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J. Dionne, M. Laganière, and Y. Desjardins

Extensive winterkill of golf greens is a major problem in northern climates. In this study, the efficiency of several protective covering materials used to shelter Poa annua golf greens from winter damages was evaluated over 2 years. The bioclimatological environment under these protective covers was studied at crown level and at 5, 10, and 20 cm under the ground Treatments (permeable and impermeable covers, curled wood Excelsior mat, straw mulch protected by an impermeable cover, geotextile material with an impermeable cover, and air space under an impermeable cover) were compared to a control treatment without protection. Results indicate that temperature profile was strongly influenced by both winter protection covers and snow depth Temperatures at crown level were stable and just below 0C under plots covered with a significant amount of snow. However, temperatures varied considerably, when snow cover was <15 cm. Snow thermal conductivity was increased by periods of rain during the winter. Impermeable covers minimized the negative effect of this change in the insulation properties of the snow cover by limiting temperature fluctuations at the crown level. Temperature profiles under permeable covers were similar to profiles observed on control plots. Temperature profiles were comparable for 5 and 10 cm air space treatments and were not significantly different when compared to impermeable covers spread directly on the turf. Straw with an impermeable cover and Excelsior mats maintained crown level temperatures at >0C and the incidence of disease was higher under these highly insulative materials.

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Marie-Anne Boivin, Marie-Pierre Lamy, André Gosselin, and Blanche Dansereau

A green roof system was installed on an existing 35-year-old building. The purpose of the study was to evaluate the effect of three substrate depths on low-temperature injury of six herbaceous perennials: bugleweed (Ajuga reptans), sandwort (Arenaria verna `Aurea'), sea pink (Armeria maritima), whitlow grass (Draba aizoides), creeping baby's breath (Gypsophila repens), and stonecrop (Sedum xhybridum). Plants in 4-inch (9-cm) pots were transplanted into three substrate depths: 2, 4, and 6 inches (5, 10, and 15 cm) and evaluated over a 3-year period. The analysis of the results showed that the species have different winter hardiness, therefore some species were subject to more freezing injury than others. Stonecrop had significantly more damage at 2-inch than 4- or 6-inch depths during the two winters. Bugleweed and creeping baby's breath showed more damage at 2 inches in 1996-97, not in 1995-96. Substrate temperatures were measured from Oct. 1995 to May 1997. Low temperature injury was more pronounced at 2 inch than at 4 or 6 inch depths. Minimum daily temperature and temperature variations measured in fall and spring of these 2 years were also higher at 4- and 6-inch depths.

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D.A. Raworth and S.J. Clements

Red raspberry (Rubus idaeus L. cv. Willamette) primocanes were artificially defoliated to various degrees and at two dates in each of 2 years to simulate defoliation caused by the twospotted spider mite (Tetranychus urticae Koch). The effect on primocane diameter, lateral length, yield and four yield components was determined. When defoliation occurred evenly along the length of the primocanes, and all floricanes and excess primocanes were removed in early Aug. 1989, yield was reduced 26% at 25%, 50%, and 75% defoliation and 55% at 100% defoliation compared with nondefoliated controls. The number of canes per stool, number of fruit per lateral, and weight per fruit were reduced when defoliation occurred earlier, in August rather than September, but the number of laterals per cane increased with early defoliation. The effect of increasing defoliation on plant growth and yield was generally nonlinear. When defoliation occurred in sections along the lower 2 m of all primocanes, and all floricanes and excess primocanes were removed in Nov. 1992, no significant differences in yield or three yield components were detected. The effects of primocane defoliation are not necessarily predictable, so T. urticae should be controlled before mite-induced defoliation occurs.

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Nadia Hakam, Jennifer R. DeEll, Shahrokh Khanizadeh, and Claude Richer

Chlorophyll fluorescence (CF) was evaluated as a technique to assess chilling injury of rose (Rosa sp.) leaves exposed to low temperatures. In the more susceptible genotypes, variable fluorescence (Fv) decreased dramatically as the temperature was lowered. In the less susceptible genotypes, Fv was more stable and decreased more slowly as temperature fell. Our results suggest that measurement of CF may provide a rapid method to prescreen genotypes for chilling susceptibility, as required in plant breeding.

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Shengrui Yao

's Day and an even more severe one in early February. Crops across the state suffered various kinds of winter damage depending on their hardiness and location. For fruit crops, stone fruit suffered more damage than pome fruit. The last disastrous freeze

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David Mettler and Harlene Hatterman-Valenti

plants and thereby prevent winter damage. Treatment 1 was a 6-mm-thick polyethylene black plastic (Warp Bros, Chicago, IL) with corn stover mulch (BPC). Treatment 2 was the same black plastic but with wheat straw mulch (BPW) from 1-year-old unprotected

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Shengrui Yao, James J. Luby, and David K. Wildung

) for mulched and unmulched treatments, respectively, which probably led to the severe winter damage observed in the Spring and Summer 2007 ( Fig. 2 ; Table 1 ). There was almost no snow coverage until late Feb. 2007, so during the cold periods of

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Shengrui Yao and Carl J. Rosen

raspberries, compare commercially available cultivars, monitor crop nutrition, pests, and diseases, and assess possible winter damage in a USDA plant hardiness zone 3b area. Materials and methods This study was conducted at the North Central Research and

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William K. Harris, Joyce G. Latimer, John F. Freeborn, Margaret Aiken, and Holly L. Scoggins

Ornamental grasses have recently increased in popularity in the landscape and nursery industry ( Cameron, 2004 ; Thetford et al., 2009 ). Most ornamental grasses are grown in containers, and are inherently more susceptible to winter damage from

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Paul E. Cappiello

Lowbush blueberry (Vaccinium angustifolium) is a major fruit crop in costal, Northern New England and Atlantic Canada. One of the factors affecting production is low temperature damage of flower primordia. In addition to mid-winter damage, much of the damage occurs in spring due to late frosts. A study was designed to examine the seasonal variation in the LT50 of fruit buds and to determine the location of the tissue damage.

Field-collected stems were exposed to controlled temperature drops and examined for damage. Three types of damage were identified; destruction of flower primordia, browning of vascular tissue within the fruit-bud, and browning of stem tissue at the base of the bud. The seasonal variation of the occurrence of this damage will be discussed.