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How does delaying spur-pruning to the onset or after bud burst impact vine performance? Insights from recent studies

By Michela Centinari

Now that harvest is finally over and wines are tucked away in the cellar, it is time to prepare for the next year. One of the first concerns that many growers feel in a new growing season is that worry of spring frost and the associated potential risk of vine injury. In the spring of 2016, for example, an unusually warm March was followed by a very cold start to the month of April, which resulted in damaging frost incidences in some vineyards of the Mid-Atlantic region.

Susceptibility to frost injury increases with advanced phenological growth stage [1], therefore, growers and scientists have explored different techniques for delaying bud burst of grapevines to increase the chance of avoiding spring frost damaging events. Vegetable-based oils (e.g., Amigo oil) can be sprayed on the canes/buds during the winter to slow down bud de-acclimation and delay the resumption of vegetative growth in the spring [2; 3; study at Penn State]. Delaying pruning until late winter can also be used to delaying bud burst of vines growing in frost prone areas.

Canes of cordon-trained vines can be pruned to 2-3 node spurs late in the winter or even when apical buds begin to open to delay bud burst of basal buds. Due to the strong apical dominance of Vitis vinifera cultivars, apical buds of an unpruned cane tend to burst first, which inhibits development and growth of median and basal buds [4] (Figure 1).

Figure1. Spur pruning vines while the apical buds are bursting. Photo source: McGourty, The case for double—pruning. Practical Winery &Vineyard.

Figure1. Spur pruning vines while the apical buds are bursting. Photo source: McGourty, The case for double—pruning. Practical Winery &Vineyard.

What may happen if we wait until the onset of bud burst or even later to prune the vines?

Spur-pruning the vines when the apical buds of un-pruned canes are already open may not only delay bud burst of the basal nodes, but may also postpone other phenological growth stages such as bloom, fruit-set, or even veraison with potential consequences for vine yield and fruit chemical composition at harvest [4].

I recently read two articles on this topic published in the American Journal of Enology and Viticulture (Post-bud burst spur-pruning reduces yield and delays fruit sugar accumulation in Sangiovese in central Italy [5] ) and in Frontiers in Plant Sciences (Phenology, canopy aging and seasonal carbon balance as related to delayed winter pruning of Vitis vinifera L. cv. Sangiovese grapevines [6]).

The studies described in these articles aimed to assess if and how delaying winter spur-pruning of Sangiovese vines to the bud swelling stage or later, after bud burst, impacted the annual growth cycle of the vines and its productivity.

The studies were conducted in Italy and the researchers were specifically interested in assessing if vines pruned around or after bud burst exhibited a delay in grape ripening as compared to those pruned during the winter, resulting in lower sugar accumulation and higher acidity in the fruit at harvest. A steady trend of increased warming is, indeed, pushing some Mediterranean grape growing regions toward accelerated ripening [7], which could lead to excessive or overly fast sugar accumulation in the fruit, high alcohol in the wine, unacceptably low acidity, high pH, and also atypical grape flavors and aromas [5].

Although excessive or overly fast sugar accumulation may not be a problem in our region, it’s still important to understand if delaying winter pruning to extremes could be used to delay bud burst and reduce risk of frost damage, as well as the impact this practice may have on vine yield, and fruit and wine chemistry. This is a topic of further interest in light of changing climatic conditions and the potential increase of unpredictable weather patterns like early spring warming and late spring frosts [8].

Below, I will summarize the two previously mentioned studies emphasizing results which can be of interest to wine grape growers in our regions.

Both studies were conducted on mature Sangiovese (Vitis vinifera L.) vines. The first study was established in a commercial vineyard in central Italy, whereas the second study was conducted on vines growing outdoors in 10-gal pots at a research station in northern Italy. Groups of vines were assigned to different pruning treatments. Vines assigned to the standard grower practice treatment were spur-pruned to 2 basal nodes during the winter when buds were dormant. Vines assigned to the other treatments were spur-pruned at more unusual times from the bud swelling to full bloom (Figures 2 and 3A).

Figure 2. Phenological growth stages of the apical shoot at the time vines were pruned to 2-node spurs. *BBCH scale was used to assess phenological stages [9] in studies described below.

Figure 2. Phenological growth stages of the apical shoot at the time vines were pruned to 2-node spurs. *BBCH scale was used to assess phenological stages [9] in studies described below.

Did delaying vine spur-pruning to after bud-burst consistently delay the whole annual growing cycle?

Basal buds of Sangiovese vines spur-pruned when apical shoots were about 1.6″ long (called late pruning treatment; Figure 3A central panel) burst 17 days later than those of vines pruned in the winter, when buds were dormant (called standard pruning treatment; Figure 3A left panel). Pruning the vines even later, when apical shoots were about 4.7-5.5″ long (called very-late pruning treatment;  Figure 3A right panel) extended the delay in bud burst to 31 days as compared to vines pruned in the winter Unfortunately no phenology data were recorded for vines pruned at bud swelling stage (study 1).

The delay in phenological growth stage decreased over the season. For example, late-pruned and very-late pruned vines reached veraison 3 and 13 days, respectfully, after those pruned in the winter (Figure 3C). Shoots of vines pruned after bud burst developed later in the season under higher air temperature than those of vines pruned during the winter. Greater air temperature may have helped shoots of late- and very-late pruned vines to reach bloom and veraison in fewer days as compared to those pruned earlier [6].

By harvest the delay was fully off-set for the late-pruned vines: they reached the sugar level set for ripening (~ 19 ºBrix) three days before those pruned in the winter. Grapes of very-late pruned vines reached 19 ºBrix 6 days after those pruned in the winter.

Figure 3. Vine appearance at the time of pruning (A) and at bloom (B) and veraison (C). Note: standard winter pruning was taken as a reference for bloom and veraison. Photo courtesy Dr. Stefano Poni (professor of Viticulture, Universita’ Cattolica del Sacro Cuore, Italy).

Figure 3. Vine appearance at the time of pruning (A) and at bloom (B) and veraison (C). Note: standard winter pruning was taken as a reference for bloom and veraison. Photo courtesy Dr. Stefano Poni (professor of Viticulture, Universita’ Cattolica del Sacro Cuore, Italy).

Spur-pruning vines after bud burst significantly reduced crop yield compared to standard winter pruning

Vines pruned at bud swelling growth stage had similar crop weight, number of clusters per vine, and cluster weight than those pruned when buds were still dormant. Pruning vines after bud burst, however, reduced yield as compared those pruned during the dormant season. For example, late pruned vines (spur-pruned when apical shoots were about 1.6″ long; Figure 3A central panel) had 26% lower crop yield as compared to those of the standard pruning control group (spur-pruned before bud burst). Reduction of crop yield was related to lower cluster weight and lower number of berries per cluster. While there is not a clear explanation on why late-pruned vines had fewer berries per cluster, several hypotheses were presented including increased production of gibberellins during the initial flush of growth in the late-pruned vines [6].

Waiting even longer to prune the vines had a detrimental effect, reducing not only cluster weight but also the number of clusters per vine. For example, vines pruned to two basal nodes when the apical shoots were already flowering had no crop at harvest. When vines were pruned so late the basal shoots did not develop flowers and remained vegetative after pruning. I am not sure why any growers would want to wait until bloom to prune the vines, but it’s still interesting to see how such a drastic treatment may limit sources of carbohydrates for developing cluster primordia [5].

Although uncertainty still exists, the authors suggested that delaying spur-pruning until after bud burst, but not to extremes, may have the potential for reducing crop yield in high-yielding cultivars such as Sangiovese planted in specific regions of Italy. However, long-term field studies are necessary to assess if it is possible to calibrate winter pruning date for managing yield reductions and/or fruit maturation rate.

Did delaying vine spur-pruning to bud swelling stage or after bud burst consistently impact fruit chemistry?

The effect of the timing of spur-pruning on fruit composition at harvest varied between studies and with the extent of the pruning delay. For example, Sangiovese vines late pruned (apical shoots 1.6″ long) had higher total soluble solids (+ 1 °Brix), total anthocyanins and phenolics than winter-pruned vines. However, vines growing in a commercial vineyard (study 1) and spur-pruned to two basal nodes later in the season, when inflorescences of apical shoots were already swelling (Figure 3C), had lower sugar concentration (-1.6 °Brix) and higher TA (+1.8 g/L tartaric acid) than those pruned during the winter, but at the same time they also had higher anthocyanins and phenolic concentrations.  This result suggests that spur-pruning canes after bud burst may decouple the accumulation patterns of total soluble solids and anthocyanins, phenolic metabolites. This could be intriguing for growers trying to delay fruit sugar accumulation and acid degradation, while maintaining wine color, but on the another hand it could also come with a  reduction in crop yield, quantified to over 50% in this study [5].

Did delaying winter spur-pruning have negative carry-over effects on the following season?

