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Stratford H. Kay, David W. Monks and Ross B. Leidy

In 1992, we initiated a study to determine the effects of fluridone in irrigation water applied to container-grown azaleas. Azaleas (Rhododendron indicum L. `George Tabor') were grown in containers with a 3 pine bark: 1 sand mixture and were irrigated daily for 5 weeks (except weekends) with solutions containing fluridone concentrations ≤2000 g·L−1. The threshold for appearance of visible injury symptoms (bleaching of new growth) was 250 g·L−1 at 5 and 12 weeks after treatment initiation. Visible symptoms did not appear until at least 35 days after treatments began. No statistically significant injury occurred to azaleas treated with solutions containing fluridone concentrations <250 g·L−1. This treatment rate was well above the maximum fluridone concentration (<90 g·L-1) normally occurring in ponds immediately following fluridone application. It appears unlikely that even long-term irrigation of `George Tabor' azaleas from fluridone-treated ponds would cause any significant injury.

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Norman Pellett and David Heleba

Chopped newspaper at 3.5 and 7.0 kg.m-2 enclosed in white polyethylene sheeting or enclosed in nylon netting at 3.5 kg.m-2 was compared with two layers of 0.64-cm microfoam as winter covering of four taxa of container-grown nursery plants. White polyethylene-enclosed newspaper moderated winter temperatures more than net-enclosed newspaper or two layers of microfoam under white polyethylene. All coverings provided protection against winter injury, as evidenced by container temperature, but net-enclosed newspaper at 3.5 kg.m-2 resulted in a minimal percentage of Daphne burkwoodii `Carol Mackie' plants with three or more shoots longer than 2 cm in the spring. Gaillardia grandiflora, covered by newspaper during winter, had less spring growth than plants covered by microfoam, but all coverings provided protection for Juniperus horizontalis `Prince of Wales' and Physostegia virginiana.

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Virginia Thaxton, Ed Bush, Ann Gray and Paul Wilson

Proper irrigation practices are important in the production of container-grown woody ornamentals. When choosing irrigation methods, nurserymen must attempt to maximize production and comply with public policies mandating decreased water usage and runoff. One of these methods schedules irrigation based on plant demand, using tensiometers to measure matric potential of the substrate. While tensiometers have been used successfully with agronomic crops in the field, their effectiveness in irrigation management of large container-grown woody ornamentals has not been extensively tested. The objective of this study was to determine the effect of four irrigation treatments (7 cb tensiometer setting, 14 cb tensiometer setting, 1 time a day application, 4 times a day application) on the production of the ornamental tree Bald Cypress over a 9-month period. Growth differed significantly among treatments. The highest growth index was observed in the 4 times a day and the 7 cb tensiometer treatments, followed by the 1 time a day and 14 cb treatments, respectively. Effluent and leachate (pH, EC, N, P, K) were also measured. Percent effluent volume was highly variable, with maximum volume occurring in June for the 7 cb setting (82%) and in October for the 1 time a day treatment (47%). Higher pH values (7.0 to 8.0) initially occurred in the timed irrigation treatments and higher EC values (2.0–6.0 mmhos) were found in tensiometer treatments; over time, differences among treatments decreased for both variables. Substrate concentrations of N, P and K varied significantly among treatments, while no significant differences were found in the leaf tissue analysis.

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Larry J. Kuhns, Tracey Harpster and Clyde Elmore

SpinOut is a commercial product containing copper hydroxide that is designed to prevent the development of circling roots in container grown ornamentals. Our objective was to determine the effect of two root-inhibiting herbicides (oryzalin and trifluralin) on the development of circling roots in container grown ornamentals when painted onto the inside surface of the containers or on stakes inserted around the walls of the containers. Rooted cuttings of wintercreeper euonymus (Euonymus fortunei Hand.-Mezz) were planted in a 1 peat: 1 perlite: 1 soil mix on 8 to 10 Feb. 1995. There were 16 containers for each of 20 treatments. Eight were rated for circling roots then harvested 17 to 22 May, and eight were rated and harvested 6 to 7 July 1995. Root circling was rated on a scale of 1 to 5, with 1 indicating no circling roots and 5 indicating many circling roots. Following harvest stem growth was measured and the dry weights of the roots, stems, and leaves were determined. Treated stakes did not prevent circling roots Trifluralin in Vapor Gard reduced the amount of circling roots, but not to acceptable levels. Trifluralin in latex paint was ineffective at 0.5%, slightly reduced the development of circling roots at 2%, and at 4% reduced circling rooting to the same extent as the SpinOut. Surflan at 0.5% in Vapor Gard reduced the development of circling roots to the same extent as the SpinOut. All other rates of Surflan, in both carriers, almost totally eliminated circling roots. There were no significant differences in root weight or total plant weight among any of the treatments at either date of evaluation.

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Jennifer L. Dwyer, N. Curtis Peterson and G. Stanley Howell

Studies were conducted with Physocarpus, Weigela, Hibiscus, Euonymus, Forsythia, Spiraea, Lonicera, and Taxus to evaluate the effects of warming temperatures on shoot dehardening. Container-grown plants were stored pot-in-pot, allowing shoots to receive natural outdoor conditions until early March. Control plants remained at 0C (32F), while treatment plants were placed in a temperature-controlled chamber at 21C (70F) and given up to 8 days of warming. Controlled-temperature freezing was used to evaluate plant hardiness. Hardiness levels of Weigela, Spiraea, and Forsythia rapidly decreased after 1 day of warming and again after the 7th day. Hibiscus gradually decreased in hardiness until the 7th day. The influence of polyhouse storage, in which plants were stored pot-in-pot, on the dehardening of Weigela, Hibiscus, and Euonymus was compared to outdoor storage, where plants were stored pot-in-pot. The warming effects of the polyhouse decreased the cold hardiness of the species studied. Results of the warming effects will be presented.

