Practical Winery
65 Mitchell Blvd, San Rafael, CA 94903
phone: 415-453-9700 ext 102
email: Office@practicalwinery.com
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JULY/AUGUST 2010
SMART VITICULTURE
As we move on to the period from fruitset to veraison, vine moisture stress becomes more of an issue. It is my opinion that many vineyards, especially those on deeper soils, are irrigated too early in this period. This is one occasion when our eyes may give a false reading about the need for irrigation.
I strongly suggest to my clients to measure soil moisture, and not to begin irrigation unless subsoil reserves have been partially utilized. Do not begin irrigation just because the topsoil looks dry, or because you see the very first sign of plant moisture stress.
Several of us in the industry have developed a visual scorecard to detect vine water status, which, before veraison, is based on shoot tip growth. When properly used, I think this is more important than the pressure chamber, which is affected by time of day, temperature, humidity, radiation, and operator error; its results verge on being unusable.
The shoot tip scorecard, inmy experience, is easy to use, and gives quantifiable results. The goal is to stop shoot growth in the period shortly before veraison, and yet to avoid severe water stress.
Veraison
In my opinion, veraison is the most important time to assess vineyard attributes affecting wine quality. I often chide winemakers who rely on their pre-harvest berry tasting missions, saying “they are about six weeks too late, and using the wrong sense anyway” (taste not sight).
Important issues to observe are the times of onset of veraison and lignification, and the rate at which they develop. These can be quantified and are built into the smart vineyard grading system.
Also, this is a useful time to assess canopy attributes like leaf color and leaf health in general, canopy density, canopy dimensions, and fruit exposure. In addition, this is the common time to thin fruit in vineyards if the crop is considered excessive.
I published a vineyard scorecard in the 1980s, and further modified it for Sunlight into Wine, published in 1991 [see also, “The mother of all scorecards,” PWV, March/April 2003]. Now I am preparing More Sunlight into Wine, a follow-up and thoroughly rewritten version, which will include modifications to the scorecard.
At veraison some important nutrient deficiencies show up. For example, a magnesium deficiency can be seen on the basal leaves and is known to reduce photosynthetic efficiency.
Veraison to harvest
This is the ripening period that seems to attract most attention from enologists but, in my opinion, most of the important decisions affecting quality have already been made. I believe that fruit tasting is usually not a good indicator of harvest time, despite many opinions to the contrary.
The aim of irrigation during this stage is generally is to keep vines under slight moisture stress, being careful not to over- or under-irrigate. I have developed a second scorecard to help assess vine water status during this period, as one normally no longer has growing shoot tips to view.
Diseases that have significant and direct effects on fruit quality during this time are powdery mildew and botrytis bunch rot.
This is also a time when some important virus
diseases show up, such as leaf roll virus, as it is wellknown that some strains can substantially reduce fruit ripening and yield. These diseases present distinctive visual symptoms.
Conclusion
I have given many examples of how vineyard assessment using your eyes can be a useful management guide to improve quality. The accompanying photos give some examples.
I wonder how many will read this column and apply some of the practices? I am sure that many experienced viticulturists will already be doing most of the things Imention. It is a simple transition from visual observation to recording and quantification, especially using a GPS-equipped PDA in the field.
This approach is at odds with what I call the “cookie cutter” approach where the whole vineyard is given the same uniform management of irrigation, fertilization, leaf removal, and crop thinning year after year, with little supervision of labor and review of the outcome.
It would be an interesting experiment to compare these two approaches in commercial vineyards with commercial winemaking. I can help — are there any takers out there?
   
Dr. Richard Smart is rewriting and thoroughly revising Sunlight into Wine. He is happy to receive statements from growers and winemakers about their commercial success with various aspects of canopy management. Interested persons should contact Dr. Smart at vinedoc@bigpond.net.au. Dr. Smart visits the U.S. frequently, and consulting appointments can be made by email. See also www.smartvit.com.au.