Pruning vines at the bud swelling stage did not have negative effects on vine growth in the following year. It did not impact bud fertility (number of clusters per shoot) or winter carbohydrate storage, which is important for winter vine survival and following year resumption of growth. However, pruning the vines to two-nodes after bud burst, specifically when inflorescences of apical shoots were already swelling (Figure 3C), reduced bud fertility by 50% in the following year. Those vines were able to recover once standard winter pruning was applied again at the end of the study.

In conclusion:

These studies conducted on Sangiovese vines grown in Italy found that:

  • Winter spur-pruning can be applied up to bud swelling without adversely affecting vine yield, grape composition at harvest or bud fertility in the following year.
  • Vines pruned after bud burst show pronounced delay in shoot development at the beginning of the season, which increased as the pruning time was further delayed. Under the warm conditions of these studies the delay in phenological growth stage decreased or even disappeared over the season. This could be partially explained by the fact that late-pruned vines needed less time than vines pruned during the winter to reach maximum photosynthesis efficiency.
  • Delaying spur-pruning to after bud-burst may reduce vine yield, decrease sugar accumulation and bud fertility in the following year.

Delaying winter pruning of vines located in frost prone areas to the onset of bud burst or shortly after that may be used as frost avoidance technique. However, we need to further understand how a delay in shoot development and potentially a shorter growing season (number of days from bud burst to harvest) may impact fruit ripening, yield component, vine over-winter carbohydrate storages and susceptibility to winter cold temperatures, as well as the following year growth. The studies summarized here were conducted in a warm region with a growing season longer than many areas of Pennsylvania.  Further research is necessary to corroborate those results under our regional climatic conditions.

 

Literature cited

  1. Centinari M, Smith MS, Londo JP. 2016. Assessment of Freeze Injury of Grapevine Green Tissues in Response to Cultivars and a Cryoprotectant Product. Hortscience 51: 1–5.
  2. Dami I, and Beam B. 2004. Response of grapevines to soybean oil application. J. Enol. Vitic. 55: 269–275.
  3. Loseke BJ, Read PE, and Blankenship EE. 2015. Preventing spring freeze injury on grapevines using multiple applications of Amigo Oil and naphthaleneacetic acid. Scientia Hort. 193: 294–300.
  4. Friend AP, and Trought MCT. 2007. Delayed winter spur-pruning in New Zealand can alter yield components of Merlot grapevines. J. Grape Wine Res. 13: 157–164.
  5. Frioni T, Tombesi S, Silvestroni O, Lanari V, Bellincontro A, Sabbatini P, Gatti M, Poni S, Palliotti A. 2016. Post-bud burst spur pruning reduces yield and delays fruit sugar accumulation in Sangiovese in central Italy. J. Enol. Vitic. 67:419–425.
  6. Gatti M, Pirez FJ, Chiari G, Tombesi S, Palliotti A, and Poni S. 2016. Phenology, canopy aging and seasonal carbon balance as related to delayed winter pruning of Vitis vinifera cv. Sangiovese grapevine. Frontiers in Plant Sciences 7:1–14. Article 659.
  7. Jones GV, White MA, Cooper OR, and Storchmann K. 2005. Climate change and global wine quality. Climatic Change 73: 319–343.
  8. Mosedale JR, Wilson RJ, and Maclean IMD. 2015. Climate change and crop exposure to adverse weather: Changes to frost risk and grapevine flowering conditions. PLoS One 10:e0141218.
  9. Lorentz DH, Eichorn KW, Bleiholder H, Klose R, Meier U, and Weber E.1995. Phenological growth stages of thegrapevine (Vitis vinifera ssp. vinifera). Codes and descriptions according to the extended BBCH scale. Aust. J. Grape Wine Res. 1, 100–103.
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Understanding and Preventing Spring Frost/Freeze Damage – Spring 2016 Updates

By Michela Centinari

The last month has provided a temperature roller-coaster going from a very, perhaps exceptionally, warm March to a cold beginning of April. Many grape growers are keeping their fingers crossed hoping to escape frost injury. As far as I am aware, no budbreak has been observed for grapevines grown in central Pennsylvania, but budbreak may be close in other PA locations. It looks like a good time of year to review some basic concepts related to post-budbreak freeze injury and frost protection options available for grape growers.

Freeze and Frost

We often use the terms “frost” and “freeze” interchangeably to describe a meteorological event, specifically related to air temperature dropping below 32°F (0 °C). However, “frost” and “freeze” definitions reported in the literature are variable and sometimes confusing. I personally like the definitions used in the book: Frost protection: Fundamentals, practice, and economics [Food and Agriculture Organization of the United Nations (FAO), 2005; 1].  In this book frost is   defined as “the occurrence of an air temperature of 0 °C or lower, measured at a height of between 1.25 (49.2 in) and 2.0 m (78.7 in) above soil level, inside an appropriate weather shelter”, while freezeoccurs when water within the plant freezes”.

In other words a frost becomes a freeze event if ice forms within the plant tissues.

Keep in mind that:

  • It is the ice formation inside the plant tissue rather than low temperatures per se that cause the damage. The formation of ice crystals can be either inter-cellular (space between cells) or intra-cellular (within the protoplasm of cells), the latest causing cell death [1] (Figure 1). The general hypothesis is that during spring frosts, freeze injury is mainly caused by inter-cellular rather than intra-cellular ice formation [1, 2]. The formation of inter-cellular ice crystals produces a water vapor deficit/gradient between the interior and the exterior of the cells. As a result, water migrates from the inside to the outside of the cells and deposits on the ice crystals formed in the inter-cellular spaces. If ice continues to grow, the cells become more desiccated and lose their turgor [3]. Freezing-induced dehydration can also permanently damage the structure of cell membranes and other cellular components. This usually causes a flaccidity and/or discoloration of the damaged tissue [4]. Thus, the current view is that dehydration injury is the main cause of frost damage. [2].
Figure 1. Ice formation in the extra-cellular space. Source: http://ilc.royalsaskmuseum.ca/ilc1/pages/12c/13f/pf13fp2p1.htm

Figure 1. Ice formation in the extra-cellular space. Source: http://ilc.royalsaskmuseum.ca/ilc1/pages/12c/13f/pf13fp2p1.htm

  • Water within plants doesn’t always freeze during a frost event. Plants have developed avoidance strategies to avoid ice formation in the tissues, for example, by supercooling, and tolerance strategies (e.g., solute content of the cells) to survive inter-cellular ice formation without irreversible damage of the plant tissue [1].

Critical temperatures

The critical temperature is defined as “the temperature at which tissues (cells) will be killed and determines the cold hardiness levels of the plant” [5]. Many factors affect the temperature at which damage occurs including: type of plant tissue, stage of phenological development of the bud/shoot, dew point and surface moisture, probability of an ice nucleation event and pre-frost environmental conditions [6].

Why budbreak is considered the onset of the most susceptible period for cold injury?

Growing organs have a high water content, which makes them susceptible to the formation of ice at freezing temperatures. Air temperature of –2, –3°C can permanently damage green tissues [6]. Early spring growth is particularly susceptible to freeze injury. Freezing tolerance remains low during the most of the growing season and gradually increases late summer and fall (cold acclimation) and reaches its maximum peak in midwinter [6]. In midwinter grapevines are able to tolerate freezing temperature through a complex process called deep supercooling. For example, the cells within the dormant bud become resistant to lower temperature through dehydration (i.e., movement of water to inter-cellular spaces) and accumulation of so-called cryoprotectant (e.g., soluble sugars and proteins). Those compounds lower the freezing point of the water within the plant tissue and stabilize cell membranes [6] making the dormant buds able to survive temperatures well below freezing. Also, during the dormant season buds are thought to be disconnected or weakly connected to the vine’s vascular tissues, which limit their potential to take up water [7].

There are two main types of frosts

Advective frost: an advective frost is usually a regional weather event. It occurs when strong, cold winds (colder than the critical temperature) blow into a region day and/or night. The rapid, cold air movement “steals away the heat in the plant causing freeze damage” [5]. Unfortunately there is very little which can be done to protect against an advective frost. For example, wind machines are useless during an advective frost event.

Radiation or radiative frost: A radiation frost is the most common type of frost for many grape growing regions. Luckily, a radiation frost is also the easiest to protect against during a frost event. It occurs when a dry, cold air mass moves into an area when there is almost no cloud cover and no wind at night. Because plants and soil are warmer than the sky temperatures they will “radiate” heat back to their surrounding space and become progressively colder than the air [5].

Radiative and advective frosts may occur simultaneously, the classification depends on which is one is dominant (Table 1).

Table 1. Frost event terminology and typical characteristics

Table 1. Frost event terminology and typical characteristics [source FAO, 2005; 1]

What are the options available to protect your vines from freeze injury?

Passive or indirect methods (risk minimization)

Passive methods are avoidance strategies, efforts to reduce the probability and risk of freeze damage.

