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N. E. Pellett and D. Heleba

Five species of container-grown nursery plants were overwintered under treatments of no cover, 2 layers of microfoam, 15 or 30 cm of chopped newspaper and 15 cm newspaper or 22 cm straw between two layers of white copolymer. Temperatures were measured in the air under covers and in the center of the growing medium. Chopped newspaper moderated winter temperatures equal to or better than other cover treatments. All covers prevented winter injury. Baled chopped newspaper used by dairy farmers for livestock bedding is available at a reasonable cost.

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Fumiomi Takeda, Bernadine C. Strik, Derek Peacock, and John R. Clark

Transition to reproductive development and subsequent development of floral primordia (e.g., sepals, petals, stamens, and pistils) were determined in several blackberry (Rubus subgenus Rubus Watson) cultivars (Boysen, Cherokee, Chester Thornless, Marion, and Thornless Evergreen) growing in one or more locations (Clarksville, Ark., Aurora and Hillsboro, Ore., and Kearneysville, W. Va.). Also, daily maximum, mean, and minimum temperatures were recorded at three sites (Clarksville, Aurora, and Kearneysville) for the September to April sampling period. In buds of `Boysen' and `Marion' from Oregon, sepal primordia were first observed in November and December, respectively. Further floral bud development continued into January. Sepal development in `Cherokee' buds occurred in October in Oregon and in December in Arkansas. At all three sites, the buds of `Chester Thornless' blackberry remained undifferentiated until spring. The average mean temperatures in Oregon were generally well above 5 °C during the bud sampling period, but were near 0 °C on most days from mid-December to January in Arkansas and from December to late-February in West Virginia. The phenology of flower bud differentiation varied among the cultivars and was strongly influenced by prevailing winter temperatures. The results suggest that the shortening day lengths of late summer trigger flower bud development in blackberry. Floral bud development in blackberry, once initiated, was continuous; however, periods of low temperature (<2 °C) can arrest development.

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J.M. Caprio, H.A. Quamme, and R. Berard

Winter freeze events, identified by horticulturists to lower yields or kill trees (estimates vary by year from 1000 to >200,000 trees), have occurred in the Okanagan Valley of British Columbia 18 times in 94 years (1 in 5 years). To determine the association of winter temperatures and production, 72 years (1920–91) were separated into quartiles by level of production. Then, a maximum χ2 value was produced by a scanning iterative technique comparing each of the extreme quartiles with the combined mid-quartiles. A strong association was found between level of production and the low minimum temperatures in November, December, and February but not January. This result agrees with the historical records that indicate three winter-kill events occurred in November, five in December, one in January, and three in February during the same time period. Warm temperatures in September were associated with low production, indicating the possibility that warm temperatures at this time delay acclimation. Warm temperatures in January also were associated with low production, indicating a possible effect in hastening deacclimation.

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Hans Christian Wien

Simple unheated greenhouses covered with clear polyethylene, also known as high tunnels, in which plants are typically grown in the ground have become popular for extending the growing season for high-value horticultural crops. Although they are used principally to produce annual crops such as vegetables and cut flowers, increasing interest has focused on their use for perennial crops such as raspberries, blackberries, and ornamentals. Studies of temperature variation within the tunnel during the growing season have emphasized the rapid rise in air day temperature above ambient during the day and an equally rapid decrease at night. Spatial variation in temperature within the tunnel were much less marked, however, with air temperatures at the edge of a 10-m wide tunnel only ≈2 °C lower than in the center. For perennial crops, tunnel conditions during the off-season are also an important factor. In winter, air temperatures in the tunnel during sunny days rose above freezing even when ambient air temperatures stayed below freezing. Soil temperatures during the day and night fluctuated much less both inside and outside the tunnel and were significantly higher in the tunnel. Studies with nursery plants overwintered in similar structures indicate that spatial variation is again dwarfed by the overall air temperature fluctuation in these structures.

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David Mettler and Harlene Hatterman-Valenti

cultivars. Results Temperature moderation of the rowcover. Over the course of both winters there were significant differences in the ability of the rowcover treatments to moderate winter temperatures. Differences occurred only 7 of the 23 weeks during which

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Edgar L. Vinson III, Elina D. Coneva, Joseph M. Kemble, Floyd M. Woods, Jeff L. Sibley, Esendugue G. Fonsah, Penelope M. Perkins-Veazie, and J. Raymond Kessler

et al., 2000 ). Alabama has a subtropical climate, with the Gulf Coast area having the least temperature fluctuation in the winter months. Erratic temperatures and rainfall occur commonly in the subtropics, and winter temperatures in coastal Alabama

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Kevin Lombard, Bernd Maier, Franklin J. Thomas, Mick O’Neill, Samuel Allen, and Rob Heyduck

2011 and was removed from the study in 2012, whereas Viognier and Müller-Thurgau produced only in 2012 ( Fig. 2 and Table 3 ). Four Corners region winter temperatures sometimes drop below −20 °C for short periods. From 2010 to 2012, extreme winter

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Hrvoje Rukavina, Harrison Hughes, and Randy Johnson

origin and minimum winter temperature were also strongly associated ( r = 0.59, P < 0.0001). Time of fall dormancy had negative correlations with spring ( r = −0.55, P = 0.0001) and summer precipitation ( r = −0.58, P < 0.0001), but correlations

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Penelope F. Measham, Audrey G. Quentin, and Nicholas MacNair

only under a 2-°C predicted change in winter temperature ( Table 3 ) when using the field-derived chill. Table 3. Winter chill values (CP) experienced in cherry-producing regions of Australia (adapted from Darbyshire et al., 2011 ) and forecast values

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Imed E. Dami, Shouxin Li, Patricia A. Bowen, Carl P. Bogdanoff, Krista C. Shellie, and Jim Willwerth

or early autumn frosts and extreme or fluctuating winter temperatures, have caused significant economic loss to grape production by decreasing yield and increasing cost of production due to required vine retraining and replacement ( Zabadal et al