Vineyard and Winery Information Series:
Vol. 19 No. 4, July-August 2004
Dr. Tony K. Wolf, Viticulture Extension Specialist
Frances: It is an unfortunate coincidence that harvest in the mid-Atlantic region coincides with the height of the Atlantic hurricane season, and 2004 is shaping up to be another troublesome year (remember Isabel this time last year?). At this point Virginia has suffered through remnants of Bonnie, Charley, Gaston, and now Frances; however, the state has not been uniformly affected and it does look like the much of the heavier rainfall of Frances will track west of the Blue Ridge (not too good for us in Winchester though). GR Welsh, at the University of Maryland, forwarded the following ominous prediction http://wwwa.accuweather.com/adcbin/public/headlines.asp?iws=1&partner=6037
Fortunately, better weather is forecast for 10 September and we are prepared to jump into the vineyard with captan, Vangard and probably phosphorous acid for kick-back on what we know will have been a significant downy mildew infection period (lots of warm, tropical air and rain). Our Viognier and Chardonnay were very close to being ready for picking over the Labor Day weekend and I know we will take some lumps with ensuing rot and reductions in sugar concentration. We've come through rains remarkably well though in some years and it helps if the fruit is sound going into the event. We're cautiously hopeful, but have a wary eye on Ivan.
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In this and subsequent Viticulture Notes I will review Symposium presentations. The symposium presentations are posted on the ASEV-ES web site (http://www.nysaes.cornell.edu/fst/asev/) in pdf format. I encourage you to browse these informative files, as my notes only touch on some of the points made by the Symposium speakers.
Zelma Long, of Zelphi Wine opened the symposium with a discussion of the climate indices that are routinely - if not inadequately -- used to define a site's grape growing potential. Reviewed were the University of California system of "growing degree days", the Australian "mean temperature of the warmest month", the "latitude/temperature index" developed in New Zealand, and the "sum of average temperatures" used in Bordeaux. Zelma contends that more attention needs to be given to radiation (sunlight) and humidity, relationship of climate indices to vine development stage (phenology), and greater integration of key variables into predictive models. As an example, the "heat index" provided in weather reports, integrates both temperature and humidity to describe the relative degree of human discomfort to be expected on hot, humid days. Similar integrative indices should be explored to fully understand what the vine "feels"; or, more aptly, how the vine responds to the total climate.
Zelma thought that wines produced from grapes grown in humid areas should have "softer" phenolics than if the grapes were grown in more arid climates. She described a project wherein "Natural Terroir Units" were defined for 24 specific grape growing areas of South Africa. The work was done by Victoria Carey of the University of Stellenbosch. A Natural Terroir Unit is "an area with a relatively homogenous topography, climate, geology & soil". NTUs provide a rational basis for defining the environmental factors that affect wine quality and style.
Zelma focused attention on sunlight and heat effects on grape quality and reviewed work of Sara Spayd and others at Washington State University, who provided a good separation of light and temperature effects on Merlot fruit secondary metabolite formation. The underlying problem with these two variables is that sunlight, which is needed for optimal color and flavonol formation in berries, also tends to heat the berry. There is an optimal temperature range for the synthesis of these same compounds, above which the concentrations may be reduced. Spayd's study showed that higher temperatures, independent of sunlight, reduced anthocyanin content of fruit. Furthermore, sunlight, independent of heat, increases monomeric anthocyanins and flavonols. The results - which have applicability in our mid-Atlantic climate - are consistent with a generally accepted notion that all fruit clusters should receive some (or intermittent) sunlight during some portion of the day (the so-called "dappled sunlight" effect). An interesting sidebar to this discussion is the fact that sunlight levels measured in our eastern US grapevine canopies can be greater than light levels measured in a similar density canopy in Washington State. The difference is due to the presence of more diffuse, reflected light that occurs with hazy, humid conditions of the East.
