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By Richard Mendelsonand Robert Steinhauer

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Napa Valley

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This a~•ticle is excerpted from a chapterwritten by Richnrd Mendelson a~~cl RobertStei~a/~ctuer, two tuell-known wine industryexpe~•ts, aboait modern-dcty viticulture i~athe Napa Valley. Their chapter appearedin "The Science o f Viticacltacre: Volacme 1 "(K.V. Peter, editor), published last yeas• byNetu India Patblishing Agency. The chaptercovers a broacl range of topics, from theNapa Valley's viticultziral ianic~ueness andthe legal protections for this i~•~•eplctceableagricailta~ral resource to vineyard develop-me~zt (site selection, in fiastt~cactacre andplait material) a~ad farming i~a an e~zviron-mentally sound and sustainable manner.The excerpt that follows is about culturalpractices. The entire cbctpter and citationsare available at zuinesandvines.com.

ultural practicestailored to thevintage, along withvineyard designsthat augmentnatural featuresof the particularsite, determine

the ultimate wine quality in any givenharvest year. The most important culturalpractices are pruning, canopy manage-ment, irrigation, fertilization, vineyardfloor management, yield managementand harvesting. Pruning is a critical factorin managing yield and wine quality. TheNapa Valley winegrower strives for abalance between yield and vegetative vinegrowth on a consistent, sustainable basis.Optimal values include 0.66 pounds to2.20 pounds of pruning weight per meterof canopy length and between 5 and 7pounds of fruit for every pound of dor-inant vegetative growth.' Some growersrelate pounds of prunings to retained budcount. For example, an average of sevenbuds retained per pound of prunings willprovide for a balanced vine at most Cab-ernet Sauvignon sites. The experiencedwinegrower also will take into accountthe historical yields at the specific site,vine vigor, wine quality and the amountof summer trimming.There is no clear preference for cane

pruning versus spur pruning in the NapaValley. Both methods are used dependingon grower preference.The Napa Valley is subject to spring frosts.

Once bud break occurs, the green shoots canbe damaged if temperatures fall below 32°F.The most common type of frost event is aradiational freeze? On some very rare occa-sions, an advective freeze3 may occur.

Most vineyards that are vulnerable tofrost are protected in some manner. Theuse of wind machines (one per 10 -~- acres)mixes the warmer, inverted air with thecolder air on the vineyard floor. (Windmachine shogun in photo, page 32.J Dur-ing aradiational freeze, a wind machinewill raise temperatures by 2°-3°F. Theair movement of 2 to 10 miles per hourcaused by the wind machine also resultsin a shallower boundary layer, a largerheat gradient, enhanced heat transfer anda warmer leaf. As a result of these com-bined effects, wind machines can protectvines against temperatures as low as 26°F.It should be noted that wind machineswill not protect the vine, and they mayeven cause greater damage during anadvective freeze.

Overhead sprinkler systems

Another commonly used method for frostprotection is a properly designed over-head sprinkler system. Heat released bythe freezing of the applied water, whichforms an ice film around the green leaves,clusters and shoots, protects the vine bykeeping temperatures near the 32°F mark.This water application can protect toapproximately 24°F, although co-authorRobert Steinhauer has observed protec-tion down to 21°F.The overhead sprinkler system con-

sumes large volumes of water-52 gallonsper minute per acre. For most properties,large reservoirs and large pump capacityare required. In return for this investment,the sprinkler system will protect against

much lower temperatures than will a windmachine. It also will provide protection inmost advective conditions, and the samesystem is sometimes used for irrigation andcooling during summer heat spike events.l Part of the trend to sustainable practicesin Napa Valley is the management of thevineyard floor, both in-row and undervine. Best farming practices generally havemoved away from pre-emergent herbicidesunder the vine row to mechanical tillingor applications of glyphosate for weedcontrol. Generally, between rows are per-manentsod cover crops that are mowedor cultivated row centers. Currently, manysites alternate every other year betweensod cover crop and cultivated row mid-dles. Some growers plant a winter covercrop that is incorporated into the soil asa source of nutrition as well as erosioncontrol. Other growers utilize compost forthe same purpose. Typically, these manage-ment practices are site-specific.The benefits of cover crops are reduced

tractor wheel compaction, improved physi-cal properties of the soil, increased organicmatter, reduced chemical use, habitat forbeneficial insects, dust control and reduc-tion in water runoff. However, permanentsod cover crop has been found to competefor water and nutrients, which, over time,potentially reduces vine vigor.

Vine nutrition is an important compo-nent of a successful vineyard—both forthe particular vintage and for the long-term health of the vineyard. Most grow-ers rely on field observations to determinenutrient status, along with soil chemistry

WINES &VINES NOVEMBER 2011 33

analysis, bloom time petiole nutrient as fertilization by drip irrigation, mechan-status and leaf blade nutrient analysis. ical soil incorporation and materials thatThe Napa Valley winegrower has at his can be sprayed on grapevine leaves.disposal many advanced nutrient and soil The ultimate goal of the winegroweramendment application capabilities such is to produce the largest quantity of the

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34 WINES &VINES NOVEMBER 2011

very highest quality grapes that are in

the greatest demand in Napa Valley. Toachieve this goal, the viticulturist musthave a solid scientific understanding ofthe effects of cultural practices, the vin-tage and terroir, plus the historical per-spective of farming on the particular site.The grower must be flexible in adjustingcultural practices throughout the growingseason from site to site, blocle to block—and even within a block.

