By: Denise M. Gardner
Last week, Dr. Michela Centinari dived into the discussion regarding the role of potassium in the vineyard. While the issue is quite challenging to address in an established vineyard, processing grapes from high pH fruit, or fruit that has the potential to create a high pH wine (>3.70), as a result of high potassium (K or K+) concentrations is also a challenge for the winemaker.
Concentrations of 22 – 32 mmol/L K+ (860 – 1,279 mg/L K+) are considered “normal” ranges for wine grapes (Somers 1977, cited by Mpelasoka et al. 2003), while ranges in the 27 – 71 mmol/L K+ (1,056 – 2,776 mg/L K+) are considered “high” (Somers 1975, cited by Mpelasoka et al. 2003) and may lead to potential winemaking problems. Grapes and juice that come in with high levels of potassium can lead to a series of difficulties for winemakers including:
- High potassium concentrations can cause large increases in pH during primary and malolactic fermentations, which drive the finished wine into a high pH (>3.70) range.
- Color hue, intensity, and stability of red wines can be negatively affected.
- High pH wines produced throughout the Mid-Atlantic may lead to negative perceptions associated with taste and mouthfeel of both white and red wines.
- As pH is a big driver in wine stability, higher pH’s will have impacts on the microbial stability (both in terms of microflora and inhibition of growth), sulfur dioxide levels and efficacy, color stability of red and rosé wines, stability of tartaric acid, and protein stability.
- Higher pH’s leads to an increase in oxidative potential, which may cause premature oxidation for young wines.
Although the articles listed below are not peer reviewed, previous attention has been given to high potassium winemaking issues. Some of the content relayed in these 2 articles will not be discussed in this blog post:
- Really, really high pH remedies from Wines & Vines: a discussion on potassium concentrations increasing the pH of wine and utilization of ion exchange if the problem is not prevented
- High pH and high potassium wines produced in Colorado from White Hall Vineyards: Includes a discussion pertaining to malic acid concentration in high pH fruit. (Author’s note: This article discusses adding tartaric acid prior to fermentation, but not exceeding a TA of 8.0 g/L while hitting a pH of 3.60, ideally. While the practice of analytically checking your additions is encouraged, and will be discussed throughout the duration of this blog post, please note that sampling procedures and tartaric acid settling time will greatly influence your juice TA after tartaric acid addition.)
A problem for winemakers is that unless potassium uptake and management is addressed in the vineyard, they will likely have to deal with having high potassium-based fruit for several years. However, winemakers are encouraged to work with their growers, as this is a relatively newer viticultural issue that the Mid-Atlantic is facing, and it may take several years to stabilize before results are seen in incoming fruit from the vineyard.
In regions like Australia, which frequently experience high K concentrations in their fruit and wines, making tartaric acid additions to the juice, pre-fermentation is often recommended to lower the pH of the must/juice and precipitate some of the potassium as it binds to tartaric acid during primary fermentation. While a 2 g/L of tartaric acid addition to must/juice is a common recommendation for acidulating musts, it may not be enough in order to alter the effects of high potassium concentrations in the fruit. In these cases, a higher addition rate of tartaric acid, such as 4 – 6 g/L of tartaric acid, may not be out of the question.
It should be noted that must/juice acidification will have chemical and sensory implications to the finished wine. If the winemaker is aiming to produce a specific style, making large tartaric acid additions pre-fermentation may not be conducive with the desired and finished wine style. However, when dealing with high potassium issues, and hence, high pH issues, larger tartaric acid additions pre-fermentation seem to be helpful in stabilizing red wine color and improving the flavor of red wines. For those that would prefer a lower TA (<6.0 g/L tartaric acid), deacidification following malolactic fermentation of red wines is recommended. While there are limitations on deacidification practices, including the degree to which a winemaker can deacidify, this action may help improve mouthfeel and decrease the perception of acidity (sourness) in the finished wine.
Wine Trials at PSU
During the 2015 harvest, our research team confirmed that a couple of our varieties that annually had high pH problems came from sites or locations with high potassium retention in the fruit. This did not necessarily correlate with high potassium concentrations in the soil.
From our Biglerville (Adams County) research vineyard, our Merlot contained 1,682 mg/L K+ and Cabernet Sauvignon contained 1,668 mg/L K+ in the 2015 growing season. Both samples were taken from the must and analyzed by atomic absorption analysis at Enartis USA – Vinquiry.
Based on previous research from Somers (1975), both musts were considered high in potassium. The following (Tables 1 and 2) show additional harvest parameters for our Merlot and Cabernet Sauvignon musts in the 2015 season.
As previous yeast strain selection, malolactic bacteria selection, and standard (2 g/L) tartaric acid addition trials did not seem to improve color stability or flavor of the wines in past harvest years, we took the approach at comparing 3 different tartaric acid addition rates (2 g/L, 4 g/L, and 6 g/L) to the Merlot pre-fermentation and two rates (4 g/L and 5 g/L) of tartaric acid to the Cabernet Sauvignon based on previous recommendations made in the Australian literature. There were fewer treatments on the Cabernet Sauvignon due to decreased yields in 2015. Please note that these treatments were not replicated and, therefore, we have not provided any statistical parameters.
For the Merlot, the 2 g/L addition rate of tartaric acid acted as the “control,” as previous years indicated no differences in pH or TA by the end of MLF between wines fermented without tartaric acid added pre-fermentation and a 2 g/L addition treatment. There was no designated “control” for the Cabernet Sauvignon fermentations.
Table 1: 2015 Pennsylvania Merlot must chemistries in 2015; pH and titratable acidity (TA) were adjusted pre-fermentation (i.e., pre-inoculation) and given at least 3 hours of settling time before inoculation with ICV-GRE yeast
Table 2: 2015 Pennsylvania Cabernet Sauvignon must chemistries in 2015; pH and titratable acidity (TA) were adjusted pre-fermentation (i.e., pre-inoculation) and given at least 3 hours of settling time before inoculation with ICV-GRE yeast
The following table (Table 3) shows the differences in pH and TA for each pre-fermentation tartaric acid addition treatment following primary fermentation and MLF for our Merlot wines in the 2015 vintage year.
Table 3: 2015 Merlot wine chemistries (pH, TA, volatile acidity, and alcohol concentration) post-primary fermentation and post-MLF (fermentation trials were not conducted in replicate)
Trends were similar in the 2015 Cabernet Sauvignon wines, as shown in Table 4.
Table 4: 2015 Cabernet Sauvignon wine chemistries (pH, TA, volatile acidity, and alcohol concentration) post-primary fermentation and post-MLF (fermentation trials were not conducted in replicate)
While we do not quite have an explanation for the rise in TA from post-primary fermentation to post-MLF in the 5 g/L tartaric acid addition treatment in the Cabernet Sauvignon wine, we did note that post-bottling, most of the TA’s slightly decreased across all treatments in both Merlot and Cabernet Sauvignon wines. A decrease in TA would reduce the perception of sourness even further. This decrease was likely due to better removal of dissolved carbon dioxide within the wines due to the fact the wines had been moved (i.e., racked, transferred and bottled) more routinely prior to bottling.
The treatments within a varietal were also different sensorially, although this was not quantified. For example, in the Merlot, the first difference noted was the color. The Merlot wine that had been treated with 6 g/L tartaric acid had the most vibrant and red-hued color. The Merlot with a 2 g/L tartaric acid addition had a stronger purple-blue hue. We did not quantify these differences analytically. In terms of taste, the 6 g/L tartaric acid treatment had more noticeable and perceptible sourness, but many that tasted the wine agreed that it could be manipulated with some deacidification trials. The 2 g/L tartaric acid addition treatment tasted flat, had burnt rubber-like flavors and was relatively unappealing. It did not represent a typical flavor profile associated with Merlot. The 4 g/L and 6 g/L tartaric acid addition treatments had more noticeable red fruit flavors and less earthy characters.
What should you do in the winery if you think you have high pH wines as a result of high potassium concentrations in your grapes?
