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, Plant Pathology Research Technologist, Erie County and Dr. Michela Centinari, Assistant Professor of Viticulture, Department of Plant Science
This past growing and harvest season has been, accordingly to many growers, one of the most challenging ever not only in Pennsylvania but in many other eastern US regions. With the 2018 season behind us, we can reflect on what we did right and what we can improve to better manage, when possible, vines under the rainfall conditions experienced in many parts of the Commonwealth. In this article, we will mainly discuss disease and vine vigor/nutrition issues related to seasonal weather conditions. Other issues growers experienced, such as Spotted Lanternfly infestations will be addressed in future blog posts.
What was the major problem? Let’s start with the rain
In Figures 1 and 2, we reported monthly, seasonal (April 1 through October 31) precipitation and growing degree days (GDD; index of heat accumulation) collected by weather stations through the online network for environment and weather applications (http://newa.cornell.edu/) at two locations: Lake Erie Regional Grape Research and Extension Center (LERGREC) in North East (Erie County, northwestern PA) and in Reading (Berks County, southeast PA). We compared the 2018 data to the previous 19-year (1999-2017) average.
If you look at the monthly rainfall (Figure 1; Table1) throughout the growing season, it was as if Pennsylvania was divided into two regions during July, August, and September: the southern shore of Lake Erie, and the rest of the state. The Erie lakeshore was, indeed, relatively dry as compared to the rest of the state: rainfall from April to October was only about 4 inches higher than the long-term average. However, in other parts of the state rainfall was as much as 14 inches higher than average(Figure 1A: 2018 = 43.14 inches versus 1999-2017 = 28.68 inches). Berks County in southeastern PA started out with slightly above average rainfall for April and May, followed by a slightly drier than average June, but rainfall greatly increased in the second half of the season (Figure 1A). This happened not only in Berks County, but in many regions of the Commonwealth which recorded much higher than average rainfall in July, August, and September (Table 1).
Diseases that depended for development on regular rainfall, like black rot and downy mildew, were relatively easy to control for vineyards along the Lake Erie shore. Powdery mildew was in moderate supply; not light but certainly not of hardcore, epidemic proportions. To complete the picture, we did suffer more than a little from sour rot in some of our wine grapes due to the heat and return of rains in September (5 inches). We also suffered a fair amount of fruit cracking and damage from grape berry moth near harvest that led to some serious shelling and crop loss in many area vineyards. And then, on October 11, it all came to an end. Autumn, which was technically just beginning, was being ‘run out of town on a rail’; the weather suddenly took an entirely different turn and the sun and mild weather disappeared, never looking back.
In stark contrast, other parts of the state were dealing with way too much rain that created perfect conditions for the development of downy mildew and late-season bunch rots. Fortunately, from the rainfall data gathered from NEWA weather stations, it appears that rainfall in the early post-bloom period (second half of June – first half of July) was relatively average, with about 2.75 inches during that four-week period. This period is critical for fruit protection when the fruit of all grape varieties is most susceptible to all the major fungal diseases. However, by mid-July rainfall ramped up, and was especially abundant during the fruit ripening period; avoiding fruit rots was nearly impossible under those extremely wet conditions.
In addition to high disease pressure, wet conditions led to high vegetative growth and high to excessive uptake of nutrients such as potassium (K). In addition to the timely application of canopy management practices to keep vegetative growth under control and maintain an open fruiting zone, the planting of cover crops under the vines could help limit vine vegetative growth through water and nutrient competition (For more information please refer to: Why should we care about under-trellis cover crops?. Our extension team reviewed several plant tissue analysis reports from vineyards across the state and many of them had high, and in several cases excessive, leaf petiole K concentrations. For more information on K and how to manage it in the vineyard please refer to Assessing and managing potassium concentration in the vineyard.
What about heat accumulation?
The 2018 growing season in the Lake Erie region will be remembered as a hot season. Growing degree days accumulated from May 1 to September 30 were almost 3,000 at the LERGREC located along thesouthern shore of Lake Erie (Figure 2B). In contrast, one of the coldest seasons in the last 20 years was 2003 with 2180 GDD, 800 GDD lower than 2018! In 2018 it almost seemed everything happened too fast. Concord grapes at the LERGREC went from 50% bud break to harvest in less than five months, while the growing season for Vignoles (Vitishybrid) was less than 4 months long.