Zelma provided additional suggestions for defining how soil temperature may affect vine phenology, giving an example from vineyards at different elevations in the Golan Heights region of Israel (maximum soil temperature was greater than air temperature during the period of interest in late-September). In conclusion, she reiterated the recommendation that vineyard managers and researchers start paying more attention to climate and soil variables that impinge on grape and wine quality, particularly, (1) solar radiation, (2) temperature [air and soil and day and night], (3) humidity [day and night], and moisture [soil and air]. The data could be useful to better understand the specific terroir we are growing grapes in and, integrated, can be used to predict phenological events and grape and wine quality.
Greg Jones of Southern Oregon University described the use of multivariate regression models to show how climate variables interact to produce a predictable outcome. Using trend analyses from historical (1950 - 2004) phenological data from Bordeaux, Greg showed that the time to principal phenological stages of bloom, veraison and harvest have all been decreasing, or becoming more condensed. Importantly, years in which bloom, veraison, or harvest were delayed, were associated with lowered overall wine quality. Put another way, the shortening of key phenological intervals tended to increase wine quality. The number of days where air temperature exceeded 30F between flowering and harvest tended to decrease harvest date, whereas rainfall during the same period tended to delay harvest. We've seen a similar relationship in the mid-Atlantic - our hot, dry years typically result in generally (across a wide geographic area and among many varieties) superior wine quality.
Climate change? Greg Jones presented long-term data from Germany, France, and western USA that has shown a decrease in harvest date and, in the case of western USA, an increase in the total length of the frost-free growing season. The North Coast region of California, for example, currently averages a 37-day longer growing season than it experienced 50 years ago. Warmer growing seasons in the western USA have been largely driven by increased minimum temperatures (night-time lows are warmer). Modeling of temperature change in the western US points to an anticipated 3.0°F increase in average growing season temperature for all regions between 2000 and 2050. Similarly, a series of figures depicted grape growing potential of Europe, based on the Huglin index (a heat summation index), and changes that have occurred since 1950, projected through 2050. Interestingly, a cooling pattern was apparent between 1950 and 1970, but the principal, established grape production regions have all been exhibiting increased warming since 1970 and are projected to become still warmer by 2050. Translation example: for a "cool climate" location such as Geisenheim Germany, long recognized for quality Riesling and Muller-Thurgau, production of Merlot and Cabernet Sauvignon might be commonplace by 2045.
Greg also presented a comprehensive analysis of temperature trends and predictions of 27 established grape growing regions throughout the world. Of these regions, 17 have significantly increased in growing season temperature (almost 2.5°F) over the past 50 years. The trends in warming have been more significant in the northern hemisphere than in the southern hemisphere, with the northern Rhone Valley showing the most pronounced increase (over 7°F in past 50 years).
The consequences of global warming for the mid-Atlantic wine industries were not specifically discussed; however, the ramifications can be surmised from Dr. Jones' discussion. Increased night-time (and dormant season) temperatures may increase certain biological threats, an issue that has been considered with Pierce's Disease (http://www.ext.vt.edu/pubs/viticulture/463-020/463-020.html). Relatively cool areas (western Virginia and Maryland, parts of West Virginia) may have increased potential for quality wine production, although the increased variability of temperatures will still pose a challenge to winter survival. By nature, most of us tend to think in the near-term - the next year or the next five years. But I'm certain that viticulture in Virginia (varietal choice and where grapes are grown) will look much different in 40 years compared to the landscape of today, and part of that change will be driven by both growing season and dormant season warming patterns. As a sidebar, the September 2004 National Geographic contains an engaging but sobering feature article ("Global Warning") on the observed and predicted ramifications of global warming.
Phil Freese of WineGrow (Sonoma Co., CA) reviewed how viticultural practices affect wine mouth-feel, or textural qualities. Besides textural (e.g., suppleness) quality, mouth-feel comprises a tactile response, including our response to tannins, alcohol, polysaccharides, and other carbohydrates. While it sounds like a 'pat' statement, desirable mouth-feel, particularly of red wine, is only achieved with mature vines and fully ripe fruit. Phil's discussion principally focused on the viticultural means of achieving ripe fruit.
