Assessing grape maturity for harvest planning

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.

Harvest decisions

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.

Screenshot 2018-09-07 07.08.06Figure 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.

Screenshot 2018-09-07 07.08.21

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.

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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.

Sampling technique

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).

Screenshot 2018-09-07 07.07.46Figure 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.

 

Useful References

Evaluating grape samples for ripeness

Determining grape maturity and fruit sampling

https://psuwineandgrapes.wordpress.com/tag/berry-sensory-analysis/

 

 

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Late harvest insect problems

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.                                                            

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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.

Screenshot 2018-08-30 13.45.13

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.

Screenshot 2018-08-30 13.45.23

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.

Screenshot 2018-08-30 13.45.33

Tips for late season downy mildew control

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.

Highlights from my Australian sabbatical leave​

By Kathy Kelley, Professor of Horticultural Marketing and Business Managment 

I just returned from a six-month sabbatical leave in Australia where I visited many wineries and tasting rooms and talked with various industry members.  I have included a map of Australia’s wine regions for your reference.

Screenshot 2018-06-18 12.59.31

I spent a majority of my time in Adelaide which is surrounded by over 200 tasting rooms situated in the Barossa Valley (known for Shiraz), Clare Valley (Riesling), and more than a dozen other wine regions (see map below).

Screenshot 2018-06-18 12.59.57

 

Screenshot 2018-07-28 19.36.11

 

South Australia has not yet been impacted by phylloxera (http://bit.ly/2J79Xep); however, several growers and winemakers indicated that they do expect the pest to impact their vineyards at some point.  Currently, they post signs asking consumers not to walk through the vineyards and politely ask those who do to kindly leave the production area.  A few indicated that they are considering other measures (such as fencing) to protect vines near their tasting room, some of which were planted in the mid-1800s.

 

 

 

The Cube, McLaren Vale

The d’Arenberg Cube is a multi-story, Rubik’s Cube-like building (Rubik’s Cubes that look like the building are can be purchased for $10 AUS/$7.40 US).  The building includes a restaurant, a 360-degree video room where visitors can watch an artistic representation of the brand’s various wine labels, and a space for fee-based wine blending sessions.  While the Osborn family has had a presence in the Australian wine industry since 1912, the Cube opened in 2017.

Screenshot 2018-07-28 14.48.30

There is also a sensory room where visitors can squeeze a handpump and smell what they might expect in a glass of wine and an art gallery.  Visitors can download an app that provides additional information about each room and display.

Screenshot 2018-07-28 14.49.01

The tasting room is on the top floor where visitors can taste the wines (included in the $10 AUS/$7.40 US entrance fee) while looking out over the valley.  Visitors can choose from over 70 wines, including The Cenosilicaphobic (which means a fear of an empty glass) Cat (https://www.darenberg.com.au/the-experience/cellar-door/).  Apparently, there was a cat on site that had a bit of a problem with alcohol.

Screenshot 2018-07-28 14.49.54

Sidewood Estate, Adelaide Hills

Sidewood Estate is a winery and cidery located in the Adelaide Hills (https://sidewood.com.au).  The tasting room has an intimate space for couples and small groups to taste their wines while large groups are served in another space a short distance away.  Having two separate spaces provides a nice quiet area for couples/small groups who want to interact with staff and another where large groups don’t have to worry about being loud.

In addition, all guest can buy golf balls and practice their swing.  If they succeed in hitting a ball onto the small green located in the middle of the pond or get a hole-in-one – they can win a prize.  Not only does the driving range give nonwine drinkers something to do while they wait for their wine drinking friends, it also keeps visitors on site longer which then encourages them to purchase additional food and drinks.

Screenshot 2018-07-28 12.24.38.png

Hahndorf Hill Winery, Adelaide Hills

Hahndorf Hill Winery focuses on cool-climate varieties (due to the cool temperatures at night) and Austrian varieties, especially Gruner Veltliner.  Several years ago, they began propagating cuttings they imported from Austria, evaluated them, and now share the cuttings with other vineyards in the region.  They make four different styles of Gruner Veltliner wines: a classic style, a fruit-driven style, a “more opulent style,” and a late harvest style (https://www.hahndorfhillwinery.com.au/Gruner-Veltliner). The winery has a Gruner-focused blog called “The GRU Files” (https://www.thegrufiles.com.au) and one of the owners, Larry Jacobs, is called Australia’s “Grandfather of Gruner” (https://www.thegrufiles.com.au).

Screenshot 2018-07-28 12.49.44

Terrior, several wine regions

While the staff did not overly focus on terroir, several tasting rooms did display soil samples, profiles, and maps where their vineyards are located.  Below are some examples of the various ways they displayed these items.

Yalumba Family Vignerons c. 1984. A map of their vineyards and corresponding soil samples are displayed at the tasting bar.  Yalumba, located in Barossa Valley, “is one of only four wineries around the world to have its own cooperage” (https://www.yalumba.com)

Screenshot 2018-06-18 12.37.02

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Chateau Tanunda is “home to some of the earliest plantings of vines in Barossa Valley” with some planted in the 1840s (https://www.yalumba.com).  Staff refer to soil samples and explain how production in Alluvial Clay Loam soil can differ from production in Deep Sand.

