Dr. Michela Centinari, Assistant Professor of Viticulture, Department of Plant Science
Another growing season has started for many Pennsylvania grape growers. Unfortunately, but not surprisingly, we are seeing and hearing of situations of vine winter injury across the State. This past winter, the lowest temperatures occurred at the end of January and during the first two days in February, with values around -5 °F (-20.6 °C) here in State College (central PA) and even lower temperatures were recorded at other locations.The injury seemed to have mainly affected Vitisviniferavarieties with reports of bud kill up to almost 100% for the most cold-sensitive varieties and, in some cases, trunk splitting.Growers also noticed uneven /nonuniform budburst which is typical of winter-injured vines. We ask that more growers share their experiences with us; in particular, we would like to know if growers made any pruning adjustments and what the results are/have been.
Since winter injury is a reoccurring issue for the eastern US, during certain years, we have covered topics related to vine cold hardiness, injury assessment, and pruning techniques for winter-injured vines at Extension meetings. Also, we have posted an announcement that focused on Pruning strategies for cold climate viticultureon the Penn State Viticulture and Enology Facebook page in January 2019, just before the “Arctic Vortex” event hit our region. Please do not hesitate to contact us if you have questions on how to manage cold-injured vines.
We heard from several PA growers in southern and central PA that budburst occurred earlier this year, a week to 10 days is what has been typically reported, than in 2018. This was also true for the hybrid varieties grown at the Penn State research farm at Rock Springs (central PA). I checked the growing degree days (GDD), a widely used index of heat accumulation, data calculated by the Network for Environment and Weather Applications (NEWA Cornell) for weather stations located in North East, Erie (northwestern PA), Biglerville (south-central PA), and Reading (southeast PA). Although historic data are not available, I compared the average GDD accumulated from January 1 to May 15 for 2013-2017 to those accumulated for the same period in 2018 and 2019 (Figures 1, 2 and 3).
Trends across locations/regions
Not surprisingly, it was cooler in Erie compared to south-central and southeastern PA between January to Mid-May, not just in 2019 but for each year analyzed. In 2019, approximately 158 GDD accumulated between January 1 to May 15 in Erie, while GDD were at least double in south-central and southeast PA. Differences in temperatures across regions and locations explain why budburst typically occurs much earlier in southeast PA compared to the northwestern part of the state.
Difference between years
In Erie, the GDD accumulated between January to mid-May 2019 (red line) were slightly lower than those for the same period in 2018 (blue line) and for the 2013-2017 average (black line). Also, note that there was no accumulation of GDD for a few days in May 2019 due to cool temperatures (Figure 1). The trend, however, was opposite in south-central and southeast PA, at least at the locations reported in this post. April was warmer (higher GDD) in 2019 compared to 2018 and the 2013-2017 average. While warmer spring temperatures favor earlier budburst they also increase the chance of freeze injury to green, tender plant tissues (Figure 4).
At several locations across PA, temperatures were below freezing in the early morning of April 29 and some varieties were close to or already passed budburst. Below freezing temperature does not necessarily mean freeze injury as many factors affect the temperature at which the plant tissue is damaged or killed. However, the freeze event on April 29 did cause freeze damage to vines at several locations, while others avoided the damage by using frost protection methods, such as frost dragons. Some of the varieties grown at the Penn State research vineyard at Rock Springs, chiefly Marquette and young LaCrescent vines, sustained freeze injury. It is too early to estimate crop losses, but at least we are seeing some secondary shoot development (Figure 5).
How to recognize a secondary from a primary shoot
A relatively easy way, especially for caned pruned vines, is to check the angle of projection from the cane. Primary shoots typically grow with an angle of 45°, while secondary grow at an angle of 90° (figure 5).
You can learn more about the basics of spring freeze injury and methods of protection at https://extension.psu.edu/understanding-and-preventing-spring-frost-and-freeze-damage
It is almost time for some early season canopy management practice. Please check the following articles if you need information on shoot thinning or early leaf removal:
On March 5, 2019, Penn State researchers and Extension personnel presented research findings and provided five-minute overviews of upcoming studies at the 2019 Wine Marketing & Research Board Symposium, held in conjunction with the Pennsylvania Winery Association Annual Conference.
