GRAPEGROWING WINE EAST Determining the Best Cold Hardiness Measurement Nearly two-dozen grape varieties tested for ability to withstand below-freezing temperatures A variety trial plot (shown here before the polar By Imed Dami vortex of 2014) helped researchers understand each variety’s cold tolerance.

rapes contribute more than Therefore, the limitation imposed by the searchers also investigated whether there are $5 billion per year to the sensitivity of the vinifera species has an im- better ways to estimate the CH of vines. economy of the eastern pact on the sustainable growth of the indus- Buds were collected from each variety bi- United States, and the grape try, and it is critical for growers to know the weekly between September and March for three and wine industries have cold hardiness (CH) of the newly introduced dormant seasons (2011-14) and placed in a been expanding rapidly in varieties, in addition to the standard viticul- freeze chamber. The freeze chamber was set up Gthose regions. However, the sustainability of tural and enological characteristics. Sub- indoors to conduct freezing tests that would profitable yet cold-sensitive cultivars is limited freezing temperatures below -20° C (-4° F), simulate cold damage in the vineyard. Cold by climatic constraints, primarily lethal freez- often damage V. vinifera, which is mostly hardiness was determined by thermal analysis ing temperatures that can drop well below adapted to a Mediterranean-type climate. and expressed by the lethal temperature that

0° F. The severe economic losses that result Nonetheless, information about the CH of kills 50% of the bud population, or LT50. from freezing injury continue to be a major the newly introduced vinifera varieties has We evaluated three methods to express cold setback for the continuous growth of the not been available. hardiness: grape and wine industries in this region. 1) Standard method: computing mid-winter In 2014, the polar vortex caused temperatures Ohio’s cold-hardiness study hardiness based on a single and lowest to drop to critical levels for grape survival and The purpose of the study at the Ohio Agricultural LT 50 value; resulted in widespread damage and crop losses Research and Development Center in Wooster 2) Modified standard method: computing across the Midwest and eastern United States. was to determine the cold hardiness of 23 variet- mid-winter hardiness based on multiple Ohio experienced the worst damage and crop loss ies of recently introduced V. vinifera grapes so lowest LT values; in 20 years (valued at $12 million). This problem that grapegrowers and nurseries would have a 50 was exacerbated with whole-vine loss of cold- better understanding of the ability of those variet- 3) Annual freezing tolerance (AFT, or an- sensitive species V. vinifera, which have dominated ies to survive the harsh winter conditions in the nual cold hardiness): computing LT50 new plantings in the past 15 years in Ohio. Midwest and northeastern United States. Re- not only during mid-winter, but also during fall acclimation and spring KEY POINTS deacclimation. The Ohio State University’s OARDC tested the cold hardiness of 23 varieties newly introduced in Mid- west and northeastern vineyards using three methods of testing: the standard method of indexing Cold hardiness mid-winter bud cold hardiness (LT ); a modified standard method based on regression analysis; and 50 of 23 varieties researchers developed a new cold hardiness index, the relative annual freezing tolerance (RAFT), As expected, all 23 varieties behaved similarly which compares annual freezing tolerances of these varieties with that of a benchmark variety. and followed the typical U-shaped pattern of These 23 varieties can be grouped into two distinct groups of most cold hardy (Gamay Noir, Chardon- bud cold hardiness, which consists of three nay, Pinotage, Regent and Rotberger) and most cold sensitive (Barbera, Durif, Lagrein, Sangiovese, stages: fall cold acclimation (September to Syrah, Tempranilllo and Teroldego). The remaining 11 varieties fall in the gray area, and their CH may December), followed by maximum hardiness shift one way or another depending on other factors such as weather and cultural practices in mid-winter (January to February) and deac- climation in late winter and early spring. The findings of this study provide research-based information for nurseries and on cold hardiness of However, there were differences of cold new varieties they sell. They will also guide growers making decisions on suitable varieties for sites hardiness among varieties. Gamay Noir, Rot- where winter damage is a concern. berger, Pinotage and Regent were generally

