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  • Author or Editor: Mark Rieger x
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Sixteen cultivars of citrus (Citrus spp.) and close citrus relatives were planted in Savannah, Georgia to evaluate their potential as fruiting landscape trees in an area that routinely experiences minimum temperatures of 15 to 20 °F (-9.4 to -6.7 °C) during winter. Three to six trees of each cultivar were planted in 1998, and stem dieback and defoliation data were collected in 1999, 2001, and 2002. During the 4 years of the study, air temperatures fell below 32 °F (0.0 °C) 27 to 62 times per season, with absolute minima ranging from 13 to 18 °F (-10.6 to -7.8 °C), depending on year. In general, kumquats (Fortunella spp.), represented by `Meiwa', `Nagami', and `Longevity', were completely killed (or nearly so) in their first year in the field after air temperature minima of 13.5 °F (-10.28 °C). Others experiencing 100% dieback were `Meyer' lemon (Citrus limon × C. reticulata) and `Eustis' limequat (C. aurantifolia × Fortunella japonica), which were tested twice during the study. Kumquat hybrids, including procimequat [(C. aurantifolia × F. japonica) × F. hindsii), `Sinton' citrangequat [(C. sinensis × Poncirus trifoliata) × unknown kumquat], `Mr John's Longevity' citrangequat [(C. sinensis × P. trifoliata) × F. obovat], razzlequat (Eremocitrus glauca × unknown kumquat), and `Nippon' orangequat (C. unshiu × F. crassifolia) survived freezing, but all experienced at least some defoliation and stem dieback. `Owari' satsuma (C. unshiu), `Changsha' mandarin (C. reticulata), nansho daidai (C. taiwanica) and ichang papeda (C. ichangensis) experienced only minor stem dieback but substantial defoliation in most years, except that ichang papeda was substantially damaged in the last year of the study. Seven cultivars produced fruit at least once during their first 4 years: nansho daidai, ichang papeda, `Nippon' orangequat, `Mr John's Longevity' citrangequat, `Owari' satsuma, `Changsha' mandarin, and procimequat. Based on cold hardiness, fruiting, and growth characteristics, `Owari' satsuma, `Changsha' mandarin, `Mr John's Longevity' citrangequat, and `Nippon' orangequat provided the hardiest, most precocious and desirable fruiting landscape trees in this study.

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Bananas are a popular ornamental plant in the southern U.S. However, normally only a few cultivars, such as `Lady Finger' and `Orinoco', are grown in Georgia. Thirty-three primarily commercial cultivars of bananas were grown for two years near Savannah, Georgia to determine their suitability for ornamental and nursery production. Most plants were grown from tissue culture plugs. They where given rates of fertilization used for commercial banana fruit production. Most cultivars produced 10 to 14 leaves and grew to heights of 1.5 to 2.0 m. Some displayed desirable ornamental characteristics such as pink tinted pseudostems, colorful flowers, and large graceful leaves. Many of the cultivars flowered and began producing fruit in late summer, although only `1780', `Raja Puri' and `Sweetheart' produced palatable fruit before frost in November in some years. Cultivars were also rated for their ability to produce suckers that can be used for nursery production. In year two, `1780' and `Manzano' produced the largest number of high quality suckers for nursery production. For the planting as a whole, sales of suckers at a field day averaged $7/per plant in year 2 and $17/per plant in year 3.

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Two experiments were conducted to determine the effect of drought stress on the susceptibility of Buddleia davidii Franch. `Pink Delight' to the two-spotted spider mite (Tetranychus urticae Koch). In the first experiment, drought stress was imposed by withholding water until predawn xylem pressure potential fell below -1 MPa. Shoot growth was 75% less in drought-stressed than in nonstressed plants. Mite population densities were not affected, but noninfested leaf area was 14% higher, and degree of mite damage was lower, in nonstressed plants. Evidently, the greater amount of new growth in nonstressed plants leads to lower spider mite densities by diluting populations. In a second experiment, nonstressed B. davidii `Pink Delight' plants were watered every 1 to 2 days and drought-stressed plants were watered every 3 days. Spider mite populations were monitored by sampling newly expanded and mature foliage. Mite populations on mature foliage were not affected by stress, but stressed plants grew less and had larger spider mite populations on their newly expanded foliage than did nonstressed plants.

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Bananas (Musa spp.) are a popular ornamental plant in the southern United States; however, only a few cultivars, such as Lady's Finger and Orinoco, are grown in Georgia. Thirty-three primarily commercial cultivars of bananas were grown for 2 years near Savannah, Georgia, to determine their suitability for ornamental and nursery production, and for 3 years for fruit observations. Most plants were grown from tissue culture plugs. They were given rates of fertilization used for commercial banana fruit production. Most cultivars produced 10 to 14 leaves and grew to heights of 1.5 to 2.0 m. Some displayed desirable ornamental characteristics such as pink-tinted pseudostems, colorful flowers, and large graceful leaves. Some of the most attractive tall-growing cultivars were Belle, Ice Cream, Kandarian, Manzano, Saba, and 1780. Some of the most attractive medium-height cultivars were Dwarf Namwah, Dwarf Orinoco, Goldfinger, Raja Puri, and Super Plantain. In the short category, the cultivars Dwarf Nino, Gran Nain, Kru, and Sum X Cross were among the most attractive ornamentals. Many of the cultivars flowered and began producing fruit in late summer, although only ‘Raja Puri’, ‘Sweetheart’, and ‘1780’ produced palatable fruit before frost in November. Cultivars were also rated for their ability to produce suckers that could be used for nursery production. In year 2, ‘Manzano’ and ‘1780’ produced more than six high-quality suckers for nursery propagation. Potential income for these cultivars was over $60 per plant. For the planting as a whole, sales of suckers at a field day averaged $7 per plant in year 2, and $17 per plant in year 3.