Heat accumulation was close to long-term average in Berks county (Figure 2A) and other PA regions, but with extended overcast conditions (many cloudy days!) throughout the season which might lead to moderate/low sugar accumulation in the fruit. Additionally, the overcast conditions contribute to downy mildew, black rot, and other fruit rots.
Tips for next season disease management
It is important to keep detailed records of where diseases were worst; those are the areas likely to develop disease first next year. Be sure to effectively scout those areas of the vineyard next season. For example, for downy mildew, that means beginning scouting by mid to late May. The downy mildew pathogen spends the winter inside infected grape tissue, especially leaves, that fall to the vineyard soil. The first downy mildew infections can occur during rainfall (at least 0.1 inches of rain and 50 °F) a few weeks prior to bloom, when vines have developed about 5-6 leaves per shoot.
We have several very effective downy mildew fungicides, but it is important to understand the pros and cons of each one. The old standards like mancozeb (Penncozeb, Manzate, Dithane, etc) and copper formulations are effective against downy mildew, and are great for multiple, back to back applications because they pose little risk in terms of the development of resistance, but they are not as rain-fast as some of the more modern downy mildew materials like Revus, Ridomil, and Zampro, and may need to be reapplied more often under heavy and frequent rainfall conditions. And of course, with copper, there is a risk of vine injury, that is exacerbated under wet, slow drying conditions. Copper residues from late-season applications can also interfere with fermentation. On the other hand, the more rain-fast, more modern fungicides should not be used more than two or three times per season, and even though the label may permit it, we recommend you don’t make back-to-back applications of the same chemistry, among these modern materials. Also, I purposely left out mention of the strobilurins for downy mildew control (Abound, Pristine, Reason), especially for the more intensively managed wine grape areas of southern PA; downy mildew resistance to this chemistry (FRAC 11) is common and this class of fungicides should probably not be relied upon anymore for control of this disease in many parts of Pennsylvania. And then there are phosphorus acid products which have become very popular for downy mildew control. But these materials can be overused as well. They certainly are very rain-fast and effective, but they can be lost to resistance (limit their use to two or three applications per season) and they only provide about 7-10 days of protection at each application, especially under heavy disease pressure on susceptible varieties. For more information on downy mildew control please refer to Tips for late season downy mildew control
There are cultural measures you can take to help reduce the overwintering population of pathogens. These measures are not substitutes for a solid seasonal spray program, and they all have their price, but they can make your spray program more effective. The downy mildew and black rot pathogens predominantly overwinter on the soil surface. Strict control of grape seedlings and suckers under the row in spring can reduce opportunities for these pathogens to create ‘stepping stones’ from the soil into your canopies. However, this practice needs to be balanced with the need for renewals where crown gall and the threat of winter trunk damage are perennial issues. During dormant pruning, remove all clustersnot harvested and as much diseased/dead/old wood from the trellis as is practical. Throw this material into the row middle and chop it, or better yet remove it from the vineyard and burn it (if practical). This is especially effective against Phomopsis and black rot. Upright training systems (like vertical shoot position) reduce the probability that pathogen spores will be splashed upward from cordons and trunk, into the fruit zone during rain.
A wet season like 2018 could be the start of additional disease issues heretofore not yet encountered in prior years. For example, a disease called ripe rot(Colletotrichum sp.) may have gotten a fresh foothold in some vineyards in Pennsylvania in 2018. Ripe rot is somewhat of a ‘southern’ disease, it mainly occurs in southern PA vineyards, but it was also noticed in a vineyard in central Pennsylvania in 2018 (Figure 3).
Ripe rot is identified during the ripening period by pink or orange colored slimy spore masses that appear on infected fruit after a wetting period (Figure 3, left panel).
Since downy mildew and late season fruit rot management was a major challenge for many growers in 2018, Grape Disease Management in Wet Seasonswill be discussed in more detail at the Mid Atlantic Fruit and Vegetable Convention in Hershey, PA on January 30, and again at our annual Grape Disease and Insect Management workshop on March 28. We hope to see you there.
By Jody Timer, Entomology Research Technologist, Penn State’s Lake Erie Regional Grape Research and Extension Center
What is NEWA?
