By Michela Centinari, Bryan Hed, and Kathy Kelley
The 2016 growing season was a rewarding one for many Pennsylvania (PA) wine grape growers. But before we move on with plans for next year, let’s review this past season using some interesting data we gathered from PA grape growers. In November 2016, we sent out a 5-min Internet survey developed by our team and housed on SurveyMonkey.com. A link to the survey was sent to 90 members of a PA wine grape grower extension electronic mailing list. Thirty-seven participants clicked the link and responded to questions related to the 2016 harvest and growing season.
All procedures were approved by the Office of Research Protections at The Pennsylvania State University (University Park, PA). Upon completion of the survey, each participant was entered into a raffle to win one of three $25 gift certificates that could be redeemed toward any Penn State Extension wine or grape program fee.
This article is based on our observations and feedback we received from survey participants. We welcome more PA wine grape growers to share their stories and to send us (Michela Centinari; Bryan Hed) their contact information so they can be included in future surveys (where else do you have a chance to win a gift card for a Penn State Extension event?).
First, some information about the respondents
Thirty-three survey participants (89%) indicated the region where they grew grapes. The majority of the respondents (11) were from the Southeast region, followed by Northwest (7), Northeast (6), South Central (4), North Central (3), and Southwest (2) regions.
Data that described what species of grapes survey participants grew were: Vitis vinifera (e.g., Riesling, Cabernet Franc, Chardonnay), Vitis interspecific hybrid (e.g., Chambourcin, Traminette, Vidal Blanc), abbreviated in Table 1 as vinifera and hybrid, respectively, and native (e.g., Concord, Niagara) cultivars (Table 1).
What did we ask the survey participants?
Participants were asked to rank the average yield of the grapes they grew in 2016 from “poor” to “record crop.” They were also asked to rank the average quality of the fruit from “poor” to “excellent,” and the insect and disease pressure experienced from “below average” to “above average.” Respondents were then directed to open-ended questions where they indicated what cultivars performed below or above average and why.
Survey participant responses
- Yield: The majority of the respondents (88%) indicated that average crop yield was “average” “above average,” or “record crop” (Figure 1). Only four participants (12%) indicated that average yield was “below average” or “poor.”
Of those four respondents, two attributed “poor” or “below average” yield to disease issues (e.g., powdery mildew, black rot). One survey participant from the Southeast region indicated problems with freeze injury as the vines were approaching bud burst. Specifically, the participant wrote: “My whites especially Chardonnay were light (lower crop yield than average) this year. I believe the whites were hit hard with the early April freezes when we had three nights in a row dip down into the 20’s. I believe many of the primary buds froze. Most of the white grape clusters were much smaller than usual.”
An unusually warm March was indeed followed by a very cold start to the month of April. Between April 3 and 10, there were several nights in the 20’s ºF in many regions of PA. While there was no sign of bud burst, as far as we are aware, for grapevines grown in central or north PA, some were approaching bud burst in several areas of south central and southeast PA.
The fourth respondent from northwest PA commented that “Vines are still recovering from 2014 winter injury, and that is too expensive to replant large percentage.” Despite long-term issues with winter injury recovery, finally, after two harsh winters (2013-2014; 2014-2015) PA grape growers were able to enjoy the winter without having to worry about their vines. In many regions of PA, winter temperatures did not reach critical low values that tend to injure many of the cultivars grown in the Commonwealth. However, on February 14 temperatures reached -10°F and below in northeast PA. The lowest temperature recorded (-19°F) was in Potter County. Despite this isolated event, we did not receive inquires of growers concerned about winter injury.
- Fruit quality: The majority of the respondents (83%) ranked fruit quality as “above average” or “excellent,” which was consistent across cultivars and regions. Only one grower rated fruit quality as “below average” as a consequence of high disease pressure.
A few survey participants from southeast PA who rated fruit quality from “above average” to “excellent” commented:
“Early veraison and high heat degree days in September allowed the early varietal to ripen in almost perfect condition. The Bordeaux reds .. in late September and early October soaked up a lot of rain and didn’t recover completely from this. I harvested Merlot clusters bigger than I have ever seen them”
“Bordeaux varieties (Cabs, Merlot, Petit Verdot) were at least 23ºBrix with a high of 25. Nice and ripe with good flavors”
“Grüner, Riesling, Merlot, Chambourcin, and Cabernet Franc achieved mature ripe flavor. Acids were in ideal range”
Other survey participants from across the state also indicated that in 2016 the grapes reached “Optimal ripeness and acidity level,” “Good acid balance,” “Berry size, color, acids, pH, and sugars were the best ever,” “Excellent cultivar character.”
Several respondents pointed out that “Hot and dry weather played an important role in the quality this year” and commented that fruit was clean from major diseases.
- Insect and disease pressure: Almost half of the growers who participated in the survey (47%) experienced “below average” insect and disease pressure during the 2016 growing season, while 41% answered “average” and only 12 % “above average.”
Of the four participants who reported “above average” disease pressure, one indicated problems with spotted Lanternfly an invasive insect who unfortunately is making its way to some areas of PA (Spotted Lanternfly: A new invasive pest detected in Pennsylvania). Two respondents reported issues with powdery mildew. Powdery mildew was indeed very much “alive and well” in many vineyards in 2016. In Erie County, we witnessed flare-ups of this disease on fruit during late June and early July, despite relatively prudent control measures and relatively few primary infection periods. This disease requires rainfall events early in the season for spore release only (minimum of 0.1 inches of rain and temperatures above 50ºF), but once spores are released the pathogen does not require wet plant surfaces to infect susceptible tissue and generate subsequent waves of its parasitic life cycle. This is very much unlike most of the other fungal pathogens we deal with each year. Note that even California growers spend a boatload of time and treasure controlling this disease every year. In short, it is a disease management issue wherever grapes are grown, every year, everywhere. Fortunately, aside from a few horror stories where there were gaps in spray intervals around bloom, most growers managed to get decent commercial control of this disease on their grapes in 2016.
Weather conditions during the growing season
A look at the weather conditions through the online network for environment and weather applications (http://newa.cornell.edu/) can help interpreting survey participant responses. In Figure 4 and 5, we reported data collected by the two new weather stations located nearby the Penn State Fruit Research and Extension center (FREC) in Biglerville (Adams County, south central PA) and at the Lake Erie Regional Grape Research and Extension center (LERGREC) in North East (Erie county, northwestern PA). We compared the 2016 monthly growing degree days (GDD) (index of heat accumulation) and precipitation to the mean values for April through October for a three-year period (2013-2015) (Figures 4, 5).
Temperature: Despite a cool start to the 2016 season (see April and May) the rest of the season was warmer than average in PA and other parts of the eastern U.S. Indeed, the heat accumulated (GDD) from June through October in 2016 was above that of the previous three-year average (Figure 4).
The warm weather led in many cases to great fruit ripening conditions, as indicated by the majority of the respondents, but in a few instances may have hindered fruit sugar accumulation as noticed by one of the participants: “I think that heat in August slowed ripening and resulted in lower Brix than other years but all fruit did achieve ripeness.” High temperatures might increase plant respiration rates to a greater degree than photosynthesis rates, which in other words means lower carbon gain /sugar accumulation for the vine and fruit. A detailed explanation of why this happens can be found in the September issue of Viticulture notes edited by Tony Wolf (Professor and Viticulture Extension Specialist at Virginia Tech).
Precipitation: Rainfall in the spring and early summer was well below average in Erie County (northwestern PA) with 2.1, 1.9, and 2.7 inches of rain in May, June, and July, respectively (Figure 5B). Dry weather often comes hand in hand with a higher number of sunny days and higher temperatures; two additional factors that stymie fungal pathogen growth.
Peak grape disease susceptibility generally occurs during June and early July in PA. Both June and July were drier than average in many parts of the state: see for example Biglerville (south central PA) with only 2.7 and 0.2 inches of rain in June and July, respectively (Figure 5A), or other sites across the state (Table 2: Lewisburg, State College, and Cabot). This helps to explain the large percentage of growers reporting average to below average disease pressure. However, in other parts of the state or near the eastern PA border it was not quite as dry but still warm (Table 2, numbers in bold font).
In places and months where rainfall amounts were well above average, rainfall was often heavy and punctuated by well defined, often lengthy dry periods in which growers could easily keep up with their protective fungicide sprays. Unfortunately, there were a few locations where diseases like black rot flared out of control, but those were the exceptions rather than the rule (Figure 3).
In summary “dry, sunny, and warm” sums up the weather for the majority of the growing season for many regions of the state, with local and ample variations on precipitation amount. For the most part, these conditions are rather hostile to the fungal or fungal-like pathogens that are responsible for the majority of our grape disease issues every year. This was very fortunate for a number of reasons, not the least of which was the fact that 2016 was following a year that left many vineyards with well above average levels of overwintering inoculum for diseases like black rot and downy mildew. This was especially true in northwestern PA; downy mildew could be found in pretty much every vineyard in Erie County in 2015, despite the fact that the vast majority of the grape acreage is planted to Concord, a variety with relatively low susceptibility to downy mildew. A wet spring and early summer could have left growers really struggling hard to keep those diseases under control on fruit this year. But downy mildew literally “took a vacation” in the Lake Erie region in 2016. It was the most downy mildew-free season Bryan experienced over his 18 seasons of working with grapes. You might say that many PA grape growers got a small taste of what it’s like to grow grapes in California.
When ripening begins, our attention naturally turns toward controlling bunch rots on susceptible varieties. Varieties that produce “tight,” compact clusters are most at risk, and for these control measures are essential. Fortunately, survey participants did not indicate bunch rot issues this season. In Erie, as well as many other locations in PA rainfall resumed by the second week in August (Figure 5), and the ripening period was actually relatively wet through September. As you know, rainfall during ripening leads to bunch rot problems (Late summer/early fall grape disease control) and we did see rot problems develop early in vineyards of Pinot Gris and Pinot Noir with extremely tight clusters despite measures to reduce cluster compactness and a barrage of fungicide applications. In those vineyards, the crop had to be harvested early, before optimum ripeness. However, at LERGREC, rot control was especially good in Vignoles (another cultivar susceptible to bunch rot) where we applied mechanized pre-bloom fruit zone leaf removal in combination with Botrytis specific fungicides at veraison and beyond.
In conclusion, it was a rewarding growing season for many PA wine grape growers. Warm, (mostly) dry conditions favored the production of a high-quality vintage and we are looking forward to tasting this season’s wines!
By: Dr. Michela Centinari
It is August already, which, for many grape growers in Pennsylvania, means veraison and the beginning of fruit ripening. It seems a good time to comment on the seasonal weather and how it can affect the vines. In July, above average temperatures were recorded in Pennsylvania , and drought conditions varied from ‘none’ to ‘severe drought’ across the state (Figure 1). The regions most affected by drought are North Central, Northwest, and some areas of Northeast PA .
In Figures 2 and 3 I reported the cumulative growing degree days (GDDs) (April to July) and precipitation (March to July) recorded at the two Penn State research and extension stations located in the South Central (Biglerville, Adams County) and Northwest (North East, Erie County) part of the state (http://newa.cornell.edu/). I also included the 2014 and 2015 data so you can compare the heat accumulation (GDDs), precipitation patterns and amount this year with those of the two previous seasons.
When looking at figures 1, 2, and 3, please keep in mind that local weather conditions vary greatly, shower and thunderstorm activity was hit or miss across the state. It is indeed recommended that growers install a weather station at their site to carefully monitor weather conditions and assist with disease control programs.
Compared to 2014 and 2015, this growing season started with lower heat accumulation in some areas of Pennsylvania, such as the Northwest (Figure 2A) and South Central (figure 2B) regions. Higher than average temperatures recorded in July however, pushed GDDs close to or above those of the same period last year. For example, in Erie County, cumulative GDDs were, by the end of July, above those accumulated in 2015 or 2104. In South Central PA GDDs are reaching the 2015 values and they are above those accumulated in 2014 for the same period (April-July).
The hot temperatures recorded in July can accelerate fruit ripening . For example, in Central Pennsylvania, Noiret (Vitis hybrid), which is not one of our earliest varieties, started to turn color last week (i.e., the first week of August), approximately 10 days earlier than last year.