 

 

Pooley Wines, established in 1985 and located in Tasmania, is the state’s first certified environmentally sustainable vineyard (for more information about the program: http://bit.ly/2NResYy).  A fairly unique display shows the soil profiles for two vineyards: a) Sandy Loams over Sandstone in which they grow Syrah, Cabernet Sauvignon, Merlot, Reisling, Chardonnay, and Pinot Noir and b) Dolerite, black crackling clays, limestone over sandstone, in which they grow Chardonnay, Pinot Noir, Pinot Grigio, and Riesling (http://www.pooleywines.com.au/the-vineyards).

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Bleasdale, Langhorn Creek

In addition to seeing several vineyards that were planted in the mid to late-18oos, it was also incredible to see the various artifacts that wineries had kept from this period.  Bleasdale was established by Frank Potts in 1850 (https://www.bleasdale.com.au). Mr. Potts came to South Australia in 1836 and established the first winery in Langhorne Creek in the late 1850s.  As you can see in the images below, he was a skilled craftsman and built machinery that he then used to make wooden plugs for wine corks and vats, and also made his own vats and lever presses.

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The image below shows a red gum lever press that was built by Frank Potts’ sons in 1892.   It is the second press that was built on the property, the first one was built by Mr. Potts in the 1860s and had just one basket.  The design is based on basket presses Mr. Potts saw in Portugal.

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According to a sign at the winery: “Both presses were build of red gum, with the density of the wood meaning the levers would not need to be pushed down to provide mechanical advantage.”   The sign also stated that “the two presses stood side-by-side for around 20 years until the first press was deconstructed circa 1910-1915.”

Now, a little of what I saw in the marketplace.

A cider & wine concoction

While it has been on the market for a bit in Australia and New Zealand, Jacob’s Creek (Australia’s largest wine brand) released an alcoholic beverage that is a combination of white grape and apple juice called Pip & Seed.  Flavor profiles include: fruity (“exploding with the flavour of fresh, sweet apples and pears”), crisp (“bright floral aroma and fresh, crunchy apples on the palate), and sweet (“sweet taste sensation bursts with apple and pear aromas while sweeter, juicier apples party on the palate”) (http://www.jacobscreek.com/au/pip-and-seed).  At the time of this posting, the price for one 500mL bottle was $3.88 US.

Screenshot 2018-06-18 13.01.52

Is your wine at the correct temperature to drink?

Taylors Wines, a third generation wine business located in Clare Valley, South Australia, has taken the guesswork out of knowing when a wine is at the optimum temperature for drinking.  I found this bottle of Taylors Estate 2015 Cabernet Sauvignon ($14.42 US dollars) in a wine shop – and though it was mixed in with several other brands, the bottle neck tag attracted my attention.

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The neck tag instructs the purchaser to compare a glass of the red wine at room temperature and at the optimum temperature, per the temperature sensor on the label on the back of the bottle.

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Below, I’ve included an image of the temperature sensor printed on the back label.  According to their winemaker, this wine’s optimal drinking temperature is between 16 and 18C (60.8 to 64.4F), which correlates to the “raspberry” color section on the scale.  In the top-right portion of the image, you can see that the current temperature indicator is “lilac” which is in the range considered “too warm.”

Screenshot 2018-06-18 13.02.11

These are just a few of the winery tasting rooms and products that I saw in Australia.  There are many other wineries in these regions and others that provide visitors with an amazing experience and fabulous wine.  I will share more observations in future blog posts.

 

 

 

 

 

 

 

​Viticultural considerations during bloom and early fruit development

In this week’s blog, you will find updates and information from several of our authors with an emphasis on disease and insect management and vine nutrient status.

Bloom and early fruit set disease management

By Bryan Hed, Department of Plant Pathology and Environmental Microbiology, Penn State Extension

Well, the 2018 season has gone from 0 to 100 mph over the past four weeks, and grapevine shoots are currently growing at a rate of at least an inch a day. Trying to keep grape tissue protected with pesticide sprays can be a bit of a challenge when canopies double or triple in size each week. However, now it’s time for the most critical fungicide applications of the season; the immediate pre and post-bloom sprays. This is your annual reminder. Fruit ($$) of all grape varieties are most vulnerable to infection from all the major fungal diseases at this time (black rot, Phomopsis, powdery and downy mildew), and in many places across Pennsylvania the previous 4 weeks have been warmer and wetter than average; the perfect setup for fungal disease development on fruit. There’s no more critical time to “spare no expense” than immediately before bloom to about 2 weeks (juice grapes) to 4 weeks (wine grapes) after bloom. Use best materials, apply for best coverage, and allow no more than 10-14 days between these next 2 to 3 sprays. At this time, do not rely on materials that we know are slipping in efficacy, or have already slipped in efficacy, due to the development of resistance in many parts of the East (ie, strobilurins and sterol inhibitors).  

When I hear from growers that have experienced problems with fungal fruit infection in the past, breaches in disease control are most often traced to the period of grapevine development around bloom.  Some common mistakes include: i) use of the wrong materials (there was resistance to what they used, their mix didn’t cover all diseases, their choice of materials wasn’t very effective, etc), ii) stretching of spray intervals (more than 10-14 days between the immediate pre and post bloom spray), iii) less than optimal coverage (canopies were too dense, canopy management was lacking, sprayers weren’t adjusted for maximum coverage, etc), iv) taking a vacation from farming during this period of time (all of the above?).