NEWA is The Network for Environment and Weather Applications network which has the capacity to connect you with data from weather stations across the Northeast. NEWA was created in 1995 by the NewYork State IPM. It is an online agricultural decision support system that uses real-time weather data, streamed over the internet from 573 weather stations throughout the Northeast, Midwest, and mid-Atlantic. (newa.cornell.edu) NEWA models and resources are available free of charge and are used to make informed localized crop management decisions.
Although provided free on the internet, it is funded through the New York State IPM program. It provides insect and plant disease pest management tools, degree days, insect models, crop production models, National Weather Service forecasts, and localized weather information for growers, consultants, Extension educators, faculty, researchers, and others. Interactive forecast models automatically compute and display results to inform crop production and precision IPM practices.
The information specific to grape production includes; Downy mildew, Phomopsis, Black rot, Powdery mildew, and Grape berry moth. This information can advise grape growers of best spray timing, wetting periods, and peaks in Grape berry moth generations specific to their area. A weather station at your farm or business improves the precision and accuracy of NEWA tools. NEWA interfaces with RainWise stations.
On the home page of NEWA (newa.cornell.edu) is a map of the Northeastern U.S. marked with the locations of hundreds of weather stations where historical and ‘up to the hour’ weather data can be viewed. Click on a weather station near enough to you (denoted by a leaf/raindrop icon) to get weather, insect pest, and disease information you need to make important management decisions. Clicking on ‘grapes’ under ‘crop pages’ will give you access to forecasting models for all the major diseases, as well as the grape berry moth degree-day model that will improve your timing of grape berry moth insecticide. You can replace your own grape bloom date with the one provided on the NEWA page to get a more precise prediction of recommended spray timings for grape berry moth generations.
Each model forecast is accompanied by helpful disease management messages and explanations. These suggestions for grape production are reviewed yearly by the Cornell and Penn State research and extension grape team.
Contact your NEWA state coordinator before making any station purchase decision. NEWA partners with member states throughout the eastern and central United States to provide local grower support and expertise. Your coordinator can provide information specific to your state, answer questions about the NEWA platform, direct commodity questions to appropriate extension or university resources, and identify possible training opportunities for you. Click here to view a list of NEWA state coordinators.
There is also a youtube video on the NEWA weather station network: https://youtu.be/Av8mlZEXZ8M?t=30
By Dr. Michela Centinari, Assistant Professor of Viticulture, Department of Plant Science
If just one adjective was chosen to describe the 2018 growing season to date, many of us might suggest ‘rainy.’ In many Pennsylvania regions, grape growers faced persistent rainfall for the majority of the summer. For example, in central PA, State College has had an accumulation of 29 inches (737 mm) of rainfall for the months of April through August. Growers really had to be on top of their fungicide spray schedule and canopy management plans to minimize the risk of disease so that fruit will be healthy at harvest time. Recently, Bryan Hed and Jody Timer wrote blog posts that provided recommendations for late-season downy mildew control (late season downy mildew control)and insect problems (late season insect problems). While the weather forecasted for harvest season is weighing heavily on the minds of many grape growers, a post-veraison task critical for a successful harvest is collecting grape samples to measure the progression of fruit maturity.
This article provides a brief review on what fruit ripeness parameters you should measure and how to collect berry or cluster samples to best assess fruit maturity. While this information could be particularly useful for new grape growers approaching their first vintage, experienced growers should review the information to ensure that they are using the best techniques for collecting representative fruit samples.
Grapes are typically harvested when they reach desired fruit quality parameters (e.g., sugar content, pH, flavor, color) which vary depending on the wine type or style the winemaker aims to produce. Grapes should be sampled periodically until harvest to monitor how parameters associated with fruit maturity (e.g., sugar, pH, organic acids, flavors) evolve through the ripening season. However, there are many other factors involved in selecting a harvest date, which may or may not directly relate to optimal fruit maturity. These factors include:
- Fruit health condition (is the fruit deteriorating due to rot or other disease or insect damage?),
- disease and insect pressure,
- short and long-range weather forecasts,
- available labor,
- space available at the winery to process the grapes, and
- type or style of wine that will be made.
What fruit ripeness parameters to measure
The evaluation of the overall fruit ripeness involves quantitative parameters (sugar content, pH, titratable acidity) but also measurements that go beyond analytical techniques(berry sensory analysis).