- Find out if potassium concentrations may be a culprit. Now is the time to find out what you are dealing with. In last week’s blog post, Michela recommended getting petiole samples to determine vine nutrition. However, you can also test the fruit (must, juice) and the wine for potassium concentrations as well. We recommend sending your samples to an ISO accredited lab to confirm potassium concentrations in those wines that you believe may be suspect.
- Make tartaric acid additions pre-fermentation (pre-inoculation). With very high potassium concentrations, a 4 – 6 g/L addition of tartaric acid pre-fermentation may not be a detriment to wine quality. However, it is best to know the concentration of potassium you are dealing with before adding up to 6 g/L of tartaric acid pre-fermentation as this can have obvious effects on the wine’s taste and flavor as a finished wine (i.e., make the wine thin or overly sour).
- If you are unwilling to test to the potassium concentration, but have a wine with frequent high pH problems during production, use a 4 g/L tartaric acid addition pre-fermentation instead of 2 g/L. The 4 g/L tartaric acid addition rate is a relative “good guess” zone. Depending on the potassium concentration in your wine, this will either work or it will not work. If you refer to Tables 3 and 4, we can see that the 4 g/L addition rate was not a bad choice for the Merlot as it resulted in an ideal pH (3.63) and a workable TA (5.96 g/L), but for the Cabernet Sauvignon, the wine resulted in a high pH (>3.70) and a high TA (>6.00 g/L). This high pH, high TA situation can make the wine both difficult to manage for stability reasons (e.g., making applicable sulfur dioxide additions) while retaining a relatively sour taste.
- White wines can also suffer from high potassium. While the content of this blog post has focused on red wines and the effects of color stability and flavor associated with higher pH’s and high potassium concentrations, white wines can also be affected by high potassium concentrations. In most instances, high potassium can relate to a high pH in the finished wine, which makes the white wine difficult to stabilize or add proper sulfur dioxide additions in order to minimize microbial risk. Also, many of these wines have low TA’s, giving the white wine a fat, round, or flat mouthfeel (dependent on the variety). Stylistically, this may not be undesirable, but it is a sensory component that winemakers should be aware of that may occur in these chemical situations.
- Alter your pH and sourness post-malolactic fermentation. If the wine tastes too sour for your preference, the time to de-acidify is post-MLF with these wines. By that time, the color pigments will be fully extracted from the red skins and the flavors will be as optimal as they can be for the variety. For our Merlot wines, we made additions using (ironically) potassium carbonate, but calcium carbonate can also be used to de-acidify wines. I usually recommend Patrick Iland’s book for practical information on how to make de-acidification trials in wine. WSU also provides appropriate options and instructions for deacidifying wine.
Mpelasoka, B.S., D.P. Schachtman, M.T. Treeby, and M.R. Thomas. (2003) A review of potassium nutrition in grapevines with special emphasis on berry accumulation. Australian Journal of Grape and Wine Research. 9:154-168.
Somers, T.C. (1975) In search of quality for red wines. Food Technology in Australia. 27:49-56.
Somers, T.C. (1977) A connection between potassium levels in the harvest and relative quality in Australian red wines. Australian Wine, Brewing and Spirit Review. 24:32-34.
By Michela Centinari
Potassium (K) plays a critical role in many plant physiology and biochemistry processes (e.g., photosynthesis, osmoregulation, enzyme activation, etc.). Inadequate supply of K can result in reduced shoot, root and fruit growth as a result of reduced xylem sap flow, and can also increase the risk of drought stress . Potassium deficiency leads to inhibition of photosynthesis and to sugar (sucrose) being “trapped” in the leaves which adversely affects yield, fruit ripening and berry soluble solid concentration .
While grape growers should monitor vine health to avoid K deficiency, at the same time they should also be on the lookout for excessive concentration of K in vine tissues (e.g., leaf, berry) because of its potential negative impact on vine health and wine quality.
When looking back at the past two years of inquires received from Pennsylvania wine grape growers related to vine nutrient or nutrient-related problems, we (Denise and I) found that the number of those concerning excessive concentration of K and related issues (e.g., high/unstable wine pH) were more common than inquiries related to K deficiency, which mostly occurred in young vineyards.
This short article will review problems related to high/luxury absorption of potassium, briefly discuss how soil mineralogy and pH can affect K uptake, why it is important to regularly monitor vine nutrient status, and what environmental and cultural factors may impact K uptake and accumulation in plant tissues. In-depth information on mode of uptake and transport of K in the plant, and functions of K can be found in “A review of potassium nutrition in grapevines with special emphasis on berry accumulation” by Mplelasoka et al. 2003 .
Also, you can refer (as I did) to the valuable web-resources recently published by Virginia Tech University (Dr. Tony Wolf and Russel Moss), which includes edited information to supplement Chapter 8 of The Wine Grape Production Guide of Eastern North America:
Potassium in Viticulture and Enology, May 2016
Why high/excessive concentration of K in the grape berries may negatively impact wine quality?
Grape berries are a strong sink for K during ripening. Potassium accumulates mainly in the berry skin tissues (Figure 1) and is the most abundant cation (K+, hereafter referred to as K) in grape juice . Mature grapes may have, indeed, almost twice as much K as nitrogen ; for example one ton of mature grapes contains about 11 lbs (5 kg) of K .High concentration of K in grape juice (e.g., > 50 mmol/L) may result in a high juice pH (e.g., > 3.8) and negatively impact wine quality . During winemaking, high concentration of K causes precipitation of free acids, mainly tartaric acid, leading to an increased wine pH . The high pH may reduce color stability of red wines due to a shift of anthocyanins to the non-colored forms . High concentration of K may also reduce respiration and the rate of degradation of malic acid and consequently increase malolactic fermentation .
While many studies linked high juice/wine pH to high juice/wine K concentrations (see for example Figure 2) it is also true the other factors, aside from K, can affect wine pH and that wines with low pH (e.g., < 3.25) may also have high K concentration . Moreover, there are varietal differences in the relationship between juice pH and K concentration (see Chardonnay vs. Shiraz, Figure 2), as well as between wine K and juice K .pH can be adjusted during winemaking through addition of tartaric acid, adding additional costs for the wineries. Ensuring adequate concentration of K in the grapes at harvest will not only help reduce winemaking costs but is also likely to improve wine quality .
In next week’s blog post, Denise Gardner will discuss options for dealing with high K concentrations in juice and wine. However, the first step is to determine if there is or there may be a potential problem with K in your vineyard (either deficiency or excess level).
Potassium availability in the soil
It is well known that concentration and availability of K vary with soil type and is greatly affected by the physical and chemical properties of the soil . Potassium in soil is classified into four groups in relation to its availability to the plants: 1) water-soluble (K dissolved in soil solution), 2) exchangeable (on cation exchange sites of surfaces of clay minerals and humic substances), 3) non-exchangeable and 4) structural forms .
The water-soluble and exchangeable pools (1 & 2) represent only » 0.1-0.2% and 1-2% of the total soil K, respectively . Both forms are readily available for plant root absorption. The majority of the K is bound in mineral structures, such as mica and feldspar, or it is part of secondary minerals such as vermiculite  and thus considered a (very) slowly-available source of K for plants. Clays also have different capabilities of binding K as well as different rates of K release . For example, micas release K at a remarkably faster rate than feldspar .
Since clay mineralogy impacts the release of K into the soil solution over time and the K supplying power of the soil, it is important to have detailed information concerning the soil structure and composition of your vineyard (i.e., does your site have high levels of exchangeable K?).
Other important factors affecting K availability are soil pH and relative concentration of K to that of the other cations, such as magnesium (Mg2+) and calcium (Ca2+). Low/acidic soil pH (<6) increase K availability and potentially increase its uptake while reducing uptake of Ca2+ and Mg2+ . Excess K can decrease concentrations of Ca2+ and Mg2+ in plant tissues and induce symptoms of Mg deficiency  (Figure 3).
Assessing K concentration in the vine
Conducting plant tissue (petiole) testing on a regular basis (annual or every two years) to monitor vine nutritional health (K and other essential nutrients) and promptly correcting problems related to nutrient imbalance is strongly recommended. Visual observations of foliar symptoms of nutrient deficiency or toxicity are important clues (Figure 4), but a nutrient management program should not be exclusively based on visual observations because: 1) it is possible to be misled by symptoms that are not nutrient related (e.g. mite injury, virus, etc.) and 2) to develop an appropriate nutrient management program it is crucial to understand the nutritional requirements of the vines .