While drought conditions have not been recorded in the Southeast and most of the Southwest regions, it has been dryer than average in the rest of Pennsylvania. For example, in North East (Erie County, Northwest) cumulative precipitation from March to July (13.6²) was 40% and 36% lower as compared to last year (22.6²) and two years ago (21.12²). In Biglerville (Adams County, South Central) cumulative precipitation from March to July (12.7²) was 33% and 31% lower as compared to last year (19.2²) and two years ago (18.4²).
Drought doesn’t always equal water stress
In- and across-season precipitation patterns in the eastern US are unpredictable. In our humid climate, precipitation and the soil water reservoir are usually sufficient to meet (or exceed) vine water requirements through ripening. Even if a drought period occurs, its duration and severity are not usually sufficient to warrant concern about moderate or severe vine water stress. Growers do however need to be aware that non-irrigated grapevines in temperate climates can occasionally face water stress during drought periods in the growing season [3; 4].
Hot temperatures, like those recorded in July, increase evapotranspiration and how much water the vine needs. This could facilitate the occurrence of vine water stress in areas that have been experiencing persistent lack of rain. The risk of water stress, indeed, not only depends on the amount of soil water available (supply), but also on how fast this water is used by the vines (demand) .
Along with seasonal rainfall and winter soil moisture other factors affecting the amount of water available (water supply) to the vines are:
- Soil water holding capacity which is determined by the soil textural properties: heavier soils (loam and clays) hold more water than light sands or gravels. For example, a unit volume of sandy-loam soil can hold about 50% as much water as a clay soil .
- Soil depth: deep soil can hold a greater volume of moisture than shallow soil  allowing grapevines, in the absence of restrictive layers, to develop a more extensive and deeper root system which can access deep resources of water during drought periods.
- Grapevine root system size and rooting depth: In addition to soil characteristics, also the age of the vine will influence root system size and rooting depth. Young vines have restricted root systems and rooting volume for several years, thus they are more sensitive to water stress than mature vines with well-established root systems .
- Presence of competitive plants, as green and actively growing cover crops and weeds in the middle-row and in-row areas.
Water demand is primarily driven by weather conditions (solar radiation, air temperature and humidity). For example, evaporation from an open pan under hot and dry weather (i.e., California) can be around 8-10 inches of water per month, whereas under cool and humid condition, typical of the northeast US can be less than 5 inches . Also the amount of sun-exposed transpiring leaf area and crop load will affect the amount of water used by the vines . For example vines trained to GDC or high-wire cordon tend to have greater sun-exposed leaf area that can capture more sunlight and use more water than those trained to vertical shoot positioning (VSP) . Heavily cropped vine vines also require more water for fruit ripening than vines with a smaller crop .
Vine response to water stress varies with the severity of the stress and the timing of the season it develops
Growth processes (i.e., shoot growth, early berry growth) are more sensitive to water deficit than photosynthesis . Therefore, a mild/slight water stress between fruit-set and veraison can favorably diminish vegetative growth and reduce berry growth leading to smaller berries with potentially higher skin to pulp ratio without compromising photosynthesis and carbohydrates/sugars production . Under moderate to severe water stress conditions, however, photosynthetic activity is reduced possibly leading, early in the season, to poor canopy development and function. Later in the season (after veraison) a reduction in photosynthesis can decrease sugar accumulation in the berries with a negative effect on fruit ripening and flavor development. Further, a reduced storage of carbohydrates and other nutrients in perennial organs may occur. Thus, it is crucial to maintain a healthy and functional canopy after veraison to avoid negative effects on fruit or wine quality and cold hardiness. Furthermore, because after veraison, berry growth is quite resistant to water stress, a post-veraison water deficit is not as effective in reducing berry size as a pre-veraison one .
Growing up in Italy, I remember the old-world “wine dilution theory” that supported the idea that any irrigation after veraison would lead to an increase in berry size (due to water dilution) and a reduction in wine quality . There was not strong scientific evidence, however, supporting this assumption. It was actually found that water doesn’t move into the berry after veraison due to complete or partial lost in xylem functionality  which proved that irrigating the vines after veraison doesn’t actually impact berry size . Thus, nowadays it is recommended to avoid moderate to severe water stress after veraison to ensure vine health and proper ripening and flavor development.
Symptoms of vine water stress:
Since vines change in appearance under water stress conditions it is a good practice to walk through the vineyard and look for sign of water stress, starting with young vines. A comprehensive table that summarized visual symptoms of increasing water stress from mild to severe can be found in the “Wine grape production guide for eastern North America” (page 172) and also available in the July issue of Viticulture Notes  edited by Tony Wolf, professor of viticulture at Virginia Tech University.
Below I summarized some of the visual indicators of vine water status, from ‘well-watered’ to ‘severe drought’ conditions 
Well-watered vines (Figure 4):
- Shoot tips are actively elongating
- Tendrils are turgid and expand well beyond the shoot tip
- Leaves orientation: leaf blades are oriented toward the sun
- Leaf color and temperature: canopy is green and healthy and leaves are cooler than our body temperature
- Berries are turgid
Mild to moderate water-stressed vines:
- Shoot tips are compressed and they are enclosed when the last formed leaves are pushed toward the growing tip (Figure 5A)
- Tendrils are drooping or wilted
- Leaf orientation: leaves are oriented away from the sun
- Leaf color and temperature: leaves (starting from the basal leaves) are grayish-green to light-green and they are warm to touch at mid-day (> 100°F)
- If it occurs around bloom/ fruit-set, berry-set may be reduced
Severe water-stressed vines:
- Shoot growth has stopped and shoot tips are dry or aborted
- Tendrils dried or abscised
- Leaf orientation: leaves may roll and dry
- Leaf color and temperature: leaves (starting from the basal leaves) are yellow with necrotic edges (Figure 5B) and they are very warm (well above 100°F)
- Cluster rachis tip may dry if stress occurs at bloom, fruit-set may be reduced, berries may become flaccid if water stress occurs post-veraison
Water stress in a young planting must be avoided because it can compromise root system establishment and overall vine growth, delay its capability to carry a crop, and reduce cold hardiness. If you notice signs of water stress in young vines and you don’t have a permanent and functioning irrigation system in place, temporary irrigation systems could be used such as a flex tank and hose. It is a very labor intensive operation but it is crucial to ensure the long-term success of your investment. If you notice any sign of severe water stress on your mature vines and you are not able to irrigate them you may want to consider shoot and crop-thinning (especially in heavily cropped vines) to reduce vine demand for water, as well as avoid growth of weeds which can compete with vines for water supply .
- United States Drought Monitor: http://droughtmonitor.unl.edu
- Wolf TK. Viticulture Notes. Vol 31 No. 5. 23 July 2016. Virginia Tech University Cooperative Extension. Available at: http://www.arec.vaes.vt.edu/alson-h-smith/grapes/viticulture/extension/growers/current_VN_newsletter.pdf.
- Hayhoe K, Wake CP, Huntington TG, Luo L, Schwartz MD, Sheffield J, Wood E, Anderson B, Bradbury J, DeGaetano A, Troy TJ and Wolfe D. 2007. Past and future changes in climate and hydrological indicators in the US Northeast. Climate Dynamics 28, 381–407.
- Schultz HR and Stoll M. 2010. Some critical issues in environmental physiology of grapevines: future challenges and current limitations. Aust. J. Grape Wine Res. 16, 4–24.
- Lakso AN. 2000. Basics of Water Balance in New York Vineyards. 29th NY Wine Industry Workshop, NYS Agric. Exper. Sta., p 94–101.
- Wolf TK. 2008. Wine grape production guide for Eastern North America. Natural Resource, Agriculture, and Engineering Service: Ithaca, NY USA.
- Keller M. 2010. The Science of Grapevines: Anatomy and Physiology. Publisher: Academic Press.
- Hansen M. 2016. Rethinking post-veraison irrigation. Vineyard & Winery Management. July-August, 2016. 60–
- Hoheisel G, Moyer M. Grapevine management under drought conditions. Washington State University Extension. EM4831E. Available at : http://cru.cahe.wsu.edu/CEPublications/em4831e/em4831e.pdf
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 Michela Centinari, Bryan Hed, Kathy Kelley, and Jody Timer
The 2017 growing season was a rewarding one for many Pennsylvania (PA) grape growers; crop quality and yields generally met or exceeded expectations. However, this season was not without its challenges. Before we start planning for next year, let’s review this past season and discuss the important issues and concerns PA growers faced in 2017. In November a link to a 10-minute Internet survey was sent via email to 110 members of a PA wine grape grower extension mailing list. The survey was designed to solicit their feedback with regards to the 2017 growing and harvest season. Fifty participants completed the survey* and their responses form the basis of this blog article. So that we have a complete accounting for growers throughout the Commonwealth, we encourage PA wine grape growers who may not have received the email to contact us (Michela Centinari; Bryan Hed) and provide their contact information so that they can be included in future surveys.
First, some information about participant demographics
Of those who provided the region where they grew grapes (44 participants), the majority (16) were located in the Southeast region, followed by South Central (9), Northwest (8), Northeast (5), North Central (3), and Southwest (3) regions. Species of grapes survey participants grew are listed in Table 1.
What did we ask the survey participants?
Participants were asked to indicate the average yield of the grapes they grew in 2017 by selecting the appropriate category: “poor,” “below average,” “average,” “above average,” or “record crop.” Although growers often adjust crop load to meet a desired level, environmental or other unexpected factors may cause final yield to differ from expected, “average” values.
Participants were also asked to rank the overall quality of the fruit from “poor” to “excellent,” and the insect and disease pressure from “below average” to “above average.” Respondents were then directed to open-ended questions where they indicated what cultivars performed “below,” “average,” or “above average” and why.
Weather conditions during the growing season
A look at the weather conditions throughout the growing season can help to explain participants’ answers. In Figures 1 and 2, we reported monthly, seasonal (April 1 through October 31) growing degree days (GDD; index of heat accumulation), and precipitation collected by weather stations (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 2017 data to the previous 18-year (1999-2016) average.
We recognize that weather conditions might vary greatly from site to site, but some general trends were observed. For example, April GDDs were above-average in many regions of the Commonwealth. On the other hand, May was slightly cooler than the average in both the Southeast and Northwest (Figure 1). Additionally, below freezing temperatures were recorded during the early morning hours of May 8 and May 9 at the agricultural experiment station located near the Penn State main campus in State College. Some of the grape cultivars grown at this research farm, especially those that typically break bud early like Marquette and Concord, sustained crop loss due to frost damage. Fortunately, spring frost affected relatively few growers in PA and only two survey participants, one from the Southwest and another from the Northeast, reported reduced crop yield due to early May frost damage.
Growing degree day accumulations were slightly above the long-term average in June and July. However, August was noticeably cooler than the average in the Southeast and many other regions of the state, but not in Erie which remained warmer than average nearly all season (Figure 1). As the season came to a close, temperatures in September and especially October were warmer than average at both locations (Figure 1).
In most regions of the state, precipitation was abundant, particularly in June, July, and August (Figure 2 and Table 2). The one exception to this trend was in the far Northwest corner of the state where rainfall along the Lake Erie shore was well below average in July and August. September was relatively dry statewide, which was a big relief for many growers after facing a wet summer. As the season came to an end, October saw a return to higher amounts of rainfall in some areas of the state.
Survey participants’ responses
Yield: Twenty-two respondents (44% of the participants) indicated that overall crop yield was “average,” which was close to the target values (Figure 3). Sixteen percent of the participants indicated that overall yield was “above average,” or “record crop,” while for 40% was “below average” or “poor.”
“Poor” or “below average” yield was attributed to several factors, including poor or reduced fruit set, herbicide drift damage from a nearby field (for more information please refer to the newsletter article: Growth regulator herbicides negatively affect grapevine development) and/or disease issues (e.g., downy mildew, bunch rot). Two participants reported crop yield losses due to late spring freeze damage. One respondent indicated that “above average” yield was likely related to bigger berry size.
Fruit quality: Participants were asked to rate fruit quality, with the majority of the respondents (82%) rating fruit quality as “average,” “above average” or “excellent.” Only 18% of the respondents indicated that overall quality was “below average” or “poor,” although in some cases the rating varied depending on the cultivars grown as specified in a follow-up question.