If you’re growing bunch rot susceptible wine varieties, fruit-zone leaf removal around or shortly after bloom, can improve coverage and create a fruit-zone environment that is less favorable for the growth of fungal pathogens (For more detailed information see: Early season grapevine canopy management, Part II: Early leaf removal). Strict pre-bloom sucker control can delay the rise of diseases like downy mildew and black rot that emanate from the vineyard floor. Pre-bloom shoot thinning, while shoots can be easily removed by hand, will not only balance canopies with yield but also improve the efficacy and value of fruit protection sprays. Proper weed control/maintenance of row middles and cover crop height can reduce humidity in the vineyard and improve drying time of plant surfaces after rainfall. Integrating these cultural practices into your pre-bloom crop management plan will greatly assist your fungicide applications toward maximizing fruit disease control during bloom.

For more details on the various diseases and how to deal with them during this critical fruit protection period, you may find it convenient to check out previous posts from April 7 and June 16, 2017:

https://psuwineandgrapes.wordpress.com/2017/04/07/2017-pre-bloom-disease-management-review-and-discussion/

https://psuwineandgrapes.wordpress.com/2017/06/16/2017-summer-disease-management-review/

Insect updates on Grape Berry Moth and Spotted Lanternfly

By Jody Timer, Entomology, Lake Erie Grape Research and Extension Station

Grape Berry Moth (GBM):  The first grape berry moth for the season usually appear at about 150 degree days from January 1st.  This year, in the Lake Erie Grape growing region, we had a late spring which resulted in a later-than-usual emergence of GBM (around May 15th). The emergence occurred much earlier for the growers in the Southeastern portion of the state. The research we have done in the past indicates that spraying for GBM prior to the first full generation (not this emerging generation) is more effective and will not adversely affect yields at harvest.  So this generation, which starts to peak at wild grape bloom and continues for about 10 days, does not in most cases need to be sprayed. Wild grape bloom in the Lake Erie Grape growing region occurred around May 30th, it was as early as May 13th in the southeastern regions of PA.  Wild grape bloom is used as the biofix for the NEWA system to start accumulating degree days. This system uses the GBM phenology model to recommend optimal spray timings for GBM   http://newa.cornell.edu. It is important that you keep track of when wild bloom occurred in your area to allow the model to precisely track the GBM phenology. If you missed the wild bloom date, the NEWA system will calculate wild bloom for your area based on historical data. The best way to determine infestation of your vineyard is to scout for damage. This generation of GBM produces webbing on the flowers and clusters. This webbing, although harder to scout for than later berry damage, is a good indication of severity in the ensuing generations. If your vineyard has high GBM consider spraying more often during the upcoming generations.  Grape berry moth can cause considerable damage to vineyards through berry damage and late season rots.

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Spotted Lanternfly (Lycorma delicatula): This new invasive insect was first discovered in Bucks County in 2014, the affected area was placed under quarantine to prevent the movement of the insect and its egg masses. Prior to its discovery in the fall of 2014, the spotted lanternfly had not been found in the United States. This fall, when the adults were flying and laying eggs, the quarantine area saw considerable increases and movements of the population. As a result, the quarantine area has been expanded to include all of the counties in southeastern PA. There has also been a colony found in Virginia.  Spotted lanternfly host plants including fruit trees, ornamentals, hardwood trees, and grapevines. These insects are exhibiting a preference for tree of heaven (Ailanthus altissima) and vines including grapevines.  Spotted lanternfly has the potential to cause substantial damage. Some have estimated potential crop losses, which includes Pennsylvania apples, grapes, and hardwoods, at $18 billion dollars. While feeding on and damaging their host plants, spotted lanternfly also ejects a liquid called honeydew which causes sooty mold and attracts secondary insect pests. Spotted lanternfly overwinter as egg masses, which are small (about 1-4”) and greyish white. They somewhat resemble a dirt splatter.

Screenshot 2018-06-08 19.46.04

The first nymphs began to hatch in late April or May and complete four instars.  These nymphs are 4-9 mm long and wingless with black with white spots. The fourth instar develops red patches, and then emerge into adults in late summer.  This time of the season it is important to scout for egg masses, which although hatched, would indicate an infestation in your area. The black and white nymph stage will be present now.Screenshot 2018-06-08 19.47.35

There is a team of state, federal, and local public officials, academic researchers, and extension personnel working on the problems dealing with this insect. It is important to report findings of spotted lanternfly is you are not in the quarantine area. The website: https://extension.psu.edu/spotted-lanternfly as well as the PDA website has important information on this insect and includes numbers to call if you find insects outside of the quarantine area.

Assessing vine nutrient status

By Dr. Michela Centinari, Assistant Professor of Viticulture, Department of Plant Science

Proper vine nutrient management is crucial for the vineyard longevity, as it helps ensure adequate vegetative growth, fruit set and growth, and optimum wine quality. While some nutrients up-taken by the vine are recycled through fallen-leaves decomposition, the majority of nutrients leave the vineyard in harvested fruit, pruned-wood material (if the brushes are not chopped and left in the vineyard), or through leaching and runoff.  Assessing vine nutrient status should be a routine practice and used not just to confirm a suspected nutrient deficiency.