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Abstract

A dynamic heat transfer model was developed for simulation of freeze protection of young citrus trees by tree wraps and microsprinkler irrigation. Heat exchange at the surface of the tree wrap was a function of heat input from irrigation and heat losses to evaporation, radiation, and convection. A finite difference form of a transient heat conduction equation was used to calculate rates of trunk temperature change as a result of heat exchange at the wrap surface. Predicted trunk temperatures were generally within 1 SE of observed means when simulating the effects of tree wraps without irrigation, with high correlation (r = 0.99) between observed and predicted minimum temperatures. When simulating the effects of microsprinkler irrigation combined with tree wraps, however, predicted trunk temperatures were generally 1° to 3°C lower than observed means (r = 0.81). Under-prediction of trunk temperature was attributed to underestimation of sensible heat transfer from the irrigation water and/or inaccuracies in parameters associated with irrigation. The behavior of the real and model systems was qualitatively similar in a majority of validation trials. Thus, the simulation model could be used to analyze factors affecting freeze protection.

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Abstract

Computer simulation was used to study factors affecting freeze protection of young citrus trees using tree wraps and microsprinkler irrigation. Simulation results suggest tree wraps provide 1° to 2°C more freeze protection when air temperature decreased linearly rather than exponentially with time toward a minimum value. Tree wraps provided greater freeze protection when air temperature decreased rapidly (0.75°/hr) than slowly (0.5° or 0.25°/hr). Thus, variation in rate and pattern of air temperature decrease among freeze nights may be responsible for inconsistent levels of freeze protection observed with tree wraps. Changing irrigation water temperature from 12° to 7° or 17° produced changes in trunk temperature under radiative, but not advective, freeze conditions. Simulated positioning of the microsprinklers to maximize coverage of the wrap surface with water provided better freeze protection than positioning that resulted in increased water interception. Increasing windspeed from 0 to 10 m·s−1 reduced temperature of an irrigated wrapped trunk by 5°. Without irrigation, temperature of a wrapped trunk was largely unaffected by windspeed. Reducing humidity from 80% to 20% had a negligible effect on trunk temperature of irrigated wrapped trees under radiative and advective freeze conditions.

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Fruiting and nonfruiting `Washington' peach trees were grown in 2.4 (small) or 9-liter (large) containers to determine the influence of root confinement and fruiting on vegetative growth, fruit growth and quality, CO, assimilation (A), and carbohydrate content. Shoot length, fruit diameter, A, and leaf carbohydrates were measured weekly. Thirteen weeks after transplanting, trees were divided into roots, shoots, leaves, and fruit for dry weight measurement. The dry weight of all organs except fruit was reduced by root confinement, and only the weight of stems formed the previous season was not reduced by fruiting. Fruit dry weight was 30.0 g/tree for large- and small-container treatments, causing the yield efficiency (g fruit/g total dry wt) to be 50% higher for confined trees. Fruit red color, weight, and diameter were unaffected by root confinement, but higher flesh firmness and a more green ground color of the fruit surface from root-confined trees suggested that confinement delayed maturity. Vegetative growth was not reduced by lack of nonstructural carbohydrates in confined trees. A was reduced by root confinement on only the first of 11 measurement dates, whereas fruiting increased A on 5 of 8 measurement dates before fruit harvest. Fruit removal reduced A by 23% and 31% for nonconfined and confined trees, respectively, within 48 h of harvest. Leaf starch, sucrose, sorbitol, and total carbohydrate levels were negatively correlated with A when data were pooled, but inconsistent responses of A to carbohydrate content indicated that factors other than feedback inhibition were also responsible for the reduction in A on nonfruited trees. We hypothesized that a physiological signal originating in roots of confined trees reduced vegetativegrowth without reducing fruit growth.

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Container-grown Viburnum plicatum Thunb. var. tomentosum (Thunb.) Miq. `Mariesii' were planted in unamended planting holes, tilled plots, and tilled plots amended with aged pine bark. A 36-day drought was initiated 108 days after planting. Amending induced N deficiencies, reduced shoot growth, and increased root growth. Plants harvested from tilled and planting-hole plots at drought initiation had 63% and 68% more dry weight, respectively, than plants from amended plots. Between 8 and 19 days after drought (DAD) initiation, plants from tilled plots maintained higher relative leaf water content (RLWC) than plants from planting holes. Plants in amended plots maintained higher RLWC than both other treatments between 7 and 33 DAD. Amended and tilled treatments had higher relative leaf expansion rates (RLERs) than the planting-hole treatment 8, 11, 13, and 15 DAD. As the drought lengthened, plants in amended plots maintained higher RLERs than plants in tilled plots. While plants in pine bark-amended plots were more drought tolerant than those in tilled plots, it is unclear if increased drought tolerance was caused by the improved rooting environment or N deficiency.

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