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.
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:
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.
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.
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.
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).
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
- 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/).
By Dr. Michela Centinari, Assistant Professor of Viticulture, Department of Plant Science
Grape growers across Pennsylvania would agree that grapevines are breaking bud later this spring compared to the past few years. Some of you might be relieved and are hoping that a late bud break will reduce the likelihood of spring frost injury, particularly for those cultivars that tend to break buds early, while others might wonder if a late bud break will mean a shorter growing season and what impact this might have on fruit and wine chemistry.
This might be a good opportunity for a short review on bud break (or bud burst if you prefer) and some of the major factors that influence it.
What is bud break?
Bud break is one of the grapevine’s key growth or phenological stages. Phenology is defined as “the study of the timing of natural phenomena that take place periodically in plants and animals1.” Many vineyard operations related to canopy, nutrient, disease and insect management are conducted at specific phenological stages, so it is important for growers to record dates for bud break and other important growth stages.
Bud break is commonly described as “the appearance of green tissue through the bud scales2” or “the emergence of a new shoot from a bud during the spring3.” There are several systems used to precisely identify bud break and other key phenological stages. One of the systems most widely used today is the modified Eichhorn Lorenz (E-L) system, which was developed by Eichhorn and Lorenz in 1977, modified by Coombe in 19954, and later revised by Coombe and Dry in 20043. A primary reason why the E-L system was revised multiple times was that the visual characteristics during the early stages of bud growth might vary among cultivars. For example, in some cultivars buds “emerge as hair-covered cone from between the scale without any sign of green tissues” while in other cultivars buds can have “green tips visible early through the hairs1.” To avoid, or at least reduce confusion, the latest E-L system modification (2004) defines grapevine bud break when leaf tips are visible (Figure 1).
Although there might be slight differences in how growers or scientists define bud break, using a consistent method across years and cultivars is important in order to make comparisons. Photos of the modified E-L system and information on how to use grapevine phenology to improve vineyard management can be found by clicking on these hyperlinks: modified E-L system by The Australian Wine Research Institute and Grapevine Phenology Revisitedby Fritz Westover5.
Why was bud break late this year in Pennsylvania?
Grapevine phenology is strongly tied to air temperature. Once buds fulfill their chilling requirements they are in a state of eco-dormancy, which means they are dormant only because of cool or cold weather. In temperate regions, buds tend to reach this state by early winter, therefore, warm weather in late winter or early spring might result in early bud break and consequently increase the risk of spring frost injury.
An air temperature of 10 °C (50 °F) has traditionally been used as the base temperature for grapevines, as it is the temperature threshold below which grapevines will not grow. Hence, mean daily temperatures above approximately 50 °F (or, more specifically, 46 to 50 °F) induce bud break and shoot growth6. Grapevine base temperature is higher than that reported for fruit trees, such as apple, peach, cherry, and apricot (the base temperature ranges from approximately 39 to 41 °F)7. Base temperature for bud development varies between grapevine species and cultivars, and the physiological basis of this thresholds is still unclear2.
Over the years, many models have tried to use temperature data to predict bud break and other key phenological stages. Some models are based on the accumulation of temperatures above the mean daily temperature of 50 °F, for example, Growing Degree Days (GDD), while others use temperature averages rather than summations8. However, there is not(at least to my knowledge) a solid and simple formula that we can use to predict when bud break will happen.
GDD calculated from January 1 to bud break may not be a very good way to answer the question: Are we going to have an early bud break? Hans Walter-Peterson, Finger Lakes Grape Program, Cornell University, used data collected over many years in the Lake Erie region to show that the date of bud break for Concord was not well correlated with GDD (base 50 °F) accumulated from January 1 to bud break. Using the total GDD for this period, however, does not take into consideration when GDD accumulates. For example, having seven consecutive days with mean temperature above 50 °F might not be the same of having seven days with the same temperature but interspaced by a long period of cool/cold weather with mean temperatures below 50 °F.
Although further studies are needed to clarify the relationship between bud break and temperature, air temperature still remains the dominating factor affecting bud break. The number of GDD accumulated from January 1 through April 30 in 2018 across Pennsylvania was definitely lower than the accumulated GDD during the same months in 2017 (Table 1). This indeed had an influence on grapevine bud break occurring later in 2018 compared to 2017.