In this post, we have included short summaries of what each presenter discussed during their session along with a PDF/access to their presentation.
Under-vine cover crops: Can they mitigate vine vigor and control weeds while maintaining vine productivity?
Presented by Michela Centinari, Assistant Professor of Viticulture, Suzanne Fleishman, Ph.D. Candidate, and Kathy Kelley, Professor of Horticultural Marketing and Business Management
Michela, Suzanne, and Kathy discussed research conducted at Penn State related to the use of under-vine cover crops as a management practice alternative to herbicide or soil cultivation. Michela reviewed potential benefits of under-vine cover crops, such as reduction of excessive vegetative growth, weed suppression, and reduced soil erosion. She showed how the selection of cover crop species depends on the production goals of a vineyard, climate, vine age, and rootstock. Suzanne presented results from her research project. She is investigating above- and belowground effects of competition between a red fescue cover crop and Noiret grapevines, comparing responses between vines grafted to 101-14 Mgt vs Riparia rootstocks. Surveys will be administered to Pennsylvania grape growers and wine consumers in the Mid-Atlantic region. Growers will be asked to respond to questions about interest in using cover crops and benefits that could encourage their use. The consumer survey will focus on learning whether cover crops use would impact their purchasing decision and if they would be willing to pay a price premium for a bottle of wine to offset additional production costs.
Impact of two frost avoidance strategies that delay budburst on grape productivity, chemical and sensory wine quality.
Presented by Michela Centinari, Assistant professor of Viticulture
Crop losses and delays in fruit ripening caused by spring freeze damage represent an enormous challenge for wine grape producers around the world. This multi-year study aims to compare the effectiveness of two frost avoidance strategy (application of a food grade vegetable oil-based adjuvant and delayed winter pruning) on delaying the onset of budburst, thus reducing the risk of spring freeze damage. Our objectives are to: i) evaluate if the delay in budburst impacts grape production and fruit maturity at harvest, as well as chemical and sensory wine properties; ii) elucidate the mechanism of action of the vegetable oil-based adjuvant through an examination of bud respiration and potential phytotoxic effects; and iii) assess the impact of the two frost avoidance strategies on carbohydrate reserve storage and bud freeze tolerance during the dormant season.
Toward the development of a varietal plan for Pennsylvania wine grape growers.
Presented by Claudia Schmidt, Assistant Professor of Agricultural Economics, and Michela Centinari, Assistant Professor of Viticulture
Claudia Schmidt is a new Assistant Professor of Agricultural Economics with an extension appointment at Penn State. Claudia used the opportunity of the symposium to introduce herself to the industry. In her presentation, she first gave an overview on what and where Pennsylvanians buy their wines and spirits. She then talked about the research needed to develop a varietal plan for the Pennsylvania grape and wine industry to match existing and future grape production and variety suitability with anticipated consumer demand. The immediate next steps on her research agenda are to develop a baseline survey of grape production in Pennsylvania and, in collaboration with Michela Centinari, region specific cost of production of grapes.
Survey for grapevine leafroll viruses in Pennsylvania: How common is it, and how is it effecting production and quality?
Presented by Bryan Hed, Research Technologist
This is a continuing project funded by the PA Wine Marketing and Research Board, that has focused on the determination of the incidence of grapevine leafroll associated virus 1 and 3 (the two most economically important and widely distributed of the leafroll viruses) in commercial vineyard blocks of Cabernet franc, Pinot noir, Chardonnay, Riesling, and Chambourcin, across the Commonwealth. Over two years, the survey has shown that grapevine leafroll associated viruses 1 and/or 3, were present in about a third of the vineyard blocks examined. Infection of grapevines by grapevine leafroll-associated viruses can have serious consequences on yield, vigor, cold hardiness, and most notably fruit/wine quality. Bryan also discussed a second phase of the project, anticipated to continue for at least another two years within 6 vineyard blocks of Cabernet franc, identified in the survey. In these vineyards, we plan to plot the spread of these viruses, examine and report their effects on grapevine vegetative growth, yield, and fruit chemistry, and characterize the influence of inter- and intra-seasonal weather conditions on virus-infected grapevine performance.