To determine vine nutrient status in an established vineyard, plant tissue nutrient concentration should be analyzed at bloom and/or later in the season around véraison. A soil test is useful and can provide clarification, but has limited benefit. It will indicate relative nutrient availability, but it does not tell what and how much the vines absorb.

What type of tissue to collect for nutrient analyses

There is a long-standing debate about what leaf tissue (blade, petiole, or the whole leaf) best reflects vine nutrient status and correlates to nutrient requirements for optimum vine growth, yield, and fruit composition. However, in the eastern US, the sufficiency range (or target value) of each nutrient concentration is only defined for petiole tissue.

When to collect grapevine petiole samples for nutrient analyses

Collecting a petiole sample at both bloom and véraison and having it analyzed will provide meaningful insight when developing a nutrient management plan. For example, if you noticed visual symptoms of nutrient deficiency in the previous growing season (Figure 1), a nutrient test at bloom will help determine if there is an actual deficiency, and you will be able to correct it in a timely manner (1).  Nutrient concentrations in leaf tissue tend to be more stable as the season progresses, so taking a sample at véraison is typically recommended compared to taking samples at bloom, especially for routine analysis (1).

Screenshot 2018-06-07 10.50.09

How to collect grape leaf tissues for nutrient analyses

A comprehensive and illustrated guideline on how to collect whole leaf samples (which can also be used for petiole sampling) is on page 12 of the Vineyard nutrient management in Washington State extension bulletin. Be sure to sample each variety separately and to collect 50 large petioles or 100 small ones per variety.

Where to send the samples

Use a reliable lab in your area that has experience in vineyard tissue testing, and use the same lab each year so that the analysis is consistent. If you are in Pennsylvania you can send your plant tissue sample to the Penn State Agricultural Analytical Services Lab.  Please be sure to provide all the information required to interpret the lab results (e.g., type of tissue, time of the year the sample was collected). Lab results will report the concentration of each nutrient analyzed and if its level is low/deficient, sufficient, or too high/excessive. If you need assistance with interpreting your report, contact your local extension for further assistance.  You can find the contact information for your local Penn State Country Office by entering your zip code in the search field on this site: bit.ly/2J9yCPr

Reference: 

  1.  Moyer M., Singer S., Hoheisel G., and Davenport J. Vineyard Nutrient Management in Washington State, EM111e (Bulletin) Washington State University

Comments concerning insect and disease management at this time of the season (Immediate Prebloom – Early Postbloom period)  

By Andy Muza, Penn State Extension – Erie County

I’ll begin by stating that every commercial grape grower in Pennsylvania should have a copy of the 2018 New York and Pennsylvania Pest Management Guidelines for Grapes: https://store.cornell.edu/p-201631-2018-new-york-and-pennsylvania-pest-management-guidelines-for-grapes.aspx   This guideline provides a wealth of information on insect, disease and weed management with pesticide options, rates, and schedules, as well as, a chapter on sprayer technology.

Also, monitoring your vineyard(s) at least weekly throughout the season is critical for managing pests. Frequent scouting will alert you to problems developing in the vineyard and provide the information needed to make informed decisions concerning pesticide applications. (You won’t know what’s out there if you’re not).

Diseases – When thinking about disease management the first thing that commonly comes to mind are fungicide applications. However, cultural practices (e.g. shoot thinning, leaf removal in the fruit zone, etc.) are integral components of a disease management strategy and should be used whenever applicable.

As Bryan Hed mentions and deserves repeating, The Immediate Prebloom (just before blossoms open) through early post-bloom/fruit set period is a critical time for managing fruit infections caused by phomopsis, black rot, powdery mildew and downy mildew. Fungicide protection for botrytis on tight – clustered varieties at bloom (when 80 – 90% of caps have fallen) can also be important in wet seasons.

Insects – Two important insect pests that Jody Timer is covering are grape berry moth and spotted lanternfly. (For additional information on grape berry moth see: Three Phases to Managing Grape Berry Moth  https://psuwineandgrapes.wordpress.com/2017/04/28/three-phases-to-managing-grape-berry-moth/ and Grape Berry Moth: Answers to questions you should be asking about this native pest  https://psuwineandgrapes.wordpress.com/2015/05/15/grape-berry-moth-answers-to-questions-you-should-be-asking-about-this-native-pest/ ).

I will briefly mention 2 of the more widespread, leaf-feeding pests that you are likely to see sometime this season which are grape leafhopper and Japanese beetle.     

Grape Leafhopper – There are several species of leafhoppers in the genus Erythroneura that feed on grape foliage. Regardless of which of these species is prevalent, their life cycles are similar and the injury caused by these leafhoppers and their management is the same. The greatest risk for economic losses due to grape leafhopper feeding occurs during hot, dry years in vineyards with heavy crop loads and high leafhopper populations. In most years, the majority of vineyards in Pennsylvania should not require an insecticide treatment specifically for management of grape leafhopper.  However, the decision to apply an insecticide should be based on scouting information and threshold levels. (For more detailed information see: Grape Leafhoppers https://psuwineandgrapes.wordpress.com/2017/06/09/grape-leafhoppers/ ).