  • Site selection

You have probably already heard this, but it cannot be said too many times: “The best time to protect your vineyard from frost injury is before it is planted” [5]. Cold air flows downhill so mid-slope locations are warmer if there are no obstacles to cold air flow [8] (Figure2).  Thus, when evaluating potential sites for establishing your vineyard, look for a site with good air drainage. Get historic records of low temperatures, number of frost-free days, and accurate information on percent slope, aspect or exposure and elevation. You can contact your local county Cooperative Extension office for information about site suitability for a vineyard, or utilize these resources here: http://bit.ly/VydSelectionTools.

Figure 2. Cold air drains downhill and settles in low spots, where frost damage is most likely

Figure 2. Cold air drains downhill and settles in low spots, where frost damage is most likely [source FAO, 2005; 1]

  • Cultivar selection

Grapevine cultivars may vary in the average day of budbreak by up to two weeks [8]. To avoid or reduce the risk of freeze injury plant cultivars with early budbreak in the location within the vineyard with the lowest risk of frost.

  • Training system choice

Many factors related to fruit quality and economics influence the choice of a training system. With regard to risk of freeze damage, a training system which places the buds high on the trellis may reduce frost hazard (Figure 3). Frost hazard is reduced by up to 0.36 °C each 10 cm (3.94 in) above the soil level [9].

Figure 3. Comparison of freeze damage in Noiret (Vitis hybrid) shoots after a spring frost event. The vines were trained on (a) top wire cordon (6 ft. from the ground) and (b) vertical shoot position (3 ft. from the ground) (b). The two vines (a and b) are in adjacent, parallel rows.

Figure 3. Comparison of freeze damage in Noiret (Vitis hybrid) shoots after a spring frost event. The vines were trained on (a) top wire cordon (6 ft. from the ground) and (b) vertical shoot position (3 ft. from the ground) (b). The two vines (a and b) are in adjacent, parallel rows.

  • Pruning choices
    • Delay pruning: Pruning too early may accelerate budbreak. Thus, prune as late as possible in frost prone areas of your vineyard.
    • Double pruning: this is another option to delay budbreak for cordon-trained vines. The first step is to prune the canes to long spurs, 5 to 8 buds long [8]. Buds at the end of the canes will open first and suppress the growth of basal buds (Figure 3). After frost risk has passed, do a second and final pruning to cut back the long spurs to two-bud spurs. Likewise, for cane-pruned vines one option is to leave long canes (first step) and cut them back (second step) to the desired bud number later, after the frost risk has passed. Some growers opt to retain extra canes as an insurance measure and then remove them later.
Figure 4. Budbreak of apical buds and suppression of basal buds in double-pruning. Source: Ed Hellman, Texas AgriLife Extension [8]

Figure 4. Budbreak of apical buds and suppression of basal buds in double-pruning. Source: Ed Hellman, Texas AgriLife Extension [8]

  • Delaying budbreak by chemical means

Application of vegetable-based oils (e.g., Amigo oil) at nontoxic rates can slow bud de-acclimation and delay grapevine budbreak anywhere from 2 to 20 days depending on several factors including variety, number of applications and coverage [10,11].  Those oils are called “dormant oils” because they need to be applied when the buds are dormant. If you are interested in trying Amigo oil or a similar type of oil in your vineyard, begin with a small selection of vines.  Be sure to record phenology, crop yields, fruit composition (Brix, pH, TA) and quality (fruit aromas and flavors, etc.) data for un-sprayed and sprayed vines. In this way, you can assess the impact of oil application on delaying budbreak as well as potential secondary effects on production and fruit quality parameters.

  • Middle-row management

Mowing ground cover short will increase the warming of soil during the day and release slightly more heat during the night [12].  Tall cover crops and weeds may also hinder cold air drainage.

Active or direct frost protection methods (frost management)

Active or direct frost protection strategies are efforts to modify microclimate con­ditions in the vineyard and increase temperatures above injury levels. Some of the most common active frost protection methods are:

  • Wind machines (or fans)

Wind machines are well suited for radiational frosts because they use the inversion of air temperature that develops during this type of frost event. Wind machines pull down warmer air, from above the inversion layer, which may provide from 1 – 3°F of warming [3]. The minimum size vineyard recommended for a wind machine is around 7-10 acres. Wind machines may become profitable on sites where there is a 20% (1 in 5 years) or higher probability of spring frost damaging events [3]. It is worth mentioning that wind machines have been noted to produce a loud noise. Operating costs are higher than for over-vine sprinkling systems, but considerably lower than use of return-stack oil heaters and standard propane heaters [3].

  • Over-vine irrigation

Over-vine sprinkler systems have been successfully used for frost protection since the 1940s [5]. Sprinklers provide a constant amount of water covering the buds and shoots. As water freezes it releases a small amount of heat, which increases the temperature of the plant tissue. The level of protection is proportional to the amount of water applied [5].  If properly used, this method is very effective in protecting grapevines from freeze injury. It is the only active method that doesn’t rely on inversion strength during a frost event [5]. However, on the other hand, keep in mind that it requires substantial water resources, is labor intensive and if the system fails during the night/frost event it can cause more damage than otherwise applying no frost protecting strategy.

Figure 5. Over-vine sprinkler system in use and green tissue ‘wrapped’ in ice. Source: https://www.wineshopathome.com/frost-protection-vineyards-2

Figure 5. Over-vine sprinkler system in use and green tissue ‘wrapped’ in ice. Source: https://www.wineshopathome.com/frost-protection-vineyards-2

  • Heaters

Heating the vineyard for frost protection is a very old practice. In ancient Rome (at least 2000 years ago) growers used to burn piles of pruned wood and other waste to heat their vineyard during spring frost events [5]. Fossil-fueled heaters are rarely used these days because of the high cost of fuel and labor, low heating efficiency and contribution to air pollution.

Unfortunately there is not a perfect strategy which can provide complete frost protection in every situation. Quite often the combination of different methods is the best option.

If you are looking for detailed information about active frost protections strategies please check:

Understanding and Preventing Freeze Damage in Vineyards. 2007. Workshop Proceedings. University of Missouri Extension.

Evans, R.G. 2000. The art of protecting grapevines from low temperature injury. Proc. ASEV 50th Anniversary Annu. Mtg., Seattle WA, 19–23 June. p. 60–72.

Poling, E.B. 2008.  Spring cold injury to winegrapes and protection strategies and methods. Hortscience 43: 1652–1662.

 

Literature cited

  1. Food and Agriculture Organization of the United Nations. 2005. Frost protection: Fundamentals, practice and economics. Vol. 1.
  2. Wilson, S. 2001. Frost management in cool climate vineyards. Final report to grape and wine research & development corporation. Available at: http://www.gwrdc.com.au/wp-content/uploads/2012/09/UT-99-1.pdf
  3. Poling, E.B. 2008. Spring cold injury to winegrapes and protection strategies and methods. Hortscience 43: 1652–
  4. Rodrigo, J. 2000. Spring frosts in deciduous fruit trees—Morphological damage and flower hardiness. Scientia Hort. 85:155–173.
  5. Evans, R.G. 2000. The art of protecting grapevines from low temperature injury. Proc. ASEV 50th Anniversary Annu. Mtg., Seattle WA, 19–23 June. p. 60–72.
  6. Keller, M. 2010. The Science of Grapevines: Anatomy and Physiology. Publisher: Academic Press.
  7. Martinson, T. 2001. How Grapevine Buds Gain and Lose Cold-hardiness. Appellation Cornell, Issue 5. Cornell University Cooperative Extension. Available at: https://grapesandwine.cals.cornell.edu/newsletters/appellation-cornell/2011-newsletters/issue-5/how-grapevine-buds-gain-and-lose-cold
  8. Hellman, E. 2015. Frost Injury, Frost Avoidance, and Frost Protection in the Vineyard. org Available at: http://articles.extension.org/pages/31768/frost-injury-frost-avoidance-and-frost-protection-in-the-vineyard
  9. Trought, M.C.T., Howell, G.S., and Cherry, N. 1999. Practical considerations for reducing frost damage in vineyards. Report to New Zealand winegrowers. Available at: http://www.nzwine.com/assets/sm/upload/eb/fl/ot/sp/frost_review.pdf
  10. Dami, I., and Beam B. 2004. Response of grapevines to soybean oil application. Amer. J. Enol. Vitic. 55: 269–
  11. Loseke, B.J., Read, P.E., and Blankenship E.E. 2015. Preventing spring freeze injury on grapevines using multiple applications of Amigo Oil and naphthaleneacetic acid. Scientia Hort. 193: 294–300.
  12. Wolf, T.K. 2015. Viticulture Notes. Virginia Tech University Cooperative Extension. April 2016.

 

Winter notes: What is going on in your vineyard right now?

