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  • Author or Editor: Orville M. 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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The effect of water stress imposed at three dates in late summer and early fall on cold hardiness was examined in Rhododendron L. `Coral Bell', `Hinodegiri', and `Red Ruffle'. The persistence of the water stress-induced cold hardiness was also examined following plant recovery from the stress. Container-grown plants were exposed to three weeks of reduced water supply starting 8 Aug., 29 Aug., or 19 Sept., while control plants were well watered. Cold hardiness of leaves, lower, middle, and upper stems was evaluated with laboratory freeze tests. Reduced water supply independent of time initiated increased cold hardiness by 1 to 4C in the majority of the tested plant parts in the three cultivars. Cold hardiness of all plant parts tested strongly depended on the current water status of the plants as indicated by the stem water potential. In most cases, 3 weeks after rewatering, the cold hardiness of previously water stressed plants did not differ from that of nonstressed plants.

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Water status is known to have an impact on cold hardiness of plants. Cold hardiness of `Catawbiense Boursault' rhododendron was examined under continuous and periodic water stress. Under continuous stress, water content of growing medium was maintained at 0.6 to 0.75, 0.45 to 0.6, or 0.3 to 0.45 m3·m-3. Under periodic stress, water content was either maintained between 0.6 to 0.8 m3·m-3 or plants were subjected to drought episodes at various times in late summer, autumn, and early winter. During a drought episode, watering was delayed until water content was below 0.4 m3·m-3. Watering then resumed and water content was maintained between 0.3 to 0.4 m3·m-3. Cold hardiness was evaluated on detached leaves and stem sections. The effect of continuous water stress depended on its severity and duration. Moderate stress did not increase cold hardiness compared to well watered plants during the first winter, but it did so when continued into the second winter. More severe stress increased cold hardiness during the first winter, but it decreased cold hardiness during the subsequent winter. The effect of periodic water stress depended on the timing of application. During initial and final stages of acclimation, cold hardiness increased in response to water stress less than during the intermediate stages. Water-stress-induced cold hardiness gradually decreased after rewatering.

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The primary cause of losses in evergreen azaleas injured by early freeze is bark split on lower stems. Delayed acclimation in the fall is thought to permit this injury. We examined whether reduced water supply affects acclimation of Rhododendron L. `Coral Bell', `Hinodegiri', and `Red Ruffle'. Containerized plants were grown under four watering regimes and placed outdoors or in the greenhouse. The water content of the growing medium was maintained at either 0.3 to 0.4 or 0.5 to 0.6 m3·m-3 from 16 June to 30 Aug. 1993, when half of the plants under each of these regimes was switched to the other watering regime. Freeze tests were conducted on 30 Aug. and 9 (let. Injury to leaves, and lower, middle, and upper stems was evaluated visually. Acclimation of leaves and upper stems before the August test, in most cases, was not stimulated by reduced water content, while the response of lower and middle stems was cultivar- and location-specific. The lower water content treatment after 30 Aug. generally increased freeze tolerance of all plant parts regardless of the previous watering regime. The higher water content treatment after 30 Aug. either prevented or delayed acclimation. This study demonstrated that the reduced water supply provided a feasible means of promoting acclimation of evergreen azaleas in late summer.

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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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