Integrating the new pest, spotted lanternfly, to your grape pest management program.
Presented by Heather Leach, Extension Associate
Spotted lanternfly (SLF) is a new invasive planthopper in the Northeast U.S. that threatens grape production. Heather covered the basic biology, identification, and current distribution of SLF. She also presented on the economic impact of SLF in the grape industry and ways to manage SLF in your vineyard. SLF can feed heavily on vines causing sap depletion in the fall which has resulted in death of vines, or failure of vines to set fruit in the following year. While biological controls such as pathogens and natural enemies along with trapping and behaviorally based methods are being researched, our current management strategy relies on using insecticides sprayed in the vineyard. Heather showed results from the 2018 insecticide trials conducted against SLF, with efficacy from several products including bifenthrin, dinotefuran, thiamethoxam, carbaryl, and zeta-cypermethrin. You can read more about the results from this trial here: https://extension.psu.edu/updated-insecticide-recommendations-for-spotted-lanternfly-on-grape
Five-minute research project overviews
Impact of spotted lanternfly on Pennsylvania wine quality.
Presented by Molly Kelly, Extension Enologist
The Spotted Lanternfly (SLF) presents a severe problem both due to direct damage to grapevines as well as their potential to impact wine quality. Insects are known to produce or sequester toxic alkaloid compounds. The objectives of this study include characterizing the chemical compounds in SLF and production of wines with varying degrees of SLF infestation. We can then provide winegrowers with recommendations for production of wine from infested fruit. Toxicity studies will be conducted to determine the levels of toxic compounds in finished wine, if any, using a mouse bioassay.
Exploring the microbial populations and wild yeast diversity in a Chambourcin wine model system.
Presented by Chun Tang Feng, M.S. Candidate, and Josephine Wee, Assistant Professor of Food Science
In Dr. Josephine Wee’s lab, we are interested in the microbial population and diversity associated with winemaking. When it comes to wine fermentation, not only are commercial yeasts involved in this process, but also many indigenous yeasts. Our research goal is to isolate the wild yeasts and assess their feasibility of wine fermentation. We are expecting to explore the unique yeast strains from local PA which are able to make a positive impact on wine flavor.
Rotundone as a potential impact compound for Pennsylvania wines
Presented by Jessica Gaby, Post-Doctoral Scholar and John Hayes, Associate Professor of Food Science
This study will examine Pennsylvania consumers’ perceptions of rotundone with the goal of determining whether a rotundone-heavy wine would do well on the local market. This will be examined from several different perspectives, including sensory testing of rotundone olfactory thresholds, liking and rejection thresholds for rotundone in red wine, and PA consumer focus groups. The ultimate aim of the study is to determine the ideal concentration of rotundone in a locally-produced wine that would appeal to PA consumers.
Defining regional typicity of Grüner Veltliner wines
Presented by Stephanie Keller, M.S. Candidate, Michela Centinari, Assistant Professor of Viticulture, and Kathy Kelley,
Grüner Veltliner(GV) is a relatively new grape variety to Pennsylvania, and while climatic conditions are favorable to its growth, the Pennsylvania wine industry is still becoming familiar with the varietal characteristics of GV grown and produced throughout the state. This study focuses on defining typicity of Pennsylvania-grown GV wines. Typicity is described as the perceived representativeness of a wine produced from a designated area, and defining typicity can improve wine marketing strategies. This study uses multiple experimental sites across the state to create wines from a standardized vinification method. The wines will be analyzed using both instrumental and human sensory methods.Surveys will be administered to Pennsylvania grape growers and white wine consumers in the Mid-Atlantic region. Growers will be asked their interest in growing GV and what perceived and real barriers may impact their decision to grow the variety. The consumer survey will focus on understating how to introduce them to a wine varietal they may be less aware of and what promotional methods may encourage them to purchase the wine.