Japanese Beetle – Adult beetles feed on over 300 species of plants including grape. They prefer smooth, thinner types of grape leaves which are characteristic of many wine grape varieties (e.g., Chardonnay, Traminette, and Vidal Blanc). Feeding injury, depending on severity, can result in leaves having a skeletonized appearance due to consumption of the soft leaf tissues between veins. Research has shown that grapevines can tolerate a fair amount of leaf area loss without detrimental effects. However, no economic threshold level has been established for leaf injury on grapes caused by Japanese beetle.  Since young vineyard blocks, vines in grow tubes and many wine varieties are vulnerable to serious leaf loss by Japanese beetle feeding consistent monitoring is important. (For more detailed information see: Japanese Beetle: A Common Pest in the Vineyard                                                      https://psuwineandgrapes.wordpress.com/2016/07/09/japanese-beetle-a-common-pest-in-the-vineyard/).

Botrytis Bunch Rot: Winemaking Implications and Considerations

By Dr. Molly Kelly, Enology Extension Educator, Department of Food Science

In a previous post, Bryan Hed discussed early fruit zone leaf removal and its effects on the development of Botrytis bunch rot and sour rot. This is a good time to review the implications of molds and fruit rots on wine composition and quality. I will also discuss remedial actions in the winery.

Screenshot 2018-06-01 08.49.50Here we will focus on the most common bunch rot pathogen of mature berries, Botrytis cinerea. How severe can Botrytis bunch rot be before wine quality is impacted? This will depend on the type of rot as well as winemaking techniques however, even low levels of infection have been shown to negatively impact wine quality. Red wine quality was shown to be affected by as low as a 5% infection rate of B. cinerea. Extended skin contact in red winemaking can increase the effect of bunch rots on the finished wine.  While B. cinerea can be linked with sour rot, it is more commonly associated with other fungi including Aspergillus spp. Sour rot is caused by yeast, acetic acid and other bacterial growth. When acetic acid bacteria, yeast and filamentous fungi are present together, high levels of acetic acid can result. Berries infected with sour rot have a distinct vinegar smell that may be combined with the presence of ethyl acetate. Ethyl acetate is an ester described as smelling like nail polish remover.

Laccases are enzymes produced by fungi. They break down anthocyanins and proanthocyanidins which are important phenolic compounds that contribute to palate structure and wine color. In white wines, some aromatic compounds can be oxidized resulting in the production of earthy aromas.

The largest change in must chemistry as a result of Botrytis growth is seen in amounts of sugars and organic acids. Up to 70 to 90% of tartaric and 50-70% of malic acid can be metabolized by the mold. Resulting changes in the tartaric:malic ratio cause titratable acidity to decrease and pH to increase.

There may also be clarification issues as a result of infection. The fungi produce polysaccharides including β1-3 and β1-6 glucans as well as pectins as a result of the production of enzymes capable of degrading the cell wall. In the presence of alcohol, pectins and glucans aggregate causing filtration difficulties. To mitigate this issue, pectinolytic and glucanase enzymes can be used. When adding enzymes allow at least six hours prior to bentonite additions.

Botrytis cinerea strains differ in the amount of laccase produced. This enzyme can lead to oxidation of aroma/flavor compounds and browning reactions. It can be resistant to sulfur dioxide and not easily removed with fining agents. Bentonite may remove enough laccase to minimize oxidative problems. For varieties where the potential for oxidation is increased, ascorbic acid additions can be added to juice. Since Botrytis uses ammonia nitrogen there is less available for yeast metabolism. Vitamins B1 and B6 are also depleted. Therefore supplementation with nitrogen and a complex nutrient is required. Yeast assimilable nitrogen (YAN) should be measured and adjusted accordingly to avoid stuck fermentations and production of hydrogen sulfide. Also consider inoculating with low nitrogen-dependent yeast and use more than the standard amount of 2 lbs. /1000 gallons.

Wine off-flavors and aromas result from a number of compounds when made from grapes with Botrytis(and other bunch rot organisms). Descriptors include mushroom and earthy odors from compounds such as 1-octen-3-one, 2-heptanol and geosmin. Since fruitiness can be decreased, the use of mutés (unfermented juice) from clean fruit can be added to the base wine to improve aroma. Botrytis also secretes esterases that may hydrolyze fermentation esters. Monoterpenes found in varieties such as Muscat, Riesling and Gewürztraminer can also be diminished.

When Botrytis infection is present, consider the following processing practices in addition to those mentioned above.