Canopy managementWhile many factors influence the selec-tion of grape variety and the ultimatewine character and quality, site (terroir)and season (vintage) are perhaps the mostdramatic. In terms of farming practices,canopy modification and irrigation strate-gies are demonstrated mechanisms formanipulating wine quality. The responseto these and other management practicesis dependent upon variety, row orienta-tion and trellising.Canopy management is important

because filtered light has a positive influ-ence on fruit composition. However, toomuch light and high fruit temperaturesare deleterious to wine quality; therefore,the foliage must protect the fruit from

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sunburn and dehydration. Additionally,sunlight on the shoots will improve budfruitfulness the following year.Most Napa Valley winegrowers retain

about five shoots per foot of canopy. Thespacing of the shoots generally allowsfor optimum sunlight on the leaves. Theshoot length on a balanced vine should beuniform and grow to between 3.5 feet and5 feet by veraison (the point at which thegrape berries turn from green to their finalcolor, representing the change from berrygrowth to berry ripening.) The shootsshould stop growing about two weeksbefore veraison and retain about 12 to 15active leaves that remain green and healthyuntil harvest. The grape clusters typicallyare protected by filtered light throughone or two layers of leaves. Growers maydecide to remove basal laterals or lateralsplus a few leaves based on observations ofthe site and leaf cover. Row direction andleaf size (Merlot and Zinfandel are variet-ies that have large leaves) will influencethe decision about leaf removal to obtainthe desired amount of fruit exposure.North-by-south row direction may requireleaf removal on the east (morning sun)side and no leaves on the west side of thecanopy to shade the fruit.

The water status of the vine has a ally receives enough rainfall from Novem-major effect on the canopy and ultimate ber through April to fill the soil profile.fruit and wine quality. As such, irrigation Normally, very little rain occurs duringmanagement is one of the most important the summer and fall months. Almost allviticultural tools. The Napa Valley gener- Napa vineyards are either dry farmed or

WINES &VINES NOVEMBER 2011 35

equipped with drip irrigation systems. Fol- ments and their effects on vine physiologylowing the advent of drip irrigation, water and wine quality have been completed.use by Napa Valley growers has become There are sites with deep loam or clayvery efficient and prescribed. A tremendous loam soils that require no irrigation oramount of research on irrigation treat- are intentionally dry farmed. Many grow-

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ers advocate deficit-irrigation strategies.These irrigation strategies maintain thevine water status post-veraison at 70%-80% of the evapo-transpiration rate.Most growers understand spatial varia-tions in the vineyard and adjust irrigationwithin blocks or sub-blocks of the vine-yard. Along with constant visual inspec-tion to determine the water status of thevines, many growers rely on soil moisturemeasurements and gauge the midday leafwater potential utilizing a pressure cham-ber. Many growers will not start irrigatinguntil the vines get to -10 bars of middayleaf water potential. Along with the soiland plant water measurements, the fieldobservation of vine status, especiallyobserving shoot tips, is critical.

Cluster removal, known as thinning,occurs just prior to veraison or at verai-son in almost every ultra-premium vine-yard in Napa Valley. Typically, the growerremoves the clusters that are touching orare compacted together in order to pro-vide light to the berries and also reducethe potential for fungal disease.Many growers, especially the producers

of red grape varieties, "color thin" at 80%-95% veraison by removing any green orpartially green clusters. This process is un-

dertaken in an attempt to achieve uniformmaturity at harvest. Some growers willremove clusters in excess of one cluster pershoot. This process is gaining favor amongsome ultra-premium producers of Caber-net Franc, Cabernet Sauvignon, Pinot Noirand certain other varieties.Growers understand that thinning

early, while the berries are in the growthphase, will increase the size of the remain-ing berries. For this reason almost allgrowers wait to thin until veraison.Winemaker demands for concentrated

flavor and supple tannins at harvesthave led to the practice of leaving grapeson the vine for days or weeks after thetraditional harvest date. This practice iscommonly referred to as "hang time."This requires continued maintenanceirrigation to keep leaves green until justbefore harvest.