Soil testing is an extremely useful tool in the pre-planting stage for determining the potential of a vineyard site and the amendments needed, and also for monitoring soil pH over the years (after the vines are planted). However, soil testing only tells one side of the story: what is potentially available to the vine. Again, the recommended and preferred method to assess vine nutritional health and to effectively identify potential nutrient (in this specific case K) deficiency or excess is plant tissues (petiole) testing.
Some limitations of the soil testing include:
- Soil samples are often limited to the first 10-20 inches. Roots of mature vines tend to be sparse and, in deep soils, they can grow much deeper than 10-20 inches. Thus soil testing may not be a good indicator of the soil/plant interaction.
- Soil testing may underestimate the reservoir of K available to the vines . The laboratory nutrient extraction analysis is run over minutes while vines have much longer to absorb/extract nutrients [6,9].
Thus, don’t be too surprised if results of K soil testing are poorly correlated with those of plant tissue testing [6,7,9].
When is the best time to conduct leaf petiole testing?
The preferred time for leaf petiole testing is bloom and late-summer (70 to 100 days after bloom). Assuming bloom was in June, you may still have time left this season to conduct the test. In case of suspected K or other nutrient deficiency the samples can be collected anytime during the season . It is important to have a standardized tissue-sampling procedure. For example, at bloom collect 60 to 100 petioles of healthy leaves opposite to the flower cluster (first or second) for each cultivar. Don’t collect more than one or two petioles per vine. Late summer samples should be collected from “the youngest fully expanded leaves of well-exposed shoots, usually located from 5 to 7 leaves back from the shoot tip”. If the shoot has been hedged, collect “primary leaves near the point of hedging” .
More information on how to collect leaf petiole samples and interpret the results can be found at Monitoring Grapevine Nutrition (eXtension.org) and in the Wine Grape Production Guide for Eastern North America, chapter 8 .
Reference values of K concentration in grape leaf petioles for bloom- and late summer-collected samples are reported in Table 1. (Note: the source used is the Wine Grape Production Guide for Eastern North America , sources from other regions may provide slightly different standards).
Table 1. Reference values for K concentration in grape leaf petioles for bloom- and late summer-collected samples.
In table 2, I included the results of a petiole test conducted at a research vineyard in south central Pennsylvania. At bloom, K concentrations in the leaf petiole of Cabernet Sauvignon and Merlot vines were slightly above the ‘excessive’ range. We repeated the analysis around veraison and found that at that time K concentrations were greatly above the 2% ‘excessive’ threshold. Not too surprisingly, at harvest, both varieties had high grape juice pH and high K concentration according to reference values reported by Mpelasoka et al. 2003  (Table2). Soil testing showed a high level of exchangeable K, and low pH (below 6), the vines were highly vigorous: all factors that can contribute to luxury uptake of K.
Table 2. Potassium concentrations in the petiole of Cabernet Sauvignon and Merlot leaves at bloom and veraison. Potassium concentration and pH of the grape juice was measured at harvest.
What to do next?
In case of K deficiency (petiole and soil testing and visual observations) (Figure 4) you can consult with an extension educator in your county or a viticulture consultant who can assist with the development of an appropriate fertilization program.
For those of you who may have missed it, Tony Wolf (professor and viticulture extension specialist at Virginia Tech university) recently issued an important update on K fertilization recommendations . The lower limit of optimal soil K reported in the “Wine Grape Production Guide for Eastern North America”  has changed from 75 ppm (150 lbs/ac) to 40 ppm (80 lb/acre) (Note: those values are based on Mehilch-3 extraction protocol which is the one used by Penn State Agricultural Analytical Services Lab but not by Virginia Tech). In the July issue of Viticulture Notes Tony Wolf wrote:
“Potassium fertilizer is not recommended pre-plant or to existing Virginia vineyards if the soil test results are at or above 40 ppm (80 lbs/acre) actual K as determined by Mehlich-3 test procedures, or 28 ppm (56 lbs/acre) actual K as determined by Mehlich-1 test procedures. However, young vines should be visually monitored and irrigated under drought conditions to avoid potential K deficiency on soils that are inherently low in exchangeable K.”
How can K concentration and uptake by the vines be reduced?
In the pre planting stage, if the soil selected for planting the vineyard has high exchangeable K levels, an option is to select rootstocks that accumulate low concentration of K. Rootstocks, and grapevine varieties in general, differ in their capacity of K uptake and translocation . For example, rootstocks with V. berlandieri genetic background tend to have reduced K uptake as compared to others, as those with V.champini parentage . In northern California, Chardonnay, Cabernet Sauvignon and Zinfandel vines grafted on 101-14 Mgt and 3309C (V. riparia x V. rupestris), two commonly-used rootstocks in the eastern US, consistently had leaf petiole K concentrations within the intermediate range compared to those of the same varieties grafted on V. berlandieri (lowest K concentrations) and V. champinii (highest K concentrations) crosses . A study conducted at Winchester, VA, by Tony Wolf research group found that the use of 420-A (V. berlandieri x V. riparia) rootstock reduced juice pH in Cab Sauvignon vines as compared to those grafted on 101-14 Mgt and Riparia .
However, it is important to consider that the performance of rootstocks in terms of K uptake varies depending on rootstock-scion combination (i.e., the same rootstock may have variable effects on different scion varieties), soil type, climate, and management practices.
Another aspect to consider when selecting rootstocks is their vigor or growth-potential. Vigorous rootstocks or rootstocks that convey high vegetative growth and yield potential to the scion may cause increased K uptake as a result of increasing vine demand.
Growth drives K uptake: Factors such as high vine vigor, leaf area, and extensive root system can enhance K uptake, translocation, and accumulation in the grape berries. Soil moisture increases the dissolution of K from clay particles, thus facilitates K supply and uptake by the roots. High soil water availability also leads to increase vegetative growth which may indirectly affect K uptake and its accumulation in the berries.
Shaded leaves are a source of K translocation to the grape berries: Canopy microclimate and mainly foliage shading can affect the accumulation of K in the berries. For example, artificial (shading cloths)  or natural (canopy) shading  was found to increase K concentration in berries and juice. We don’t know exactly why this happens yet, but it is possible that in conditions of low sugar accumulation, as under foliage shading, the increasing accumulation of K in the berries helps regulating osmotic potential, maintaining cell turgor and thus minimizing reduction in berry growth which may occur with low sugar content .
Can crop load be regulated to reduce K accumulation in the fruit?
Since berries after veraison are the primary sink for K, we would expect that regulation of crop load (commonly defined as the ratio of fruit weight to pruning weight or to leaf area) can affect K translocation and accumulation in the berries . However, results from previous studies are inconclusive. For example, in hot climate regions (Israel, California) cluster thinning reduced berry K in one study  while having no effect on juice K in another study . Factors such as grape variety, timing of thinning, and the amount of crop retained can greatly affect outcomes and explain why the effect of crop load on accumulation of K in the berries still remains unclear. Making matters more complicated, manipulation of crop load may also affect vegetative growth, and the degree of foliage shading, thus indirectly impacting K translocation into the berries.
Generally speaking, over cropping may result in a lower or insufficient amount of K in the vine tissues (K deficiency tends to be more pronounced on heavily cropped vines after veraison). At the same time if yield is very (too) low the shoots may become competitive sinks for K and as a result its accumulation in the berries may be reduced .
Vineyard management practices that decrease leaf shading may reduce K accumulation in the berries. Reducing canopy density and shading, either through a) the removal of lateral shoots, b) lateral and top-hedging, or c) basal leaf removal reduced K concentration and, in some cases, pH in juice and wine of Tannat vines in Uruguay (Figure 5) . The use of divided-trellis systems could also be a method to manage highly vigorous vines and decrease leaf shading .
In conclusion, if you suspect a problem with high vine K and/or high juice/wine pH, here a few things you can do:
- Plant tissue (petiole) analysis to assess the K level of your vines and to confirm that high/excessive K is the real issue. Again, don’t rely exclusively on soil testing, which is still useful to assess soil pH and other factors that may affect K uptake.