Sources and characteristics of tannins, including those from seeds, grape skins, stems and barrels were described. For example, polymerization of tannins ("methylated chickenwire") can be accelerated or otherwise modified to improve wine quality; vegetative tissue (stems) can be intentionally retained in the must or fastidiously removed depending on the desired product, and greater or lesser barrel exposure can be used to modify tannin attributes. All of these techniques and inputs impact the scale of "hard" to "soft" tannins.
Phil reviewed the vine management, varietal, and environmental (climate and soil) interactions that have a bearing on our goal of achieving ripe fruit; a conceptual model that remains a cornerstone of sound vineyard management. Implicit in that model is a balance between the vine's vegetative production and its reproductive (fruit) development. Commonly used vine balance indicators (e.g., leaf area to fruit ratio, cane pruning weight to fruit ratios, shoot density, canopy leaf layer number, etc.) were listed, as were their desirable values.
Allow me to digress here: Practitioners of good canopy management techniques would be quite familiar with these vine balance indicators or parameters. We recognize that the holy grail of "balance" can be a frustrating goal in humid environments such as Virginia, where soil moisture is often at a surplus. One of the take-home messages for me from Phil's (and many of the other Symposium) presentations is that we should explore more novel means of approaching vine balance. While past efforts have focused on remedial means of reducing excess vegetation (e.g., shoot hedging), and on canopy division to accommodate vigor, it is past-time to consider more radical approaches such as:
Hurricanes such as Frances remind us that we have limitations in our ability to deprive vines of moisture in the mid-Atlantic, but if we can do a better job with vine balance, our odds of consistently harvesting high quality grapes will be significantly improved.
Phil's discussion continued with a description of how vine water status can be modified to intentionally affect vine balance. Again, water management is an admittedly more predictable tool in an arid environment than in a humid region. Effects of canopy density and fruit exposure on fruit composition were also reviewed.
The remainder of Phil's discussion provided a roadmap for achieving balance, and many of these methods have direct applicability. Phil stressed the need to achieve uniformity of grape ripening -- a narrowing of the bell-shaped ripeness curve of our berry population at harvest. He advocated first looking critically at the spatial differences of our sites - such as soil variability from the top of a slope to the bottom. Site differences can impart substantial differences in canopy density, crop level, and crop ripening rates. At minimum, those differences should be recognized and accommodated by altering the harvest date to reflect spatial differences in rates of crop maturation. More proactively, we can attempt to reduce variability of crop ripeness by adjusting vineyard management practices across the known lines of vineyard variance. At minimum, differences in soil depth or drainage capacity can and should be evaluated and factored into row spacing, choice of rootstock, and choice of training for a given variety. Variation in crop ripening can be reduced by "green thinning" of fruit that is retarded in development, thinning of crop from weak shoots and, again, conducting sequential or multiple harvests to "block" crops into similar ripeness categories.
I would comment that many of our more progressive growers are using all of these techniques, including the last, which requires a skilled picking crew to discern differences in grape ripeness.
The review of the symposium presentations will be continued in the September-October Viticulture Notes.
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This seminar has been arranged by Mark Chien of Penn State and Rutger de Vink, commercial vineyardist here in Virginia. The speakers are touring several vineyards/wineries in the region and have graciously agreed to present this two-hour seminar on a very short notice. Please note from Mark's information below that the registration capacity is 30 persons.
From Mark Chien's information: Alfred Cass landed in Sonoma from his native South Africa via study with Malcolm Sumner at the University of Georgia. Cass has focused his talents on understanding exactly what constitutes a soil from which fine wine can be derived. He has used this knowledge to help find and evaluate some of the best vineyard sites in California, primarily in the north coast counties. Daniel Roberts has a PhD in soil science and was one of the first to recognize the importance of rootstocks to high quality wine production in Napa Valley. He now runs a consulting firm called Integrated Winegrowing that works with some of the great properties in Napa and Sonoma.