With the exception of the Northwest region, several participants across the state pointed out that despite the wet summer conditions the warm and dry fall weather favorably influenced fruit ripening, especially for late ripening cultivars.
For example, some of them commented:
- “Early cultivars were of lower quality than later cultivars due to the cold, wet weather in the August and early September time frame. The warm and dry later half of September and most of October benefited the later.”
- “Pinot Gris, Sauvignon Blanc, Viognier, Chardonnay all had excellent sugar levels and good pH and acidity. Flavors were well concentrated. Reds were average to good. Some like Merlot had low sugar levels while later varieties had better sugars like Cabernet franc and Cabernet sauvignon. The late reds seemed to ripen more quickly than normal.”
- “Later varieties were above average due to smaller crop size and better weather conditions.”
Disease pressure: Half of the growers who participated in the survey experienced “above average” disease pressure during the 2017 growing season, while 41% reported “average” disease pressure and only 9% reported that the disease pressure was “below average.” This contrasts markedly with results obtained in 2016 when 47% of survey participants experienced “below average” disease pressure (Looking back at the 2016 season).
The major disease problem identified by the growers was downy mildew followed by bunch rot. A few respondents indicated that downy mildew pressure was particularly high in August. This is not surprising; downy mildew pressure is very dependent on rainfall and the threat of this disease would be particularly high in areas where recorded rainfall had been above average for most of the season (for example, Berks County).
It is important to note that areas of the state that experienced “above average” disease pressure may have a relatively high overwintering population of the pathogen(s), particularly if a fair amount of disease was actually observed in the vineyard. This can easily translate into higher disease pressure in 2018, especially if conditions remain wet.
In contrast to the majority of grape growing areas in PA, growers in the Lake Erie region experienced a second consecutive dry season, and disease development in many of the region’s vineyards was limited to powdery mildew in 2017. Therefore vineyards in the Lake Erie region will generally carry relatively low overwintering pathogen levels into 2018, with the exception of powdery mildew (a disease that is only dependent on rainfall for the first primary infections in early spring).
Despite the above-average wet conditions, respondents pointed out that fruit was clean from major diseases: “low fruit disease despite wet season,” and “given the weather conditions during the growing season overall our grapes were kept almost disease free.”
Several of them attributed their ability to keep disease pressure under control to a “persistent spray program,” “solid spray program and very good protective materials available,” and that “rainy season required that growers stay on top of their disease management program. Botrytis, downy and powdery mildew could have been rampant.”
A respondent pointed out that in addition to a solid spray program new canopy management implemented likely helped to reduce Botrytis infection in susceptible varieties: “I also started to leaf pull pre-bloom which I believe has loosened our clusters up and has allowed for better spray penetration and overall less rot.”
Insect pressure: Twenty-two participants (45% of the respondents) experienced “average” insect pressure during the 2017 growing season, while 31% answered “above average” and 24 % “below average.”
The majority of the growers who experienced “average” or “above average” insect pressure indicated problems with late-season insect pests, such as Spotted Wing Drosophila (SWD), wasps and hornets (for more information on those insect pests and how to manage them please refer to: Is Spotted Wing Drosophila a problem in my wine grapes?; Late season insect management)
Some of them commented:
“SWD seems to be more present at the end of the season,” “Drosophila was the primary insect,” “SWD was above normal.”
Japanese Beetles were also named, although answers were divided: some respondents indicated “Japanese beetle pressure was lower than in previous years” while others answered that “Japanese beetles were the most prevalent insect” and they were “very aggressive in the vineyard.” A respondent observed a new insect in the vineyard, the grape leafhopper. Grapevines can tolerate fairly high populations of leaf hoppers and Japanese beetles without harm to the crop. Populations of fewer than 20 leafhopper nymphs/leaf usually does not require spraying (Japanese Beetle: A common pest in the vineyard).
In the Lake Erie region the grape berry moth was once again the most destructive insect present. The unusually dry summer kept a potentially large population to average numbers. Brown Marmorated stink bug damage is beginning to be noticeable in some Lake Erie vineyards (Will the Brown Marmorated stink bug be a problem in wine and juice?)
Unfortunately, the insect who made its big entry this season into southeastern PA vineyards was the Spotted Lanternfly (Lycorma delicatula). Spotted Lanternfly (SLF) is an invasive insect first discovered in Berks County in 2014 and is now threatening parts of southeastern PA and Southern New York (Invasive insect confirmed in New York). Half of the respondents from the Southeast region (8 participants) observed the Spotted Lanternfly in their vineyards, and this was the first year for many of them.
Some of them commented:
- “At the end of the season I started seeing Spotted Lanternfly.”
- “Lantern fly moved into my vineyard this year. Some of us believe honeydew from lantern fly is attracting yellow jackets and other bees, which were really bad.”
- “The Spotted Lanternfly in our vineyard continues to put pressure on the crop; we estimated that we killed 1/2 million adults in September.”
- “The significant increase in the adult Spotted Lantern Fly population this season in our area causes significant concern for our vineyard longevity. While many of the sprays were able to knock the populations back quickly only so many applications could be made. Within a few days of spraying and killing the adults, new adults migrated into the vineyards.”
The quarantined area for SLF at the beginning of the season included three counties of southeastern PA, but by the end of the season, SLF populations had decidedly increased causing the quarantine area to be markedly expanded. The PA Department of Agriculture does not have the quarantine map completely updated at this time, however, they do have a search quarantine map where you can put in your location to check to see if you are included in the quarantine. (https://www.agriculture.pa.gov/spottedlanternfly; http://www.agriculture.pa.gov/plants_land_water/plantindustry/entomology/spotted_lanternfly/pages/default.aspx)
Information on SLF and measures that can be taken to stop its spread can be found at: https://extension.psu.edu/spotted-lanternfly, additional resources are listed on the Penn State Extension website. As stated in the article: “Penn State is at the forefront of education and research aimed at stopping the spread of this exotic species.” Penn State is seeking to hire an entomologist extension associate to coordinate outreach and response efforts for the SLF.
We are also planning to discuss Spotted Lanternfly management options at the Penn State Grape Disease & Insect Management Workshop, soon to be announced through the Penn State extension website and our listserv.
We would like to thank all the growers who participated in the survey. Their time spent responding to these questions provides us with valuable information that research and extension personnel can utilize to customize efforts to help the industry grow and improve. The more responses we receive, the more accurately our efforts can target the needs of our stakeholders statewide. Despite some challenges, it was a rewarding growing season for many PA wine grape growers. We are looking forward to tasting this season’s wines!
* All procedures were approved by the Office of Research Protections at The Pennsylvania State University (University Park, PA). Upon completion of the survey, each participant was entered into a raffle to win one of three $25 gift certificates that could be redeemed toward any Penn State Extension wine or grape program fee.
By: Maria Smith and Dr. Michela Centinari, Dept. of Plant Science
In the previous post, we discussed shoot thinning as a method to achieve vine balance and improve the canopy microclimate (Part I: Shoot Thinning). In this post, we will discuss the use early leaf removal (ELR), a canopy management practice implemented around bloom. ELR primarily serves to reduce the severity of Botrytis bunch rot infection in susceptible varieties (Wines and Vines: Benefits and Costs of Early Leaf Removal), but may also be an effective practice for reducing crop yield.
ELR is currently considered an experimental canopy management practice for vineyards. While it shows great promise within the research and Extension literature (1, 2, Cornell Cooperative Extension 2016), Penn State Extension does not currently recommend implementing ELR as a replacement for traditional methods (i.e., cluster thinning, fungicide sprays) for yield and rot control. However, growers curious about the effects of ELR may find it useful as a supplementary canopy management practice, especially for disease management and crop reduction.
Throughout this post, we will discuss the effects of ELR on:
- Crop level in highly-fruitful varieties that produce a high number of clusters (3-4 per shoot) or large clusters such as vinifera cvs. Grüner Veltliner, Sangiovese, and Barbera.
- Botrytis bunch rot infection.
- Fruit and wine composition.
What is Early Leaf Removal (ELR) and how does it work?
ELR is the removal of basal leaves of the main shoots and, optionally, lateral shoots developed from the basal nodes (http://gph.is/2r3ZLc0; Figure 1).
ELR is typically performed shortly before (pre-bloom) or at the beginning of bloom (trace-bloom; Figure 2A). In some cases, however, it has been performed later during full-bloom or at the onset of fruit-set (Figure 2B).
Before and during bloom, the oldest basal leaves have a major role in providing carbohydrates (e.g., sugars) to support the growing shoot and inflorescence (i.e., flower clusters). In contrast, young leaves on the middle and top part of the shoot are still developing and not very photosynthetically ‘active’ at this time (3). Literature suggests the removal of basal leaves at bloom may starve the inflorescence for a carbohydrates food source (4). The lack of carbohydrate resources reduces fruit-set (i.e., the percentage of flowers that will develop into berries), which likely reduces the number of berries per cluster at harvest (5). When ELR is performed later, at the onset of fruit-set, removing basal leaves may induce a reduction in berry size and an increase in berry abscission due to carbohydrate limitation at the onset of fruit development (6). Therefore, yield reduction achieved with ELR is the result of reduced cluster weight (reduced number of berries per cluster and/or reduced berry weight). In contrast, yield reduction achieved by cluster thinning is the result of a reduced number of clusters per vine.
Why are ELR practices currently under research investigation?
An increased number of studies is investigating the use of ELR as a potential alternative to cluster thinning techniques used for crop yield control in highly-fruitful wine grape varieties (5, 6, 7). As opposed to traditional cluster thinning, ELR can be more easily mechanized. (Author’s note: for more information on mechanization, see Additional Resources at the bottom of the post.) ELR may additionally confer benefits such as:
- Reduced severity of Botrytis rot infection
Cluster compactness, or the tightness of berries on the cluster, has been positively related to the severity of Botrytis bunch rot infections (8). It is suggested that more compact clusters experience more rot. ELR decreases cluster compactness by reducing the number of berries per cluster and/or the berry size. Decreased cluster compactness through implementing ELR has reduced Botrytis rot infections in several tight-cluster varieties such as Pinot Noir, Riesling, Chardonnay, and Vignoles (1, 9, 10, 14). As an additional benefit, the removal of basal leaves increases sunlight penetration and air movement in the fruiting zone, which is important for improving spray penetration within the canopy (2016 Post Bloom Disease Management Review).
- Improved fruit and wine composition
ELR has consistently been reported to alter fruit composition, particularly for red Vitis vinifera varieties in Mediterranean climates (Tempranillo, Sangiovese, Barbera, etc.; 2, 5, 6, 12). In several instances, fruit harvested from ELR vines had higher levels of total soluble solids (TSS, °Brix), phenolic compounds (e.g., flavonols), and total anthocyanins compared to un-defoliated vines (2, 11, 12). ELR can also reduce methoxypyrazines, ‘herbaceous’ aromas found in higher concentrations among immature grapes at harvest, and may contribute to improved wine color intensity (13). ELR may alter three important parameters associated with berry development and ripening (2):
- Decreased berry size – Smaller berries tend to have greater skin-to-pulp ratio and higher concentrations of desirable phenolic and aroma compounds which are mainly present in the skin.
- Increased leaf area-to-yield ratio on a per shoot basis – A greater leaf area-to-yield ratio may translate into higher sugar produced per shoot. More sugar availability could contribute to better fruit ripening.
- Improved canopy microclimate – ELR, like traditional leaf removal, improves the microclimate of the fruiting zone through decreased leaf density and increased sunlight penetration to the fruit. Higher temperatures coupled with increased sunlight exposure in the fruiting zone can be especially important under cool or cloudy ripening conditions, as they may accelerate berry ripening, resulting in higher TSS, decreased malic acid, increased anthocyanin concentration, and degradation of green volatile aroma compounds such as methoxypyrazines that may mask fruity or floral aromas. Higher ultraviolet (UV) radiation in the fruiting zone in response to increased sunlight penetration may increase production of flavonols, as flavonols biologically act to protect berries from UV exposure (3, 11). Flavonol compounds along with anthocyanin influence red wine color and are used as determinants of quality in fruit (11).