164 WINES&VINES January 2017 WINE EAST GRAPEGROWING among the most cold-hardy variet- a given variety’s cold hardiness and COLD HARDINESS FOR THREE SEASONS ies with the lowest LT50 values, has been reported as such by re- while Tempranillo, Lagrein, Bar- search institutions in several states 0 bera and Durif were among the conducting this type of work in the most cold-sensitive varieties with past 30 years. In Ohio, we found Gamay Noir Tempranillo the highest LT50 values. that mid-winter cold hardiness var- Also, this study showed that not ied between LT = -18.3° C Dolcetto 50 -5 all varieties acclimated, de-accli- (-0.9° F) and LT50 = -24.8° C (-12.6° mated or reached maximum hardi- F). “Cold Hardiness Based on Stan- ness at the same time and same dard Method” shows that Gamay level. “Cold Hardiness for Three Noir was the most cold-hardy vari- -10 Seasons” shows three varieties to ety, whereas Tempranillo was the illustrate this finding. Gamay Noir most cold sensitive in this study. (°C) (°C) was the most cold-hardy variety We also found that the standard 50 (lowest LT in mid-winter) and method has a few drawbacks: a) LT 50 -15 was the quickest (steepest slope) the lowest LT50 in mid-winter is to cold acclimate in the fall. Tem- generally based on a single LT50 pranillo was the most cold sensitive measurement; b) not all varieties (highest LT in mid-winter) and reached their maximum cold hardi- 50 -20 was the quickest to deacclimate in ness on the same date; and c) wide late winter. Dolcetto acclimated the variability of LT50 within each cul- slowest in the fall and reached tivar made it difficult to distinguish maximum cold hardiness later cold hardiness between two variet- -25 than Gamay and Tempranillo. ies if the difference between their 252 287 312 341 3 46 82 LT was less than 3° C (5.4° F). 50 Day of Year Methods of assessing During the polar vortex in cold hardiness January and February 2014, the Cold hardiness changes of Gamay Noir, Dolcetto and Tempranillo in the Standard method: Mid-winter bud research vineyard in Wooster ex- Wooster research vineyard by day of year for three seasons. Plot points cold hardiness (LT ) is the most perienced successive low tempera- 50 represent LT50 (lethal temperature that kills 50% population) collected for three commonly used index to estimate tures that dropped below the seasons. Note the U-shaped trend lines of cold hardiness in the three varieties.

MATERIALS AND METHODS

Varieties tested: Vitis vinifera—Arneis, Barbera, Cabernet Franc, Cabernet Sau- vignon, Carmenère, Chardonnay, Dol- cetto, Durif, Gamay Noir, Kerner, Lagrein, Malbec, Malvasia Bianca, Merlot, Pino- tage, Rotberger, Sangiovese, Sauvignon Blanc, Siegerrebe, Syrah, Tempranillo, Teroldego; and Vitis sp.—Regent (a Ger- man cross of Diana and Chambourcin)

Rootstock: 101-14 Mgt. (V. riparia × V. rupestris)

Location: OSU Research Vineyard at OARDC in Wooster, Ohio (lat. 40°44’16” N; long. 81°54’12” W)

Elevation: 1,165 feet above sea level

USDA Plant Hardiness Zone: Zone 6a (-10° F to -5° F).

Spacing: 9 feet x 6 feet (row x vine)

Training: Bilateral low cordon (40-inch height) with vertical shoot position (VSP)

Pruning: Spur pruning to 30 buds per vine (two to three buds per spur)

Janaury 2017 WINES&VINES 165 GRAPEGROWING WINE EAST

COLD HARDINESS BASED ON STANDARD METHOD -14

-16

-18

-20

(°C) (°C) -22 50 LT -24

-26

-28

-30

Syrah Durif Arneis Regent Lagrein Merlot Dolcetto Malvasia Barbera Pinotage Rotberger Teroldego Gamay Noir Carmenère Siegerrebe Sangiovese Tempranillo

Sauvignon Blanc Cabernet Sauvignon Cultivar

Cold hardiness is calculated based on the lowest LT50 of each variety in mid-winter. ANNUAL FREEZING TOLERANCE FOR CALCULATING COLD HARDINESS -13

-14

-15

-16

-17 AFT (°C) AFT (°C) -18

-19

-20

Syrah Durif Regent Arneis Merlot Kerner Malbec Dolcetto Lagrein Barbera Pinotage Teroldego Rotberger Siegerrebe Carmenère Gamay Noir Chardonnay Sangiovese Tempranillo Cabernet Franc Malvasia Bianca Sauvignon Blanc Cabernet Sauvignon Cultivar

The annual freezing tolerance (AFT) is based on computing LT50 throughout the dormant season.