- If your vines are highly vegetative you could test the effect of reducing foliage shading on juice/wine pH and K. Reducing canopy density may also have additional benefits for the health of the grapes and quality. Canopy practices such as basal leaf removal, hedging, shoot positioning and thinning can be used. It is a good practice to leave a block of untreated vines (no additional canopy management) as a control. At harvest measure juice pH and K concentration in the treated (less shaded) and untreated (more shaded) vines to assess if the extra canopy management mitigate the K/pH level in the grape juice.
If you have tried or panning on trying to manage K levels in your vineyards we would be happy to hear about your experience and methods/results.
- Keller M. 2010. The Science of Grapevines: Anatomy and Physiology. Publisher: Academic Press.
- Mpelasoka BS, Schachtman BP, Treeby MT, Thomas MR. 2003. A review of potassium nutrition in grapevines with special emphasis on berry accumulation. Aust. J. Grape Wine Res. 9, 154–168.
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- Wolf TK. Viticulture Notes. Vol 31 No. 5. 23 July 2016. Virginia Tech University Cooperative Extension. Available at: http://www.arec.vaes.vt.edu/alson-h-smith/grapes/viticulture/extension/news/vit-notes-2016/vit_notes_july_2016.pdf
- Walker RR, Blackmore DH. 2012. Potassium concentration and pH inter-relationships in grape juice and wine of Chardonnay and Shiraz from a range of rootstocks in different environments. J. Grape Wine Res. 18, 183–193.
- Zörb C, Senbayram M, Peiter E. 2014. Potassium in agriculture – Status and perspectives. J. Plant Physiol. 171, 656–669.
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- Moss R. 2016. Potassium in viticulture and enology. Virginia Tech University Cooperative Extension. Available at: http://www.arec.vaes.vt.edu/alson-h-smith/grapes/viticulture/extension/news/vit-notes-2016/kinvitandeno.pdf
- Wolf TK. 2008. Wine grape production guide for Eastern North America. Natural Resource, Agriculture, and Engineering Service: Ithaca, NY USA.
- Wolpert JA, Smart DR, Anderson M. 2005. Lower petiole potassium concentration at bloom in rootstocks with Vitis berlandieri genetic backgrounds. Am. J. Enol. Vitic. 56:163-169.
- Rojas-Lara BA, Morrison JC. 1989. Differential effects of shading fruit or foliage on the development and composition of grape berries. Vitis 28, 199–208.
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By: Bryan Hed
We’re in the final leg of the season and it’s time to size up our remaining challenges through the ripening period. Fruit are no longer susceptible to many of the major diseases like powdery and downy mildew and black rot that can cause crop loss during earlier stages of berry development. But for some grape varieties, particularly wine grapes that produce compact clusters, there is another major hurdle to work through to harvest; late season bunch/sour rot. I am referring to the rotting of fruit in clusters that occurs during the later stages of the ripening period, just a few heartbreaking days or weeks before harvest. Bunch rot can involve the colonization of fruit by a number of different microorganisms, both fungi and bacteria. But the main culprit in most regions of the Northeastern U.S. is the fungus, Botrytis cinerea (Figure 1). Fortunately, we have a number of chemical control options that are quite effective against this fungus that I have listed below. I have organized them according to the FRAC (Fungicide Resistance Action Committee) group that each product belongs to. Basically FRAC groups are fungicide chemistries with the same or similar mode of action, so that pathogen resistance to one fungicide is going to confer cross resistance to another, within that same FRAC group. For example, notice that Vangard and Scala are in the same FRAC group; 9. This means that if a population of Botrytis in a vineyard has developed resistance to the active ingredient in Vangard, then it will also be resistant to the active ingredient in Scala, even though the active ingredients may be different (cyprodinil in Vangard and pyrimethanil in Scala). The mode of action (the way in which the fungicide disrupts a specific metabolic pathway in the fungus, killing it) of these two chemistries is the same, or similar enough that pathogen resistance to one chemistry will confer resistance to the other.
- FRAC group 2: Rovral, 7 day pre-harvest interval
- FRAC group 7: Endura, 14 day pre-harvest interval
- FRAC group 7 (and 3, which is not for Botrytis): Luna Experience, 14 day pre-harvest interval
- FRAC group 7 and 11: Pristine, 14 day pre-harvest interval
- FRAC group 9: Vangard, Scala, 7 day pre-harvest interval
- FRAC group 9 (and 3, which is not for Botrytis): Inspire Super, 14 day pre-harvest interval
- FRAC group 9 and 12: Switch, 7 day pre-harvest interval
- FRAC group 11: Flint, 14 day pre-harvest interval
- FRAC group 17: Elevate, 0 day pre-harvest interval
No doubt many wine grape growers have already applied a bloom, pre-bunch closure, and veraison spray to bunch rot susceptible varieties. However, one or more applications may be necessary in some vineyards. Populations of the Botrytis fungus are quite adept at developing resistance to these fungicides; be mindful to rotate FRAC groups and limit the application of any one FRAC group to one or two per season to delay the development of that resistance. If you have to use a FRAC group more than once per season, it would be better to compose one of those two applications with a material that contains a second FRAC group for Botrytis. For example, if you already used Scala, it would probably be better to apply Switch (after you’ve already rotated to FRAC group 2, 7, 11, or 17) than to apply Vangard or another Scala spray. Most of these materials are considered ‘high risk’ for resistance, so rotation is extremely important to maintaining the effectiveness of these products. Also, pay attention to pre-harvest intervals which range from 0 to 14 days. That said, you can’t spray your way completely out of the damage that Botrytis and other microorganisms can cause; consistently effective bunch rot control programs must be integrated with a generous dose of cultural practices like fruit zone leaf removal, sanitation, canopy management, and vine balance. And, unfortunately, these chemistries listed above are specific for Botrytis and will not control many of the other microorganisms that may make up the bunch rot complex or that lead to the dreaded sour rot complex.
I’ve already alluded to one of the major predisposing factors for bunch rot (including sour rot) in grape clusters, and that is cluster compactness. The compactness of clusters is responsible not only for initiating much of the fruit rot that occurs in clusters, but perhaps more importantly, for the rapid spread of rots throughout the cluster (Figure 2). Rots can be initiated in loose grape clusters as well (by bird or insect damage, for example), but generally do not spread beyond the damaged berry or berries. However, in compact clusters, a single damaged berry can spread rot to large sections of the cluster by virtue of the close contact between those berries. Contact between berries in compact clusters also reduces cuticle thickness, an important barrier to rot pathogens, and reduces pesticide penetration into clusters for protection of berry surfaces against Botrytis and damage by insects. Cluster compactness also increases the effects of retained bloom trash (dead flower parts) inside clusters that can provide a substrate for Botrytis, increasing fruit rot by harvest. Taken together, this generally makes berries in compact clusters much more susceptible to invasion by fruit rot pathogens than berries in loose clusters.
A series of greenhouse experiments we conducted years ago also suggested that latent (dormant) infections of Botrytis can be activated by the kind of berry injury that occurs in compact clusters. Latent Botrytis infections are infections that occur during bloom and the early fruit development period for which you apply that bloom and pre-closure spray. Years ago, we monitored the incidence of latent infections in our block of Vignoles and found that even though the incidence appeared to increase throughout the berry development period, most of these infections did not lead to fruit rot by harvest. In fact, when we inoculated clusters of potted, greenhouse grown Chardonnay vines with Botrytis shortly after bloom, generating high levels of latent infection in berries, the berries did not rot during ripening if they remained intact in the greenhouse, unexposed to weather, birds, insects, or compactness (the clusters were thinned after inoculation and thinned berries were used to determine latent infection levels). However, when we surface sterilized the berries (to eliminate any Botrytis on the outside of berries) and created small injuries at the berry/pedicel interface of ripe berries (the kind of injury that commonly occurs in overcrowded clusters) the vast majority of the inoculated berries quickly rotted compared to berries that were not inoculated with Botrytis (checks).
