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Home , Canopy (grape), Deficit irrigation

PRACTICAL WINERY & GRAPEGROWING

A small sensor called an iButton is situated in clusters located on the interior and exte- rior to log temperatures every 10 minutes.

Deficit How low can you go? By Melissa Hansen

t’s often thought that if some is good, more must be better. But that axiom does not apply to regu- lated deficit irrigation, according to research conducted by Washington State University (WSU) scientists. Regulated deficit irrigation is a management strategy used by grapegrowers to fine-tune Icanopy development and improve fruit-quality attributes.1 “Though some stress can often help improve Earlier research has suggested that relatively severe deficit quality, there is such a thing as not providing enough irrigation can achieve significant water savings compared to mod- water for the vine,” says Dr. Markus Keller, lead investigator erate deficit irrigation and can have additional effects on vine of regulated deficit irrigation research supported by the Wash- performance.3,4 But that research raised two questions: 1) How ington State Wine Commission, a state agency representing severe is too severe? 2) Can water be saved and grape quality all wine grape growers and wineries. Keller, a horticulturist improved without sacrificing long-term vine productivity? at WSU’s Irrigated Agriculture Research & Extension Center The impact of increased water supply during ripening and in Prosser, specializes in vine physiology, irrigation and cold its relationship to alleviating drought-induced berry shrinkage hardiness and is author of The Science of Grapevines: Anatomy was examined because little research in this area has been and Physiology. conducted in the field. Recommendations in the “Guidelines The research by Keller et al. could help wine grape growers for Integrated Production of ” from the International save up to 30% of the water used to irrigate grapevines and save Organization for Biological and Integrated Control declare that energy costs to pump the water without sacrificing grape yields irrigation of vines for wine production must not be applied after and quality. Throughout the world, water availability is a growing véraison (or is highly restricted) to guarantee “good wine.”5 problem due to a changing climate. During the 2015 drought in But withholding water after véraison is at odds with recom- Washington state, water was rationed in prime irrigated acreage mendations to avoid inappropriate water stress during ripen- in the Yakima Valley, where high-value crops such as apples, ing.6 Some studies have suggested that late-season irrigation grapes and hops are grown.2 may help alleviate drought-induced berry shrinkage and does The WSU study showed that regulated deficit irrigation not increase berry size.7 (hereafter referred to as deficit irrigation), while generally beneficial, can be taken to extremes and go too low. Vines receiving only 25% of crop (ETc) in the This text was condensed from a report study were economically unsustainable due to reduced yields in the American Journal of Enology & .

MARKUS KELLER, WSU and vine decline compared to other treatments in the trial.

June 2017 &VINES 49 GRAPEGROWING PRACTICAL WINERY & VINEYARD

SUMMARY OF WEATHER CONDITIONS net Sauvignon grapevines (clone ducted in the three years leading FPS 08). up to the present trial.9 Seasonal temperatures (d)b Precipitation (in) Cold Creek Vineyard was irri- The overall goal of this study GDD >86ºF >95ºF <59ºF <50ºF gated using drip irrigation with was to investigate the impact on Year (°F)a PV/RP PV/RP S/F S/F Annual Seasonalc pressure-compensating, 1-gallon- fruit and wine composition from 2011 2,959 32/16 2/2 20/9 1/1 3.6 2.1 per-hour emitters spaced 3.5 feet more widely contrasted irrigation 2012 3,305 50/4 15/0 7/9 1/4 4.0 1.8 apart. Vine spacing was 6.8 feet regimes than were previously between vines with 9.8-foot-wide studied.10 The study measured 2013 3,528 55/19 16/1 10/6 0/0 1.9 1.5 tractor rows. Vines were trained vine growth and compo- 1995- to bilateral cordons at 3.5 feet nents, plant water status and gas 2013 3,245 53 13 10/9 0/2 4.7 2.2 aboveground and spur-pruned in exchange and microcli- Data were collected by an on-site weather station located less than 400 meters winter to 67 nodes. were mate. Although experimental from the experimental vineyard block in southeastern Washington. loosely positioned between two wines were made by co-investiga- a Cumulative growing degree-days (>50°F) from April 1 to Oct. 31. foliage wires, and the trial re- tor Dr. Jim Harbertson’s team, the b Number of days from April 1 to Oct. 31 with maximum temperatures above or ceived standard applications of effects on fruit and wine composi- below four threshold temperatures. (PV: pre-véraison/RP: ripening; S: spring/F: fall). , and other tion are not covered here but will c Cumulative rainfall from April 1 to Oct. 31. pest- and -management prac- be contained in other reports. tices as other blocks in the vine- Irrigation regimes were imple- VIGOR AND VINE SIZE yard. Because the vineyard did mented when shoot growth c not receive enough precipitation stopped, which typically occurred Shoot lengtha Lateral weight Weak canes (inches) (per shoot) (ounces/foot) (%) in winter months to replenish the soon after fruit set. The four irri-