It is important to keep in mind that yield reduction is not desirable in all grape varieties. The use of ELR with varieties that do not typically over-crop may result in under-cropped situations with potential negative effects on fruit quality and vine health, in addition to unnecessary yield reductions and thus revenue loss.
How many leaves should be removed to induce yield reduction?
Unfortunately, there is no “one size fits all” number of leaves to remove when implementing ELR as a vineyard management practice. The required number of leaves removed to significantly reduce yield through reduced fruit-set depends on several factors, including shoot length and the shoot leaf area at the time of removal. For example, by pulling 5 basal leaves on a shoot with only 8 leaves at trace-bloom, we would remove about 63% of the total number of leaves. The percentage of leaf area removed would be even higher as the remaining leaves at the top of the shoot are much smaller than those removed from the bottom of the shoot. In contrast, a longer shoot with 15 leaves total will only lose 33% of the leaf area when 5 basal leaves are pulled. Thus, removing 5 leaves from a short shoot would have a more severe effect of depriving the inflorescence of sugar resources than removing the same number of leaves on long shoots (Figure 3).
Sometimes the degree of ELR is severe in order to induce a yield reduction commensurate with the more traditional cluster thinning technique. For example, Pinot Noir grown in southwestern Michigan showed a reduction in yield from 6.1 tons per acre in non-defoliated vines to 3.6 tons per acre when about half (8 out of 15) of the leaves on the shoots were removed (1). This was a 40% reduction in yield. Comparatively, when 4 or 6 leaves were removed from the Pinot Noir, no significant effect was found in crop yield (1).
With the high potential for crop yield reduction, Dr. Michela Centinari’s lab has been experimenting with ELR for the past two years. We have been examining the effects of ELR at trace-bloom on Grüner Veltliner (V. vinifera) grown in Central Pennsylvania. Grüner Veltliner is highly fruitful, typically producing 2-3 large clusters per shoot. In our experimental practices, we removed 5 basal leaves at trace-bloom. Our objective was to compare the use of ELR to cluster thinning for crop yield reduction. Our first year of data found that the implementation of ELR decreased yields by only about 15% (10.7 tons per acre in the non-defoliated control to 9.3 tons per acre in defoliated vines). In comparison, vines thinned to 1 cluster per shoot had a 45-50% reduction in yield compared to the un-thinned control (10.7 tons per acre to 6.5 tons per acre).
This suggests that a greater leaf removal intensity may be needed for this variety to produce yield reduction comparable to cluster thinning, and we are currently testing different intensity levels of trace-bloom ELR to evaluate if the amount of leaf area removed correlates with reduction of fruit-set and yield at harvest.
Again, ELR is still considered an experimental canopy management technique. For those growers growing high yielding varieties and looking to reduce crop level, cluster thinning is still the recommended practice. For more information on how to implement appropriate CT techniques, please see Cornell Cooperative Extension Fruit thinning in wine grapes and Crop thinning: cluster thinning or cluster removal.
Considerations regarding ELR
Other factors to consider if you are interested in applying ELR:
- Fruit-set percentage – One of the factors facing the unpredictability of ELR is the weather conditions between bloom and fruit set. Since weather can have a large effect on the percentage of fruit-set (Fruit set in grapes 101), ELR may potentially exacerbate ‘poor’ fruit-set if extended periods of wet, cool (< 59°F), overcast, or very hot (> 90°F) weather conditions occur following leaf removal. Additionally, berry sunburn may be a potential concern with ELR when performed under chronic high light and temperature intensity.
- Bud Fruitfulness – While it is generally acknowledged that increased sunlight exposure is positive for bud development, a potential reduction in bud fruitfulness (number of clusters per shoot) may occur in the following season as a result of bud damage from ELR (14). Although still uncertain, bud damage may be the result of physical damage during leaf removal and/or reduction of carbohydrate supply during bud development.
- Carbohydrate Storage in Cool Climate Grown Vines – Carbohydrates are the main energy source for grapevine growth, stress defense, and fruit ripening. Post-harvest carbohydrate storage in perennial tissues is a determinant of vine overwinter survival and is fundamental for shoot development in the following season. Removing leaves during ELR may alter the amount of carbohydrates produced by the leaves over the season and how carbohydrates are distributed among the vine organs. Currently, limited information is available on how ELR affects carbohydrates storage in perennial tissues and how this relates to dormant tissue (buds and canes) cold hardiness. This is a point of current interest to Centinari’s lab at Penn State, with current research being conducted in vinifera and hybrid wine grape varieties.
- Crop Estimation – Yield predictions based on ELR use is currently not available. In this regard cluster thinning is a more conservative approach. Unlike ELR, which is performed very early in the season, cluster thinning severity can be decided upon estimation of final yield.
ELR holds potential as a way to reduce yield and Botrytis rot infection for some grape varieties grown in the Mid-Atlantic and other cool-climate regions. However, more research is needed to better understand the consistency of ELR practices on vine physiology, yield reductions, and fruit quality. Current efforts are on-going by the Centinari lab and Bryan Hed at the Lake Erie Grape Regional Extension Center (LEGREC) to evaluate the use of manual and mechanized ELR in hybrid and V. vinifera varieties across Pennsylvania.
PSU Wines and Grapes blogs: An Overview of Cluster-Zone Leaf Removal Strategies for Cool Climate Vineyards and 2016 Post Bloom Disease Management Review
Intrieri C, Filippetti I, Allegro G, et al. 2008. Early defoliation (hand vs mechanical) for improved crop control and grape composition in Sangiovese (Vitis vinifera L.). Aus. J. Grape Wine Res. doi: 10.1111/j.755-0238.2008.00004.x
- Acimovic D, Tozzini L, Green A, et al. 2017. Identification of a defoliation severity threshold for changing fruitset, bunch morphology and fruit composition in Pinot Noir. J. Grape Wine Res. doi: 10.1111/ajgw.12235
- Bubola M, Sivilotti P, Janjanin D, and Poni S. Early leaf removal has larger effect than cluster thinning on cv. Teran grape phenolic composition. AJEV. doi: 10.5344/ajev.2016.16071
- Illand P, Dry P, Proffit P, and Tyerman S. Photosynthesis. In The Grapevine, from the science to the practice of growing vines for wine. pp. 91-107.
- Coombe BG. The effect of removing leaves, flowers and shoot tips on fruit-set in Vitis vinifera L. J. Hortic. Sci. 37:1-15.
- Poni S, Casalini L, Bernizzoni F, et al. 2006. Effects of early defoliation on shoot photosynthesis, yield components, and grape composition. AJEV. 57: 397-407.
- Tardaguila J, Martinez de Toda F, Poni S, and Diago MP. 2010. Impact of early leaf removal on yield and fruit and wine composition of Vitis vinifera Graciano and Carignan. AJEV. 61(3):372-381.
- Silvestroni O, Lanari V, Lattanzi T, et al. Impact of crop control strategies on performance of high-yielding Sangiovese grapevines. AJEV. doi: 10.5344/ajev.2016.15093
- Vail ME and JJ Marois. 1991. Grape cluster architecture and the susceptibility of berries to Botrytis cinerea. Phytopathology 81:188-191.
- Sternad Lemut M, Sivilotti P, Butinar L, et al. Pre-flowering leaf removal alters grape microbial population and offers good potential for a more sustainable and cost-effective management of a Pinot Noir vineyard. J. Grape Wine Res. doi: 10.1111/ajgw.12148
- Hed B, Ngugi HK, and Travis JW. Short- and long-term effects of leaf removal and gibberellin on Chardonnay grapes in the Lake Erie region of Pennsylvania. AJEV. 66(1): 22-29.
- Moreno D, Vilanova M, Gamero E, et al. Effects of preflowering leaf removal on phenolic composition of Tempranillo cv. in semi-arid terroir of western Spain. AJEV. doi: 10.5344/ajev.2014.14087
- Risco D, Pérez D, Yeves A, et al. Early defoliation in a temperate warm and semi-arid Tempranillo vineyard: vine performance and grape composition. Aus J Grape and Wine Res. doi: 10.1111/ajgw.12049
- Sivilotti P, Herrera JC, Lisjak K, et al. 2016. Impact of leaf removal, applied before and after flowering, on anthocyanin, tannin, and methoxypyrazine concentrations in ‘Merlot’ (Vitis vinifera) grapes and wines. J. Agric. Food Chem. 64:4487-4496.
- Sabbatini P, and Howell GS. 2010. Effects of early defoliation on yield, fruit composition, and harvest season cluster rot complex of grapevines. HortScience 45(12):1804-1808.
Maria Smith is a viticulture PhD candidate with Dr. Michela Centinari in the Department of Plant Science. She specializes in cold stress physiology of wine grapes. She was the previous recipient of the John H. and Timothy R. Crouch Program Support Endowment, an endowment founded and funded by the Crouch brothers, original owners of Allegro Winery in Brogue, PA. She is currently funded by the Northeast Sustainable Agriculture Research and Education (NE-SARE) program, a program from the USDA National Institute of Food and Agriculture (NIFA).
By: Maria Smith and Dr. Michela Centinari, Dept. of Plant Science
This is the first of two posts on grapevine canopy management in the early growing season from bud burst to bloom. The second in the series will be post in two weeks and will focus on pre- or trace-bloom leaf removal for crop level and disease pressure control.
This week, our blog post will focus on shoot thinning, the first canopy management practice of the growing season. As seen in the pictures below, we spent last week shoot thinning Grüner Veltliner (V. vinifera) vines in a central Pennsylvania vineyard (Figure 1).
In the following sections, we will highlight the benefits and costs associated with shoot thinning while providing a few general shoot thinning guidelines for both V. vinifera and hybrid cultivars in the Mid-Atlantic region.
Benefits of Shoot Thinning Grapevines
While dormant pruning (https://psuwineandgrapes.wordpress.com/tag/dormant-pruning/) is the primary tool used by grape growers to maintain vine structure, canopy architecture and regulate crop level, shoot thinning provides an additional canopy management tool to bring vines into vegetative and fruiting balance by reducing shoot density and the number of clusters per vine. Cluster thinning later in the season may be needed in order to balance highly-fruitful vines.
In addition to improving balance between vegetative growth and fruit biomass, other benefits of shoot thinning include:
- Reduction of canopy density and fruit shading: through removal of selected shoots, shoot thinning reduces overcrowding of shoots in the canopy thus reducing the number of leaf layers and improving sunlight exposure to fruit (1).
- Reduction of disease pressure: reducing canopy density improves air circulation and sunlight penetration that promotes quicker drying of leaves and fruit, as well as increases spray penetration.
Timing of Shoot Thinning
Shoot thinning should be done early in the growing season, when shoots are approximately 5-6 inches long and not more than 10-12 inches long. Shoot thinning should be timed after the date of last ‘expected’ frost, such that secondary or non-damaged primary shoots can be retained in the event of a late spring frost.
When shoot thinning is performed before inflorescences are visible (shoots 0.8 inch to 4 inches), increased vigor of the remaining shoots and lateral shoot growth may occur as a response, negating the benefits of shade reduction (1). When performed too late (shoot longer than 10 inches), shoots become lignified at the base and difficult to remove. If performing late thinning, pruning shears should be used if there is risk of damaging the arm of the vine. It also takes longer to thin longer shoots, potentially decreasing the cost-effectiveness of this practice.
Shoot Spacing and Density Recommendations
Generally, shoot thinning on cane-pruned vines is easier, faster, and more straight-forward than spur-pruned vines, which require substantially more decisions regarding what shoots to retain or remove, and where shoots should be spaced along the cordon (2; Figure 2).
Plant genotype, soil, and climate are all factors influencing vine vigor potential and capacity to fully ripen a crop. Therefore, these factors indirectly affect the appropriate number of shoots to retain at thinning. Many Cooperative Extension websites provide recommendations on range of optimal shoot density based on cultivars grown in their region. [Author’s note: for the eastern US see the additional resources section at the bottom of the post.]
Shoot density targets for Pennsylvania regions:
- For vinifera cultivars it is recommended to leave 3 to 5 shoots per linear foot of canopy (3, 4; Figure 3). The general rule of thumb is to retain fewer shoots in red varieties and more in white varieties. However, other factors (i.e., cultivar disease susceptibility) must be taken into consideration.