Boosting polyfunctional thiols and other aroma compounds in white hybrid wines through foliar nitrogen and sulfur application?
Presented by Ryan Elias, Associate Professor of Food Science, Helene Hopfer, Assistant Professor of Food Science, Molly Kelly, Extension Enologist, and Michela Centinari, Assistant Professor of Viticulture
The quality of aromatic white wines is heavily influenced by the presence of low molecular weight, volatile compounds that often have exceedingly low aroma threshold values. Polyfunctional varietal thiols are an important category of these compounds. This project aims to provide research-based viticultural practices that could lead to increases in beneficial varietal thiols in white hybrid grapes. The expected increase in overall wine quality will be validated both by measuring the concentrations of these desirable compounds (i.e., thiols) in finished wines using instrumental analysis and by human sensory evaluation, thus providing a link between the viticultural practice of foliar spraying and the improvement of overall wine quality.
By Bryan Hed, Andy Muza, and Michela Centinari
For this week we would like to devote our blog to Jody Timer, our grape insect pest specialist at the Lake Erie Regional Grape Research and Extension Center in North East, PA, who retired at the end of February.
Jody came to work at the Penn State research center in August of 2004, filling a position long since vacated by her predecessor, Sudha Nagarkatti. With an M.S. degree in Biology and many years of experience monitoring water quality and chemistry for a company in the North East area, Jody was hired to work at the North East lab as a skilled technician for Dr. Michael Saunders of the Entomology Department at the University Park campus. From day one, Jody was a passionate researcher for grape growers in the Lake Erie Region and eventually the whole state for almost 15 years (how the time flies!). Her main research has always focused on control methods for the grape berry moth and how this knowledge can be applied to management programs. In that regard she and her technician, Mike Schultz, have spent countless hours each season monitoring berry moth populations on several local commercial farms in the Lake Erie region, and working closely with Andy Muza, Erie County extension, to provide real-time updates on pest pressure for local juice grape growers.
She has also played key roles in the study of a number of invasive pests like Japanese beetle, Multicolored Asian Lady Beetle, Brown Marmorated Stinkbug, Spotted Wing Drosophila, and most recently, Spotted Lanternfly. One of my most memorable moments in working with Jody was my involvement in one of her experiments to taste test stink bug tainted Concord grape juice; one of the reasons I shudder at the mere mention of ‘cilantro’.
Jody’s position was mostly devoted to conducting research but she often played the part of teacher through extension presentations of science-based recommendations for grape growers at regional meetings like the Mid-Atlantic Fruit and Vegetable Convention in Hershey, PA; statewide meetings like the spring grape disease and insect pest workshop; and local extension meetings such as coffee pot meetings and the mid-summer chicken BBQ in the Lake Erie region. Jody is also a world traveler and, having been to many exotic places across the world, she has a unique and heightened perspective that most people only experience through TV and books. I’m sure that she is looking forward to seeing many more places with her husband, Rich, after her retirement. For those of us who worked closely with Jody over the years, she will also be remembered for her hard work ethic, devotion to her family, and her great sense of humor. Jody’s retirement will leave a large hole in our grape team and our efforts to serve the grape growers of Pennsylvania. We wish her well in her retirement.
By: Conor McCaney, Graduate Assistant, Department of Food Science & Technology
The winemaking process is a dynamic one: from crush, to fermentation, on to post fermentation cellar procedures, aging, and bottling. Each step along the way allows for the potential ingress of oxygen, whether wanted or not. While oxygen is considered by many to be the enemy of wine, this is not always the case. In fact proper use of enological oxygen at crucial steps in the winemaking process is paramount to wine development. That said, many winemakers dutifully aim to eliminate it from the process altogether particularly in partial tank headspace. Proper gassing regimens and selection of the correct gas for a particular application is something that many do not do well and fail to fully understand the principals at play. Managing proper inert gas procedures is tricky. Most protocols are generally arbitrary ones copied from bad information and the proliferation of poor techniques passed on anecdotally from winemaker to winemaker. In general it is a procedure that is often over looked and never given much thought. This usually means the use of a high pressure cylinder (most often nitrogen), and a ¼” or ½” hose that is allowed to run for an arbitrary amount of time, generally 15 to 20 minutes. The results are the improper use of inert gases from the failure to measure gas volumes delivered (using a flowmeter), monitoring results with the use of a dissolved oxygen meter, using an under or oversized delivery system and unsubstantiated cost analysis pertaining to gas type and volume needed.