By loosening clusters, damage from berry overcrowding can be minimized and bunch/sour rot development can be greatly alleviated. Unfortunately, loosening clusters in a consistently effective AND cost effective way is not always an easy thing to accomplish. Over the years we have examined a number of potential methods for cluster loosening with varying levels of success. Treatments such as pre-bloom fruit zone leaf removal have provided the most consistently significant reductions in cluster compactness and fruit rots in most years. The pre-bloom timing of fruit zone leaf removal simply combines the benefits of an open, sun lit fruit zone (which has been well documented by many investigators over the past several decades) with a reduction in cluster compactness and rot susceptibility. In our experiments, this treatment has typically been applied by hand, but the technology exists to mechanically remove leaf tissue around inflorescences (pre-bloom) without serious damage to them, and trials are being conducted to evaluate the mechanization of the pre-bloom leaf removal on a number of grape varieties. So far, results have been mixed depending on variety and trellis training system. In vineyards where we were able to compare pre-bloom mechanized leaf removal with pre-bloom leaf removal by hand and post-bloom mechanized leaf removal, the effects of pre-bloom mechanized leaf removal (increased light exposure of clusters, looser clusters, less rot, yield reduction) generally fell somewhere between the two latter treatments. The hope of this research is to expose growers to some new possibilities for fruit rot control and increase the potential for its adaptation to commercial vineyards and adoption by growers. We’ve examined other technologies with potential for cluster loosening and improved fruit rot control, but unfortunately their adoption is more problematic. For example, we have found that inexpensive gibberellin sprays around bloom have also been effective at loosening clusters and enhancing rot control on Vignoles and Chardonnay with little or no serious negative side effects. But they are currently ‘off label’ and are very unlikely to ever become legal applications in the United States. Also, the effects of gibberellin sprays are variety specific and therefore must be examined and defined for each variety: in our experience, low rates (5-20 ppm) can have serious negative side effects on Vitis vinifera Riesling, whereas rates as high as 100 ppm have had little or no effect on Vitis interspecific hybrid ‘Chancellor’.
More recently, work conducted by Megan Hall, a grad student of Wayne Wilcox at Cornell University, has shown that additional pesticide applications during the latter stages of ripening can significantly reduce the development of sour rot. Her work has shown a close connection between fruit flies and sour rot development; the presence of the flies is important to the accumulation/generation of acetic acid in rotting fruit. Treatments composed of weekly, tank mix applications of an insecticide (to control the flies) and an antimicrobial (to kill bacteria) have been found to reduce sour rots by 50-80% over unsprayed vines. So far, the best results appear to occur when weekly sprays are initiated before sour rot symptoms are observed (preventive sprays before about 15 brix). This exciting work should provide yet another effective option for sour rot control in the wet, humid parts of the eastern U.S. and we are looking forward to hearing more about this rot control option in the near future.
LATE SEASON LEAF DISEASE CONTROL
Beyond the management of bunch rot on susceptible wine varieties, there is also the matter of keeping canopies (leaves) as clean and functional as possible, for as long as possible. Diseases like powdery and downy mildew can continue to be of concern into late summer and early fall, especially for growers of Vitis vinifera. The mildews can greatly reduce leaf function if allowed to spiral out of control. The ability of the canopy to continue to photosynthesize is crucial to the ripening of the crop and canes and the storage of sugars (starch) in trunks, arms, and roots, which relates to winter hardiness. The winters of 2014 and 2015 are harsh reminders of just how important this can be. Allowing grapevines to go into winter dormancy with less than optimal preparation can leave them more susceptible to damage by severe cold and another plague of crown gall to have to deal with for years to come.
Good control of powdery mildew up to about Labor Day can also go a long way to reducing overwintering inoculum and disease pressure the following spring. This finding was the result of some excellent research conducted by Wayne Wilcox, Dave Gadoury and graduate students at Cornell University. When powdery mildew infected leaves die by that first hard frost in fall, the mildew on those leaves stops developing and also dies…unless it has had time to form fully mature, winter resistant resting structures called chasmothecia. If the chasmothecia in a powdery mildew colony do not have time to fully mature before the grape tissue dies (as from infections that were roughly initiated after early September), they will not survive the dormant period (winter) and will not contribute to the bank of primary inoculum that infection periods draw upon the following spring. Knowing this, a grower can get a better handle on the ‘size’ of the powdery mildew problems he/she will potentially face next spring. If, for example, you had heavy mildew development earlier in this season (on clusters and/or leaves), expect to have to deal with powdery mildew early next season and take appropriate action during early shoot growth stages with preventive fungicide sprays. This is particularly important if you are growing Vitis vinifera and much less important for growers of native varieties like Concord and Niagara.
Downy mildew appears to be much less a widespread problem this year. In fact, in our ‘neck of the woods’ along the southern shore of Lake Erie, droughty conditions have prevailed throughout most of the season, and only now are we even beginning to see a few downy mildew infections on leaves close to the ground. At this point in the season regular scouting for this disease is the first line of defense, and in areas that remain relatively dry, perhaps the only control measure needed (?). However, in areas where the disease has remained active throughout the season, be vigilant about keeping it under tight control. Late season epidemics of this disease can quickly strip susceptible wine varieties of their leaves, effectively bringing an early halt to ripening.
For further reading on this and many other disease management topics, refer to the 2016 New York and Pennsylvania Pest Management Guidelines for Grapes. If you don’t have a copy, you can get one through Cornell University press. Every commercial grape production operation should have one!
By: Denise M. Gardner
Well, the time is here – harvest season! And if you haven’t geared up already, it is now crunch time.
In my travels across the state, I am seeing a lot of good things in the vineyard, which makes me eager for the 2016 crop to come into the winery where it can be made into wine. While the drought has impacted a large portion of the state, I’m also seeing good color, tannin, and flavor development in fruit, and am hoping for a nice 2016 vintage. This picture of ripening Pinot Grigio from the Endless Mountains region shows just how far along the fruit is coming into its developed stage.
With all that work that went into a good growing season, please don’t forget that harvest is also about taking the care and time required to make a clean, quality wine. Otherwise, all of that hard work in the vineyard may be lost in the wine! While taking a few short cuts here-and-there can be appealing during the busy harvest season, some short cuts can detrimentally impact final wine quality or even lead to flaws when things like cleaning and sanitation steps are forgotten or minimally implemented in the cellar.
The following blog post will review a few practical steps that winemakers and the cellar crew can take now in order to prepare for the first lot of incoming fruit in an effort to try to minimize stress and chaos during a hectic time of year.
1. Order your harvest materials
While “free shipping” July has passed, if you haven’t ordered your harvest supplies yet, now is the time to do it. Take a few hours and figure out what you will need to get through harvest. This includes anything from sugar and acid to yeast and malolactic bacteria. Don’t forget your sanitizers. There is a PSU Wine Made Easy Fact Sheet that gives a more thorough list of supplies you should make sure to have in the winery and properly stored for use prior to the start of harvest.
2. Get last year’s wines bottled
It goes without saying that getting last year’s inventory moved into bottles will free up tank, barrel and storage space for this year’s incoming fruit. It makes for a much easier transition if all of your wines that need bottling are bottled before harvest season starts. Bottling during harvest is not only chaotic, but it will tire your employees (and you!) and may lead to harvest decisions that may be regretted later.
Always make sure to get your bottled wines properly stored and away from any “wet areas” on the production floor. If possible, bottled wines should have a separated storage area with an ideal storage environment that is physically separated from production. From there, stored wines can be moved into retail space when needed.
3. Check and prepare equipment
Many wineries experience equipment failures during harvest as most of the equipment has been left in storage throughout the winter, spring and summer months and was not routinely used. This lack of use can be wearing on equipment and may lead to equipment failures during production.
Therefore, we recommend pulling out your crusher/destemmer and press to get it up and running before the first grapes arrive. As the equipment is probably dirty, give it a good physical cleaning and sanitation regime to ensure that it is in its best condition before grapes come anywhere near it. I have seen many presses with left over rice hulls inside of them, and cellar staff should be reminded that left over debris are potential contamination sources for microbial spoilage. Additionally, old debris may alter the flavor for this year’s wines, which would minimize the efforts that were taken in the vineyard to mature fruit. To make fresh, clean wines, cleaning and sanitation is quite important.