  • Remove as much rot as possible in the field and sort fruit once it arrives at the winery. Using sorting tables is a great way to improve overall wine quality.
  • Whole-cluster press whites, using very light pressure, and discard the initial juice.
  • Harvest fruit cool and process quickly. Sulfur dioxide can be added to harvest bins to inhibit acetic acid bacteria.
  • Enological tannin additions will bind rot-produced enzymes. They can also bind with protein and decrease the bentonite needed to achieve protein stability. Note: Remember to not add tannins and commercial enzymes at the same time since tannins are known enzyme inhibitors. After an enzyme addition allow six to eight hours before adding tannins.
  • Minimize oxygen uptake since laccase activity is inhibited in the absence of oxygen. Inert gas can be used at press, during transfers and to gas headspace.
  • Use a commercial yeast strain that will initiate a rapid fermentation. The resulting carbon dioxide will help to protect against oxidation.
  • Once fermentation is complete, rack right away. Both Botrytis and laccase settle in the lees.
  • Phenolic compounds are the main substrate for fungal enzyme activity. Removal of undesirable phenolic compounds can be achieved using protein fining agents (ex: gelatin, casein, isinglass). The synthetic polymer PVPP can also be used in juice or wine to remove oxidized phenolic compounds.
  • Only cold soak clean fruit. Avoid cold soak and extended maceration on Botrytisinfected fruit as this may encourage fungal and bacterial growth.

As always, it is best to avoid rot-compromised fruit, however, using these practical winemaking tips should help to minimize negative impacts on wine production and quality.

References

DeMarsay, A. Managing Summer Bunch Rots on Wine Grapes, Maryland Cooperative Extension.http://extension.umd.edu/sites/extension.umd.edu/files/_docs/programs/viticulture/ManagingSummerBunchRots.pdf. Accessed 7 May 2018.

Ribereau-Gayon, P. 1988. Botrytis: Advantages and Disadvantages for Producing Quality Wines. Proceedings of the Second International Cool Climate Viticulture and Oenology Symposium. Auckland, New Zealand, pp. 319-323.

Steel, C., J. Blackman, and L. Schmidtke. 2013. Grapevine Bunch Rots: Impacts on Wine Composition, Quality, and Potential Procedures for the Removal of Wine Faults. J. Agric. Food Chem. 61: 5189-5206.

Zoecklein, B. 2014. Fruit Rot in the Mid-Atlantic Region, On-line Winemaking Certificate Program, Wine Enology Grape Chemistry Group, Virginia Tech. http://www.vtwines.info/. Accessed 16 April 2018.

Zoecklein, B. 2014. Grape Maturity, On-line Winemaking Certificate Program, Wine Enology Grape Chemistry Group, Virginia Tech.http://www.vtwines.info/. Accessed 16 April 2018.

 

 

 

GRAPE DISEASE CONTROL 2018, Part 2

Bryan Hed, Department of Plant Pathology and Environmental Microbiology, Penn State Extension

With a new season underway, I’d like to talk about some of the recent grape disease research that’s being conducted at Penn State. For this blog, we revisit Grapevine leafroll disease and leaf removal for fruit rot control.

Grapevine leafroll disease or GLD is associated with the presence of phloem inhabiting plant viruses of the family Closteroviridae. These viruses generally cause a degeneration of the primary phloem in shoots, leaves, and cluster stems. There are currently five species of grapevine leafroll-associated viruses; GLRaV-1, 2, 3, 4, and 7, and these viruses, especially GLRaV-1 and 3 have been spread across long distances (worldwide) through the sale and distribution of infected nursery material. Short distance spread of GLRaV-1, 3, and 4, within the vineyard or between adjacent vineyards, can occur by phloem-feeding insect vectors, specifically species of mealybugs and scales. No vectors have yet been discovered for GLRaV-2 and 7, which don’t appear to be as commonly found in northeastern vineyards.

The most obvious symptoms of the disease are cupping and loss of chlorophyll in the leaves in late summer and fall, during the ripening period. On red-fruited varieties, like Vitis vinifera‘Cabernet Franc’, leaves of infected vines can display red coloration of the interveinal tissue, while veins remain green. On white-fruited varieties like Chardonnay, symptoms are less noticeable and leaves tend to look yellowish and cupped. These symptoms are not necessarily diagnostic of the disease and may be confused with symptoms of nutrient deficiencies, water stress, and even crown gall. Therefore confirmation of infection by GLRaVs can only be made in the laboratory through serological or molecular analysis of phloem tissues in leaf petiole or dormant cane samples of suspect vines. More significant, and perhaps less recognized effects of GLD are reduced yield and vegetative growth, and even lower cold hardiness–a factor of critical importance for varieties grown in the northeastern U.S. GLD can also lead to a delay in fruit maturity with negative effects on fruit chemistry at harvest (lower soluble solids, higher titratable acidity), and reduced color development in red grapes of V. vinifera grapevines; all factors that might adversely impact perceived wine quality. Vineyards can be scouted annually for GLD during the ripening period, and tissue samples from symptomatic vines can be sent to a laboratory for confirmation.

There is no curative treatment for GLD as infection by GLRaVs is permanent, and the disease is best managed through removal or roguing of infected vines and replanting with certified virus-free material. So if you’re planning to order vines soon for planting a new Vitis vinifera vineyard next spring, I would strongly suggest the use of certified material. Research has shown that local spread of GLRaV-1, 3, and 4 can be minimized by targeting mobile stages of the vectors (mealybug and soft scale crawlers) with well-timed insecticide applications. There are no known sources of resistance to GLRaVs among Vitis species and these viruses have been found in V. labrusca, to Vitis interspecific hybrids, and V. vinifera. Infections of V. labrusca appear to remain latent or dormant and have not been shown to result in visual symptoms of the disease or economic impact, though research on native varieties has been minimal. On the other hand, V. vinifera is severely affected, and GLD has been shown to result in substantial economic losses among those cultivars.