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Mark V. Yelanich and John A. Biernbaum

A model constructed to describe nitrogen dynamics in the root zone of subirrigated container-grown chrysanthemum was used to develop and test nitrogen fertilization strategies. The model predicts the nitrogen concentration in the root zone by numerical integration of the rates of nitrogen applied, plant nitrogen uptake, and nitrogen movement to the medium top layer. The three strategies tested were constant liquid N fertilization, proportional derivative control (PD) based upon weekly saturated medium extraction (SME) tests, or PD control based upon daily SME tests. The optimal concentration of N to apply using a single fertilization concentration was 14 mol·m–3, but resulted in greater quantities of N being applied than if PD controller strategies were used. The PD controllers were better able to maintain the predicted SME concentration within 7 to 14 mol·m–3 optimal range and reduce the overall sample variability over time. Applying 14 mol·m–3 N at every irrigation was found to be an adequate fertilization strategy over a wide range of environmental conditions because N was applied in excess of what was needed by the plant.

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Monica L. Elliott and Timothy K. Broschat

A commercially available microbial inoculant (Plant Growth Activator Plus) that contains 50 microorganisms, primarily bacteria, was evaluated in a soilless container substrate to determine its effects on root bacterial populations and growth response of container-grown plants at three fertilizer rates. The tropical ornamental plants included hibiscus (Hibiscus rosa-sinensis `Double Red'), spathiphyllum (Spathiphyllum `Green Velvet') and areca palm (Dypsis lutescens). The bacterial groups enumerated were fluorescent pseudomonads, actinomycetes, heat-tolerant bacteria, and total aerobic bacteria. Analysis of the inoculant before its use determined that fluorescent pseudomonads claimed to be in the inoculant were not viable. The plant variables measured were plant color rating, shoot dry weight and root dry weight. Only hibiscus shoot dry weight and color rating increased in response to the addition of the inoculant to the substrate. Hibiscus roots also had a significant increase in the populations of fluores-cent pseudomonads and heat-tolerant bacteria. From a commercial production point of view, increasing fertilizer rates in the substrate provided a stronger response in hibiscus than did addition of the microbial inoculant. Furthermore, use of the inoculant in this substrate did not compensate for reduced fertilizer inputs.

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Rita L. Hummel

Four film-forming antitranspirants, Vapor Gard, Envy, Wilt-Pruf, and Folicote, and a new metabolic antitranspirant UC86177 were applied to container-grown Ulmus parvifolia Jacq. (Chinese elm), Malus sargentii Rehd. (Sargent's crabapple), Viburnum plicatum tomentosum Thunb. (doubleflle viburnum), Lycopersicon esculentum Mill. `Early Giant' (tomato), Petunia × hybrids Hort. Vilm-Andr. `Royal Pearls' (petunia), and Impatiens wallerana Hook. f. `Blitz Orange' (impatiens) plants. Water status was assessed by the following methods: transpiration as water loss per unit leaf area, wilt by visual evaluation, and xylem pressure potential (XPP) determined with a pressure chamber. Antitranspirant treatment had no beneficial effect on water status of doublefile viburnum. In comparison to control plants, results of wilt ratings, XPP, and transpiration measurements for the elm, crabapple, tomato, petunia, and impatiens plants can be summarized as follows: UC86177-treated plants showed significantly less stress in 11 measures and were not different once; Wilt-Pruf was beneficial 10 times and not different twice; Folicote was beneficial nine times and not different three times; Vapor Gard produced eight beneficial results and four similar results; and Envy was beneficial three times and no different nine times. Species differences in response to antitranspirants as well as differences in product efficacy were demonstrated. UC86177 antitranspirant was shown to be as or more effective in controlling water status than the film-forming antitranspirants and may have potential for protecting various plant species against water stress.

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Deborah C. Smith-Fiola and Anne B. Gould

Phytophthora wilt, caused by the root-infecting fungus Phytophthora cinnamomi, is a serious disease of rhododendron. The symptoms of this disease include wilt, dieback, and death of nursery cuttings as well as large plants. The effects of two soil additives, Supersorb (a hygrogel) and Aquagro (a wetting agent), with and without Metalaxyl (Subdue 2E), were assessed on decreasing the incidence of Phytophthora wilt in container grown `Nova Zembla' rhododendron. Rooted cuttings grown in amended or non-amended mix were inoculated with P. cinnamomi. Metalaxyl treatments were applied once at the full label rate of 4 fl oz/100 gal at planting, or twice (at planting and 8 wks later) at 1 or 2 fl oz/100 gal. Trials were conducted from June to September in the greenhouse (1990) and outdoors (1991). Plant growth and disease incidence were evaluated weekly. In both trials, the Supersorb and Aquagro treatments did not affect disease incidence, although they did significantly affect plant growth. All metalaxyl treatments reduced disease incidence significantly when compared to controls.

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Carolyn F. Scagel, Guihong Bi, Leslie H. Fuchigami and Richard P. Regan

; Dong et al., 2004 ; Rikala et al., 2004 ). Most research on fertilizer uptake by container-grown nursery crops has primarily focused on N because it is commonly cited as the most important nutrient for plant growth and losses from nursery production