It is imperative to pull out all of your pumps and ensure that they are actually working before those first grapes arrive. Pull down hoses and ensure they are all properly cleaned. Give the hoses an inspection, clean and re-dry before their first use.
While it is busy work, and it may be tedious, having clean and working equipment is a life saver during the actual harvest period.
4. Double check you have plenty of analytical supplies to get you through harvest
For those that have analytical labs, make sure that your labs are properly stocked with hydrometers, Clinitests, refractometers, pipettes, glassware, pH probes, and all of the associated chemicals that you will need during harvest season. This way, everything is ready to go when you need it.
Get your spreadsheets or data collecting systems prepared prior to when the grapes arrive so that you can easily input data throughout harvest season when you are crunched for time.
5. Timing is everything
If you are like many winemakers in Pennsylvania, you may be making several Pennsylvania-grown fruit wines. Remember that several other fruits can be cold-stored (e.g., apples) or frozen (e.g., strawberries, blueberries, raspberries) until after the grape harvest is completed. When the grape fermentations start to slow down, you can remove the stored fruit for processing and fermentation. This allows you to focus on your grape wines first and then alter your focus to the fruit wines after the busy season associated with the grape harvest has passed.
On a positive side, freezing the other fruits helps to concentrate their flavors and will provide a fruitier base for fermentation.
6. Consider your resources
Remember that Penn State Extension is available to answer questions you may encounter during the harvest season. It is always easier to prevent problems as opposed to fixing them in the wine, so please do not hesitate to use this resource.
Additionally, we have a full 2-page fact sheet and check list for considerations prior to harvest that may be helpful to many winemakers: http://extension.psu.edu/food/enology/wine-production/wine-made-easy-fact-sheets/preparation-for-harvest
When in a pinch, remember that there are calculators online to help you make product additions or alterations:
By: Kathy Kelley
Just a few months ago, On June 1, La Cité du Vin (City of Wine), a.k.a. “the world’s first wine theme park” and “a Guggenheim for grape lovers” (http://bit.ly/1qKzP1h) welcomed its first visitors. I was able to visit this amazing facility at the end of June as part of the 10th Annual American Association of Wine Economists’ Conference that took place in Bordeaux, France (http://www.wine-economics.org). Just as I provided a bit of information about last year’s visit to the Brotte Wine Museum, Chateauneuf du Pape, France (http://bit.ly/2c325uQ), I wanted to share some images from my La Cité du Vin visit with our readers.
The impressive structure resides along the Garonne River and took three years to complete and cost approximately 91.5 million U.S. dollars (excluding Value Added Tax, http://bit.ly/2cavUJU). According to the architects, the design reflects “a space shaped by symbols of identify: gnarled vine stock, wine swirling in a glass, eddies on the Garonne. Every detail of the architecture evokes wine’s soul and liquid nature” (http://bit.ly/2bcpEB9). Even from a great distance it is fairly easy to navigate to the building as it shimmers in the sunlight.
Click on the following URL to see an aerial view of the structure: http://bit.ly/2be9ep6
As I’m sure you can imagine, our group of 100+ was anxious to get inside and explore. As soon at the doors opened at 9:30 a.m. (the entrance time that was booked for us) little time was wasted before we climbed a flight of stairs to the permanent exhibit.
Though tickets (approx. $22) are sold with entrance times on the hour and half hour, there is no limit as to how long visitors can spend in the permanent exhibit. Because of our group’s schedule for the afternoon (which consisted of a winery tour and tasting and a visit to Saint Emilion, a small town in the region), we had approximately one and a half hours to explore. With so much to see and since many displays are interactive – we could have easily spent half a day or more in La Cité du Vin. With a restaurant and café on site – we could have probably spent the entire day. What I describe below is just a portion of what we saw during or short time in the permanent exhibit.
Learning about some of the basics
One of the first displays that we visited was called e-vine. The handheld audio device that we received at the exhibit’s entrance allowed us to scan codes on the display and learn about topics such as biodiversity and specific grape varieties. For example, by scanning the code on the Viognier leaf I could either listen to a narrator talk about the grape, aromas, wines made from the grape, main producing countries, and similar or read the text that appeared on my device’s screen.
Wine portraits: The six major wine families
Other displays in La Cité du Vin also had this level (or greater) degree of interactivity. After entering the wine portraits display (below), we were encouraged to enter one of six bottle-shaped booths, each focusing on one of the “six major families” (http://bit.ly/2bt2moE): dry white, red, rosé, sparkling, fortified, and sweet.
I first chose the sparkling display. By touching the screen I could make “bubbles” and pull up a menu of related topics that included production methods, economic importance, history, and sensory characteristics.
A tête-à-tête with wine experts & testing my wine knowledge
Imagine being able to have a one-on-one (sort of) with some of the world’s most renowned wine experts. During my visit, I had the opportunity to learn from Olivier Poussier (winner, world’s best sommelier, 2000) about the intricacies of wine. While he did all of the talking, it was a pretty interesting way of learning about his thoughts and his approach to enjoying wine.
I also got the chance to test my wine knowledge. After selecting one of the four levels of difficulty, ranging from young audiences to expert, I answered 10 true/false and multiple choice questions. Again, an interesting and interactive way to learn about wine.
“The Buffet of the 5 Senses”
Anyone visiting the La Cité du Vin would expect a display or two on the senses and wine, thus “The Buffet of the 5 Senses” exhibit. Do you want to really experience the aromas of what can be detected in wine? This can be achieved by leaning into a funnel connected to a bell jar that is filled with lemons/lemon oils, honey combs, etc. By simultaneously pumping a black rubber squeeze bulb and breaking in through the nose – visitors can experience the pure essence of these and other “everyday smells” such as pencil shavings and mint.
How important is wine to cultures and economies?
Interested in learning about how wine economies across the globe differ? Perhaps you are even interested in learning about how wine has impacted culture and how the industries have evolved in old and new world wine countries. Or, perhaps you would like a refresher on how climate impacts what grape varieties are grown in different regions and where they originated. In the worlds of wine display visitors can spin different globes and learn about these topics specific to various regions and/or countries. The corresponding information is then projected on the screen attached to the globe.
By spinning the wine and economy globe and positioning the screen in front of western Europe – I could see symbols that represent the extent to which the wine industry impacts each country’s economy.
How Bordeaux has changed over time
Not only do visits learn specifically about wine, but how Bordeaux has changed in appearance, size, and purpose since the Middle Ages. In essence, “how a great commercial port gave birth to a land of mythical wine” (http://bit.ly/2bzwoZe).
In the “Bordeaux: the city and its wine” display, visitors can place one of the four different chess-piece like figurines, each representing a specific period in time, on the interactive board. A series of corresponding digital images and text then appears on the screen above. For example, by placing the figurine that corresponds to the medieval period (that I have circled in red, see image below) on one of the white circles on the interactive board (at the point of the red arrow) I was able to explore the city as it would have appeared prior to the 16th century, including the port of Tropeyte, which (as you might guess), wine was “the main export product” (https://nda.revues.org/2577#tocto1n2).
A tasting and a view
How else could you end a tour of this much anticipated, experiential wine theme park? With a wine tasting of course. The entrance fee includes a tasting of one wine or, for those who don’t imbibe or children, grape juice. Never had the chance to try Chinese, Croatian, or Greek wine? You can taste one of these at the Belvedere – a tasting room 115 feet above street level.
Though wine glasses are not allowed on the deck surrounding the tasting room, visitors can enjoy a nearly 360 degree view of the Garonne River and the surrounding cityscape.
Plenty of souvenirs available to commemorate a visit
Just as you might pick up a souvenir at a traditional theme park, there are plenty of items for purchase at La Cité du Vin. In addition to the tradition gift shop and the types of items you might expect to find, visitors can walk through Latitude20 and view more than 800 wines with selections from Syria, Ethiopia, Namibia, Peru, Bali, and Tahit. If buying a bottle doesn’t appeal, there are 50 wines that are sold by the glass.
