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GRAPEGROWING Dehydration Management: Generally, the weight loss from dehydration is about 15% but can reach a maximum of 30% before harvest. In hot American viticultural areas (AVAs) that experience several weeks of continuous sunlight, the berries may completely dehydrate, dry up and shrivel. Unlike sunburn, controlling late-season dehydration through management practices is a major challenge as the causes are unknown. In case of severe incidence, one strategy is to harvest the grapes and use them for making quality wines of a desired style. Minor incidences of dehydration may not compromise overall fruit quality. Bunch stem necrosis Dehydrated clusters are easy to identify: Their dimpled berries resemble golf balls. Late-season dehydration As this type of shrivel commonly occurs during advanced stages of ripening, it becomes more and more conspicuous prior to commercial harvest. The dehydrated clusters are observed on both east and west aspects of the canopy, but mostly on the west aspect. The causes of late-season dehydration are unknown; it has, however, been attributed to prolonged dehydration coupled with cessation of sugar import and backflow into the vine late during the ripening period. Consequently, these lead to a systematic development of dimples in the form of small polygonal indentations throughout the once-stretched skin over the flesh. Visually, the dimpled berry resembles a golf ball, which is the main distinguishing feature of this type of shrivel. Despite the dimpling of the skin, the bloom maintains its integrity, and the bunch stem remains healthy (see photo above.) Since dehydration causes weight loss, it leads to yield losses and eventually low payments to those growers whose contract identifies grape sale prices based on tonnage. On the contrary, in tandem with weight loss, concentration of sugars proceed without much affecting fruit quality, thus the clusters with dehydrated berries are suitable for making wine. Until recently, Syrah led as the poster child for this unique disorder. Lately, it has been known to occur more often in other varieties also, especially Cabernet Sauvignon. Bunch stem necrosis (BSN) is another type of shrivel that occurs after veraison, either early or late in the ripening process. It is commonly observed in parts of the canopy where clusters are shaded by the shoot system. Visible symptoms of BSN include darkened lesions that may develop anywhere on the bunch stem (collective term for peduncle, wing, rachis and pedicel.) These lesions expand and girdle the affected region, causing necrosis and loss of green color, the prominent feature of BSN. The girdling of the bunch stem blocks the supply of water, nutrients and sugar to the berries distal to (farther away from) the necrotic region. Consequently, these berries dry up, shrivel and eventually develop raisin-like wrinkles (see photo below.) Bunch stem necrosis The girdling of the bunch stem blocks the supply of water, causing berries to shrivel. The bunch stem in the region distal to the necrosis also dehydrates and turns brown. On the contrary, all structures proximal to the necrotic region remain healthy. Of all the ripening anomalies, BSN is the most-researched disorder with no distinguishable causal factors. However, it has been associated with vine vigor, over cropping, severe hedging, heavy or frequent rainfall (high humidity) and calcium or magnesium deficiency. Compared to late-season dehydration, BSN results in a very high concentration of sugars (e.g., 43��Brix), rendering such clusters unsuitable for making table wine. Nonetheless, these clusters can be harvested and used for making wines of a different style depending on the timing of inception. Management: Canopy shading and/or cold weather conditions during ripening can increase the severity of BSN. In Europe, foliar sprays of nutrients (e.g. magnesium and calcium) to clusters beginning at veraison have been shown to reduce incidence of BSN; elsewhere, however, such sprays have not been very effective. These contradictory results suggest that additional abiotic forces work in tandem with nutrients to influence BSN. SOUR Shrivel SOUR (suppression of uniform ripening) shrivel, also known as SAD (sugar accumulation disorder) and berry shrivel, causes great yield losses and deterioration of fruit quality characteristics in both white and red cultivars. It is a recurring phenomenon, especially in Washington, where the disorder is observed every year to some degree in both young and established vineyards. Since SOUR shrivel occurs in a wide variety of soils, cultural and environmental conditions, no particular pattern of occurrence could be deduced from its distribution in the vineyard. Thus, SOUR shrivel may well distress any vine in a given vineyard. Following the affliction, SOUR shrivel is either confined to just a single cluster, irrespective of its position in the shoot, or all clusters in that shoot become symptomatic. Within a cluster, either only a few berries are afflicted or the whole cluster is transformed into SOUR-shriveled berries. Any berry, regardless of its position within the cluster framework, may develop symptoms, although berries at the tip of the cluster frequently develop symptoms. Win es & Vin es JA N UA RY 20 13 97