Quantitative measurements to determine grape ripeness:
The information reported below is adapted and summarized from the factsheet Determining grape maturity and fruit sampling written by Dr. Imed Dami, Ohio State University. To access the entire document click the following link Determining grape maturity and fruit sampling.
Sugars, organic acids, and pH are the primary indicators of technological or commercial grape maturity, which is different from physiological maturity that occurs at or soon after veraison when seeds are ready to germinate.
Sugars: Sugars, specifically glucose and fructose, are the main soluble solids in grape juice. Sugar content is typically measured in degree Brix (°Brix); 1 degree Brix corresponds to 1 gram of sugar per 100 grams of grape juice. Desirable levels of sugar content are typically between 18 and 24ᵒBrix, depending on grape variety and wine style.
Sugar level is relatively easy to measure in the vineyard with a handheld refractometer (Figure 1). However, sugar content is not always related to an accumulation of flavor compounds. Even within the same variety, the desired varietal flavor can be reached at different sugar level in different vintages. Similarly, two varieties might have the same sugar level, but one might have fully developed varietal flavors, while the other may not.
Figure 1. Handheld refractometer used to measure soluble solids (sugars) content.
Organic acids: Titratable acidity (TA; sometimes referred to as total acidity) indicates the total amount of acids in the grape juice. The two major organic acids in grapes are tartaric and malic acids. TA is determined by titration of the juice sample with a standardized solution of sodium hydroxide (NaOH). The amount of NaOH used to neutralize the acid in the juice is used to calculate juice TA.
Although acid levels at harvest vary across vintages and varieties, they generally fall between 0.6 and 0.8 grams of titratable acids / 100 mL of juice (or 6 – 8 g/L of juice).
pH: pH (power of Hydrogen) measures the strength of acidity, which is the reactivity of H+ ions in the juice solution. pH is generally measured with a pH meter. Typically, the lower the pH the higher the acidity in the juice; however, there is no direct relationship between TA and pH. It is possible to find juice (or wine) with high pH and high TA. Generally, white grapes are harvested at a lower pH than red grapes (white varieties = pH of 3.1 to 3.3; red varieties = 3.3 to 3.5). High pH levels (> 3.70) can negatively influence wine microbial and physical stability.
Berry sensory analysis:
It is a good exercise for growers and winemakers to periodically monitor fruit ripeness (e.g., development of flavor, color) both visually and using sensory evaluation of the berry skin, pulp, and seeds separately. Berry sensory analysis may seem difficult at first, but you can easily master the technique with some practice and good record keeping.
The procedure involves putting berries in your mouth, crushing them gently to press out the juice, and evaluating its sweetness and acidity. The next step is to separate the seeds from the skin and place them in your hand for visual observation (green seed = immature seed; brown seed = mature seed; Figure 2). Lastly, crush the berry skin and put it on your cheeks to assess the degree of astringency. For more detailed information refer to the following article written by Dr. Joe Fiola, University of Maryland: Evaluating grape samples for ripeness.
Figure 2. Seed – visual and taste evaluation (Photo credit: Denise Gardner)
You can learn more about berry sensory analysis techniques and protocols available by reading Berry sensory analysis, written by Dr. B. Zoecklein, Virginia Tech University, and Assessing ripeness through sensory evaluation, written by Dr. Mark Greenspan.
One way to quantify and record subjective fruit ripeness criteria is to use a scorecard, one of which has been developed by The Ohio State University. You can find the scorecard on page 2 in the article: Determining grape maturity and fruit sampling.
When to start sampling grapes and how often
You should begin sampling grapes after veraison, and increase how often you sample as harvest approaches (i.e., from every other week to weekly to every couple of days).
How to collect a representative sample
Before you start walking down your vineyard rows, it is important to understand your vineyard’s variability in order to collect samples that are representative of the entire vineyard, which can effectively assist with your harvest scheduling-decisions.
Variation within a vineyard can be due to soil characteristics, topography, vine age, etc., which creates differences in vine growth and subsequent ripening. Make sure to collect a separate sample from each area of your vineyard that produces vines with different growth. The number of samples to collect depends on the vineyard size, but also on the level of variation in growth, disease, and other stress amongst vines. A higher level of variation amongst vines will require a greater number of samples.