By Michela Centinari

This past November and December were surprisingly warm months in Pennsylvania with temperatures rising into the 60s and even 70s °F (Figure 1a, b). In January temperatures dropped to single digits in many eastern U.S. regions [1] followed by a virtual temperature rollercoaster ride in the next months (Figure 1).  On a positive note, viticulture specialists from Virginia Tech (T. Wolf and T. Hatch) did not observe any winter injury in Cabernet Sauvignon and Merlot buds and canes collected on January 8 (northern Virginia) [1].

Figure 1. Daily maximum and minimum temperatures recorded in (A) northeast PA, near Scranton (Lackawanna County) and in (B) south central PA, York Springs (Adams County) during the 2015-2016 fall and winter. Dashed line indicates freezing temperature (32 degrees F).

Figure 1. Daily maximum and minimum temperatures recorded in (A) northeast PA, near Scranton (Lackawanna County) and in (B) south central PA, York Springs (Adams County) during the 2015-2016 fall and winter. Dashed line indicates freezing temperature (32 degrees F).

In many regions of Pennsylvania temperatures in January and February did not reach the critical low threshold (Figure 1B) that tends to injure many of the cultivars grown in PA and we are not currently concerned about winter injury in the majority of the state. However, on February 14 temperatures of -10°F and below were recorded in some areas of the state (report from growers from northeastern PA and Figure 1A).  The lowest temperature in Pennsylvania (-19°F) was recorded in Potter County on February 14 [2].

Although we are not aware of the extent yet, we anticipate winter injury in some of the cultivars grown in those areas.

A few reminders about the cold hardiness process:

In late summer/early fall, cold-tender grapevine tissues produced during the growing season gradually acquire cold hardiness and transition to a cold-hardy stage (known as cold acclimation) as a response to low temperatures and decreasing day length [3] (Figure 2). Bud (and other tissues) cold hardiness reaches its maximum level in mid-winter (known as maximum hardiness). Later in the winter as temperatures increase, the buds begin to lose hardiness (known as deacclimation) [4]. The deacclimation stage ends in budbreak and active growth.

Figure 2. Profile of bud cold hardiness in grapevines.  Figure from Zabadal et al. 2007.

Figure 2. Profile of bud cold hardiness in grapevines. Figure from Zabadal et al. 2007.

It is a well-known fact that bud cold hardiness depends heavily upon the grapevine species and cultivar. For the past two winters (2013-2014; 2014-2015) many growers in the eastern and midwestern U.S. have had the unfortunate opportunity to test this in their own vineyards.  However, in addition to its genotype, the cold hardiness of a specific cultivar is determined by environmental conditions, such as seasonal temperatures and their variation, and by vineyard management practices [3].  It is important to remember that exposure to decreasingly lower temperatures plays a major role in the ability of the vine to acquire its maximum cold hardiness. In other words:

  • The colder the region, the closer a vine gets to its maximum cold hardiness potential [4]. For example, bud cold hardiness of Chardonnay and Riesling in the Finger Lakes region of NY (cooler region) was found to be 2 to 3°F greater than that of the same cultivars grown in Virginia (warmer region) [4] (Figure 3).
Figure 3. Profile of bud cold hardiness of the same grapevine variety in a cold (New York) and a warm (Virginia) region.  Figure from Zabadal et al. 2007.

Figure 3. Profile of bud cold hardiness of the same grapevine variety in a cold (New York) and a warm (Virginia) region. Figure from Zabadal et al. 2007.

  • “The type of winter determines the extent of bud cold hardiness” [5], thus the absolute cold temperature that injures the same cultivar may vary between winters. J. Londo (Geneticist, USDA, Grape Genetics Research Unit, Geneva, NY) reported that the average mid-winter LT50 (lethal temperature for 50% of the buds) for labrusca varied from -24.71 °F in 2012-2013 (defined as a mild-cool winter in upstate NY) to -26.8°F in 2013-2014 (cold winter but with big swings in temperatures) to -26.5°F in 2014-2015 (sustained cold winter) [5]. However, species and cultivars may vary in their response to different temperatures/winters. For example, Tim Martinson, senior viticulture Exten­sion associate at Cornell University, did not observe a decrease in bud hardiness of Riesling vines this year as compared to last year [1].

A few of the things that Penn State Extension recommends to growers:

  • Plan on pruning the hardiest cultivar first and finish with the least hardy [4]. If a cold event occurs late in the winter, like in the middle of February, and cold-sensitive cultivars were not pruned yet, you can still assess bud cold damage and adjust pruning severity accordingly [3]. Leaving extra buds on the vines, and adjusting shoot number after bud break certainly cost growers more money, but it also increases the chance to produce a crop, hopefully close to normal.
  • If your site is an area with moderate to high risk of cold damage events, consider keeping some freeze-tolerant grape cultivars in the mix to reduce the economic downside risk. These are considered cultivars that you can rely upon to “pay the bills.” Cold-hardy cultivars, most of which were released by the breeding program of the University of Minnesota (i.e. Marquette, La Crescent, Frontenac, etc.), are increasing in popularity mostly, but not only, in regions where vinifera or other inter-specific hybrid varieties are not well suited or have struggled to survive and perform well in the long term.

Thanks to The Northern Grapes Project we are gaining a better understanding of how to optimize viticultural, winemaking, business management and marketing practices of these fairly new cold-hardy cultivars. For example, important information on Cost of Production in Cold Hardy Grapes was recently published in the Northern Grapes Project newsletter [3]. The fact that most consumers may still be unfamiliar with those varieties and the wine styles they produce doesn’t necessarily mean that they not will have chance to stand alone as a varietal wine if they produce high quality wines.

  • As Zabadal et al. [4] pointed out Minimizing winter injury is usually not the primary goal of a grape grower; however it must be given attention because of its huge impact on profitability”. Each grower should carefully evaluate if the cost of vine management practices that reduce vine winter injury can increase the business profit.
  • Finally, the most important step, making informed decisions before planting a vineyard and always applying good viticulture practices, which includes keeping the vines healthy and in balance.

Only time will tell what weather conditions the rest of winter and early spring will hold in store for us. However, if your vineyard is located in a frost prone area and you have dealt with spring (post-budbreak) freeze damage in previous years, this would be a good time to review the frost protection practices available and assess if and what options could be used for your specific  situation (see for instance: Frost Protection in Orchards and Vineyards by R. Evans, USDA or Methods of Vineyard Frost Protection by P. Domoto, Iowa State University).

A two-year study was conducted by our research team at Penn State to evaluate “low-cost” frost protection practices for their efficacy to avoid/reduce crop losses due to spring freeze injury. We tested the effect of a vegetable-based oil (Amigo oil) to delay budbreak on two vinifera (Lemberger and Riesling) and two inter-specific hybrid cultivars (Noiret and Traminette). We also tested the impact of KDL (Agro-K’s Potassium Dextrose-Lac®), sprayed shortly (»24 hours) before a frost event, on reducing frost damage to young grapevine shoots. The impacts of Amigo oil and KDL applications on yield components, fruit composition and perceived wine quality were also assessed. Results from this trial will be presented at the 2016 Pennsylvania Wine Marketing and Research meeting: http://bit.ly/PAWMRB2016Symposium.

 

References

  1. Jones McKee L. 2016. Cold hardiness and dormancy, pp58-64. Wines and Vines, March 2016.
  2. Eherts F. 2016. February 2016- Pennsylvania Weather Recap. The Pennsylvania Observer. March 2016.
  3. Martinson, T. 2001. How Grapevine Buds Gain and Lose Cold-hardiness. Appellation Cornell, Issue 5. Available at: https://grapesandwine.cals.cornell.edu/newsletters/appellation-cornell/2011-newsletters/issue-5/how-grapevine-buds-gain-and-lose-cold
  4. Zabadal, TJ, Dami, IE, Goiffinet, MC, Martinson, TE, and Chien, ML. 2007. Winter injury to grapevines and methods of protection. Extension Bulletin E2930. Michigan University Extension.
  5. Londo J. 2015. The Big Chill: bud dormancy and cold hardiness in grape. Northern Grapes webinar, December 8, 2015. Available at: http://northerngrapesproject.org/?page_id=257
  6. Northern Grapes News. 2016. Vol. 5, Issue 1, February 18, 2016. Available at: http://northerngrapesproject.org/?page_id=213

 

All of the cool V&E Research Covered at the 2015 PA Wine Marketing & Research Board Symposium

April 22, 2015 marked the 4th annual PA Wine Marketing and Research Board (PA WMRB) Symposium, held at the Nittany Lion Inn in State College, PA. It was a very successful program, hosting over 86 industry members concurrently with the PWA’s Annual Conference, which was held on both April 21st and 22nd. To read more about the PA WMRB, please visit their website here.

