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  • Author or Editor: Orville Lindstrom x
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Leyland cypress [×Cupressocyparis leylandii (A.B. Jacks. and Dallim.) Dallim. and A.B. Jacks.] plants were transplanted into the field monthly from Aug. 1989 through Mar. 1990, and laboratory cold-hardiness estimates of these transplants were obtained monthly for two winter seasons. Cold hardiness estimates obtained in Dec. 1989 and Jan. 1990 revealed that the Nov. and Dec. 1989 transplants were 6C less cold-hardy than those transplanted into the field earlier in the year. There was little difference in cold hardiness due to transplant date during Feb., Mar., and Apr. 1990. In the second year of the study, on the same transplants, cold hardiness varied among transplanting dates. In Dec. 1990 and Jan. 1991, those transplanted in Jan.-Mar. 1990 were up to 9C less cold-hardy than those transplanted earlier in the season. However, in Mar. and Apr. 1991, those transplanted in Jan.-Mar. 1990 were equally or more cold-hardy than those transplanted earlier in the season. Transplanting Leyland cypress into the field in August to November appears to be the best time to ensure development of cold hardiness in early winter, whereas January to March planting appears to promote greater cold hardiness in the spring months.

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Whole, half, and quarter leaves and leaf disks were used to make laboratory estimations of the cold hardiness of Magnolia grandiflora. The effects of ice nucleation temperatures, length of exposure to nucleating temperatures, rates of temperature drop, thawing regimes, and methods of injury analysis were investigated for each leaf type in the fall and midwinter. In general, whole and half leaves responded more consistently to freezing tests than did quarter leaves and leaf disks. The most critical factors in the freezing procedure are the temperature at which the samples are nucleated with ice crystals and the regime in which the samples are warmed. These data suggest that whole and half leaves can effectively be used to reliably predict the cold hardiness of southern magnolia leaves.

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The cold hardiness of seven deciduous hardwoods, red maple (Acer rubrum L.), white oak, (Quercus alba L.), green ash (Fraxinus pennsylvanica Marsh.), sweetgum (Liguidambar stryaciflua L.), sugar maple (Acer saccharum Marsh.), river birch (Betula nigra L.) and black cherry (Prunus serotina Ehrh.) were evaluated weekly during the fall, winter and spring for three consecutive years. All trees evaluated were established (20-40 years old) and locatd on the Georgia Station Griffin, GA. Each species developed a maximum cold hardiness of at least -30 C by mid-January or early February each season. Response to temperature fluctuations varied with species. Red maple, for example, lost less cold hardiness due to warm mid-winter temperatures than the other species tested, while white oak tended to respond more quickly to the temperature fluctuations. Data will be presented comparing the response of cold hardiness to mid-winter temperature fluctuations for each species for the three year period.

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Cold hardiness levels of six cultivars of Chinese elm (Ulmus parvifolia Jacq.), `Select 380', `Orange Ribbon 740', `Emerald Isle', `Emerald Vase', `Drake', and `King's Choice', were determined over eight sample dates from 31 Aug. 1988 to 16 May 1989 and for `Emerald Vase' and `Drake', over three dates from 14 Feb. 1988 to 25 Apr. 1988. All cultivars tested achieved a maximum cold hardiness in December and January of – 21 to – 24C, except `King's Choice', which survived exposure to at least – 30C. `Emerald Isle' and `Emerald Vase' acclimated earlier (both – 9C on 31 Aug.) and reacclimated later (– 6 and – 9C, respectively, on 16 May) than other cultivars tested. `Emerald Vase' and `Drake' exhibited similar cold hardiness levels over the two years tested.

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To date, few summer and fall flowering azaleas exist. Recently, Rhododendron oldhamii, a summer-flowering species, was hybridized with several commercial hybrids. These crosses produced various sizes and colors of flowers that bloom throughout the summer until frost, and again in the spring. However, the cold hardiness level of these azaleas is unknown. Therefore, we evaluated their cold hardiness during several months of the fall and winter. Laboratory cold hardiness tests revealed that there was a range of cold hardiness levels among the new hybrids. `Fashion' and hybrids 02003 and 4003 tended to acclimate earlier than the others, maintain a good level of midwinter cold hardiness, and retain their hardiness into the early spring. Hybrid 15001 acclimated early and had good midwinter cold hardiness, but lost its cold hardiness in the late winter, while 04003 and 09004 acclimated late in the fall and did not attain a high level of cold hardiness in the winter. `Lee's Select' and hybrid 08002 seemed to fall between the groups previously mentioned showing intermediate cold hardiness throughout the winter season. The laboratory cold hardiness results were similar with field observations.