b soil-moisture profile, the root gation treatments were: ET25 27 b 10 b 2.2 c 33 a zone was irrigated to near field • 100% ETc (ET100) ET 35 a 16 b 3.9 b 25 b 70 25/100 capacity prior to break. • 70% ETc (ET ) ET 36 a 23 a 4.6 ab 27 ab 70 Weather data collected daily • 25% ETc (ET25) from an on-site weather station • 25% ETc before véraison, ET100 39 a 22 a 5.6 a 22 b owned by Ste. Michelle Wine Es- 100% ETc thereafter (ET25/100) tates is summarized in the table All treatments were fully irri- 2011 41 a 23 a 3.6 b n.d. “Summary of Weather Condi- gated after in preparation 2012 31 b 15 b 3.8 b 30 a tions.” Cumulative growing de- for winter. Although there was 2013 32 b 15 b 4.9 a 23 b gree-days were calculated from yearly variation in the three grow- daily maximum and minimum ing season temperatures, the ef- Cabernet Sauvignon grapevines irrigated at various fractions of crop evapo- temperatures, with a base tem- fects from irrigation treatments (denoted by subscripts of ETc) from fruit set to harvest over three perature of 50° F from April 1 to were consistent between years. years; ET refers to 25% ETc before véraison and 100% ETc thereafter. 25/100 Oct. 31. Four temperature thresh- Deficit irrigation treatments a Length of primary shoots at harvest. olds were counted separately to did not enhance water-use effi- b Means followed by different letters differ significantly at p < 0.05 identify the number of hot and ciency: Lower seasonal irrigation by Duncan’s new multiple range test. very hot days (temperatures water supply was also associated c Proportion of canes with less than five nodes (not determined in 2011). above 86° F and greater than with lower yield, but deficit irriga- 95° F) during pre-véraison and tion did reduce water use. The YIELD AND YIELD COMPONENTS ripening, and two temperature average amounts of irrigation Yield Berries/ Berry weight Yield: pruning thresholds were used to identify water supplied over three years (tons/acre) cluster (g) weight (pounds) the number of cool and cold days varied from 16.0 inches (1.3 acre-

a (less than 59° F and less than feet) in the ET treatment; 12.6 ET 2.1 b 69 c 0.84 c 7.3 a 100 25 50° F) in the spring and fall. inches (1.05 acre-feet) in the ET ET 3.8 a 89 a 0.95 b 8.2 a 70 25/100 Four irrigation regimens were vines; 11.4 inches (0.95 acre-feet)