In addition to their other tasks, the PA WMRB financially supports a series of research projects, in which topics vary from a multi-state variety trial to frost protection in the vineyard and into experimentation with sulfur-containing aromatic control in wines. All research topics have been identified as prevalent interests to, or “problem areas” for, Pennsylvania industry members, and results have applicability to all producers.

In an effort to expand awareness of the various research programs taking place at Penn State, the following researchers have summarized their talks from the 2015 Symposium. Most of this research is in their beginning stages, and will continue into the current vintage.

All researchers would like to thank the Pennsylvania grape and wine industry and PA WMRB for their continued support.

 

Clonal Selection and New Interesting Varieties for Pennsylvania

By: Diego Barison, NovaVine, Inc.

  • Two Italian white varieties that show potential for Pennsylvania’s growing region include Tocai Friulano and Moscato Giallo. Tocai Friulana is an early ripening variety, has potential for barrel aging from a winemaking perspective. Moscato Giallo tends to have a subdued aromatic profile compared to other Muscat varieties, but on years that Botrytis pressure is high, it will retain a higher crop yield. Moscato Giallo can be used to make still and sparkling wines.
  • Two Italian red varieties that show potential for Pennsylvania’s growing region are Lagrein and Toraldego. Both varieties are common in northern Italy. Lagrein has a good tannin structure and good acidity, which is preferred for red wine aging. Toraldego has been planted at a few vineyards throughout the Mid-Atlantic region.
  • For more information on grape varieties and clonal selection, you can visit NovaVine’s website.
  • Additionally, Vitibook, co-authored by Diego, is a valuable resource for vineyard owners throughout the U.S.

 

Cold Temperature Stress in Grapevine: Impact of Management Practices and Varietal Selection

By: Maria Smith

  • Cold stress is one of the biggest limiting factors to high quality wine grape production in Pennsylvania.
  • Two types of relevant cold stress in PA include
  1. Dormant-season cold injury
  2. Late spring frost injury
  • Current experiments that I am involved with to evaluate management practices and varietal selection on impacts of cold stress:
  1. Crop load regulation using early leaf removal and cluster thinning, evaluating 2 over-cropping varieties: Chancellor (hybrid) in 2014 and 2015, and Gruner Veltliner (vinifera) in 2015 and 2016.
  2. Variety evaluation in 2015 for tolerance and recovery from late spring frost event. Which includes 4 potted varieties: Marquette (hybrid), Le Crescent (hybrid), Riesling (vinifera) and Lemberger (vinifera). These varieties will be exposed to an artificial frost ‘event’ at 26.5-28°  The physiological response and recovery of vines will be monitored.

 

The Role of Copper in the Evolution of Sulfur Compounds in Wine

By: Gal Kreitman

  • In order to mitigate wine oxidation, reductive winemaking is becoming more commonplace.
  • Reductive winemaking preserves important varietal thiols which provide aroma characteristics of passionfruit, grapefruit, citrus zest, blackcurrant. Reductive winemaking also preserves reduced sulfidic odors such as hydrogen sulfide and methanethiol.
  • Winemakers commonly add copper to wine to remove the reduced odors which very quickly removes hydrogen sulfide and methanethiol.
  • Copper does have downsides as it doesn’t remove disulfides and thioacetates which can significantly contribute to reduced odors in wine.
  • Copper can also remove some of the beneficial varietal thiols.
  • Residual copper in wine post-bottling can actually lead to higher formation of reduced odors in wine and other redox mediated reactions.
  • My research goals are to elucidate the mechanism for copper-mediated thiol redox reactions, and provide winemakers with tools to have a better control over sulfur-containing aroma compounds.

 

Assessing Spotted Wing Drosophila Injury Potential on Grape Production

By: Jody Timer and Michael Saunders

Spotted wing drosophila (SWD), Drosophila suzukii, is an invasive vinegar fly that was introduced into the United States in 2008. It was introduced into Pennsylvania in 2010. S. suzukii is a highly polyphagous pest, whose serrated ovipositor allows it to lay its eggs on undamaged ripening fruit. Adult females can lay 100 to 600 eggs in fruit, as the fruit starts to color and sugar levels begin to rise. SWDs’ lifecycle consists of adults, eggs, larva (3 instars) and pupa overwintering as adults. They differ from other fruit flies because of the serrated ovipositor which allows them to infest intact fruit by laying eggs inside of the undamaged fruit. Damage is often not discovered until the fruit goes to market. SWD is considered a major problem in grape vineyards and damage to wine grape crops has been reported in many states.

Red traps containing yellow sticky cards, baited with apple cider vinegar and the new dual Trece lure have shown to be the most effective and easiest way to trap SWD. Trapping is the most efficient way to determine if SWD is in a vineyard, and also to determine when it is time to check the grapes for infestation. Trapping in Erie County has shown that the SWD are appearing earlier each year, and the numbers of insects captured in the traps is increasing with each subsequent year. The best way to check for infestation in the vineyard is to add crushed grape berries to salt solution: 1 cup water to ¼ cup salt and the larva will float to the top. Larva found in recently ripened fruit is most likely SWD. SWD was discovered from emergence studies on Concord, Chambourcin, Niagara, and Vidal. No-choice, 2-choice-and 4-choice studies were conducted on these four grape varieties. All varieties in the no-choice trials were infested with SWD. They showed a slight preference for Niagara grapes in the 2 and 4 choice testing. Research was done bagging clusters with net bags containing SWD. All clusters became infected with SWD after being bagged. Pesticides in three activity groups have shown efficacy against SWD. It is not recommended to spray unless you have a known infestation in your vineyard.

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Updates on Grape Disease Management Research

By: Bryan Hed

Early leaf removal and Botector for bunch rot control:

  • Bunch rot control = fruit wound control. Many factors cause wounds to fruit: birds, insects, powdery mildew, cluster compactness. We typically make great efforts to minimize the effects of all of these factors, with the exception of compactness.
  • Compactness creates wounds that cause direct fruit rot. Compactness also activates latent Botrytis infections, increases the effect of retained bloom trash in clusters on bunch rot development, and reduces pesticide penetration into clusters.
  • We have investigated many methods of reducing cluster compactness over the years, and early leaf removal has been the most consistently effective method. Mechanization of this method will improve its cost effectiveness and increase adoption.
  • Botector, a biological pesticide was compared to synthetic fungicides and early leaf removal for control of bunch rot disease on Chardonnay and Vignoles grapevines.
  • Botector was not effective in either trial, but fungicides and early leaf removal were equally effective at reducing bunch rot disease, when compared to the control. An integrated treatment of both fungicides and early leaf removal was the most effective treatment.

The effects of rainfall on fungicide (Mancozeb) residue retention.

  • Mancozeb is one of the most widely applied fungicides for grape disease control. We monitored the effects of rainfall on mancozeb residues on grapevine leaves.
  • Over two seasons, high pressure liquid chromatography (HPLC) and inductively coupled plasma mass spectrometry (ICP) were used to quantify mancozeb residues on grape leaves. Both methods were equally effective in year one, but ICP appeared to be more effective and consistent in year 2. As ICP is less expensive and samples are easier to store, its use for quantifying mancozeb residues may improve the accuracy and reduce the cost of this research.
  • In the field, the first inch of rain removes about 60-70% of mancozeb residue, the second inch 70-80%, and the third inch 80-90% of the mancozeb residue.
  • Future research will focus on bioassays to determine the efficacy of varying concentrations of rain challenged mancozeb residues for disease control and the need for subsequent fungicide applications.

 

Wine Marketing Strategies for the Mid-Atlantic Region

By: Abigail Miller

  • Social media is a conversational marketplace; not just two-way, it’s multi-way.
  • Two-thirds of core wine drinkers (those who drink wine about once a week) and 40% of marginal wine drinkers (those who drink wine less frequently) use the Internet in some form to get information about wine (Guenther, 2013).
  • At least 30% of survey participants felt that a Facebook Page was mandatory for a winery. Fifty-four percent of 21- to 24-year-olds, specifically, responded in this manner.
  • Though percentages for Instagram were lower, 18.3% of those 21- to 24-year-olds responded that this tool is mandatory.
  • Younger Millennials are the primary users of Instagram and winery tasting rooms should consider posting on this network to reach these consumers.
  • Websites for promoting products and promoting purchases should be also be a part of a winery tasting room’s repertoire.
  • Content for all outlets could focus on serving and pairing suggestions, coupons, promotions, and discounts, as well as other components that appealed to survey participants.

