The elongation of celosia seedlings was reduced by soaking seeds in 10, 50, 200, or 500 mg paclobutrazol/L solutions for 5, 180, or 360 min. However, these reductions were negligible and without any practical application.

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Gladys A. Andiru, Claudio C. Pasian, Jonathan M. Frantz and Pablo Jourdan

Controlled-release fertilizers (CRFs) have not been extensively used in floricultural production, perhaps due to lack of grower experience and research-based information with their use in herbaceous plant production. Any information about the correct use of CRF should increase growers’ confidence in using this type of fertilizer. The objective of this research was to compare the growth and quality of bedding impatiens (Impatiens wallerana XTREME™ ‘Scarlet’) when grown with typical water-soluble fertilizer (WSF) and with different combinations of longevity and rates of a single formulation of CRF. The CRF 16N–3.9P–10K consisted of different longevities (3–4, 5–6, 8–9, or 12–14 months) and application rates (1.4, 3.4, 6.8, 10.2, or 13.6 kg·m−3). Plants were grown in the greenhouse, and consumer evaluations were performed at market maturity. Plant canopy cover, flower cover (FC), and shoot dry weight (DW) were also determined. Commercially acceptable plant quality was achieved with CRF application rates between 3.4 and 6.8 kg·m−3. At low CRF application rates, the faster release rate (shorter longevities) CRFs produced larger plants [DW and leaf canopy cover (LCC)] with greater flowering potential (FC) than slower release rate CRFs. At higher application rates, slower release rates (longer longevities) outperformed the faster release CRFs for the same parameters. CRF-grown plants were smaller than WSF plants when CRFs were applied at the lowest rates. No differences in any of the three variables measured were found when plants were grown at a rate of 6.8 kg·m−3 CRF of any longevity or with WSF. Growers should adjust CRF application rates according to CRF longevity.

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Paul R. Fisher, Ron M. Wik, Brandon R. Smith, Claudio C. Pasian, Monica Kmetz-González and William R. Argo

The objective was to evaluate and compare foliar spray and soil drench application methods of iron (Fe) for correcting Fe deficiency in hybrid calibrachoa (Calibrachoa × hybrida) grown in a container medium at pH 6.9 to 7.4. Untreated plants showed severe chlorosis and necrosis, stunting, and lack of flowering. An organosilicone surfactant applied at 1.25 mL·L-1 (0.160 fl oz/gal) increased uptake of Fe from foliar applications of both ferrous sulfate (FeSO4) and ferric ethylenediamine tetraacetic acid (Fe-EDTA). Foliar sprays at 60 mg·L-1 (ppm) Fe were more effective when Fe was applied as Fe-EDTA than FeSO4. Increasing Fe concentration of foliar sprays up to 240 mg·L-1 Fe from Fe-EDTA or 368 mg·L-1 Fe (the highest concentrations tested) from ferric diethylenetriamine pentaacetic acid (Fe-DTPA) increased chlorophyll content compared with lower spray concentrations, but leaf necrosis at the highest concentrations may have been caused by phytotoxicity. Drenches with ferric ethylenediaminedi(o-hydroxyphenylacetic) acid (Fe-EDDHA) at 20 to 80 mg·L-1 Fe were highly effective at correcting Fe-deficiency symptoms, and had superior effects on plant growth compared with drenches of Fe-DTPA at 80 mg·L-1 Fe or foliar sprays. Efficacy of Fe-DTPA drenches increased as concentration increased from 20 to 80 mg·L-1 Fe. An Fe-EDDHA drench at 20 to 80 mg·L-1 Fe was a cost-effective option for correcting severe Fe deficiency at high medium pH.

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Adam F. Newby, James E. Altland, Daniel K. Struve, Claudio C. Pasian, Peter P. Ling, Pablo S. Jourdan, J. Raymond Kessler and Mark Carpenter

Greenhouse growers must use water more efficiently. One way to achieve this goal is to monitor substrate moisture content to decrease leaching. A systems approach to irrigation management would include knowledge of substrate matric potentials and air-filled pore space (AS) in addition to substrate moisture content. To study the relationship between substrate moisture and plant growth, annual vinca (Catharanthus roseus L.) was subject to a 2 × 2 factorial combination of two irrigation treatments and two substrates with differing moisture characteristic curves (MCCs). A gravimetric on-demand irrigation system was used to return substrate moisture content to matric potentials of −2 or −10 kPa at each irrigation via injected drippers inserted into each container. Moisture characteristic curves were used to determine gravimetric water content (GWC), volumetric water content (VWC), and AS at target substrate matric potential values for a potting mix consisting of sphagnum moss and perlite and a potting mix consisting of sphagnum moss, pine bark, perlite, and vermiculite. At each irrigation event, irrigation automatically shut off when the substrate-specific weight of the potted plants associated with the target matric potential was reached. Irrigation was triggered when the associated weight for a given treatment dropped 10% from the target weight. VWC and AS differed between substrates at similar matric potential values. Irrigating substrates to −2 kPa increased the irrigation volume applied, evapotranspiration, plant size, leaf area, shoot and root dry weight, and flower number per plant relative to irrigating to −10 kPa. Fafard 3B had less AS than Sunshine LB2 at target matric potential values. Plants grown in Fafard 3B had greater leaf area, shoot dry weight, and root dry weight. Leachate fraction ranged from 0.05 to 0.08 and was similar across all treatment combinations. Using data from an MCC in conjunction with gravimetric monitoring of the container–substrate–plant system allowed AS to be determined in real time based on the current weight of the substrate. Closely managing substrate matric potential and AS in addition to substrate water content can reduce irrigation and leachate volume while maintaining plant quality and reducing the environmental impacts of greenhouse crop production.