ET70 3.9 a 76 bc 1.08 a 7.1 a applied in four replicated blocks to in the ET25/100, and 6.8 inches (0.5 replace a range of crop evapotrans- acre-feet) in the ET . On average, ET100 4.4 a 80 ab 1.06 a 6.9 a 25 piration (ETc) fractions from fruit deficit irrigation reduced the set to harvest. Evapotranspiration amount of water supplied by 22% 2011 2.5 b 70 c 1.18 a 6.6 a (ET) is the sum of evaporation of in the ET70, 31% in the ET25/100, 2012 3.8 a 79 b 0.84 c 8.6 a water from the soil and plant tran- and 56% in ET25. 2013 4.3 a 88 a 0.93 b 7.0 a spiration and uses a reference crop Cabernet Sauvignon grapevines irrigated at various fractions of crop evapo- surface such as grass, without any Vine vigor transpiration (denoted by subscripts of ETc) from fruit set to harvest over three water stress, multiplied by a grape- Vines in this trial exhibited most vine-specific and seasonally vari- of their shoot growth before fruit years; ET25/100 refers to 25% ETc before véraison and 100% ETc thereafter. a Means followed by different letters differ significantly atp < 0.05 able crop coefficient to calculate set. Though primary shoots in all by Duncan’s new multiple range test. the crop’s water use.8 treatments stopped growing be- The trial was designed to vary fore véraison, lateral shoots in the

Deficit irrigation regimes planted in 1981 in the Columbia the timing and extent of water ET100 and ET70 vines continued to A deficit-irrigation study was Valley appellation in southeast- deficit from no water stress to grow through harvest. Effects on conducted at Cold Creek Vine- ern Washington state. The trial relatively severe stress. The same vine vigor, size and density of yard, a property owned by Ste. was conducted in 2011, 2012 vineyard was part of previous canopy from irrigation were con- Michelle Wine Estates that was and 2013 on own-rooted Caber- deficit-irrigation research con- sistent across the three years.

50 WINES&VINES June 2017 PRACTICAL WINERY & VINEYARD GRAPEGROWING

Vine vigor was measured ences in canopy , through multiple parameters (see small sensors called iButtons were table “Shoot Vigor and Vine Size”) used to log temperatures at AQUEOUS TANNINS by tru/tan and included shoot length (mea- 10-minute intervals. The iButtons - sured at harvest), number of lat- were placed on the exterior and tru/tan aqueous tannins are a unique blends of eral leaves per shoot and pruning interior faces of grape clusters ellagitannin and gallotannin that are entirely oak weights. A new way to capture (see photo of iButton in grape derived and retain all of the aromatic freshness vine vigor (called percentage of cluster on page 49). Daytime tem- and potency of stave quality oak while maximizing weak canes) was developed by peratures of sun-exposed clusters ease of application. determining the proportion of were often around 20° F warmer canes with less than five nodes. than ambient air temperatures;

Vine vigor between the ET100 however, at night these same clus- and ET70 regimens was not sta- ters were only a few degrees tistically different. However, the below the ambient air tempera-

ET25 treatment resulted in very ture (see “Exterior and Interior weak vines and had the lowest Cluster Temperatures,” below). pruning weights, shortest shoots While temperatures of the few with few laterals and the great- shaded clusters did not differ est percentage of weak canes of between irrigation amounts, the all four treatments. These vines sun-exposed clusters of the ET25 also showed yellowing and vines (the warmest of the four some leaf abscission. treatments) were almost 10º F Treatment carryover effects warmer during midday than on shoot vigor in the following those of the ET100 vines. The year were observed in the ET25 smaller and more open canopy vines, which had shorter inter- and small number of lateral nodes and fewer main and lat- leaves in the ET25 vines allowed eral leaf numbers at fruit set, more light and resulted in higher even though all the deficit irriga- temperatures in the fruit zone tion treatments received the compared to other treatments. same amount of water before The ET25 clusters experienced al- fruit set and abundant amounts most twice the number of hours after harvest. The decreased above 95° F and fewer hours berry number per cluster in the below 68° F compared to clusters second and third years of the in the ET100 treatment.

ET25 treatment suggests that the severe deficit limited clus- Berry dilution? ter formation in the . Similar The ET25 treatment resulted in carryover effects in reduced vine the lowest yield, smallest berries capacity and yield were observed and smallest number of berries in a long-term trial in Argentina per cluster (see table “Yield and with Malbec.11 Yield Components”). Although berry weight was smaller in the Canopy microclimate ET25/100 treatment than fruit in To understand treatment differ- the ET and ET treatments, 70 100 aquadolce was developed to retain the maximum amount of confectionery oak compounds, which INTERIOR AND EXTERIOR CLUSTER TEMPERATURES offer aromatic richness and a softer, rounder, more 122 elegant experience on the palate.

