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  • Author or Editor: Robert L. Wample x
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At approximately two week intervals starting in mid-December, sets of four vines were pruned either 24, 48, or 72 hours prior to sampling for low temperature exotherm (LTE) analysis of buds. Prepruned samples were compared with unpruned samples. Buds for cold hardiness were taken from the fourth to the sixth node positions from each of the four vines. A total of 30 buds from each of the treatments were used for LTE analysis. In addition to these samples, analysis of bud cold hardiness was also made of these prepruned vines after approximately 3, 6, and 9 weeks and compared to unpruned vines.

Despite the popular view that prepruning or pruning of grapevines during the winter reduces cold hardiness of the remaining buds, no differences were found between treatments during December, January, and February. Additional data on winter injury and budbreak will be presented.

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Cold-hardiness evaluations and soluble and insoluble-nonstructural carbohydrate analysis of dormant Vitis vinifera L. cv. Cabernet Sauvignon buds and cane tissue indicate a positive relationship between soluble carbohydrates and primary bud cold hardiness. Seasonal variations in soluble and insoluble carbohydrates appear to be related to changes in air temperatures and the dormancy status of the tissues. No differences were found in bud cold hardiness and only limited differences in carbohydrate levels of buds or stem tissues collected over 3 years from early harvest, normal harvest, or unharvested vines. These findings contrast with the widely held opinion that delayed harvest or failure to remove fruit results in reduced cold hardiness as a consequence of low storage carbohydrate content of the plants.

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The relationship between heat tolerance and cold hardiness was examined during the winter of 1992-93. Dormant canes of Cabernet Sauvignon were collected from an experimental vineyard at approximately two to three week intervals. Samples were held overnight at 0-3 C. Subsamples were removed from storage and subjected to either room temperature for 4 1/2 hours, 45 C for 35 minutes followed by room temperature for 4 hours or held at 0-3 C. Samples were then subjected to either heat treatment (52, 54, 56, 58, or 60 C for 30 minutes) or low temperature exotherm analysis.

Pretreatment at 45 C improved the heat tolerance but did not change cold tolerance. Holding samples at room temperature resulted in a slight improvement in heat tolerance. Additional implications of these findings will be presented.

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An increase in mechanical pruning of Concord grapevines in Washington has led to a marked increase in yield. In 1993 the average yield for the 20,000 plus acres was slightly greater than 12 ton/acre. As part of a long term study, initiated in 1987, to evaluate the effects of mechanical pruning on Concord yield and fruit quality, we have also followed bud cold hardiness and winter injury over several years. Cold hardiness was monitored using low temperature exotherm analysis of excised buds. Winter injury was evaluated by visual examination of bud and cane tissues collected from vines with different croploads. In 1990 the average yield for mechanically pruned vines was 13T/ac and for balance pruned vines about 8T/ac. Winter injury during December 1990 showed significantly less injury to mechanically pruned vines whether primary, secondary or tertiary buds were examined. During the winter of 1991-92 and 1993-94 bud cold hardiness of individual vines showed no relationship to cropload per vine.

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Paclobutrozol PP333 = (2R,3R + 2S,3S)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl) pentan-3-ol at concentrations of 11.6, 58.0, and 116.0 mg of active ingredient per liter caused significant reductions in water use of sunflowers (Helianthus annuus L.) but there was no significant influence on leaf diffusive resistance. The primary mechanism for reduced water use is by a reduction in leaf expansion. PP333 inhibited internode elongation which causes increased leaf shading. Under nonstress conditions there was no effect on leaf water potential or its components. At the highest concentration, photosynthetic rate was reduced. Fresh and dry weight of shoots was reduced proportional to leaf area. Gibberellic acid reversed the effect of PP333 of shoot height, leaf area, evapotranspiration, and shoot fresh and dry weight.

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The location of the Columbia and Yakima valleys present vineyard managers in eastern Washington with significant concerns, particularly low rainfall and wind erosion. Cover crops, as part of a complete management system, can reduce the effects of wind erosion in vineyards by stabilizing soil particles and reducing runoff. Cover crops also reduce weed biomass. During research conducted at Prosser, Wash., 175 foreign and domestic species were assessed for performance as cover crops. Using a screening process, nine species were chosen for evaluation in large commercial plots. Grass species included cereal rye, crested wheatgrass, Sherman Big Blue wheatgrass, perennial rye, pubescent wheatgrass, and three fescues. Legume species included two annual clovers (Trifolium spp.) and two reseeding annual medics (Medicago spp.). Unseeded, resident vegetation served as a control. Vine and soil water statuses were monitored regularly. Initial establishment of all species was delayed because of low rainfall throughout the growing season; thus performance varied for each species. Drought-tolerant grass species had better germination and establishment than legumes, due to planting method. In-row water status and vine water potentials remained constant throughout the main portion of the growing season. A mix of crested wheatgrass, perennial rye, and pubescent wheatgrass (Canada mix) gave especially good cover without affecting vine or soil water status. Weed biomass was reduced in most cases, with legumes having least effect; cereal rye, crested wheatgrass and the Canada mix had the greatest effect. Season-long suppression was best achieved with the Canada mix because of the nature of establishment. In this study, most drought-tolerant grasses performed better than legumes; however, with proper establishment, legumes can be a beneficial part of a sustainable agriculture system.

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A computerized system capable of controlling the freezing rate and collecting, storing, and analyzing data from multiple samples to determine their freezing point using low-temperature exotherm analysis is described. Details include electrical diagrams of modifications to the multiplexer/amplifier interface to provide additional signal amplification and permit control of the freezer's compressor. Computer software is described that permits variable temperature decline rates. Data analysis consists of a program in “C” that sequentially compares each data point in a low-temperature exotherm profile. Low-temperature exotherms are identified by a user-specified minimum differential between sequential data points. Examples of exotherm output and data analysis are given.

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Three canopy management methods, hand pruning (HP), mechanical prepruning with hand shoot thinning (MP+HT), and mechanical box-pruning with mechanical shoot thinning (MP+MT), were applied with the objective of achieving similar and commercially marketable ‘Cabernet sauvignon’ grape (Vitis vinifera) yields while maintaining vine balance and comparing labor operations costs. Canopy management system labor operation cost estimates indicated a 62% and 80% labor savings with the MP+HT and MP+MT treatments, respectively when compared with HP. The total shoot density of the vines was unaffected by the treatments applied. However, the contribution of count shoots increased with the concomitant addition of mechanization to canopy management. All treatments achieved similar canopy architecture and microclimate. The treatments did not affect photosynthetically active radiation (PAR) intercepted in the fruiting zone of canopy at veraison. All treatments had similar yield, total soluble solids (TSS), juice pH, and titratable acidity (TA) at harvest. Berry skin total phenolics, anthocyanins, and tannins when measured at harvest were also similar among the treatments applied. All treatments tested were within acceptable Ravaz index limits of 5 to 10 lb/lb. However, only MP+MT treatment reached a near optimum leaf area to fruit ratio of 1.2 m2·kg−1 and pruning weight of 1.0 kg·m−1 for warm climate viticulture. The results of this study provide commercially acceptable mechanical canopy management options that may provide labor cost savings for winegrape growers in the San Joaquin Valley (SJV) of California.

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