Grapevine leafroll disease is nothing new to most of the world and symptoms of the disease were noted in French vineyards 165 years ago. But it seems relatively new to the northeastern U.S. grape and wine industry partly because V. vinifera grapevines, the species most dramatically affected, are relatively new to this industry. Therefore, as the acreage of V. vinifera in the northeast continues to expand and become a larger part of the premium wine industry, our encounters and frustrations with GLD will likely increase.

Surveys conducted in New York, Virginia, Ohio, and more recently, Pennsylvania, have confirmed the presence of these viruses throughout the major grape growing regions of the northeast. In Pennsylvania, we began our efforts by conducting an online survey to collect information from grape growers. In July of 2017, a link to a brief online questionnaire was sent out to 105 Pennsylvania wine grape growers across the Commonwealth to collect information about what varieties they grow, whether or not they have seen symptoms of leafroll virus in their vineyards, and if they would be willing to cooperate in the confidential collection of tissue samples from their vineyards blocks for determining the presence of these viruses.

In this initial phase of the project, sample collection focused on four cultivars of Vitis vinifera (Cabernet franc, Pinot noir, Chardonnay, and Riesling) and one French hybrid cultivar, Chambourcin, that were deemed among the most important cultivars in the PA industry. Twenty-eight cooperators were growing these cultivars and were selected for tissue collection. Growers were individually contacted via email and arrangements were made to collect leaf petiole samples from their vineyard blocks. Of these 28 growers, 22 reported they had seen leafroll-like symptoms in their vineyards. In late summer/early fall of 2017, samples were collected from 42 vineyard blocks from 16 locations. Samples were collected from symptomatic and non-symptomatic vines, in a randomized manner, and transported back to the laboratory and stored at 4°C until serological analysis by enzyme-linked immunosorbent assay or ELISA.

Overall, about 36% of the 42 blocks were positive for leafroll virus in 2017. Fourteen percent of the Chambourcin blocks sampled contained vines that tested positive for leafroll virus 1 and/or 3. Amongst the V. vinifera blocks sampled, 39% contained vines that tested positive for leafroll virus 1 and/or 3. Specifically, 29, 38, 42, and 50% of the Riesling, Pinot noir, Chardonnay, and Cabernet franc blocks were positive for leafroll virus, respectively. At one location where we were able to collect data on all four V. vinifera cultivars and where there were many vines positive for leafroll virus among all cultivars, there was a good correlation among red varieties between vines that showed symptoms (red, curled leaves) and vines that tested positive. However, among white varieties (Riesling and Chardonnay) the correlation was poor. This may indicate that it is harder to visually identify suspicious vines among white cultivars than it is among reds.

It appears that grapevine leafroll viruses are widespread and can be found in many grape growing areas of Pennsylvania. Among the varieties sampled in 2017, Cabernet franc was the most heavily infected by the viruses. However, this could change as we plan to expand the survey into more vineyards in 2018 which we were not able to reach in 2017. We also have identified healthy and infected grapevines within the same vineyard. These vineyards can be revisited in subsequent seasons to test disease spread to healthy vines. Furthermore, studies will be performed to test the impact of grapevine leafroll disease on grape quality and productivity in Pennsylvania, with the ultimate goal to mitigate the economic impact of the disease on the PA wine industry.

These surveys are an important and necessary first step toward determining the impact of GLRaVs and their associated disease. These viruses can have a significant impact on vineyard health and fruit quality, especially for those operations invested in the culture of premium V. vinifera. It is therefore essential for academic institutions to continue to develop research programs around this important group of pathogens and create a growing body of information that will help vineyard managers reduce their spread and impact. Below are some references that I drew from for this bit on leafroll viruses and GLD. The last reference is available free, online, and is a great review of GLD by some of the leading experts from New York, California, and Washington.

Bahder, B., Alabi, O., Poojari, S., Walsh, D., and Naidu, R. 2013. A Survey for Grapevine Viruses in Washington State ‘Concord’ (Vitis x labruscana L.) Vineyards. Plant Health Progress, August 5, 2013. American Phytopathological Society (online).

Compendium of Grape Diseases, Disorders, and Pests. 2nd edition, 2015. Editors Wayne F. Wilcox, Walter D. Gubler, and Jerry K. Uyemoto. The American Phytopathological Society. Pp. 118-119.