- For most of the hybrid cultivars it is recommended to leave 4 to 6 shoots per linear foot of canopy (5).
- For Concord and other native cultivars, as many as 15 shoots per linear foot of canopy can be retained (4).
- In divided canopies trellis systems, the same shoot density along each cordon should be retained (Figure 4).
In addition to the number, the position of the shoots along the cordon is important. Ideally, the shoots retained should be equally spaced to promote a uniform, balanced canopy.
What types of shoots should you remove?
- Weak, non-fruitful shoots especially if they grow in crowded areas of the canopy.
- Secondary and tertiary shoots, if a primary healthy shoot has emerged.
- Shoots arising from the trunk that are not retained for renewal wood (e., new trunks and canes or cordons).
Does shoot thinning improve fruit composition and wine sensory perception?
The associated costs with manual labor and labor shortages are reasonable considerations before implementing vineyard management practices. This is also true for implementing shoot thinning techniques into a vineyard. Nonetheless, it is also important to consider the potential benefits from implementing a new practice.
The effects of shoot thinning practices on hybrid varieties are a bit unclear. A previous study on shoot thinning found that shoot thinned Marechal Foch (red interspecific hybrid of Vitis) vines exhibited higher total soluble solids (ᵒBrix) and berry anthocyanin concentrations as compared to un-thinned vines (6). The increase in berry anthocyanin, however, did not translate into higher anthocyanin concentration in the final wine, and furthermore, shoot thinning did not impact the sensory perception of “fruitiness” of the wines (6). In contrast, a study focusing on Corot noir (red interspecific hybrid of Vitis) implementation of shoot thinning provided inconsistent results in grape and wine quality across a two-year (2008-2009) evaluation, which was determined by ᵒBrix, pH, titratable acidity (TA), wine anthocyanin, berry and wine tannin content (7). Shoot thinning increased berry ᵒBrix, wine alcohol concentration and anthocyanin content only in second year of this study. While berry TA at harvest was lower (e.g., 2008, un-thinned = 8.6 g/L, shoot thinned = 7.6 g/L), there were no differences in the TA of wine in either year (7). Shoot thinning also decreased berry seed tannin in 2008 and berry skin and wine tannin in 2009, which could have negative implications for final wine, considering generally low tannin concentrations in hybrid red wines (7). In an effort to compensate for costs associated with shoot thinning and yield loss, this study on Corot Noir suggested growers increase the price of grapes by 11 to 20% per ton, depending on the average annual market price and yield loss (7).
A study in Fayetteville (Arkansas) on three highly-fruitful French-American hybrid cultivars (Aurore, Chancellor, and Villard noir) found that shoot thinning increased fruit sugar accumulation (ᵒBrix) only in Chancellor and without changes in pH or TA, while a more intense juice color was associated with shoot thinned vines of both red cultivars (Chancellor and Villard noir; 8). In addition, shoot thinning favorably decreased the Ravaz index (yield to pruning weight ratio) for all three cultivars, improving vine balance (8).
The results of these studies suggest that in some situations the costs of shoot thinning may not outweigh the benefits, especially for hybrids that do not command a high market value (Finger Lakes Grape Prices 2016). However, none of these studies account for potential reduction in disease infections, which may help justify the implementation of shoot thinning in a given vineyard. For example, it has been found that higher shoot density may contribute to the increased incidence of Botrytis rot infections in susceptible cultivars such as Seyval Blanc (9) and Vignoles (4).
In other cases, shoot thinning improved fruit composition in Pinot Noir and Cabernet Franc for two consecutive vintages (1), and also increased color intensity, phenolic content, and total anthocyanins of Cabernet Franc berries (1). Benefits of shoot thinning on fruit quality and wine sensory perception have been reported for other vinifera cultivars, such us Barbera (10) and Sauvginon blanc (11).
Unless your vineyard is located in a low or moderate vigor site, shoot thinning is strongly recommended for vinifera cultivars growing in the Mid-Atlantic region.
If you want to assess the effects of shoot thinning on fruit composition, plan to leave half of a row of vines un-thinned and thin the remaining half to a consistent number of shoots per foot (e.g., 4 shoots per foot). Alternatively, use two rows (of the same variety and cultivar) to assess the impact of shoot thinning in your vineyard: one row thinned and the adjacent row un-thinned. These two methods should help evaluate the effect of shoot thinning on berry composition at harvest and if possible, on wine chemistry and sensory perception assuming that the lots of berries can stay separated through wine production.
Effects of shoot thinning on vine physiology
Impacts of shoot thinning on vine physiology and performance are complex. A study conducted in Italy evaluated the whole-canopy photosynthetic response to shoot thinning using spur-pruned Barbera vines (V. vinifera; 10). Vines were thinned to 5 shoots per foot, reducing the total shoot number by 50% as compared to un-thinned control. In this study (10) shoot thinning significantly improved grape sugar content, color, and phenolics. Despite the benefits provided by shoot thinning on fruit composition, which has been already reported by other studies, what makes this study unique and interesting it that they investigated the mechanisms behind the improvement in grape quality through the measurement of whole-canopy net carbon assimilation. Although the shoot-thinned vines had initially lower photosynthesis (carbon assimilation) than un-thinned vines due to the removal of photosynthetic source (leaf), they had regained photosynthetic capacity to levels similar to the un-thinned vines within 17 days of treatment. This occurred as a result of a substantial increase in both main leaf size and amount of lateral leaves as a result of shoot thinning (10). Therefore, individual shoots of thinned-vines had a higher supply of assimilates (e.g., sugar) per unit of crop, which can increase sugar accumulation during ripening. This may explain why shoot thinning improved grape composition in Barbera under these growing conditions.
Additional Shoot Thinning Resources
- Cornell Cooperative Extension (CCE) video tutorial on shoot thinning: https://www.youtube.com/watch?v=5wyFolawc-s
- Fiola, J. 2017. Canopy Management – Shoot thinning and positioning. “Timely Vit” from UMD Extension. https://extension.umd.edu/sites/extension.umd.edu/files/_docs/programs/viticulture/TVCanopyMgmtShootThinPos.pdf
- Martinson, T and Vanden Heuvel, J. Shoot density and canopy management for hybrids. http://www.fruit.cornell.edu/grape/pdfs/Canopy%20Management%20for%20Hybrids%20-2007.pdf
- Reynolds AG., et al. 2005. Timing of shoot thinning in Vitis vinifera: impacts on yield and fruit composition variables. 56, 343-356.
- Intrieri, C and Poni, S. Integrated evolution of trellis training systems and machines to improve grape and vintage quality of mechanized Italian vineyards. AJEV. 46, 116-127.
- Fiola, J. 2017. Canopy Management – Shoot thinning and positioning. “Timely Vit” from UMD Extension.
- Walter-Peterson, H. 2013. Shoot thinning: Good for the vines, but good for the wines? Finger Lakes Vineyard Notes.
- Martinson, T and Vanden Heuvel, J. Shoot density and canopy management for hybrids. CCE. http://www.fruit.cornell.edu/grape/pdfs/Canopy%20Management%20for%20Hybrids%20-2007.pdf
- Sun Q., et al. 2011. Impact of shoot thinning and harvest date on yield components, fruit composition, and wine quality of Marechal Foch. AJEV. 62:1, 32-41.
- Sun Q., et al. 2012. Impact of shoot and cluster thinning on yield, fruit composition, and wine quality of Corot noir. AJEV. 63:1, 49-56.
- Morris, JR. et al. 2004. Flower cluster and shoot thinning for crop control in French-American hybrid grapes. AJEV. 55:4, 423-426.
- Reynolds, AG et al. 1986. Effect of shoot density and crop control on growth, yield, fruit composition, and wine quality of ‘Seyval blanc’. J. Amer. Soc. Hort. Sci. 111, 55-63.
- Bernizzoni, F. et al. 2011. Shoot thinning effects on seasonal whole-canopy photosynthesis and vine performance in Vitis vinifera L. cv. Barbera. Aus. J. Grape Wine Res. 17, 351-357.
- Naor et al. 2002. Shoot and cluster thining influence vegetative growth, fruit yield, and wine quality of ‘Sauvignon blanc’ grapevines. J. Amer. Soc. Hort. Sci. 127(4), 628-634.
Maria Smith is a viticulture PhD candidate with Dr. Michela Centinari in the Department of Plant Science. She specializes in cold stress physiology of wine grapes. She was the previous recipient of the John H. and Timothy R. Crouch Program Support Endowment, an endowment founded and funded by the Crouch brothers, original owners of Allegro Winery in Brogue, PA. She is currently funded by the Northeast Sustainable Agriculture Research and Education (NE-SARE) program, a program from the USDA National Institute of Food and Agriculture (NIFA).
By: Bryan Hed
We’re in the final leg of the season and it’s time to size up our remaining challenges through the ripening period. Fruit are no longer susceptible to many of the major diseases like powdery and downy mildew and black rot that can cause crop loss during earlier stages of berry development. But for some grape varieties, particularly wine grapes that produce compact clusters, there is another major hurdle to work through to harvest; late season bunch/sour rot. I am referring to the rotting of fruit in clusters that occurs during the later stages of the ripening period, just a few heartbreaking days or weeks before harvest. Bunch rot can involve the colonization of fruit by a number of different microorganisms, both fungi and bacteria. But the main culprit in most regions of the Northeastern U.S. is the fungus, Botrytis cinerea (Figure 1). Fortunately, we have a number of chemical control options that are quite effective against this fungus that I have listed below. I have organized them according to the FRAC (Fungicide Resistance Action Committee) group that each product belongs to. Basically FRAC groups are fungicide chemistries with the same or similar mode of action, so that pathogen resistance to one fungicide is going to confer cross resistance to another, within that same FRAC group. For example, notice that Vangard and Scala are in the same FRAC group; 9. This means that if a population of Botrytis in a vineyard has developed resistance to the active ingredient in Vangard, then it will also be resistant to the active ingredient in Scala, even though the active ingredients may be different (cyprodinil in Vangard and pyrimethanil in Scala). The mode of action (the way in which the fungicide disrupts a specific metabolic pathway in the fungus, killing it) of these two chemistries is the same, or similar enough that pathogen resistance to one chemistry will confer resistance to the other.
- FRAC group 2: Rovral, 7 day pre-harvest interval
- FRAC group 7: Endura, 14 day pre-harvest interval
- FRAC group 7 (and 3, which is not for Botrytis): Luna Experience, 14 day pre-harvest interval
- FRAC group 7 and 11: Pristine, 14 day pre-harvest interval
- FRAC group 9: Vangard, Scala, 7 day pre-harvest interval
- FRAC group 9 (and 3, which is not for Botrytis): Inspire Super, 14 day pre-harvest interval
- FRAC group 9 and 12: Switch, 7 day pre-harvest interval
- FRAC group 11: Flint, 14 day pre-harvest interval
- FRAC group 17: Elevate, 0 day pre-harvest interval
No doubt many wine grape growers have already applied a bloom, pre-bunch closure, and veraison spray to bunch rot susceptible varieties. However, one or more applications may be necessary in some vineyards. Populations of the Botrytis fungus are quite adept at developing resistance to these fungicides; be mindful to rotate FRAC groups and limit the application of any one FRAC group to one or two per season to delay the development of that resistance. If you have to use a FRAC group more than once per season, it would be better to compose one of those two applications with a material that contains a second FRAC group for Botrytis. For example, if you already used Scala, it would probably be better to apply Switch (after you’ve already rotated to FRAC group 2, 7, 11, or 17) than to apply Vangard or another Scala spray. Most of these materials are considered ‘high risk’ for resistance, so rotation is extremely important to maintaining the effectiveness of these products. Also, pay attention to pre-harvest intervals which range from 0 to 14 days. That said, you can’t spray your way completely out of the damage that Botrytis and other microorganisms can cause; consistently effective bunch rot control programs must be integrated with a generous dose of cultural practices like fruit zone leaf removal, sanitation, canopy management, and vine balance. And, unfortunately, these chemistries listed above are specific for Botrytis and will not control many of the other microorganisms that may make up the bunch rot complex or that lead to the dreaded sour rot complex.