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The purpose of the present study was to determine whether water stress affects tolerance of Rhododendron L. `Catawbiense Boursault' to rapid freezing. Tolerance to freezing at cooling rates of 2 or 6C/hour in stems and leaves of plants subjected to continuous and periodic water deficit stresses was examined. Under continuous stress treatments, water content of the growing medium was maintained in a range of 0.60 to 0.75, 0.45 to 0.60, or 0.30 to 0.45 m3·m–3 between 24 Aug. 1992 and 11 Feb. 1994. Under periodic stress treatments, water content of the growing medium was maintained near field capacity, i.e., 0.6 to 0.8 m3·m–3, for the duration of the study or plants were subjected to the periodic stress at various times between 15 July and 19 Feb. during 2 years. Watering of water-stressed plants was delayed until water content reached below 0.4 m3·m–3, and then was resumed to maintain water content in the range of 0.3 to 0.4 m3·m–3. Cold hardiness was evaluated in the laboratory with freeze tolerance tests on detached leaves and stem sections. In most cases, cooling at 6C/hour caused injury at higher temperature than cooling at 2C/hour. The difference in lethal temperature between the two cooling rates depended on the level of the plant's cold hardiness. In plants cold hardy to about –25C, freezing at 6C/hour caused injury at a temperature ≈3C higher than freezing at 2C/hour. The effect of cooling rate was not evident in plants cold hardy to about –18C. Subjecting plants to continuous or periodic water stress did not have an effect on this relationship.

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Leyland cypress (×Cupressocyparis Leylandii) is becoming increasingly important as a live-cut Christmas tree yet it differs from trees currently familiar to most customers. Results of a consumer survey provide an opportunity for growers to adjust planting and marketing decisions. Questionnaires were completed while respondents displayed the tree at their residences. Opinions about the tree referred to tree features and compared them with features of other types of Christmas trees and inquired about the care given to the tree and its disposal. In general, respondents were consistent in their favorable assessment of Leyland cypress as a live Christmas tree with respect to several characteristics including tree shape twig density, and maintenance of fresh appearance over time. Recycling was the primary form of tree disposal.

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Magnolia has graced southern landscapes for many years. However, its northern distribution is limited due to injury at low, freezing temperatures. Laboratory methods are available to assess the cold hardiness of many plants, but specific methods for Southern magnolia have not been established. Effects of exposure time, temperature at which plants were frozen, rate of warming, sample size and methods of injury evaluation were investigated. With exposure to -1.5 and -4C the leaves and stems were not injured when frozen for up to 7h. Stems and leaves that were nucleated with ice at -4C underestimated the cold hardiness as compared to similar plants that were nucleated at -1.5 and -3C. Samples warmed as taken from the temperature bath at 4C or at 4C/hr in the bath exhibited less injury than those taken directly out of the bath and exposed to room temperature. Similar cold hardiness determinations were obtained using whole and half leaf samples, while a quarter of a leaf or a leaf disk exhibited high variability and resulted in unreliable cold hardiness determinations. Visual analysis for injury was compared to electrolyte leakage and similar cold hardiness levels were obtained using the two methods.

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It is more important than ever to produce a quality Christmas tree because of increasing competition in the Christmas tree market. Grade standards are intended to reflect quality, as defined by the consumer, to the grower. The USDA revised a set of voluntary standards for Christmas trees effective October 30, 1989. The existence of different grade standards cause the existence of several prices that correspond to each grade. The price differentials among grades should reflect the quality or desired consumer attribute. Therefore, a description of a grade that is not reflective of that desired by the consumer can lead to missallocation of resources by producers resulting in economic losses. The new USDA standards did not include consumer opinion information into the new standards, therefore, we feel these standards are more applicable to producer-wholesale transactions, and not that of the producer-consumer. It was found that over 75% of surveyed growers in Georgia sold almost 80% of their trees as choose and cut, not wholesale. Consumer demand will drive the Christmas tree market and, therefore, consumer preferences need to be incorporated into the grade standards.

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Magnolia has graced southern landscapes for many years. However, its northern distribution is limited due to injury at low, freezing temperatures. Laboratory methods are available to assess the cold hardiness of many plants, but specific methods for Southern magnolia have not been established. Effects of exposure time, temperature at which plants were frozen, rate of warming, sample size and methods of injury evaluation were investigated. With exposure to -1.5 and -4C the leaves and stems were not injured when frozen for up to 7h. Stems and leaves that were nucleated with ice at -4C underestimated the cold hardiness as compared to similar plants that were nucleated at -1.5 and -3C. Samples warmed as taken from the temperature bath at 4C or at 4C/hr in the bath exhibited less injury than those taken directly out of the bath and exposed to room temperature. Similar cold hardiness determinations were obtained using whole and half leaf samples, while a quarter of a leaf or a leaf disk exhibited high variability and resulted in unreliable cold hardiness determinations. Visual analysis for injury was compared to electrolyte leakage and similar cold hardiness levels were obtained using the two methods.

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