Typical gas choices are: carbon dioxide, nitrogen, and argon. Most wineries choose to use carbon dioxide and nitrogen because they believe it provides the best cost-benefit in terms of oxygen displacement per unit cost. This is not the case. To understand this, we must first delve into some fundamental principles of gases. In the wine industry, we typically use gas by volume, either in standard cubic feet or molar volume delivered from a standard steel pressurized cylinder in which the gas is compressed. These gas volumes are usually measured at 25°C and 1 atm. If you happen to purchase gas by the pound it is necessary to divide the gas by its molecular weight before you can compare gases to one another. The approximate molecular weights are: 40 g/mole for argon (Ar), 44 g/mole for carbon dioxide (CO2), 28 g/mole for nitrogen (N2), and 29 g/mole for air. One mole of any of these gases measured at standard pressure (1atm) and temperature (25°C) occupies one molar volume, roughly equivalent to 22.4 liters, 5.92 gallons, or 0.8 standard cubic feet. Using the ideal gas law PV = nRT the behavior of gases can be described in which pressure and volume is a fixed proportion in relation to the number of moles of gas at absolute temperature. This indicates that gas molecules take up the same amount of space regardless of their mass when they are at the same temperature and pressure (Avogadro’s Law). Thus one mole of any gas contains the same number of molecules (i.e., 6.02 x 1023). This also indicates that the head space in a tank, barrel, or other container will fluctuate regularly throughout the day in response to temperature and pressure changes. Tanks that are kept outside experience greater temperature changes throughout the day compared to a tank kept inside at a constant temperature. Changes in barometric pressure and temperature can cause the headspace in a tank to pump 3% to 7% of its volume in and out daily. This ultimately means that the headspace in a tank is not a static system and could be constantly changing.
Air is roughly composed of 78% nitrogen, 21% oxygen, and 1% argon, so in essence nitrogen is air without the oxygen. In any gassing procedure it is ideal to reduce the percentage of oxygen in the headspace to below 1% or even below 0.5% to inhibit the growth of aerobic microbes and prevent wine oxidation. The most commonly used gas in winemaking is nitrogen (N2) with a molecular weight (MW) of 28 g/mole making it moderately lighter (less dense) than air at 29 g/mole MW. Graham’s law of diffusion (also known as Graham’s law of effusion) states that the rate of effusion of a gas is inversely proportional to the square root of its molar mass at constant temperature and pressure. This principle is often used to compare the diffusion rates of two gasses such as nitrogen and air. The diffusion rates of nitrogen and air are almost identical meaning that nitrogen does not provide adequate layering, but rather readily mixes with air and does not remain in contact with the wine surface for an extended period of time. This also means that in order to reduce the O2level from 21% to less than 1%, the headspace needs to be flushed with a volume of nitrogen that is five times the volume of the headspace. So if the tank has a 100 gallons of head space it would take 500 gallons of nitrogen to reduce the O2level from 21% to below 1%. The cost of nitrogen is approximately $0.05 per cubic foot (Praxair, Inc). However, because nitrogen requires five times the volume equivalents to reduce the O2percentage from 21% to less than 1%, the cost to gas a barrel (60 gallons) is $2.00, 100 gallons of headspace is $3.34 and 1,000 gallons of headspace is $33.42. This is significantly higher than the cost of using argon for the same O2reduction in the equivalent headspace volumes. This is why headspace gassing with nitrogen requires a substantial effort and time commitment on the part of the winemaking team to be effective. It takes substantially more nitrogen and a greater application time compared to argon to achieve the same reduction in oxygen percentage with a shorter effective shelf life.