I’ve already alluded to one of the major predisposing factors for bunch rot (including sour rot) in grape clusters, and that is cluster compactness. The compactness of clusters is responsible not only for initiating much of the fruit rot that occurs in clusters, but perhaps more importantly, for the rapid spread of rots throughout the cluster (Figure 2). Rots can be initiated in loose grape clusters as well (by bird or insect damage, for example), but generally do not spread beyond the damaged berry or berries. However, in compact clusters, a single damaged berry can spread rot to large sections of the cluster by virtue of the close contact between those berries. Contact between berries in compact clusters also reduces cuticle thickness, an important barrier to rot pathogens, and reduces pesticide penetration into clusters for protection of berry surfaces against Botrytis and damage by insects. Cluster compactness also increases the effects of retained bloom trash (dead flower parts) inside clusters that can provide a substrate for Botrytis, increasing fruit rot by harvest. Taken together, this generally makes berries in compact clusters much more susceptible to invasion by fruit rot pathogens than berries in loose clusters.
A series of greenhouse experiments we conducted years ago also suggested that latent (dormant) infections of Botrytis can be activated by the kind of berry injury that occurs in compact clusters. Latent Botrytis infections are infections that occur during bloom and the early fruit development period for which you apply that bloom and pre-closure spray. Years ago, we monitored the incidence of latent infections in our block of Vignoles and found that even though the incidence appeared to increase throughout the berry development period, most of these infections did not lead to fruit rot by harvest. In fact, when we inoculated clusters of potted, greenhouse grown Chardonnay vines with Botrytis shortly after bloom, generating high levels of latent infection in berries, the berries did not rot during ripening if they remained intact in the greenhouse, unexposed to weather, birds, insects, or compactness (the clusters were thinned after inoculation and thinned berries were used to determine latent infection levels). However, when we surface sterilized the berries (to eliminate any Botrytis on the outside of berries) and created small injuries at the berry/pedicel interface of ripe berries (the kind of injury that commonly occurs in overcrowded clusters) the vast majority of the inoculated berries quickly rotted compared to berries that were not inoculated with Botrytis (checks).
By loosening clusters, damage from berry overcrowding can be minimized and bunch/sour rot development can be greatly alleviated. Unfortunately, loosening clusters in a consistently effective AND cost effective way is not always an easy thing to accomplish. Over the years we have examined a number of potential methods for cluster loosening with varying levels of success. Treatments such as pre-bloom fruit zone leaf removal have provided the most consistently significant reductions in cluster compactness and fruit rots in most years. The pre-bloom timing of fruit zone leaf removal simply combines the benefits of an open, sun lit fruit zone (which has been well documented by many investigators over the past several decades) with a reduction in cluster compactness and rot susceptibility. In our experiments, this treatment has typically been applied by hand, but the technology exists to mechanically remove leaf tissue around inflorescences (pre-bloom) without serious damage to them, and trials are being conducted to evaluate the mechanization of the pre-bloom leaf removal on a number of grape varieties. So far, results have been mixed depending on variety and trellis training system. In vineyards where we were able to compare pre-bloom mechanized leaf removal with pre-bloom leaf removal by hand and post-bloom mechanized leaf removal, the effects of pre-bloom mechanized leaf removal (increased light exposure of clusters, looser clusters, less rot, yield reduction) generally fell somewhere between the two latter treatments. The hope of this research is to expose growers to some new possibilities for fruit rot control and increase the potential for its adaptation to commercial vineyards and adoption by growers. We’ve examined other technologies with potential for cluster loosening and improved fruit rot control, but unfortunately their adoption is more problematic. For example, we have found that inexpensive gibberellin sprays around bloom have also been effective at loosening clusters and enhancing rot control on Vignoles and Chardonnay with little or no serious negative side effects. But they are currently ‘off label’ and are very unlikely to ever become legal applications in the United States. Also, the effects of gibberellin sprays are variety specific and therefore must be examined and defined for each variety: in our experience, low rates (5-20 ppm) can have serious negative side effects on Vitis vinifera Riesling, whereas rates as high as 100 ppm have had little or no effect on Vitis interspecific hybrid ‘Chancellor’.
More recently, work conducted by Megan Hall, a grad student of Wayne Wilcox at Cornell University, has shown that additional pesticide applications during the latter stages of ripening can significantly reduce the development of sour rot. Her work has shown a close connection between fruit flies and sour rot development; the presence of the flies is important to the accumulation/generation of acetic acid in rotting fruit. Treatments composed of weekly, tank mix applications of an insecticide (to control the flies) and an antimicrobial (to kill bacteria) have been found to reduce sour rots by 50-80% over unsprayed vines. So far, the best results appear to occur when weekly sprays are initiated before sour rot symptoms are observed (preventive sprays before about 15 brix). This exciting work should provide yet another effective option for sour rot control in the wet, humid parts of the eastern U.S. and we are looking forward to hearing more about this rot control option in the near future.
LATE SEASON LEAF DISEASE CONTROL
Beyond the management of bunch rot on susceptible wine varieties, there is also the matter of keeping canopies (leaves) as clean and functional as possible, for as long as possible. Diseases like powdery and downy mildew can continue to be of concern into late summer and early fall, especially for growers of Vitis vinifera. The mildews can greatly reduce leaf function if allowed to spiral out of control. The ability of the canopy to continue to photosynthesize is crucial to the ripening of the crop and canes and the storage of sugars (starch) in trunks, arms, and roots, which relates to winter hardiness. The winters of 2014 and 2015 are harsh reminders of just how important this can be. Allowing grapevines to go into winter dormancy with less than optimal preparation can leave them more susceptible to damage by severe cold and another plague of crown gall to have to deal with for years to come.
Good control of powdery mildew up to about Labor Day can also go a long way to reducing overwintering inoculum and disease pressure the following spring. This finding was the result of some excellent research conducted by Wayne Wilcox, Dave Gadoury and graduate students at Cornell University. When powdery mildew infected leaves die by that first hard frost in fall, the mildew on those leaves stops developing and also dies…unless it has had time to form fully mature, winter resistant resting structures called chasmothecia. If the chasmothecia in a powdery mildew colony do not have time to fully mature before the grape tissue dies (as from infections that were roughly initiated after early September), they will not survive the dormant period (winter) and will not contribute to the bank of primary inoculum that infection periods draw upon the following spring. Knowing this, a grower can get a better handle on the ‘size’ of the powdery mildew problems he/she will potentially face next spring. If, for example, you had heavy mildew development earlier in this season (on clusters and/or leaves), expect to have to deal with powdery mildew early next season and take appropriate action during early shoot growth stages with preventive fungicide sprays. This is particularly important if you are growing Vitis vinifera and much less important for growers of native varieties like Concord and Niagara.
Downy mildew appears to be much less a widespread problem this year. In fact, in our ‘neck of the woods’ along the southern shore of Lake Erie, droughty conditions have prevailed throughout most of the season, and only now are we even beginning to see a few downy mildew infections on leaves close to the ground. At this point in the season regular scouting for this disease is the first line of defense, and in areas that remain relatively dry, perhaps the only control measure needed (?). However, in areas where the disease has remained active throughout the season, be vigilant about keeping it under tight control. Late season epidemics of this disease can quickly strip susceptible wine varieties of their leaves, effectively bringing an early halt to ripening.
For further reading on this and many other disease management topics, refer to the 2016 New York and Pennsylvania Pest Management Guidelines for Grapes. If you don’t have a copy, you can get one through Cornell University press. Every commercial grape production operation should have one!
By: Bryan Hed
Once again, we’ve arrived at that part of the season just beyond the immediate pre bloom and first post bloom spray. For many years now, research has shown that those two sprays are absolutely essential to a fruit disease management program, at least for control of the four major grape diseases (powdery and downy mildew, black rot, and Phomopsis). We have always emphasized the use of ‘best’ materials, shortened intervals, best coverage, etc., for those two sprays, EVERY YEAR!…a no brainer. No matter what varieties you grow, those two sprays are most often the most important for protection of your crop.
Fortunately for some of these diseases, fruit susceptibility is short lived and most control of fruit diseases like powdery mildew is achieved by management right around/shortly after bloom. Indeed, work conducted by Wayne Wilcox and his grad students over the years has shown that fruit are generally susceptible to powdery and downy mildew for only about 2-3 weeks after capfall. Varieties of Vitis vinifera tend to be susceptible a little longer than native varieties like ‘Concord’, but for all varieties, the period of time during the first 2-3 weeks of fruit development is the most critical for fruit protection. Whenever I am approached with questions from growers as to why they ended up with a boatload of fruit disease in a given year, the answer almost invariably lies within the spray program during early fruit development.
Beyond that, things tend to get a little more complicated in terms of ‘what do I spray now?’ It depends on a number of things like the weather (past, present, and future), the variety grown/susceptibility of the host, your overwintering inoculum load (how much disease you had last year and the amount of old wood and debris in your trellis system this year) and your current disease levels. If you’re growing Concord grapes in the Lake Erie region in 2016, where rainfall during June has been scarce and sunshine and low humidity have dominated, diseases have been relatively easy to control so far. For example, there have been but four brief downy mildew (Figure 2) infection periods to date. As a result, this disease simply cannot be found in most maintained vineyards in the Lake Erie region, despite an abundance of downy mildew overwintering inoculum from the widespread occurrence of this disease last year. And, there have been just two mild black rot (Figure 1) infection periods since bud break. The immediate pre bloom and first post bloom spray probably provided all that was needed for control of powdery and downy fruit infections. The threat of black rot fruit infection remains (Concord is susceptible to this disease for about 4-6 weeks after capfall; V. vinifera about a week or two longer), though in vineyards that did not have black rot problems last year and where current disease is almost non-existent it is unlikely that black rot will spiral out of control at this point unless the current weather pattern suddenly turns very wet. Regular scouting of your vineyard will reveal whether or not this disease has gotten started in your vineyard (at this point in the season, it takes about 14 days for symptoms of black rot fruit infections to manifest themselves after an infection period).
The threat of Phomopsis infections depends to a large degree on how much overwintering inoculum is available. Since current season Phomopsis infections (Figure 3) generally do not produce spores until the following seasons (unlike the other fungal diseases we deal with each year), the development of this disease is dependent on overwintering inoculum sources that are normally ‘milked out’ by seasonal rainfall from May through mid-July. That means that in an average rainfall year, there are few spores left to cause infections by mid-July, even though fruit of many varieties do not appear to lose their susceptibility to Phomopsis (research by Mike Ellis and his students at Ohio State University). If spore sources are not being depleted in regions that have experienced a dry spring this year (like the Lake Erie region), enough inoculum may still be available in overwintering sources to cause fruit infections (Figure 3) past the mid-July period, should conditions turn wet. As one would expect, this is more of a concern for vineyards with a previous history of this disease. In addition, vineyards trained to trellis systems that retain lots of older and/or dead wood (cordons as opposed to canes, machine pruning as opposed to hand pruning) and/or vineyards that have not been receiving early shoot (3-6” shoots) sprays in previous years, will be more at risk of retaining significant amounts of overwintering inoculum of Phomopsis past the mid-July period during years with dry springs.
For Lake Erie region juice grape growers, powdery mildew remains in spite of the dry weather. Recall that powdery mildew primary infection periods require rainfall of at least 0.1” (and temperatures above 50 F). However, once primary infections have occurred, the disease can proceed to build without rainfall from spores produced by those primary infections. I suspect the dry, sunny weather will keep disease development moving at a slower than average pace (direct sunlight kills powdery mildew), but the disease will continue to build as it always does. Juice grape vineyards with low to average size crops may require little beyond the first or second post bloom spray for mildew. But keep in mind that we’ve a long way to go and if cloudy, humid conditions become entrenched, it can speed epidemic development. Also, poor ripening conditions after veraison can greatly reduce a mildewed canopy’s ability to ripen a crop, especially a large crop.
For wine grape growers, wherever you are in PA, it’s a ‘given’ that protection against all the major diseases should continue well past the first post bloom spray, for fruit and for leaves. As mentioned earlier, fruit are still susceptible to black rot and Phomopsis, and if you’re in an area experiencing at least some rainfall this year, downy mildew is definitely a continuing threat. As detailed above, the threat of powdery mildew goes without saying and every day is a powdery mildew infection period. So, for the second post bloom spray on wine grapes, include active ingredients for control of all diseases.