Again, that is just a portion of what you will find when you visit La Cité du Vin. Just like visiting a theme park – visitors would benefit from planning their day in advance. To prepare for your visit, click on the link to La Cité du Vin: http://www.laciteduvin.com/en. In addition, the following article published by the Decanter provides information on traveling to Bordeaux, finding the La Cité du Vin, and a helpful presentation of the floor plan: http://bit.ly/2bfEVeC.
By: Kevin Martin, Penn State Extension Educator
The following article illustrates the business cycle of the juice grape market. Long-term demand for juice has been stagnant. Long-term demand for boutique and local wine has been growing slowly. At the moment the U.S. wine industry is hitting its stride and in a very different stage of the price cycle. In fact, the U.S. wine industry is providing an important buffer to juice grape growers, which are finding more and more of their commodity being used in fermented and craft beverages.
Despite the differences in trends and the business cycle wine grapes remain a global economic market subject to a similar business cycle. Small growers and value added growers will remain somewhat isolated from macroeconomic trends but will likely still see some exposure to these risks. The following observations illustrate the importance of using working capital when prices are relatively higher to prepare an agricultural operation for periods of declining prices.
Current juice grape markets also directly impact the actual price of some native grape varieties as well as the relative value of hybrid grape varieties. Growth in the wine industry is driving an increase in the price of acid, relative to the price of sugar. While brix previously defined commodity value, earlier harvest dates allow juice to be utilized to support newer trends in wine production. We are now seeing a shortage of acid in the market and a shift of actual acreage and production toward fulfilling that need.
As Lake Erie vineyard owners move through this grape market cycle, observing the various strategies employed to position the operations for future continued success is both interesting and informative. While bulk prices have fallen by 60% from peak, farm gate value of Concords with markets has fallen between 20% and 60%. While there is no average grower, the weighted average decline in farm gate value is 30%.
Growers entering the period of price decline in varying financial positions. As a result, we are seeing varying strategies on operations. Equipment investments are almost holding steady. Primarily the focus has been on mechanization and renewal of depleted assets. Many of these investments are sometimes less than optimal for the vineyard but they remain evidence of strong farm finances thus far. Controlling capital expenses can improve financial efficiency, unless the investments provide significant improvements in operational efficiency. That being said, it does indicate that some growers remain in a position of relative strength.
As markets were disrupted by marketing contract cancellations and reductions, we are seeing an increase in the growth of average farm size. These investments make a great deal more sense. The increase in farm size usually shows a decrease in the amount of capital per acre. Over the long-term these investments, when priced correctly, should provide positive returns for these growers. The main concern in increasing business size during a commodity price trough is planning cash flow for the entire length of the recovery.
In prior cycles we have seen this work out to varying levels of success. With credit now tightening a bit growers that over extend themselves sometimes rely on reducing production costs in an attempt to weather the storm. Sometimes in a dry year like this, there is money to be saved on spray applications. Overall, though, consistent and forced frugality based on available finances tends to lead to vineyard decline. In a business where maximum production is highly correlated with maximum gross profit, this can undermine a business plan that justifies a mortgage very quickly.
On the other side of things, growers that have the financial resources and make conservative yield and price estimates tend to do well. For instance, if a grower can make a land purchase work operating under the assumption of 85% of historical yields at current prices for 5 years, that grower is in a sustainable position to survive under some of the greatest historical challenges the industry has faced. His risk would be a challenge of unprecedented proportions based on a new normal, rather than historical information.
We are seeing some growing pains as the number of vineyard operators managing more than 300 acres is growing very quickly. Despite multi-row equipment, new harvesters, and innovative strategies at these sizes full-time laborer(s) are a new normal. Traditionally the growth of acreage has not outstripped the pace of technological innovation. Now we are seeing a dramatic increase in paid labor costs between May and August. This was a period in time when only the largest growers hired help. Now, we have a significant number of 100 – 200 acre growers finding a need for full time labor. Those growers are no longer the largest growers in the industry.
At 200 acres a farm can justify some year-round paid labor. With the average age of growers very close to social security early retirement age, I don’t see outside labor putting an undue strain on farms if kept to a minimum and managed well. There’s the rub, of course. Growers typically specialize in growing, not managing a workforce. Farms less than 175 acres also require year round labor that should likely total less than full-time, unless the grower owner is above retirement age.
One real struggle with full-time labor management will be the balance of a growers’ ability to pay as compared with the workers’ ability to find opportunities elsewhere. The trend of increasing paid labor during the growing season began during the 2007 downturn, when local unemployment got very close to double digits. Contrast that with today, a market with declining unemployment, increasing wages and low grape prices.
A typical model is about one FTE per 100 acres of grapes, minus the first 100 acres. So a typical grower would have 1 FTE on a 200-acre farm or 2 FTE on a 300-acre farm. All of the labor is not new. Typically, year round labor does replace many of the functions and services traditionally provided by seasonal and temporary work. Even so, as a point of reference, every dollar of wage increase is an additional cost of three cents per vine or $20 per acre.
Growing a farm from 100 acres to 200 will require the development of some labor management skills. Effectively using and managing hired help and delegating tasks will increase the efficiency of hired labor to allow for adequate compensation and the relative growth of farm profitability.
For some perspective on justifying the cost of labor to increase farm size, we only need to look as far as capital and depreciation. A 100-acre grower would usually see a decline in depreciation from over $300 per acre to $200 per acre by doubling farm size. Furthermore, the capital invested in the farm, on a per acre basis would also decline. Capital investment would decline from $7,250 to $6,500.
The decline in depreciation and capital investment are operating on many of assumptions but those assumptions are based on typical farms we observe. A relatively frugal farm would have relatively lower expenses. A farmer with newer and more advanced equipment would have higher expenses. Generally speaking, the relative savings is somewhat uniform. More specifically, though, we should address the extremes. A grower likely to over-invest in capital will be much more successful with a larger farm. A grower that drifts toward being overly frugal will operate with more relative success on a smaller farm. He will still improve efficiency by growing, but perhaps less so. As an example, eventually the repair work on the Mecca harvester becomes cost prohibitive and represents a strategic risk for the business and its ability to harvest before processors close.
Despite the example above, generally speaking the grower that tends to be overly frugal on capital expenditures, but not operating costs, will likely be the most successful of all grower types as that grower expands his operation and remains flexible and open to strategic and important capital investments.
The strategic expansion of vineyards will continue to be a long-term trend. For individual operations, expansions should be timed when cash-flow, resources and labor allows. Growers with an ability to meet those criteria are the most likely to find expansion sustainable. Given the current market climate, the ability of growers to take on significant acreage is surprising. It does bode well for the long-term sustainability of the industry, as it appears most of these investments are likely sustainable.
Despite some recent indications that prices are rising very slightly, those trends are young and processor specific. When planning out over the next 2 – 5 years, I do think it is fair to plan for relatively flat prices. I don’t expect dramatic declines in price at this point. Some upside, at some point, is inevitable. Trying to determine exactly when that happens is impossible. I might expect higher prices in the next 5 years, but when planning for business operations I would not count on it.
By: Dr. Michela Centinari
It is August already, which, for many grape growers in Pennsylvania, means veraison and the beginning of fruit ripening. It seems a good time to comment on the seasonal weather and how it can affect the vines. In July, above average temperatures were recorded in Pennsylvania , and drought conditions varied from ‘none’ to ‘severe drought’ across the state (Figure 1). The regions most affected by drought are North Central, Northwest, and some areas of Northeast PA .
In Figures 2 and 3 I reported the cumulative growing degree days (GDDs) (April to July) and precipitation (March to July) recorded at the two Penn State research and extension stations located in the South Central (Biglerville, Adams County) and Northwest (North East, Erie County) part of the state (http://newa.cornell.edu/). I also included the 2014 and 2015 data so you can compare the heat accumulation (GDDs), precipitation patterns and amount this year with those of the two previous seasons.
When looking at figures 1, 2, and 3, please keep in mind that local weather conditions vary greatly, shower and thunderstorm activity was hit or miss across the state. It is indeed recommended that growers install a weather station at their site to carefully monitor weather conditions and assist with disease control programs.