In contrast to nitrogen is carbon dioxide (CO2), which is significantly heavier than air at 44 g/mole compared to 29 g/mole and by Graham’s law has a much slower rate of diffusion compared to air. This allows for a more significant displacement of air compared to nitrogen. However, when CO2is delivered from a compressed tank, it is difficult to achieve the desired laminar flow necessary for successful layering. This results in substantial mixing of CO2and air. A more effective alternative for CO2delivery is dry ice (solid CO2) which leads to more efficient layering of CO2and subsequent displacement of air but does not form a permanent layer. However, it should be noted that CO2cannot be considered inert in the same way as nitrogen and argon. Because of Henry’s Law, which states that the solubility of a gas is directly proportional to the partial pressure of the gas above the solution, CO2readily dissolves into wine under standard conditions and its solubility can be increased or decreased with changes in pressure. This dissolution of CO2into the wine causes the pressure in the tank to fluctuate and results in the intake of air from the outside environment through an airlock to replace the lost volume of gaseous CO2. If there is no vacuum release valve on the tank, this could cause the tank to implode. Carbon dioxide dissolved in the wine will also alter the acid, flavor, and textural profile of the final wine. Carbon dioxide is much more effective when deployed early in the winemaking process at juice stage or when the wine is young as there will be substantial time to allow excess dissolved CO2to come out of solution. The use of dry ice to protect grape must is an effective way to protect wine must from excess oxygen exposure, deter fruit flies, and subsequently cool the must.
This leaves argon with a molecular weight of 40 g/mole, making it substantially heavier than air (29 g/mole) and similar in weight to CO2but more inert. A major opposition to the use of argon regularly in wine production is because it is significantly more expensive compared to the other two gases. It is true that when purchasing gas by volume argon is roughly three times as expensive as nitrogen or carbon dioxide. However it is much more effective at displacing air and creating a more permanent blanket that remains in contact with the wine surface longer while also remaining inert compared to CO2. Less volume is also needed to achieve the same desired results. At approximately $0.11 per cubic foot (Praxair, Inc) not including daily tank rental fee, a barrel (60 gallons) can be completely gassed with argon for $0.88, 100 gallons of head space for $1.47, and 1,000 gallons of headspace for $14.71. This cost is relatively insignificant to a winery’s bottom line in terms of the degree of quality preservation that argon can provide.
When using any of the gases discussed previously, it is important to select the proper pressure gauge, hose diameter, hose length, flowrate, and the use of a t-valve in order to deliver the gas under laminar conditions. The use of a lower velocity, will encourage laminar flow delivery and reduce any chance of turbulence and subsequent mixing with air, thus creating a more layered effect.
It is ideal to keep the flow velocity to 1 meter per sec or less. To determine the velocity divide the volumetric flow rate in cubic meters per second by the cross sectional area in meters of the hose being used. If using cubic feet instead of cubic meters, perform the same calculation but convert the units from cubic meters to cubic feet and meters to feet. Table 1 shows that it is best to use a 1.5” or 2” diameter line with a t-valve to deliver an adequate amount of gas in a reasonable amount of time. This will require the use of an oversized regulator compared to the typical 0.25” regulator used on most compressed gas cylinders.
In essence it is best practice to recommend the use of argon as the headspace gas for the majority of wine production processes. Carbon dioxide and nitrogen have their respective roles but when it comes to headspace gassing argon it the number one choice. In the production of high quality wine, it is imperative to establish proper gassing procedures. This includes the successful training of staff in all aspects of gassing procedures and the selection of the correct gas for the appropriate task. This also requires selecting the correct regulator size, hose diameter and length, the use of T-valves, measuring gas flow using a flowmeter, and finally verifying results with the use of a dissolved oxygen meter to monitor oxygen levels in the tank headspace pre and post gassing. The proper investment of time and resources in this often overlooked area of winemaking can have a profound effect on wine quality and preservation in the long run. It can also reduce long term costs by reducing the amount of gas and time required to achieve the desired reduction in the amount of oxygen present in a tank headspace.