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166 WINES&VINES January 2017 WINE EAST GRAPEGROWING critical temperature of -20° C (-4° F) five times RELATIVE ANNUAL FREEZING TOLERANCE (-20.1° C [-4.2° F] to -24.5° C [-12.1° F]). All 23 varieties sustained trunk damage, with the 3 exception of Regent. The extent of whole-vine damage was assessed in late summer 2014, and vine death was recorded. 2 In general, variety vine mortality corre- sponded to the computed LT50. For example, 1

Tempranillo, with the highest LT50 (most cold sensitive), sustained the highest vine mortal- Merlot Gamay Noir Pinotage Rotberger Chardonnay Regent Malvasi Siegerrebe Carmenère Cabernet Sauvignon Sauvignon Blanc Cabernet Franc Malbec Arneis Dolcetto Kerner ity (100%), while Gamay Noir, with the lowest 0 Durif RAFT (˚C) LT 50 (most cold hardy), sustained the least Syrah Lagrein Barbera

vine mortality (17%). Therefore, the 2014 -1 Teroldego Tempranillo winter damage sustained in the vineyard co- Sangiovese incidently confirmed our cold hardiness de- -2 termination in the laboratory. Modified standard method: This method based on regression analysis was explored to -3 alleviate the limitation of the standard method. Cultivar It proved superior to the standard method since Annual cold hardiness is shown relative to that of Merlot, computed by subtracting the annual mean LT50 of it distinguished the CH between two varieties each variety from that of Merlot (baseline 0º C). at 2° C (3.6° F). However, it was not possible to obtain estimates for all varieties tested since trary measure of CH, which will vary with time of -2.5° C, meaning Gamay is more hardy than more LT50 observations were needed. and space. In other words, one cannot extrapo- Merlot by ~2.5° C. However, Barbera has a RAFT

A new index–the AFT: The annual freezing late LT50 published values determined in one of ~1.5° C, meaning Barbera is less cold hardy tolerance (AFT) or annual cold hardiness con- location (e.g., in New York) to equate the ac- than Merlot. In other words, if a region is known sisted of averaging LT50 throughout the dor- tual LT50 in another region (e.g., in Missouri). to have Merlot as a borderline variety for winter mant season. AFT has several advantages over This may be common knowledge within the survival, then a grower should not even think the standard method currently used by nurser- research community, but it is frequently misin- about planting Barbera in the same region. ies, growers and researchers. First, AFT pro- terpreted by vineyard owners and nurseries. Finally, among the three methods, AFT pro- vides an estimate of CH across all stages of cold To overcome this issue, we propose to com- duced the best prediction of whole-vine CH. acclimation (i.e., autumn acclimation, mid- pare the CH of varieties to a standard or bench- winter maximum hardiness and spring deac- mark variety grown in the same location. We Imed Dami is professor of viticulture in the Department climation). As a result, the AFT had the least call the new index the relative annual freezing of Horticulture and Crop Science, Ohio Agricultural Research and Development Center, The Ohio State LT 50 variability, and differences between two tolerance, or RAFT. Merlot was selected since varieties were detected at the 1° C (~ 2° F) it is a common variety grown in different re- University, in Wooster, Ohio. level (see “Annual Freezing Tolerance for Cal- gions worldwide and has mid-range CH. The author thanks project participants Dr. Yi Zhang and culating Cold Hardiness”). Second, the stan- The figure above illustrates RAFT with nega- Shouxin Li and the USDA-NIFA (agreement No. 2010- dard method provides an LT50 of a given variety tive numbers indicating more cold-hardy varieties 51181-21599), Ohio Grape Industries Program and OSU determined on a specific date and location. and positive numbers more cold-sensitive variet- Department of Horticulture and Crop Science for their EasternWineLab_Mar09.qxp 1/22/09 9:47 AM Page 1 Hence, this absolute value provides an arbi- ies than Merlot. For example, Gamay has a RAFT financial support.

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