Every vineyard manager or winemaker has a preferred method for collecting grape samples. While some might prefer to collect whole clusters, others prefer to collect individual berries from multiple clusters and combined them into one sample for each block (Figure 3).
Figure 3. Berry samples collected around veraison (Photo credit Don Smith).
Each sampling method has its own pros and cons; however, regardless of the technique you decide to adopt it is critical to:
- Avoid sampling from edge rows, vines at the beginning or end of the row, or ‘unusual’ vines.
- Collect ‘random’ samples and avoid looking at the cluster when sampling. Although subconsciously, we tend to preferentially collect good looking, large, and sun-exposed clusters, as well as the ripest berries. This can lead to an overestimation of the actual sugar content of the whole fruit biomass used for winemaking.
- Collect berries or clusters from both sides of the vine and from shoots at all positions on the vines (near the trunk, middle of the cordon/cane, end of the cordon/cane) and across the entire fruiting zone of the vine. Select clusters from basal and distal nodes, but not from clusters that you will not harvest, such as those from lateral shoots.
- Collect the sample from a large number of vines. For example, if you collect 100 berries per vineyard block, they should be from at least 20 clusters from 20 different vines.
- Be consistent. Use the same standardized protocol throughout the season and across seasons. If possible, the same person should do the sampling each time.
- With berry sampling, it is also important to collect berries from all parts of the cluster: top, center, bottom, front, and back. Sampler bias can favor berries collected from the top and bottom of the cluster, missing, or underrepresenting the central region of the cluster.
It is also important to remember that:
- The larger the sample the more accurate the measurement will be. For example, if you collect individual berries you need 2 samples of 100 berries to be within +/- 1.0 °Brix accuracy level at harvest. To improve accuracy and be within +/- 0.5 °Brix of actual sugar at harvest you need to collect 5 samples of 100 berries. If you are sampling clusters, 10 clusters are required to be within +/- 1.0 °Brix. The number of samples also depends on vineyard variability.
- Weather condition might affect the values of fruit ripeness parameters. Try to collect your samples at the same time of the day each time you collect the berries.
Process the sample
Samples should be processed within 24 hours of collecting them. Until you are able to process them, store berries in sealed plastic bags and clusters in a container/bucket, and keep the fruit in a refrigerator.
You can crush the berries in a clear plastic bag and visually check to see that all of them have been crashed, or you can use a food mill or another piece of kitchenware. After crushing the fruit, filter the juice using a cheesecloth, coffee filter, or paper towel.
We encourage PA wine grape growers to share their experience with grape sampling; what works for them and what doesn’t.
By: Jody Timer, Entomology Research Technologist, Erie County
The grape berry moth (GBM): The most destructive grape insect pest in the Eastern US is the native Grape Berry Moth, Paralobesia viteana. This insect is becoming increasingly harder to control as result of shorter residual time of insecticides, resistance to insecticides, and abandoned vineyards. GBM larval burrow into the grape berry soon after hatching, making precise timing of spray applications a critical component of control. This insect has four generations per year. Each generation increases in number exponentially if control measures are not applied to the early generations. Although in early season this insect pest has distinct peaks in generational emergence, by August the peaks have overlapped making complete control almost impossible. Growing areas with large populations require a second generational spray in July and/or August. If these sprays have not been applied and there are GBM problems in your vineyard, it is a good idea to spray for this fourth generation in September. Spray timings can be calculated by following the NEWA model recommendations. Although much of the damage may have already occurred, this spray will help prevent the generations from starting the season next year farther into your vineyard. If you are dropping your crop from the end rows because of the excessive berry moth damage, collecting the dropped grapes as opposed to dropping them under the trellis will greatly reduce overwintering populations from remaining in your vineyard. More GBM information can be found on extension pages and on the LERGP Podcasts.
