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May 2018 WINES&VINES 87 WINE EAST GRAPEGROWING composition and quality issues required for economic success. 4. Water and nutrition: Excessive water and nutritional stress will reduce photosynthesis while re- ducing carbohydrate accumulation and consequently cold hardiness. Too much water and mineral nutri- tion, in particular nitrogen, can extend vegetative growth at the expense of carbohydrate storage and therefore vine cold hardiness. There has been some suggestion in the literature that K and/or Ca ap- plications can improve vine hardi- ness. To date studies have not shown any benefit of such applica- tions when the elements are in the non-deficient range. Management issues: establishment and production issues Management goals regarding cold hardiness should be focused on sunlight penetration to leaves as- sociated with shoots that will be retained as bearers for the follow- ing season's production. Cultural manipulations should be intro- duced to create adequate exposed leaf area to mature the crop, ma- ture the canes that will be the next season's bearers, distribute carbon fixed via photosynthesis to peren- nial vine structures and for stor- age in roots to initiate the spring growth flush and complete the differentiation of cluster and flo- ret structures for the coming sea- son. In short, the task of the viticulturist is to manage vines in a manner that allows for maxi- mum expression of the cultivar's genes for hardiness. As noted above in the discus- sion of cultivars, there are a num- ber of cultural conditions that can reduce the vine's ability to express its genetic capacity for hardiness. Excess crop is one of these. Car- bohydrates are the energy which drives the metabolic machinery of the vine and that includes cold hardiness. The vine will preferen- tially send carbohydrates to ripen- ing fruit and the potential for excess crop coupled with a short period between harvest and leaf loss makes careful crop control a major component in any effort to favor vine hardiness. We expend considerable money and labor creating and maintaining mechanical systems to which we attach grapevines. Viticulturists do so in order to create an effective "light trap." Training vines to this structure, and the subsequent ma- nipulation of the canopy, are all done with a goal of facilitating the penetration of light into the fruit- ing and renewal zone. The deci- sions on which to base this decision for a specific cultivar are related to vine vigor and resulting vine size (as measured by the weight of an- nual cane prunings). These are important bases for determining whether a single or divided (either horizontally, as with Geneva double curtain or lyre, or vertically as with Scott- Henry, Smart-Dyson or Sylvoz) canopy will serve best. The best choice for hardiness is the one that favors photosynthesis in the re- newal zone with resultant maxi- mal darkness of cane periderm color for that cultivar (see the photo on page 84). Leaf removal and shoot position- ing also aid light penetration into the fruiting and renewal zone and will have impact on cold hardiness similar to that of training system choice and for the same reason. Pruning – an annual exercise – is the first effort that has impact on the amount of crop that the vine may produce. Pruning has a growth-stimulating influence on vines. This means that viticulturists would prefer to do the practice as late in the dormant season as is pos- sible and still get the effort finished before bud burst. Practical consid- erations often dictate that the effort begin prior to mid-winter. This dilemma can be resolved by selecting the most-hardy culti- vars that are least responsive to winter temperature fluctuations and begin the effort with them. Least hardy cultivars will be pruned last as that will also allow a final, pre-pruning assessment of bud and cane survival and can help determine the amount of "spare parts" to retain. Conclusion Many factors will influence whether vines will be damaged by winter freeze episodes. Many are beyond the control of the viticulturist once planting has occurred. No single decision by the prospective grape grower can be more important than choice of site, with specific empha- sis on macro- and meso-climate. Rationally, we must start there. It makes sense to begin with decisions that will be most difficult to change once the vineyard has been established. Increasingly difficult would be the necessity to change cultivar. Replanting means a loss of at least three to four years of production while the conversion occurs, not to mention the cost of vines, plus the labor for planting and training those vines. However, the most expensive change will be the re- sult of a rational rejection of the selected site for culture. Vineyard site selection and re- tention, like all real estate value judgments, revolves around three overriding principles: location, lo- cation, location. Spending time to evaluate locations for potential grape production is the single-most valuable effort made in vineyard establishment and indeed for the long-term economic survival of the vineyard. The quality of this initial effort can save or cost much money and can determine whether the enterprise has a long-term future. In conclusion, the ideas here reinforce the importance of effec- tive, timely application of cultural practices appropriate for the loca- tion of culture and the cultivars being grown. Nurture cannot pro- duce hardiness levels above those made possible by the vine's ge- nome. However, inadequate, poorly-timed application of prac- tices can negatively influence the expression of the genes the vines possess for cold hardiness. All three authors are located at Michigan State University. Paolo Sabbatini is as- sociate professor of horticulture, G. Stanley Howell is professor emeritus of viticulture and enology, and Josh Vander- Weide is a graduate student in the de- partment of horticulture. The references for this article are available online at winesandvines.com/features