Compared to 2014 and 2015, this growing season started with lower heat accumulation in some areas of Pennsylvania, such as the Northwest (Figure 2A) and South Central (figure 2B) regions. Higher than average temperatures recorded in July however, pushed GDDs close to or above those of the same period last year. For example, in Erie County, cumulative GDDs were, by the end of July, above those accumulated in 2015 or 2104. In South Central PA GDDs are reaching the 2015 values and they are above those accumulated in 2014 for the same period (April-July).
The hot temperatures recorded in July can accelerate fruit ripening . For example, in Central Pennsylvania, Noiret (Vitis hybrid), which is not one of our earliest varieties, started to turn color last week (i.e., the first week of August), approximately 10 days earlier than last year.
While drought conditions have not been recorded in the Southeast and most of the Southwest regions, it has been dryer than average in the rest of Pennsylvania. For example, in North East (Erie County, Northwest) cumulative precipitation from March to July (13.6²) was 40% and 36% lower as compared to last year (22.6²) and two years ago (21.12²). In Biglerville (Adams County, South Central) cumulative precipitation from March to July (12.7²) was 33% and 31% lower as compared to last year (19.2²) and two years ago (18.4²).
Drought doesn’t always equal water stress
In- and across-season precipitation patterns in the eastern US are unpredictable. In our humid climate, precipitation and the soil water reservoir are usually sufficient to meet (or exceed) vine water requirements through ripening. Even if a drought period occurs, its duration and severity are not usually sufficient to warrant concern about moderate or severe vine water stress. Growers do however need to be aware that non-irrigated grapevines in temperate climates can occasionally face water stress during drought periods in the growing season [3; 4].
Hot temperatures, like those recorded in July, increase evapotranspiration and how much water the vine needs. This could facilitate the occurrence of vine water stress in areas that have been experiencing persistent lack of rain. The risk of water stress, indeed, not only depends on the amount of soil water available (supply), but also on how fast this water is used by the vines (demand) .
Along with seasonal rainfall and winter soil moisture other factors affecting the amount of water available (water supply) to the vines are:
- Soil water holding capacity which is determined by the soil textural properties: heavier soils (loam and clays) hold more water than light sands or gravels. For example, a unit volume of sandy-loam soil can hold about 50% as much water as a clay soil .
- Soil depth: deep soil can hold a greater volume of moisture than shallow soil  allowing grapevines, in the absence of restrictive layers, to develop a more extensive and deeper root system which can access deep resources of water during drought periods.
- Grapevine root system size and rooting depth: In addition to soil characteristics, also the age of the vine will influence root system size and rooting depth. Young vines have restricted root systems and rooting volume for several years, thus they are more sensitive to water stress than mature vines with well-established root systems .
- Presence of competitive plants, as green and actively growing cover crops and weeds in the middle-row and in-row areas.
Water demand is primarily driven by weather conditions (solar radiation, air temperature and humidity). For example, evaporation from an open pan under hot and dry weather (i.e., California) can be around 8-10 inches of water per month, whereas under cool and humid condition, typical of the northeast US can be less than 5 inches . Also the amount of sun-exposed transpiring leaf area and crop load will affect the amount of water used by the vines . For example vines trained to GDC or high-wire cordon tend to have greater sun-exposed leaf area that can capture more sunlight and use more water than those trained to vertical shoot positioning (VSP) . Heavily cropped vine vines also require more water for fruit ripening than vines with a smaller crop .
Vine response to water stress varies with the severity of the stress and the timing of the season it develops
Growth processes (i.e., shoot growth, early berry growth) are more sensitive to water deficit than photosynthesis . Therefore, a mild/slight water stress between fruit-set and veraison can favorably diminish vegetative growth and reduce berry growth leading to smaller berries with potentially higher skin to pulp ratio without compromising photosynthesis and carbohydrates/sugars production . Under moderate to severe water stress conditions, however, photosynthetic activity is reduced possibly leading, early in the season, to poor canopy development and function. Later in the season (after veraison) a reduction in photosynthesis can decrease sugar accumulation in the berries with a negative effect on fruit ripening and flavor development. Further, a reduced storage of carbohydrates and other nutrients in perennial organs may occur. Thus, it is crucial to maintain a healthy and functional canopy after veraison to avoid negative effects on fruit or wine quality and cold hardiness. Furthermore, because after veraison, berry growth is quite resistant to water stress, a post-veraison water deficit is not as effective in reducing berry size as a pre-veraison one .
Growing up in Italy, I remember the old-world “wine dilution theory” that supported the idea that any irrigation after veraison would lead to an increase in berry size (due to water dilution) and a reduction in wine quality . There was not strong scientific evidence, however, supporting this assumption. It was actually found that water doesn’t move into the berry after veraison due to complete or partial lost in xylem functionality  which proved that irrigating the vines after veraison doesn’t actually impact berry size . Thus, nowadays it is recommended to avoid moderate to severe water stress after veraison to ensure vine health and proper ripening and flavor development.
Symptoms of vine water stress:
Since vines change in appearance under water stress conditions it is a good practice to walk through the vineyard and look for sign of water stress, starting with young vines. A comprehensive table that summarized visual symptoms of increasing water stress from mild to severe can be found in the “Wine grape production guide for eastern North America” (page 172) and also available in the July issue of Viticulture Notes  edited by Tony Wolf, professor of viticulture at Virginia Tech University.
Below I summarized some of the visual indicators of vine water status, from ‘well-watered’ to ‘severe drought’ conditions 
Well-watered vines (Figure 4):
- Shoot tips are actively elongating
- Tendrils are turgid and expand well beyond the shoot tip
- Leaves orientation: leaf blades are oriented toward the sun
- Leaf color and temperature: canopy is green and healthy and leaves are cooler than our body temperature
- Berries are turgid
Mild to moderate water-stressed vines:
- Shoot tips are compressed and they are enclosed when the last formed leaves are pushed toward the growing tip (Figure 5A)
- Tendrils are drooping or wilted
- Leaf orientation: leaves are oriented away from the sun
- Leaf color and temperature: leaves (starting from the basal leaves) are grayish-green to light-green and they are warm to touch at mid-day (> 100°F)
- If it occurs around bloom/ fruit-set, berry-set may be reduced
Severe water-stressed vines:
- Shoot growth has stopped and shoot tips are dry or aborted
- Tendrils dried or abscised
- Leaf orientation: leaves may roll and dry
- Leaf color and temperature: leaves (starting from the basal leaves) are yellow with necrotic edges (Figure 5B) and they are very warm (well above 100°F)
- Cluster rachis tip may dry if stress occurs at bloom, fruit-set may be reduced, berries may become flaccid if water stress occurs post-veraison
Water stress in a young planting must be avoided because it can compromise root system establishment and overall vine growth, delay its capability to carry a crop, and reduce cold hardiness. If you notice signs of water stress in young vines and you don’t have a permanent and functioning irrigation system in place, temporary irrigation systems could be used such as a flex tank and hose. It is a very labor intensive operation but it is crucial to ensure the long-term success of your investment. If you notice any sign of severe water stress on your mature vines and you are not able to irrigate them you may want to consider shoot and crop-thinning (especially in heavily cropped vines) to reduce vine demand for water, as well as avoid growth of weeds which can compete with vines for water supply .
- United States Drought Monitor: http://droughtmonitor.unl.edu
- Wolf TK. Viticulture Notes. Vol 31 No. 5. 23 July 2016. Virginia Tech University Cooperative Extension. Available at: http://www.arec.vaes.vt.edu/alson-h-smith/grapes/viticulture/extension/growers/current_VN_newsletter.pdf.
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- Lakso AN. 2000. Basics of Water Balance in New York Vineyards. 29th NY Wine Industry Workshop, NYS Agric. Exper. Sta., p 94–101.
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- Keller M. 2010. The Science of Grapevines: Anatomy and Physiology. Publisher: Academic Press.
- Hansen M. 2016. Rethinking post-veraison irrigation. Vineyard & Winery Management. July-August, 2016. 60–
- Hoheisel G, Moyer M. Grapevine management under drought conditions. Washington State University Extension. EM4831E. Available at : http://cru.cahe.wsu.edu/CEPublications/em4831e/em4831e.pdf