Viticulturists in Napa Valley are divid-ed on the effects that yield (expressed astons per acre) has on wine quality. Under-cropping (too few clusters) can lead a vineto excessive vegetative growth, vegetativewine flavors and high total pH. At the op-posite extreme, overcropping (too manyclusters) a vine can lead to low alcoholand light, poor-quality wines. A majority

of growers believe that precision farm-ing for small yields produces the highestquality ultra-premium wines. The successof these growers makes it difficult toargue with this position. Another group,

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however, believes that precision farmingfor balanced capacity and vine vigor isthe best avenue to produce ultra-premiumwines. Whichever approach is correctdepends ultimately on a multitude of fac-

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tors. Dr. Mark Matthews reports, "Priorresearch has shown no effect of yield onwine quality." He also states, "Qualitycannot be measured by a scientist becauseit is so subjective:'Most viticulturists agree that for the

ultra-premium wine market, small yieldsthat are balanced with the vine's vigorresult in superior wines. The Napa Valleyaverage yield for Cabernet Sauvignonfrom 1986 to 2004 was 3.8 tons per acre.By contrast, the. California average forCabernet Sauvignon for this same periodwas 5.55 tons per acre.The Napa Valley climate allows for the

full maturity of even late-ripening variet-ies like Cabernet Sauvignon and CabernetFranc. For many years, harvest date wasdetermined by measuring sugar, acid andpH. These measurements are still madetoday, but the winemaker also tastes thefruit to determine when to harvest. Forred varieties, most winemakers look forripe, intense flavors with supple tanninstructure. They also want the grape seedsto be brown and mature. Bibiana Guerradescribes an Australian research projectabout Syrah confirming that seed color isa good indicator of physiologically ripeberries, ready-for harvest. A given vineyardmay be harvested block-by-block or evensub-block-by-sub-block on different days,based upon the flavor profile of the fruit.Most ultra-premium fruit is harvested

by hand. However, the mechanical har-

38 WINES &VINES NOVEMBER 2011

vester technology is so advanced that asubstantial amount of Napa Valley fruit is

now machine harvested.Harvest is the culmination of grow-

ers' efforts. Before and during harvest,the winegrower and the winemaker(sometimes one and the same) observethe conditions of the vines and determinehow best to meet the winemaker's param-

eters for the fruit. They observe condi-tions down to the level of the blocks andsub-blocks (precision farming), and thegrower then adjusts the cultural practicesaccordingly, including irrigation, fertiliza-tion and canopy management.When harvest concludes, the wine-

gro~ver and winemaker focus on thewine to determine if modifications to thecultural practices would improve yieldsand quality. The grower then considerswhether to adjust those practices in future

vintages, cognizant that each vintage yearwill present its own unique conditionsand challenges.The winegrowers and winemakers

of Napa Valley understand that theyare fortunate to grow grapes and makewine in such favorable terroir. Wine-growers and winemalcers work collabor-atively to ensure that their grapes meetthe wine quality parameters and willvinify high-quality wines. This strategicalliance of winegrower and winemaker

is a key component of the success orfailure of a vineyard.The grower and winemaker also

constantly work together to improve their

know-how and stay at the forefront oftechnology. They recognize, respect andappreciate that each winegrowing regionof the world has its own valuable history,tradition, science and practices that maydiffer from those of the Napa Valley, andthey remain open to learn and adapt theirskills and practices to improve the qualityof Napa Valley wines. This commitmentto excellence has been evident in theNapa Valley for many generations,resulting in the well-deserved internation-al reputation that Napa Valley has longenjoyed.

Richnrcl Mendelson is a lacuyer specializingin vineyard and wine late with the laav fzrmof Dickenson, Pentnzan and Fogarty i~z Nnpa,

Calif. He directs the ZX~ine Lazu and Policy P~•o-

grans at the University of California, Berkeley,

School of Laav and is past preside~zt of the

Internntiona! Wine Law Association. Robert

Stei~tl~auer managed vineyard operations atBeckstofferVineyctrds from 1971 aLnti11979

n~zd Beringer Vineyards from 1979 to 2004

and is now a vitiudta~ra! conszdtant with crudco-ow~:er o f Winelctnd Consulting LLC. He is

a past president o f Nnpa Valley Vi~ztners andira 2008 received the Merit Atuctrd from TheAmerican Society for Enology and Viticaclta~re.

The nzithors acknowledge and thank Hal Hu ff-

smith and Ticker Catlin for their peer reviewo f this article.

Footnotes1. A pruning trial conducted in Napa Valley u t zing-Cabernet Sauvignon grafted to 110R rootstock

resulted in significant differences in sensory attributes. That seemed to defy the conventional wisdom.The law yields of 1.74 tons per acre resulted in "veggie aroma and flavors, bell pepper aroma, bitter-ness and astringency," while the high-yield wines of 8.98 tons per acre were "higher in red/black aroma,jam aroma and fresh fruit aroma." Other research has pointed out the need to achieve balance betweencapacity (yields) and vine vigor.

2. A radiational freeze occurs when a cold but dry (low dew point) air mass moves into the valley. Tempera-tures can be in the 60°s (Fahrenheit) in the afternoon, but after sunset radiational cooling of the soilsurface causes temperatures in the lower atmosphere to fall, sometimes by 30°F or more. Temperaturesa few hundred feet above the ground remain fairly constant, forming an inversion (temperature increasewith elevation).

3. An advective freeze occurs when a cold air mass from the Arctic regions migrates into the Napa Valley.The temperatures at the vineyard are below freezing and become colder at higher elevations.