Naidu RA, Rowhani A, Fuchs M, Golino D, Martelli GP. 2014. Grapevine leafroll: a complex viral disease affecting a high-value fruit crop. Plant Dis. 98: 1172–85. https://www.researchgate.net/publication/270339365_Grapevine_Leafroll_A_Complex_Viral_Disease_Affecting_a_High-Value_Fruit_Crop

More on Botrytis bunch rot/sour rot control from the church of fruit-zone leaf removal

The practice of leaf removal for bunch rot control is based on concepts developed many years ago by lots of research that examined its effects on fruit-zone microclimate, source limitation, and fruit set, among other things. In short, removal of leaves from nodes in the fruit-zone increases sunlight exposure, air circulation, and pesticide penetration to developing fruit. This creates a fruit zone environment that is much less conducive to the development of Botrytis and other harvest-rot-inducing microorganisms that prefer to do their dirty work in darkness, still air and high humidity. Indeed, the most consistently successful bunch rot control programs will not simply rely on Botrytis specific fungicides but will integrate cultural methods like fruit-zone leaf removal

Fruit-zone leaf removal has generally been applied between fruit set and veraison. But there is a growing body of information being developed around early fruit zone leaf removal(ELR) and its effects on the development of Botrytis bunch rot and sour rot. ELR is the removal of leaves in the fruit zone before, or at the beginning of, bloom, and interest in this area of research has increased in several areas of the world in recent years. For example, recent research in Italy by Stefano Poni and his colleagues details the effects of ELR on crop load management, fruit and wine quality, and disease control, especially for late season bunch rots. Here in the U.S., research to study the effects of ELR is being conducted in places like Michigan, Pennsylvania, and New York, among other areas. But why is there added interest in ELR for bunch rot control?

In addition to fruit zone environment, cluster compactness plays a large role in harvest rot development. A three-year study we conducted with Vignoles over 15 years ago clearly showed that the more compact the cluster (measured as the number of berries per length of the cluster), the more rot we observed developing in that cluster. It’s no accident that many of the most bunch rot susceptible varieties typically produce clusters of tight or compact architecture (Chardonnay, Pinot gris, Pinot noir, Riesling, Vignoles). The removal of the most mature, photosynthetically active leaves (those in the fruit zone) before or during bloom, starves the inflorescences for sugars and reduces the number of flowers that set fruit. Fewer berries per cluster generally result in looser clusters that develop less bunch rot. Taken together, ELR combines the benefits of an improved fruit zone environment with less susceptible clusters and generally greater reductions in bunch rot development than what would be achieved with post fruit set leaf removal (which would not, theoretically, reduce cluster compactness). When we examined ELR for six consecutive seasons in our experimental Chardonnay vineyard, we found that we could eliminate two Botrytis-specific fungicide sprays and achieve harvest rot control that was equivalent to, or better than, a full Botrytis spray program (four sprays). This adds to the appeal of ELR as Botrytis fungicides are often the most expensive fungicide inputs in rot control programs, and reducing chemical pesticide inputs is a significant response to the growing public interest in agricultural products with a healthier profile (though some may debate how relevant a healthier profile is to the consumption of wine!).

But there are potential drawbacks to ELR (it’s always something). For example, the reduction in berry number per cluster generally results in a reduction in cluster weight that can result in a reduction in yield. This can be a downside to ELR in operations where yield reduction is unacceptable to production goals. However, over the course of the six years in our Chardonnay experiment, we were able to minimize or eliminate yield reduction by ELR, while maintaining bunch rot reductions. So reductions in yield by ELR can be managed to some extent. Also, in our experience, ELR seemed more effective on some varieties (Chardonnay and Vignoles) than others (Pinots?) in terms of reducing compactness and bunch rot. There were also seasonal variations from year to year. So there is some level of inconsistency with this method; sometimes the rot reductions are statistically significant and sometimes they aren’t.

More recently, research with ELR has been taken a step further to examine the mechanization of this practice; manual leaf removal is expensive and time-consuming, and timing can be critical. Experiments over the past several years in Europe and the U.S. have shown that the use of air pulse leaf removal technology can remove enough fruit zone leaf area (about 35-50% of that which would be achieved by hand removal (100%)) to mimic the effects of manual leaf removal. As we expected, this technology appears to work most efficiently (removes the most leaf tissue in the fruit-zone) on more upright, two-dimensional training systems like vertical shoot position (VSP) or four-arm kniffen systems, when compared to more three-dimensional training systems like single, high-wire, no-tie systems. Mechanization is often the key to greater adoption of a practice, but only if it improves economic sustainability. An air pulse leaf removal system can represent an investment of tens of thousands of dollars. This would hardly be cost-effective for operations with just a few acres to treat per season. However, large farms that have lots of acres to treat may benefit through mechanization of ELR. Also, in regions where there is a concentration of wine grape acreage (ie, the Lake Erie region, Finger Lakes, etc), this machinery could be shared, or the work contracted, to ease the capital investment necessary on a per farm basis.

So ELR is not a silver bullet. I would instead consider it some buckshot in a silver shotgun shell that is still under development; it can be an important component of an effective, integrated bunch rot control program. If you have bunch rot susceptible varieties such as those mentioned above, and would like to apply this practice in your vineyard, I would recommend you test it out on a few vines first and compare the results to the rest of your vineyard (all other things being equal) to see if this is something that will work for you. As I mentioned above, the results may vary somewhat from one variety to the next and from one season to the next.

And one last thing for wine grape growers with sour rot susceptible varieties: please review Wayne Wilcox’ newsletter from last year (June 2017) regarding the Cornell research on sour rot control. Wayne’s graduate student, Dr. Megan Hall, completed some groundbreaking work on the biology of grape sour rot and the development of effective ways to minimize it by targeting fruit flies in the vineyard.