For continuing summer sprays, pay close attention to chemical classes for resistance management and always rotate modes of action. The loss of a mode of action (like the QOIs (strobies)) is a big deal to wine grape growers who have to apply many sprays within a given season for control of diseases like powdery and downy mildew. Rotation and resistance management should be an important component of your summer spray program. You’ve applied your best materials around bloom, now it’s time to rotate to other modes of action. Fortunately, we have lots of effective options for powdery and downy mildew control; use as many of them as you can, never applying consecutive sprays of anything (except the old standards like copper, sulfur, mancozeb products, ziram, captan). In Pennsylvania, we have many effective modes of action for powdery mildew like those found in Vivando, Torino, Quintec, the difenoconazole products (the newest, most powerful sterol inhibitor), and Luna Experience, Endura, and now Aprovia (the succinate dehydrogenase inhibitors). And of course, there’s always sulfur, but beware its use on red hybrids. I should mention that Aprovia is also labeled for black rot control. However, our recent tests have indicated that Aprovia’s black rot efficacy may be limited and that further testing is needed to better define this activity before it can be recommended for control of this disease.
For downy mildew we have products like Revus, Presidio, Ranman, Zampro, the old standards (copper, mancozeb products, ziram, captan), and the phosphorous acid products. Unfortunately in parts of PA, the powdery and downy mildew pathogens have developed resistance to the strobilurins, and they may not be reliable choices any longer. Also, the active ingredient in the product known as Reason, has the same mode of action against downy mildew as the strobilurins, and for resistance management purposes, Reason should be considered the ‘same’ as the strobilurins. One last thing: if you use the phosphorous acid products for downy mildew control, keep in mind that although they are extremely rain-fast, do not expect them to provide more than 10 days of protection against this disease, especially under high disease pressure.
For wine grape growers in more southerly regions of PA that have been receiving regular or heavy rainfall, Protection against all diseases obviously needs to continue. Once past the fruit protection period (which may be up to 6-7 weeks past capfall for black rot on V. vinifera), leaves of V. vinifera and some of the more sensitive hybrids will need continued protection from powdery mildew up to veraison or longer. As long as conditions remain wet, downy mildew will also remain a threat deep into the season. A clean canopy is essential for maximum ripeness and fruit/wine quality, maximum winter hardiness (recalling the cruel winters of 2014 and 2015), and minimal overwintering inoculum. For late season powdery mildew control, alternative materials may gradually be used to replace the synthetics and sulfur (particularly for reds where late sulfur applications can create wine quality issues). Avoid oils around/after veraison for powdery mildew control to avoid reducing photosynthesis. I have heard good things about potassium salt use (potassium bicarbonates and nutrol) from colleagues in Ontario, to maintain clean canopies late into the season. There are other alternatives currently available for late powdery mildew control, but for many their efficacy, especially on V. vinifera, is modest at best.
Late Summer sprays are for leaf protection, especially for varieties of V. vinifera. Sprays at this time primarily target powdery mildew, but may also include downy mildew if disease has gotten a foothold in the vineyard and conditions remain wet into fall. Regular scouting and strict attention to weather conditions at this time are very beneficial to making prudent late season spray decisions. For downy mildew, rainfall and leaf wetness is critical for epidemic development and dry late summer periods can sometimes offer relief from this disease. However, beware of heavy over-night dews which can continue to fuel downy mildew infections and sporulation without rainfall and keep the ‘fire’ alive on leaves at a slow burn. Early defoliation by downy mildew will effectively terminate the fruit and cane ripening process and leave vines weakened going into winter.
For bunch rot control, wine grape growers of bunch rot susceptible varieties may have already applied a Botrytis specific fungicide at full bloom. This is because Botrytis infections of the inflorescences can occur during bloom under wet conditions. These infections usually remain dormant and do not result in active rot…until after veraison, when injury to berries or high humidity, or some other factor (research has not completely determined all the factors involved) may lead to activation of a percentage of these infections and cause clusters to rot.
The next Botrytis fungicide application is commonly applied at just before closure of the clusters (soon). In varieties with very compact clusters, this application may be extremely important as it represents your last opportunity to get fungicides into the interior surfaces of clusters. This spray may also help to reduce latent infections that research has shown can continue to accumulate throughout the berry development period. It may also be an opportunity to ‘blow out’ bloom trash (dead cap and stamen tissue that got stuck in the clusters after bloom) from the insides of clusters. Bloom trash can provide substrate for fungi like Botrytis and serve as a focal point for bunch rots to develop later in the season, from inside clusters. The compactness of clusters plays an important role in not only the retention of bloom trash (the tighter the cluster, the more bloom trash retained), but also the effect of retained bloom trash on cluster rot; as compactness increases, the enhancement of bunch rot by retained bloom trash increases.
Another bunch rot control measure is leaf removal around clusters. Most often applied shortly after fruit set, fruit zone leaf removal exposes fruit to better air, sunlight and pesticide penetration which can improve control of ALL fungal diseases. This practice is most commonly applied to varieties of Vitis vinifera that produce tight clusters, but it is an expensive operation to add to your production costs and is most cost effectively applied by machine (machinery costs aside). It can be mechanized most effectively if vines are trained to a VSP or some other two dimensional trellis system with a relatively focused and narrow cluster zone (Figure 4A and B).
Research generally indicates that the earlier this practice is applied, the larger the effects for bunch rot control. For example, when applied at trace bloom (first flowers opening), it tends to reduce fruit set in addition to exposing clusters. This can be beneficial for varieties that naturally produce compact clusters (Pinot Noir, Pinot Gris, Chardonnay, Vignoles, Riesling) that are very susceptible to rot during ripening (Figure 5). Clusters that are looser (as a result of reduced fruit set) are easier to penetrate with pesticides, and are less apt to become damaged by overcrowding of berries before harvest. However, the potential for yield reduction may make the trace bloom timing unnecessary or undesirable on varieties that do not suffer from compactness/high susceptibility to late season rots. One note of caution: in more southerly climates, some growers remove leaves only on the east (north-south running rows) or north (on east-west rows) side of the trellis to avoid sun damage to fruit in late summer.
Fruit zone leaf removal can also reduce bloom trash retained in clusters: when comparing clusters of vines treated with and without leaf removal, we noted a significant reduction in bloom trash where leaves were removed, regardless of timing or method (by hand or machine). This can be particularly effective if utilizing air-pulse technology to remove leaves. This type of leaf removal mechanization applies high speed pulses of air to shatter leaves in the cluster zone, while blowing bloom trash from clusters.
The next fungicide application for Botrytis is made just before or at veraison. As fruit begin to soften and skins become thinner and more ‘breachable’ by fungal pathogens like Botrytis, an application at this time, to rot prone varieties, is a good way to stave off bunch rot development as fruit become more susceptible and more likely to become injured by birds, insects, excess moisture/humidity, and overcrowding of berries in tight clusters. Botrytis fungicides can protect intact fruit surfaces and may help to reduce the spread of Botrytis rot on fruit, even after they have become injured. Lastly, an application about 2-3 weeks after veraison, especially under wet weather conditions, can reduce further rot development during the last stretch of ripening. Keep in mind that Botrytis fungicides control Botrytis, and will not provide protection against sour rot organisms that often destroy fruit of overly compact clusters, despite the application of a full Botrytis fungicide program.
Don’t forget that there is abundant information available in the 2016 New York and Pennsylvania Pest Management Guidelines for Grapes. This is one of the very best guides for grape growers in NY and PA (and the Northeastern U.S. in general). It represents the compilation of many years of excellent grape research and includes the most recent updates on pesticide use and disease and insect pest control. If you don’t have a copy, get one through Cornell University press. Every commercial grape production operation should have one! At about half the cost of a single pesticide spray, it is well worth it.
By: Jody Timer
As a new grape season approaches, you all may be asking yourselves, “What is going to be my biggest headache this season?” As far as insects go, I would have to answer, as always, the grape berry moth (GBM). In this blog I would like to touch on the most recent research regarding the grape berry moth, as well as, other insects to scout for in your vineyards in the early part of the growing season.
The last two growing seasons, growers expected to see a dramatic decline in GBM populations, due to the harsh winters and record breaking cold. The opposite scenario occurred when greater than average GBM infestations materialized. So, what can we expect from this growing season? The winter of 2015-2016 was mild, the spring started off warm, and then April slowed down the accumulation of degree days. The total accumulation of degree days for this season is only slightly ahead last season’s and is forecasted to catch up in the next week to within two days, with average temperatures throughout the rest of May. With our current research, we aim to enhance the temperature-based phenology model to provide more detailed recommendations. We are researching ways to optimize the timing of generation-specific interventions, thereby providing prevention of economic damage of subsequent generations. The number of generations of grape berry moth has been increasing from the traditional three generations per year to four plus. First, and most obvious, adding generations increases the overall attack potential. Second, and largely ignored, adding generations may increase the developmental asynchrony of the population. Given the already narrow time-window of vulnerable life stages, and changes in current and future insecticides, such developmental asynchrony increases the risk that late-season generations will require more than one insecticidal application to achieve control below industry-mandated economic thresholds.
The timing of chemical control of GBM is particularly challenging because the stages most vulnerable to insecticidal applications reside inside the berry for the majority of their life cycles. The result is an extremely narrow management window. (See http://newa.cornell.edu/index.php?page=berry-moth for the online forecasting tool for your growing regions). The early season developmental synchrony in GBM is caused by the relatively synchronous forcing of diapause, as adults emerge from diapausing pupae in late spring. Later in the season the generations become less and less synchronized and the peaks of emergence become blurred. We are exploring the correlation with GBM spring emergence (DD) and the timing of wild grape bloom and the resulting asynchrony of the subsequent generations. Presently the wild grape bloom is used as the biofix for the NEWA GBM phenology forecast model. We expect GBM developmental synchrony to be dependent on multiple factors, most importantly, the rate of emergence in the spring. Our research is exploring the possibility that the closer the GBM spring emergence coincides with grape bloom the greater the survivorship of the first generation of GBM. Consequently, a large first generation emergence would result in subsequent generations, all of which would emerge in the presences of suitable hosts, exponentially proliferating. For example, in the Lake Erie grape growing region the wild grape bloom usually occurs around the first week in June and the GBM peak in emergence occurs around the end of May. However, if we experience a very warm spring and the GBM emerge sooner than the wild grape blooms, they will emerge with no suitable host and less of them will survive. Such enhanced models will allow for more adaptive generation-specific protocols of management, and could include novel control strategies. According to this model, we are expecting another heavy infestation of grape berry moth this year.
Early Season Insects:
Grape Flea Beetle– also known as the steely beetle. These beetles are small (3/16”) and metallic blue in color. Beetles overwinter in the adult stage and emerge as grape buds begin to swell, with one generation per year. This beetle primarily attacks buds of wild and cultivated grapevines. They are one of the first insect pests to appear in the vineyards in the spring. The most significant injury caused by this pest is due to adults feeding on swollen grape buds, often destroying the developing bud. They have the potential of causing considerable damage under the right conditions; specifically when we get a prolonged swollen bud stage. Look for damage from steely beetle along the edges of the vineyard. By about 1/2” growth the threat of economic loss from this pest is over. Infestations are worse on wooded edges. They get their name from their ability to jump.
Climbing Cutworms: There are several species of cutworm larvae feed on grape buds during the swell stage. The injury to buds can be confused with grape flea beetle damage. The moths are night flyers and the larvae are night feeders. Both stages hide during the day. Larvae have a brown to gray coloration with darker stripes or dots along the body, and are 30-36 mm long. Vineyards with weed cover under the trellis and areas with sandy soils are at greater risk for injury. The greatest economic injury occurs during bud swell in the spring. Scout frequently during this time.