To read more about Abby’s study on social media preferences for wineries, please visit:

 

Evaluation of Cost Effective Practices for Reducing the Risk of Spring Frost Injury in Vineyards

By: Michela Centinari

Michela presented the main findings from of a project started in 2014 to evaluate the potential of low-cost strategies to reduce the risk of spring frost injury in grapevines. Specifically two spray-on materials currently used by grape growers across the country were tested for their ability to delay budbreak (Amigo oil, soybean- based oil) and provide frost protection to young grapevine shoots after budbreak (KDL, potassium dextrose lactose; Agro-K corporation). Briefly, Amigo oil caused higher levels of delay in bud-break in V.vinifera varieties (Riesling and Lemberger) than in the hybrids varieties (Noiret and Traminette) (Figure 1). Current research efforts are investigating if the different response observed among varieties may be related to the time of oil application. In the vinifera varieties the delay in budbreak was followed by a significant reduction in yield (about 40%), with no effect on fruit composition and wine chemical parameters. Since no frost occurred in Pennsylvania in 2014 the effect of KDL was tested on 1-bud cuttings using a temperature controlled chamber. Preliminary results were shown together with current research efforts which include: testing the effect of KDL on potted vines using a controlled temperature chamber, and at multiple vineyard sites in case a frost event will occur in the next few weeks.

Figure 1. Control and oil-treated Riesling vines (May 20, 2014).

Figure 1. Control and oil-treated Riesling vines (May 20, 2014).

 

The Effect of Acetaldehyde on Red Wine Color Stability and Astringency

By: Marlena Sheridan

  • Wine oxidation can be risky for wines due to side effects of oxygen exposure, but there are important benefits of oxidation for red wines.
  • Acetaldehyde, typically formed from oxygen integration, leads to beneficial effects on red wine color and mouthfeel by binding with tannins and anthocyanins.
  • Reactions with acetaldehyde form stable, polymeric pigments as well as modified tannins with lower perceived astringency.
  • Winemakers use oxygenation techniques (e.g., micro-ox, barrel aging) to form acetaldehyde in the wine, but this includes the risk of detrimental effects of oxidation instead of acetaldehyde formation.
  • Our work aims to evaluate the efficacy of exogenous acetaldehyde treatment of red wine on improving color stability and astringency. This work will be done in real and model wine systems to fully understand the effects of acetaldehyde on wine tannins.
  • Further detail and a description of completed work can be found in my blog post from April 24.

 

The 2014 NE-1020 Variety Trial Harvest: A Comparison of North East and Biglerville, PA

By: Michela Centinari & Denise M. Gardner

Michela Centinari gave an update on the 2014 viticulture performance for the V. vinifera and inter-specific hybrids winegrape varieties established at the two variety evaluation plantings located at the Lake Erie Regional Grape Research and Extension Center (LERGREC), North West side of PA, and at the Fruit Research and Extension Center (FREC) in the southern side of PA (Table 1). The two plantings were established in 2008 as part of the NE-1020 project, a multi-state project that was developed to 1) evaluate the viticultural characteristics and wine quality potential of grape cultivars and clones of economic significance throughout the eastern US; and to 2) characterize the viticultural and wine quality potential of emerging cultivars based on regional needs.

The presentation mostly focused on winter cold temperature injury sustained by the grapevines at the two sites and on the different ability of the varieties to adapt and recover to extreme cold conditions experienced in PA in the winter of 2013-2014.

At the Lake Erie (LERGREC) planting all the vinifera varieties experienced extensive winter injury. Bud, trunk injury and crown gall symptoms were observed in all the vinifera varieties. High incidence of vine mortality was recorded in Syrah, and Muscat Ottonel. Among the vinifera varieties Cabernet franc and Grüner Veltilner vines recovered the best; healthy suckers grew from above the graft union. Lower levels of winter injury were recorded in the Southern part of PA. The most significant winter injury was observed in Tannat (almost 100% bud mortality and vascular tissue damage at cane and trunk levels). The damage on the other varieties was mostly limited to primary buds, although some vines (mostly Syrah, Malbec) sustained vascular tissue damage and collapsed throughout the summer. As a consequence of primary bud damage varieties such as Malbec, Albarino and Cabernet Sauvignon produced very low crop yield.

Table 1. List of varieties and clone designation, when known, planted at the Lake Erie Regional Grape Research and Extension Center (LERGREC), North West side of PA, and at the Fruit Research and Extension Center (FREC) in the southern side of PA.

Table 1. List of varieties and clone designation, when known, planted at the Lake Erie Regional Grape Research and Extension Center (LERGREC), North West side of PA, and at the Fruit Research and Extension Center (FREC) in the southern side of PA.

  • In 2014, 6 varieties were fermented for winemaking trials, and discussed at the recent Symposium: Vidal Blanc (North East), Chambourcin (North East), Cabernet Sauvignon (Biglerville), Merlot (Biglerville), Albarino (Biglerville), and Cabernet Franc (Biglerville).
  • The primary trend noted with Albarino is the continued low yield, which has been annually estimated at under 2.0 tons/acre since 2011. In 2014, the estimated yield for Albarino was 0.57 tons/acre.
  • The Vidal Blanc underwent a pre-fermentation juice trial based on Jose Santos’s presentation in August 2014, which can be found here. Vidal Blanc was separated into three treatment groups: Control (Brown Juice), SO2 addition, and AST addition. Attendees at the PA WMRB Symposium had the opportunity to taste wines produced from these treatments.

 

Pre-Fermentation Juice Treatments in Vidal Blanc. All treatments treated with pectinase and 24-hour settling time in cold storage. Image shown after racking.

Pre-Fermentation Juice Treatments in Vidal Blanc. All treatments treated with pectinase and 24-hour settling time in cold storage. Image shown after racking.

Chambourcin Wines in 2013 Vintage Year Showing Red Color Intensity Differences Between 2 Vineyard Sites in PA.

Chambourcin Wines in 2013 Vintage Year Showing Red Color Intensity Differences Between 2 Vineyard Sites in PA.

In addition to the support of the PA Wine Marketing and Research Board, this material is based upon funding provided by the National Institute of Food and Agriculture, U.S. Department of Agriculture, under agreement No. 2010-51181-21599.

Investigating the Inadvertent Transfer of Vitis labrusca Associated Aromas to Vitis vinifera Wines

By: Jared Smith

Polymers, such as plastics used during winemaking, can scalp (uptake) aroma compounds from juice and wine.

Aroma scalping can lead to not only the loss of desirable aromas, but also the presence of unexpected aromas in wines due to desorption of the aromas from the polymers during subsequent processing. This could especially be an issue when equipment is shared for the processing of two completely different species of grapes (ex. V. vinifera vs. V. labrusca) that have vastly different aromatic profiles.

One potential way to help remove scalped aromas from your polymeric winemaking materials is through the use of ethanolic (80%) cleaning solutions at higher temperatures (75°C) for an extended period of time.

Updates on freeze injury in grapevines

By Michela Centinari

It seems like yesterday we were looking at the weather forecast and worrying about cold winter temperature events and the potential for grapevine injury. Now that it is finally starting to get warmer here in Pennsylvania, we may be faced with another threat: spring frost. A grape grower is never bored!

It was another cold winter in Pennsylvania, particularly harsh in the Lake Erie region (Figure 1). At the Penn State Lake Erie Regional Grape Research and Extension Center (LERGREC) temperatures bottomed out at about -21 °F (-30 °C) on February 16, 2015. Unfortunately several cold events (-13, -14 and -15°F) were recorded over the following ten days. On a ‘positive’ note, the week before these extreme cold events, temperatures were lower than normal, with daytime temperature highs well below freezing, except for one day (34°F). These temperatures may have provided a positive, reinforcing maintenance of the vines’ mid-winter cold hardiness [1]. Bryan Hed and the LERGREC’s crew have been checking the extent of bud and trunk damage on Concord and other hybrid varieties.

Figure 1. Daily maximum and minimum temperatures recorded at the LERGREC during the 2014-2015 dormant season.

Figure 1. Daily maximum and minimum temperatures recorded at the LERGREC during the 2014-2015 dormant season.

Information available on cold winter injury on grapevine

At the 2015 Mid-Atlantic Fruit and Vegetable Convention I reviewed the factors that can affect grapevine cold hardiness, explained how to assess bud, cane and trunk cold damage, as well as how to manage cold-injured vines. For information on grapevine cold injury you can refer to the Grapevine cold injury, end of the season considerations blog post and references within.

If you are looking for specific information on winter injury to vine phloem you can check this recent and comprehensive review: Viticulture and Enology Extension News, spring 2015, Washington State University written by Michelle Moyer (Assistant Professor and Viticulture Extension Specialist at Washington State University).

Percentage of winter injury does not equal percentage of crop loss

In March, I attended The Northern Grapes Project Symposium in Syracuse, NY. Tim Martinson (Senior Extension Associate at Cornell University) and Imed Dami (Associate Professor and Viticulture Extension Specialist at Ohio State University) highlighted that the percentage of bud cold damage does not always equal percentage of crop loss. The answer often lies in the pruning adjustment strategies adopted by growers. Dami reported that, despite 40% of bud winter damage, Marquette produced about 5 tons/acre in Ohio last year. Those vines were pruned to 5 bud-spurs (‘hedge pruning’) to compensate for winter injury [2]. .