Time versus rate of bud break
While the number of GDD accumulated from January 1 through April 30, 2018, was lower than the same period in 2017, the number of GDD accumulated during the first week of May 2018 was, however, much higher than the number accumulated during the same period in 2017 (Table 2). Although bud development started later this year, you might have noticed a greater rate of bud break or higher speed of bud development due to consecutive days of high, above average daily temperatures at the beginning of May. The rate of bud break increases as the air temperature rises above 50 ℉ up to approximately 86 ℉ (30 °C). However, at higher temperatures, the rate of bud break might start to decline6.
Other factors to consider:
Species and cultivars: The base temperature requirements vary amongst grape species (e.g., V. berlandieri > V. rupestris > V. vinifera > V. riparia) and cultivars (for example, Riesling > Chardonnay)6. Regardless of the seasonal weather conditions, the order of bud break across different species and cultivars tends to be consistent. Those with a lower base temperature threshold will break buds earlier than those with a higher base temperature. For example, Chardonnay always bursts earlier than Cabernet Sauvignon.
Soil and root temperature: There is contradictory evidence about the role of soil and root temperature on the timing of bud break. Studies conducted in California9,10found that Cabernet Sauvignon bud break was positively correlated with soil temperature: bud break occurred several days earlier when soil temperature increased from 52 ℉ to approximately 77 °F. In a more recent study, however, soil temperature did not influence the timing of Shiraz bud break11.
Number of buds left at pruning: The number of buds (or nodes) retained at pruning (24 to 72 per vine) had little influence on bud break and other phenological stages of Sauvignon Blanc vines up to veraison12.
Bud position along the cane: When dormant canes are left upright, the more distal buds generally tend to break first and suppress the growth of the buds at the base of the cane (closer to the cordon) (Figure 2). This phenomenon is called apical dominance or, more precisely, correlative inhibition. In frost prone areas, to delay bud break of cordon trained vines, canes can be pruned back to 2-bud spurs when the distal buds reach bud break. For more information please refer to a past blog post: How does delaying spur pruning to the onset or after bud burst impact vine performance?
In some cultivars, for example, Cabernet Franc, correlative inhibition may cause inconsistent bud break in cane-pruned vines. Meaning that buds located in the central part of the cane might not open or they might develop shorter, weaker shoots than those positioned at the beginning or at the end of the cane. There are, however, practices that can be used to promote uniform bud break along the canes, these include bending or arching (Figure 3), and partial cracking of canes6.
Age of the vine: Within the same cultivar, the timing of bud break and other key phenological stages may vary between young vines that are not in full production yet (3rd leaf or younger) and mature, established vines (4th leaf or older)5.
- Iland P, Dry P, Proffitt T, Tyerman S. 2011. The grapevine: From the science to the practice of growing vines for wine. Patrick Iland Wine Promotions.
- Creasy GL and Creasy LL. 2009. Grapes. Wallingford, UK; Cambridge, MA: CABI.
- Coombe BG and Dry P. 2004. Viticulture 1 – Resources. 2nd edition. Winetitle
- Coombe BG. 1995. Adoption of a system for identifying grapevine growth stages. Aust J Grape Wine Res 1:104–
- Westover F. 2018. Grapevine phenology revisited. Wines and Vines.
- Keller M. 2010. The science of grapevines: Anatomy and physiology. Academic Press.
- Moncur MW, Rattigan K, Mackenzie DH, and McIntyre GN. 1989. Base temperatures for budbreak and leaf appearance of grapevines. Am J Enol Vitic 40:21–26.
- Malheiro AC, Campos R, Fraga H, Eiras-Dias J, Silvestre J, and Santos JA. 2013. Winegrape phenology and temperature relationships in the Lisbon wine region, Portugal. J Int Sci Vigne Vin47: 287–299.
- Kliewer WM. 1975. Effect of root temperature on budbreak, shoot growth, and fruit-set of ‘Cabernet Sauvignon’ grapevines. Am J Enol Vitic 26:82–
- Zelleke A and Kliewer WM. 1979. Influence of root temperature and rootstock on budbreak, shoot growth, and fruit composition of Cabernet Sauvignon grapevines grown under controlled conditions. Am J Enol Vitic 30:312–317.
- Field SK, Smith JP, Holzapfel BP, Hardie WJ, and Emery RJN. 2009. Grapevine response to soil temperature: xylem cytokinins and carbohydrate reserve mobilization from budbreak to anthesis. Am J Enol Vitic 60: 164–172.
- Greven MM, Neal SM, Hall AJ, and Bennett JS. 2015. Influence of retained node number on Sauvignon Blanc grapevine phenology in a cool climate. Aust J Grape Wine Res21, 290–301.