Spotted wing drosophila (SWD): Spotted wing drosophila, Drosophila suzukii,(SWD)is an invasive vinegar fly of East Asian origin that was recently introduced into the United States. It was first found in Pennsylvania in 2010. The potential infestation rate of spotted wing drosophila differs from other vinegar flies because the female possesses a serrated ovipositor that cuts into healthy fruit to lay eggs. Consequently, spotted wing drosophila (SWD) larvae can be found in fruit that is just ripening. During egg-laying, it is believed that sour rot and fungal disease can also be introduced, further affecting the fruit quality. All fruit flies carry yeast which can affect the quality of wine if these flies are present during winemaking. During peak temperatures, a female can lay more than 100 eggs a day. Such a high reproduction rate indicates the SWDs’ high potential for fruit infestation and their potential for spreading rapidly through a vineyard, with multiple generations occurring each year. Spotted wing drosophila is now one of the most serious pests of thin-skinned fruits including grapes. At this time, no action threshold is available for SWD, so the common recommendation is to increase monitoring when one fly is captured on a farm and began a spray regiment continuing through harvest, making sure to protect fruit through to harvest using registered insecticides. Female SWD are able to lay eggs into fruit from the time of first coloring through to harvest, so this period is the window of susceptibility to SWD. Because SWD populations tend to increase in the later part of the summer, we expect late-harvested fruit, such as grapes, to experience higher pressure from SWD than those that are harvested earlier in the summer such as strawberries and summer red raspberries. A number of registered insecticides have been very effective against SWD in laboratory trials, the most effective chemicals are organophosphate, pyrethroid, and spinosyn class insecticides. Under field conditions, insecticides with fast knockdown activity have performed well at protecting fruit immediately after application. When SWD are detected it is recommended that the spray intervals be tightened to prevent crop infestation before and during harvest.
Spotted Lanternfly (SLF): This newest invasive insect has the potential to be devastating to the grape growing industry. Its preferred host is the Tree of Heaven (Ailanthus altissima) and grapevines. SLF aggregate feeds on vines by piercing the vines and feeding on the phloem and xylem. This feeding causes intracellular damage as the insects siphon vast amounts of phloem which reduces the vine’s health and vigor. The insects excrete honeydew and the feeding sites leak sap, which causes sooty mold to form on the leaves reducing the photosynthesis. The sap also attracts secondary pests such as wasps and bees. The wounds make the hosts more susceptible to disease. Systemic chemicals are preferable and highly effective, but insect feeding is still damaging as there is a constant influx of insects from forest margins. Eggs are laid at the end of the season and the adult insects die. If discovered, egg masses should be removed immediately. Thirteen counties in southeastern PA are now under quarantine for this insect.
Multicolored Asian ladybird beetles (MALB): Although these insects cannot be effectively sprayed at harvest, vineyards should be scouted prior to harvesting to see if they are present. MALB feeds on damaged fruit and causes taint to wine and juice in very small numbers if harvested with the grapes.
By: Bryan Hed, Plant Pathology Research Technologist, Erie County
At this time of year, it’s so important to continue scouting leaves for the distinctive white ‘downy’ sporulation of downy mildew. Growers of susceptible varieties need to keep closely monitoring their vineyards for active sporulation and use that information in combination with the DMCast model on NEWA.
The presence of active white sporulation on the undersides of leaves means the downy mildew pathogen is capable of spreading quickly under wet conditions and can spiral out of control, strip vines of their leaves and effectively end the season (and the ripening of canes for next year’s crop).
If you find yourself trying to control this disease well into the ripening period, be aware that your list of chemical control options will start to become shorter as we get within 30 (Ranman, Reason), then 21 (Ziram, Presidio (only older stocks; can’t purchase new material anymore)), then 14 (Revus, Revus Top, Zampro) days of harvest, until in the end you’ll be left with some formulations of Captan, copper, and phosphorous acid products (0 day pre-harvest interval).
Its also important to remember that materials like Ranman, Reason, Revus/Revus Top, and Zampro contain chemistries that are prone to the development of resistance. These materials should not be used to put down an epidemic, which will speed up the resistance development process. And, although phosphorous acid products are less prone to resistance development, you will enhance the chances of losing this technology to resistance as well, by using these materials on a heavily diseased vineyard.
Also, limit your use of phosphorous acid products to three applications per season. On the other hand, fungicides like Captan or copper formulations would be least risky in terms of the development of resistance and can be an effective means of controlling downy mildew late into the growing season.
Just be mindful of varieties that may be injured by copper applications, and that copper injury will be exacerbated by application under slow drying conditions and application to wet canopies (for example, don’t make applications to dew covered canopies in the early morning). If you are protecting a non-bearing, young vineyard from downy mildew (you’re not selling/harvesting a crop), you can continue to use mancozeb products past the 66-day pre-harvest interval.