Tim Martinson reported that last year many growers in the Finger Lakes region (NY) left more buds to compensate for winter injury experienced during the 2013-2014 winter. The growers left up to five-fold more buds than they would have done in a normal year. Many cane-pruned VSP vineyards were spurred to 5-6 bud spurs. It was a pleasant surprise that in 2014 widely planted V. vinifera varieties such as Riesling, Chardonnay, and Cabernet franc, came through better than was expected based on bud mortality estimates. I know that many growers prefer cane pruning, and I understand the reasoning behind that, but please take into consideration that cane pruning is not recommended following winter injury [3].

How to train suckers of cold injured vines?

Imed Dami recommends that growers “actively” train vines back to their original training system in the same season in order to resume production quicker. Therefore, instead of training suckers vertically (they can become extremely vigorous!) they should be trained horizontally along the fruiting wire. With extremely vigorous vines, four shoots should be selected and then two can be laid horizontally on the fruiting wire. With less vigor, two shoots can be selected and laid horizontally, one to each side. Then, shoots should be tipped to stimulate lateral shoot growth. Lateral shoots growing vertically and upward will become the future spurs next season [4]. Latent buds on the lateral shoots will develop like buds from primary shoots. As long as they are exposed to sunlight and clean from disease and insects, they should have the same cold hardiness as any other buds.

Here is a valuable video regarding pruning with regards to cold injured vines: https://www.youtube.com/watch?v=r1Yhv8Rw38o

A few words on spring frost

As we get close to bud-break, the threat of spring frost is approaching. In the spring of 2014, no frost damage was recoded in grapevines in Pennsylvania and hopefully we will have another frost-free spring. If you would like to get information about frost protection strategies you can check the following websites and newsletters. Unfortunately, there is no new exciting or infallible frost protection method. Site selection remains the best way to protect vines from frost injury.

To the often asked question: If my vine gets frosted, should I remove the injured shoots?

The answer is: “There’s not much of a point,” according to Tony Wolf, Professor and Viticulture Extension Specialist at Virginia Tech University. A detailed explanation on how to handle damaged shoots and potential consequences on yield production can be found at Viticulture Notes, Vol.25, May-June 2010

Testing the cryo-protectant properties of KDL

KDL (potassium dextrose lactose; Agro-K corporation, Minneapolis, MN, USA) is a potassium based fertilizer. According to the manufacturer’s literature, spraying KDL shortly before a frost event (24-48 hours) would increase the potassium and sugar levels within the plant and reduce the frost injury on young vine tissue. Although attractive to growers, there is not scientific literature that supports the effectiveness of this product in preventing/reducing frost damage. Numerous grower testimonials are available, but growers usually do not leave an ‘untreated’ control area where the material is not applied, which is critical in order to evaluate the efficacy of KDL as cryo-protectant.

A large scale study coordinated by Tim Martinson (Cornell University) and in collaboration with the Agro-K company (KDL manufacturer) has been set up this spring to evaluate the effect of KDL at several vineyard sites located in NY and PA. Penn State is a collaborating university that is helping to work with six commercial growers that agreed to participate in the study in addition to the Penn State LERGREC in North East, PA.

Figure 2. Setting up the KDL trial with Tim Martinson and growers in the Endless Mountain region, PA.

Figure 2. Setting up the KDL trial with Tim Martinson and growers in the Endless Mountain region, PA.

Although, I’m hopeful there will not be a spring frost that growers have to deal with, if we do end up with a spring frost during the 2015 growing season, this study will hopefully provide some useful recommendations for grape growers.

References cited

  1. Wolf T.K., 2015. Viticulture Notes. Vol. 30 supplement, 17 February 2015
  2. Dami, I.E. , Ennahli S., Zhang Y. (2012). Assessment of winter injury in grape cultivars and pruning strategies following a freezing stress event. American Journal of Enology and Viticulture, 63: 106-111.
  3. Dami, I.E. 2009. Ohio Grape-Wine Electronic Newsletter Vol.3: 2-5, 6 Feb 2009.
  4. Dami I.E., 2014.Ohio Grape-Wine Electronic Newsletter, Vol.25, 3 July 2014.

 

Harvest 2014: An update to studies on frost injury

By: Maria Smith

Since I arrived in August, we have been busy at work continuing to collect field data on our current studies. In addition, we have been developing a new study which takes an in-depth look at the role of canopy management practices have on vine cold hardiness.

Harvest 2014:

After weeks of intense anticipation, monitoring berry development, and fretting over weather, harvest has finally come for us at the Centinari lab. As of last week, our commercial plots with Lemberger, Riesling, Noiret, and Traminette used to study frost tolerance and avoidance have all been harvested (Fig 1, See: “Evaluate cost-effective methods to decrease crop losses due to frost injury”). If you recall, these plots were sprayed with KDL, a commercially available cryo-protectant, and Amigo oil, a product used to delay bud break.

Fig 1. Left: Lemberger at harvest (10/9/2014), Right: Riesling at harvest (10/16/2014)

Fig 1. Left: Lemberger at harvest (10/9/2014), Right: Riesling at harvest (10/16/2014)

Our preliminary observations show that the Amigo oil treatments had noticeably lower yield in both Lemberger (Fig 2) and Riesling (data not shown) grapes harvested. Despite the lack of frost this spring, we did see a 2 week delay in bud break in Lemberger and a 1 week delay in Riesling with Amigo oil treatments. We are currently checking to see if these differences can be attributed to factors such as the number of shoots per vine between the treatments and/or cluster weight. However, if Amigo oil is in fact the cause of a decrease in yield we should see similar results over multiple years. In the case that Amigo oil has an actual affect on yield, it would be prudent to perform an economic analysis to decide if the use of Amigo oil as a frost avoidance mechanism is worth the cost in decreased yield.

Figure 2.  Lemberger yield data, 2014

Figure 2. Lemberger yield data, 2014

Winemaking:

 Winemaking is a crucial component in determining what sort of impacts delaying bud break can have on the final product. Thanks to the help of Denise Gardner and a group of students in a winemaking and enology independent study class, we have had the opportunity to crush, press, and ferment our harvested research grapes into wine (Fig 3).

Figure 3.  Lemberger processing at the PSU Food Science Wet Pilot Plant

Figure 3. Lemberger processing at the PSU Food Science Wet Pilot Plant

In the initial juice, we have noticed an increase in Brix and TA between the Amigo oil and control treatments in Lemberger, though the Brix of all treatments in Riesling were similar (Table 1). We will be running additional detailed chemical analyses on frozen berry samples taken throughout ripening in the upcoming months.

Table 1.  Juice analysis – Brix, pH, TA of Lemberger and Riesling.  Riesling was chapitalized to 21 Brix.

Table 1. Juice analysis – Brix, pH, TA of Lemberger and Riesling. Riesling was chapitalized to 21 Brix.

Future work planned for analyzing the effects of Amigo Oil and KDL include:

  • Grape Brix, TA, pH on samples from veraison through ripening
  • Wine chemistry – Alcohol, SO2, and color density
  • Sensory attributes of wine
  • Prepare for year 2 KDL and Amigo Oil application

 

Winter 2014: New work on canopy management and cold hardiness:

 We have recently begun work on a second study in cold hardiness. Canopy management practices are often used to improve the microclimate of grapes within the fruiting zone by exposing clusters to increased light and airflow. Early leaf removal (ELR) has been shown to successfully reduce cluster compactness in tight-clustering varieties, thus reducing incidents of bunch rot (Hed et al., 2014). Another common canopy management practice, cluster thinning (CT), is used to reduce fruit load of overcropping varieties to improve grape and wine quality. However, these practices may also change carbon source-sink relationships with cluster thinning removing carbon sinks and ELR removing photsynthetically active leaves (source), which could potentially alter cold acclimation and hardiness in the vine. Using ‘Chancellor’ vines under 3 imposed canopy management treatments – low-intensity leaf removal, high-intensity leaf removal, and CT – and an un-treated control at the Lake Erie Regional Grape Research and Extension Center, we plan to:

  • Quantify non-structural starches and sugars associated with bud cold hardiness between Nov. 2014 and March 2015
  • Assess how canopy management practices affect grape and wine chemistry and wine sensory perception
  • Perform an economic analysis on the cost and return of canopy management practice implementation

 

Literature:

Head B, Ngugi HK, Travis JW (in press). Short- and long-term effects of leaf removal and gibberellin on Chardonnay grapes in the Lake Erie Region of Pennsylvania. American Journal of Enology and Viticulture. doi: 10.5344/ajev.2014.14034

 

Funding:Print

The investigation of grapevine frost treatments is made possible by the John H. and Timothy R. Crouch Program Support Endowment, an endowment founded and funded by the Crouch brothers, original owners of Allegro Winery in Brogue, PA.  Additional financial support is contributed by the Pennsylvania Wine Marketing & Research Board (PA WMRB).  It is with great appreciation to investigate these projects based on funds and interest provided by the Pennsylvania wine community.