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Temperature (˚F) Temperature aquatexture helps balance the fruit and structure of wines, bringing just the right amount of barrel 50 ET Exterior Interior 25 aromatics, toast, roundness, complexity and structure Ambient ET100 Exterior Interior 32 when used during aging or finishing. 245 246 247 248 249 2 5 0 Day of the year Ambient temperature and simulated cluster temperatures are depicted one week after véraison of Cabernet Sauvignon vines irrigated at various fractions Glenn Jeffries | 707.259.4988 of crop evapotranspiration (denoted by subscripts of ETc) in 2011. Each line www.oaksolutionsgroup.com represents the average of eight iButtons placed on both the exterior and interior faces of different clusters and logging temperature at 10-minute intervals. The ambient temperature was logged hourly by an on-site weather station.

June 2017 WINES&VINES 51 GRAPEGROWING PRACTICAL WINERY & VINEYARD yields were similar and small berries were much of a good thing when it comes to water way to reduce weed growth and the need for achieved without the penalties that accompa- stress and wine grapes. herbicides or cultivation. nied the severe deficit treatment. Supplying only 25% ETc between fruit set

Although both the ET25 and ET25/100 vines and harvest was too low, economically unsus- How low can you go? received the same amount of water early in tainable and led to a decline in vine capacity While earlier field trials by the same re- the season, the ET25 treatment had smaller and yield, according to the report. The 25% searchers had found that 35% ETc is via- berries than the ET25/100 vines. One explana- ETc vines had the most open canopy and ble,4,10 the present work established that 25% tion for this is that the 100% ETc supplied at consequently the highest cluster temperatures ETc is not economically sustainable in the véraison may have alleviated pre-harvest of the four irritation treatments, the greatest arid climate of eastern Washington, where berry dehydration.12 light intensity in the fruit zone and the small- the study was conducted. Additionally, because the increase in water est yield (almost half of the other regimens The results of this study help to better un- occurred when berries ranged from blue to in two of the three years). derstand the role that deficit irrigation plays in green, research from Keller’s group suggests “By contrast, limiting water to 25% ETc fruit quality. Small berry size is often cited as that photosynthetic recovery following the early during the berry-development period and the primary reason for fruit composition im- increased water supply may increase then increasing it to 100% ETc at véraison provements made by water deficit. But this supply via flow to the berries.13 In- proved to be an interesting irrigation-manage- study suggests that potential changes in fruit deed, total soluble solids (berry ) were ment option for Cabernet Sauvignon,” the re- composition due to water deficit may be indi- intermediate in the ET25/100 vines (242 mg) port states. This treatment limited vigor and rectly related to altered canopy size and micro- compared to 213 mg for ET25 and 282 mg for berry size while keeping yields moderate—and climate, in addition to decreased berry size.

ET70 or ET100. without the penalties as in the severe deficit treatment. Moreover, the ET25/100 treatment Melissa Hansen, research program manager for the Deficit irrigation conserved irrigation water. Washington State Wine Commission, grew up in Cali- without yield penalties An indirect benefit of using less water than fornia’s Central Valley and worked in California’s grape

Though moderate water deficit in red wine ET100 was . and tree fruit industries before moving to Washington. grapes is generally associated with positive Although this study did not quantify weed She covered grapes and tree fruit for the Yakima, Wash.- attributes such as fruitier and less vegetal growth, visual observations found more abun- based Good Fruit Grower magazine for 20 years before aromas, more pigments and dant weeds in the fully watered vines of ET100 her current position. sometimes lower astringency when compared compared to other treatments. With its mea- to where abundant water is ap- ger application of water from after fruit set The references for this article are available online at winesandvines.com plied,13 the research showed there can be too to véraison, the ET25/100 treatment may be a

52 WINES&VINES June 2017