These three experts will be giving a seminar on Wednesday, September 22 at the Middleburg Community Center in Middleburg, Virginia from 5:00 to 7:00 p.m. The topics are:
The Middleburg Community Center is located at 300 West Washington Street (Rt 50). You can find information at their web site http://www.loudoun.gov/prcs/cc/middleburg.html. Their telephone number is 540.687.6375. The meeting starts at 5:00 p.m. SHARP. Please arrive at least 15 minutes early. There is no cost for this meeting; however pre-registration is required. A group dinner with them in Middleburg will be organized. Please indicate if you would like to attend dinner when you register. Bring a bottle or two of wine to share.
Please RSVP to Mark Chien at 717.391.6478 or email@example.com by September 17. Registration is limited to 30.
B. Basic vineyard establishment and operation shortcourse (29 October 2004)
This one-day workshop targets individuals who are exploring winegrape growing opportunities in the mid-Atlantic region (especially VA, PA and MD), or those who desire a "refresher" course. Topics covered include economics, site selection, varieties, and vineyard establishment, including materials and methods. Various aspects of established vineyard management (canopy management, pest management, pruning and training, cold injury avoidance, etc.) are discussed at an introductory level. Classroom principles are reinforced with a review of the AHS AREC research vineyard. As with recent years, the workshop will be team-taught by Tony Wolf (Virginia Tech), Joe Fiola (University of Maryland), and Mark Chien (Penn State University).
When: Friday, 29 October 2004; 8:00 am - 5:00 pm
Where: AHS, Jr. Agricultural Research and Extension Center, Virginia Tech, Winchester, VA.
Information: Tony Wolf, 540-869-2560 x18 (firstname.lastname@example.org) or Pat Peacock 869-2560 x11
Registration: Pre-registration is required and registration is limited to first 60 persons: $125 per person, to include morning coffee/danishes, soft-drinks, catered lunch, handouts, and to cover our invited speaker expenses. Check to be made payable to "Virginia Vineyards Association", and mailed to "Grapes", Virginia Tech, 595 Laurel Grove Rd. Winchester, VA 22602. Check must be received by 22 October 2004 to guarantee lunch. Please Note: This course typically fills quickly. Registrants are confirmed or denied registration in the order that registrations are received.
Directions: Virginia Tech's AHS Jr. Agricultural Research and Extension Center (AREC) is located approximately 7 miles southwest of Winchester, VA in Frederick County. From Interstate-81, take the Stephens City exit on the south side of Winchester. Go west into Stephens City (200 yards off of I-81) and proceed straight through traffic light onto Rt 631. Continue west on Rt 631 approximately 3.5 miles. Turn right (north) onto Rt 628 at "T". Go 1.5 miles north on Rt 628 and turn left (west) onto Rt 629. Go 0.8 miles to AREC on left.
Motels: Two suggestions for motels, within several miles of the AHS AREC are the Holiday Inn Express (540-869-0909) and the Comfort Inn (540-869-6500), both located at I-81 exit # 307 in Stephens City.
C. Virginia Grown Conference (26 - 29 January 2005)
Hold the dates for this meeting which will include the annual meeting of the Virginia Vineyards Association. Location is Holiday Inn Select in Richmond. Program plans are currently in development.
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"Viticulture Notes" is a bi-monthly newsletter issued by Dr. Tony K. Wolf, Viticulture Extension Specialist with Virginia Tech's Alson H. Smith, Agricultural Research and Extension Center in Winchester, Virginia. If you would like to receive "Viticulture Notes" as well as Dr. Bruce Zoecklein's "Vinter's Corner" by mail, contact Dr. Wolf at:
Dr. Tony K. Wolf
AHS Agricultural Research and Extension Center
595 Laurel Grove Road
Winchester, VA 22602
or e-mail: email@example.com
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