 

Acknowledgments:

A big thanks to Don Smith for his technical support in our lab and Denise Gardner for her assistance in winemaking. Also, thanks to our wine grape grower collaborators. _________________________________________________________________________________________________

Maria Smith is a viticulture PhD student with Michela Centinari, specializing in cold stress physiology of wine grapes.

Evaluate cost-effective methods to decrease crop losses due to frost injury

By: Michela Centinari

To get ready for my first growing season as a research viticulturist at Penn State University, I met several times with Mark Chien and Denise Gardner and read through all of Mark’s newsletters from the last couple of years. In the past few months I also visited several wine grape growers across the State with the objective of understanding the challenges that the PA wine grape industry is facing. By talking with Mark, Denise and growers, I established that crop yield loss related to late spring freeze injury is one of the economic challenges to the continued growth and advancement of the PA wine grape industry. It was a big relief for many growers that the 2014 spring, after a challenging winter, did not contain a (significant) freeze event recorded after grapevine budbreak. However, the cold temperatures that often occur in late spring, at the very cold-sensitive stages of shoot development, can result in severe crop losses and vine injury comparable to a severe midwinter freeze.

Below is a brief explanation of current frost damage/protection research that I have been working on at Penn State.

What can be done to reduce frost damage in vineyards?
“The best time to protect an orchard (or vineyard) against frost is when it is being established” (Humpries W.J., 1914). Selecting a site with good air drainage is extremely important to reduce the risk of freeze/frost damage. However, many vineyards are located in less than ideal sites. Best management practices for vineyards located in frost vulnerable sites include:

  • choosing the appropriate training system and variety,
  • strategies for delaying budbreak (double or delayed pruning; chemical application),
  • leaving additional canes post pruning, and
  • mowing the inter-row grass [1].

The most effective frost protection methods (i.e. wind machines, helicopters, over-tree covers, heaters, and sprinkling irrigation) may require large investments and not every grower can justify the costs involved. To enhance the profitability of growing grapes in PA the development of frost protection strategies affordable to many growers is critical.

With this in mind, in collaboration with Ryan Elias and Denise Gardner, I’m currently evaluating the effectiveness of spray-on materials (KDL and soybean oil) on reducing the risk of frost injury. In addition, the effect of these materials on vine performance, juice composition and wine sensory characteristics is being evaluated.

Specifically, we are looking at two potential ways to decrease freeze injury in vine green tissues:

1) Increase freeze tolerance of vine green tissue:
If your vineyard is located in a frost prone area, you’ve probably heard about a foliar potassium fertilizer called KDL (potassium dextrose lactose; Agro-K corporation, Minneapolis, MN, USA). According to the manufacturer’s literature, spraying KDL shortly before a frost event (24-48 hours) would increase the potassium and sugar levels within the plant and reduce the frost injury on young vine tissue. Although attractive to growers, there is not scientific literature that supports the effectiveness of this product in preventing/reducing frost damage. Numerous grower testimonials are available, but growers usually don’t leave an ‘untreated’ control area where the material was not applied, which is critical in order to evaluate the efficacy of KDL as cryo-protectant.

Freeze events are not easy to study; they are unpredictable and often variable across a single site. Therefore, a large scale study was set up in collaboration with Cornell University (Tim Martinson and other extension agents) and the Agro-K company (KDL manufacturer) to evaluate the effect of KDL at 25 vineyard sites located in NY and PA. With regards to PA, 6 commercial growers agreed to participate in the study, in addition to the PSU Lake Erie Grape Research & Extension Center. In the absence of a frost event we were unable to gather any data for the 2014 year but we hope to test the same protocol again next year (2015).

Since, as mentioned, frost events are unpredictable I am also using a temperature control chamber to simulate a frost event. In the spring, KDL was sprayed on several grapevine varieties at the PSU research vineyard established at Rock Spring. After 24, 36, and 48 hours, canes with healthy growing shoots were excised and placed in the frost simulation chamber. Several ‘frost’ runs were conducted and I am now in the process of analyzing the data.

Parallel experiments on vinifera and hybrid grapevine varieties are being conducted by Jason Londo at the USDA-Cornell University.

2) Avoid frost injury by delaying budbreak
Delaying of budbreak is a way to reduce the risk of frost and is used mostly for grapevine varieties that break bud early and are at the highest risk of spring frost injury and subsequent crop losses. Studies conducted in Ohio, reported that application of soybean oils delay grapevine bud deacclimation and budbreak anywhere from 2 to 20 days depending on several factors including variety, timing and coverage. However, since grapevine cultivars respond differently to soybean oil applications, optimal strategies for their use need to be established for grapevine varieties grown under PA environmental conditions. Moreover, the effect of soybean oils on fruit composition and wine quality needs to be evaluated, since oil applications could delay fruit ripening, affect yields, fruit chemistry and wine sensory characteristics.

In March field trails were established at two commercial vineyards in Central PA. A soybean oil-based adjuvant, Amigo (Loveland Industries, Greeley, CO) was applied at a 10% concentration (v/v) to runoff with a backpack sprayer during the dormant season (Figure 1A). Amigo oil was applied on March 7 at vineyard “Site 1” on Traminette and Noiret vines, and on March 27 at vineyard “Site 2” on Riesling and Lemberger vines. Temperature sensors were installed in the fruiting wire of selected vines to continuously monitor air temperature throughout the growing season (Figure 1B and 1C).

In the spring, control vines (not-sprayed) and treated vines (sprayed with oil) were visually evaluated for budbreak. Budbreak was determined as stage five of the Eichorn and Lorenz (1977) scale of grapevine development. The grapevine growth stage is being periodically monitored and recorded to date.

Figure 1. A) Don Smith sprays Amigo oil at Happy Valley vineyard. B&C) Temperature sensors installed at the vineyard.

Figure 1. A) Don Smith sprays Amigo oil on grapevines. B&C) Temperature sensors installed at the vineyard.

The oil application caused various levels of delay in budbreak. At “Site 2,” budbreak delay of approximately 7 and 14 days was observed in the oil-treated Riesling and Lemberger vines, respectively, compared to the control (Figure 2). Looking at Figure 2 you will see how stage 5 (budbreak) was reached on May 13 for the control Lembeger vines and on May 29 in the oil-treated Lemberger vines. Although reduced, a phenological delay was still present at bloom (stage 23) in the Lemberger and Riesling oil-treated vines.

Figure 2. Growth stage of control and oil-treated Riesling and Lemberger vines.

Figure 2. Growth stage of control and oil-treated Riesling and Lemberger vines.

Pictures of Riesling vines were taken on May 20 (Figure 3) and July 9 (Figure 4). On May 20 the difference between oil-treated and control vines was striking. On July 9: both oil-treated vines and control vines showed fully developed and healthy canopies.

Figure 3. Control and oil-treated Riesling vines (May 20, 2014).

Figure 3. Control and oil-treated Riesling vines (May 20, 2014).

Figure 4. Control and oil-treated Riesling vines (July 9, 2014).

Figure 4. Control and oil-treated Riesling vines (July 9, 2014).

The delay in budbreak was much less pronounced in the Noiret at “Site 1” (figure 5). The delay in budbreak in the oil-treated vines was only of a couple of days. Traminette data have not yet been analyzed.

Figure 5. Growth stage of control and oil-treated Noiret vines.

Figure 5. Growth stage of control and oil-treated Noiret vines.

In agreement with previous work [2] our data suggests that varieties respond differently to soybean oil application. Varieties such as Noiret may need multiple oil applications in order to increase the delay in budbreak. Moreover, environmental conditions may also in part explain the different results obtained at the two sites. Finally, it is important to remember that multiple years of evaluation are needed in order to gather meaningful results and give growers reliable recommendations

What is left to do for the 2014 research season?

  • Measure Brix, pH and TA during grape ripening and at harvest to check if the delay in budbreak may cause an un-even fruit ripening.
  • At harvest collect yield data (number and weight of cluster per vine) and make wine from the Riesling and Lemberger control and oil-treated vines. Our final goal is to analyze if the oil application has any effect on wine chemistry and sensory perception.

 

Acknowledgments

 The project “Evaluation of cost effective practices for reducing the risk of spring frost injury in vineyards” is being funded by a Pennsylvania Wine Marketing and Research Board (PWMRB) grant.

Thanks to Don Smith for his technical support and help in field data collection.

 

Literature cited

[1]. Trought et al. (1999). Practical considerations for reducing frost damage in vineyards. Report to New Zealand winegrowers.

[2]. Dami, I. and B. Beam. 2004. Response of grapevines to soybean oil application. Amer. J. Enol. Vitic. 55: 269-275.