3 – 12 INCH SHOOT GROWTH
Banded Grape Bug and/or Lygocoris inconspicuous – both of these insects have piercing and sucking type mouthparts. Banded grape bug nymphs have antennae with black and white bands, green/brown bodies and are <1/2”. Lygocoris inconspicuous nymphs are slightly smaller with light green antennae (no bands) and light green bodies. Nymphs (immature stage) of both insects feed on developing flower clusters by piercing florets, pedicels and rachises. Begin scouting when shoots are 3 – 5” in length and continue until shoots are at least 12”. See scouting video, below – Banded Grape Bug LERGPvids:
Grape Phylloxera (leaf form) –Grape Phylloxera. Grape phylloxera is an aphid-like insect with a complex life-cycle that causes feeding galls on either roots or leaves. The life cycle is different for the foliar and root forms of this insect. The root form is the more destructive of the 2 forms but is managed by grafting susceptible varieties to phylloxera resistant/tolerant rootstocks. Leaf galls are in the shape of pouches or and can contain several adults and hundreds of eggs or immature stages. Root galls are swellings on the root, sometimes showing a hook shape where the phylloxera feed at the elbow of the hook. At high densities, leaf galls can cause reduced photosynthesis. Root galls likely reduce root growth, the uptake of nutrients and water, and can create sites for invasion of pathogenic fungi. There is a wide range in susceptibility of grape varieties to both gall types. Begin scouting early in the season. Galls may become evident as soon as the 3-5 leaf stage so carefully examine the undersides of terminal leaves for warty looking, green to reddish growths. An insecticide application can be applied when first galls are forming. The most reliable method to determine if crawlers are active is to cut galls open and observe for presence of nymphs. Crawlers are extremely small so a good hand lens is needed.
Additional Insect Pests – During this time period a number of other insects (i.e., grape plume moth, grapevine epimenus, 8 – spotted forester, tumid/tomato gallmaker, grape cane gallmaker, and grape cane girdler) may also be present in the vineyard. Although injury from these insects may look alarming, damage is usually cosmetic and insecticide applications are rarely needed.
For more detailed information, please see: Andy Muza’s blog last spring: Grape Insect Pests to Watch for from: Bud Swell through Immediate Pre-Bloom Stages
Fact sheets on grape insect pests can be found at the following sites: Please click on the links below for more fact sheets specifically on insect pests found in the vineyard.
- NYS IPM Fact Sheets for Grapes; Identifying Grape Insects (Michigan State);
- Midwest Grape Production Guide (Bulletin 919) – (Chapter 4 – information on grape insect pests);
- Mid Atlantic Vineyards Grape IPM (Virginia Tech) ;Ontario GrapeIPM – Grape Insects
- Another valuable, compact resource that can be taken along in the vineyard as you are scouting is A Pocket Guide for Grape IPM Scouting of Grapes in North Central & Eastern U.S. This guide provides concise information along with color photographs on insect/mite pests, natural enemies, diseases and disorders.
By: Bryan Hed
Spring has arrived, but it sure doesn’t feel like it in many parts of the Northeastern U.S. However, the cool weather is buying us some extra time that can be used to review our pre-bloom disease management plans and familiarize ourselves with all the tools at our disposal. First, if you haven’t done so yet, acquaint yourself with the NEWA website (Network for Environment and Weather Applications) found at http://newa.cornell.edu. This is your annual reminder! On the home page is a map of the U.S. with every location of a weather station (391 locations!) that can be tapped into for historical and ‘up to the hour’ weather data. From the convenience of your computer screen, you can view weather information from eastern Nebraska to the eastern seaboard, and many places in between. In connection with each weather station is a pest forecast to help you make insect pest and disease management decisions. Use your cursor to navigate the map and click on the weather station nearest you (denoted by a leaf/rain drop icon) to view nearby temperature, rainfall, leaf wetness duration, wind speed, etc. Clicking on ‘grapes’ under ‘crop pages’ will give you access to disease forecasting models for Phomopsis cane and leaf spot, black rot, and powdery and downy mildew. You can also access the grape berry moth degree day model that will improve your timing of grape berry moth insecticide sprays later this summer. Research has shown that use of the berry moth model can improve control of this pest (and of the Botrytis and other rot that develops as a result of the damage it causes) without any increase in your management costs. Each model forecast is accompanied with helpful disease management messages and explanations. This is a great way to make use of one of those cold, rainy mornings to educate yourself and prepare for the challenges ahead.
Disease concerns during early shoot growth stages
Phomopsis cane and leaf spot is our first concern during the early stages of growth in late April and early May. This is because inoculum sources overwinter in woody tissues (alive and dead) right on the vine, and often on wood you can’t just prune out (basal nodes on year-old canes). Infected wood releases spores of the fungus during the first rain periods in spring. The inoculum sources which appear as dark scabby lesions on the first few inches of year-old canes, may be just millimeters from the first susceptible green tissue after bud break (Figure 1) and spores can infect within relatively short time periods (24 hours) at very cool temperatures (upper 40s). An examination of your vines now can provide you with some idea of the amount of inoculum present in your vineyard, and the need for early fungicide applications to prevent infections in the cluster zone. Look specifically for lesions along the first (oldest) few inches of year old canes (again, see Figure 1). Also, old pruning stubs are classic sources of inoculum, and according to work performed at Cornell University, dead wood is probably the most potent source of spores of Phomopsis as the fungus grows and sporulates especially well on this material; removal of all dead wood from the trellis at dormant pruning will help control this disease. Where inoculum sources have built up in the trellis (which is particularly a problem in machine pruned vineyards) applications of mancozeb, ziram, or captan during early shoot growth stages are a cost effective way to control shoot and cluster stem infections (Figure 2) that can lead to crop loss. It will also help to prevent the build-up of inoculum on tissues that you can’t just prune out during dormancy (those first 4-5 nodes of shoots that you need for next year’s crop!).
Figure 1. Note the dark brown lesions on the first few internode regions on these Chancellor canes. The lesions are from Phomopsis infections that occurred during early shoot growth in the previous year (when these were green shoots). The buds present are just ready to burst open with new shoot growth that will be very vulnerable to infection during subsequent rain periods.
Figure 2. Although the 1” shoot stage can be vulnerable to damage from this pathogen, the more critical stage is at 3-6” shoots, when more shoot, leaf, and cluster tissue is exposed and is highly susceptible (below).
Sprays for powdery mildew may be prudent during early shoot growth for Vitis vinifera cultivars and highly susceptible hybrids, especially in vineyards where control of this disease may have slipped last year (lots of overwintering inoculum). Unlike the fungi causing Phomopsis and black rot, the powdery mildew fungus has to have live grape tissue to grow and reproduce. It survives the winter by going dormant itself, just like their grapevine host. According to work at Cornell University overwintering inoculum will come primarily from infections that occurred before Labor Day of last year. This is because infections that occurred after that, likely do not have time to prepare for winter dormancy and overwintering survival. Then, during the following spring, primary infection periods occur with the completion of two simple weather factors: at least a tenth of an inch of rain with temperatures above 50 F. When those two factors occur in concert, overwintering inoculum (spores of the fungus) has been unleashed from its dormant stage and the potential for infection is there if green tissue is present. Applications of sulfur, oils, Nutrol, and potassium bicarbonate materials can be good choices for mildew management early on. Remember to read labels and be aware that you can’t mix sulfur and oils, or oils and captan. Powdery mildew is rarely a concern during the early shoot growth stages for growers of juice grapes, especially in the cooler Lake Erie region of Pennsylvania.
As for black rot, scout your vineyards for old fruit mummies and clusters (infected from the previous season) in the trellis. Removal of ALL old cluster material before bud break is essential to maintaining good control of this disease. Once on the ground, mummies/clusters can be buried with cultivation, reducing or eliminating their capacity to fuel new infections in spring. As I mentioned in last year’s blog, a fungicide application for black rot may not be necessary at these early shoot stages IF good control of this disease was achieved the previous year AND conscientious trellis sanitation has been implemented. On the other hand, the importance of early shoot infections should not be underestimated. For example, inoculations we performed at these early shoot growth stages (from early May to early June) simulating wet weather and an overwintering inoculum source (mummies) in the trellis, went on to produce leaf and shoot infections in the cluster zone (Figure 3) that released spores during early berry development stages and resulted in crop loss of 47-77%! An application of mancozeb, ziram, or captan for Phomopsis will also provide control of early black rot infections.
Figure 3. Early black rot leaf infections in the cluster zone provide inoculum that can add to problems with controlling fruit infection after capfall. The two small tan lesions on the leaf at node 2 are just inches from the developing inflorescence found at node 3. These lesions will release spores during rainfall periods that could easily be splashed to highly susceptible cluster stems pre-bloom, and developing fruit after capfall. Resulting fruit infections will lead to crop loss.
At about 10-12” shoot growth or the 5-6 leaf stage: The importance of applying sprays at this stage is also dependent on the level of overwintering inoculum, that is, the level of control maintained the year before. In other words, if you had trouble controlling diseases last year, a fungicide spray at this time is going to be more critical than if you kept your vineyard clean last year. This is particularly true for the more susceptible V. vinifera and French hybrid varieties.
This stage also marks the point at which the downy mildew pathogen first becomes active. The first infections arise from inoculum that has overwintered on the ground; leaves and other plant material that was infected during the previous season. Therefore, vineyards that developed a fair amount of leaf/cluster infection last year will be at higher risk than vineyards in which infections were controlled. Infection of grapevines by downy mildew is very dependent on the creation and maintenance of wet plant surfaces by rainfall. Pay close attention to spring precipitation periods: when temperatures are above 52 degrees F during rainfall, infective spores are produced that cause the first infections. Spring leaf infections are identified by the classic yellow oil-spot symptom on the tops of leaves (Figure 4), coinciding with white, downy sporulation of the pathogen on the undersides of leaves. Inflorescences can be blighted and show sporulation as well. Sporulation occurs through night time hours under high relative humidity, and is often readily apparent during a morning scout of the vineyard. First symptoms are most likely to be seen on leaves close to the ground or on sucker growth (because the pathogen comes from the ground) in wetter areas of your vineyard (because of longer hours of wetness after rainfall and higher humidity in these areas); start your scouting there first. Like a flame, the downy mildew pathogen kills everything it ‘touches’, and infected material eventually turns brown and dies, as if scorched by fire. Good control early is very important in years with frequent wetness. Under optimum temperatures of 70-75F, only an hour or two of plant surface wetness may be required for infection to occur. Once established, downy mildew can spread very quickly under wet, warm conditions; it only requires 4-5 days at those optimum temperatures for new infections to go on to produce more spores for the next round of infections.
Mancozeb products offer some of the best control options for downy mildew, while also controlling Phomopsis and black rot infections at this time. Ziram is a little weaker on downy mildew, and Captan a little weak on black rot, but these may also be a viable option at this stage if these diseases are not a huge threat at this time (but they are all a priority at this time on Vitis vinifera and susceptible hybrids). Keep in mind that all these materials are surface protectants; they do not penetrate plant tissue (they are designed that way because they can injure plant tissue) and are therefore subject to wash-off by rainfall. This means that under heavy, frequent rainfall conditions, application intervals will need to be squeezed down from 14 days to more like 7-10 days between sprays, especially for highly susceptible varieties. Other options for downy mildew exist that are more rainfast, like Presidio, Revus, Revus Top, Pristine, Reason, Zampro, Ranman, and the phosphorous acid products.
Keep in mind that shoots are growing at break neck speed at this time of year, and may double or more in length within a short period of time. This leaves increasingly larger amounts of unprotected, highly susceptible tissue within that typical two week fungicide interval, regardless of what fungicide is used.
Figure 4. Yellow oil-spot symptoms of downy mildew on young spring leaves.
One last reminder with regard to black rot that I mentioned earlier; black rot leaf infections at this time will create more sources of inoculum in the cluster zone (often on leaves at nodes 4-7) and can make black rot control more problematic during the fruit protection period (after capfall). If you see lesions on leaves in the cluster zone, make sure your subsequent black rot sprays are applied effectively and timely over the next several weeks during the fruit protection period.
Powdery mildew (Figure 5) should also be addressed at this time for Vitis vinifera and susceptible hybrids, but this disease is much less of a concern for juice grapes. Sulfur is an inexpensive option for powdery on non-sensitive varieties at this time and a reliable standard, even at cool temperatures. The sterol inhibitor fungicides may also be good choices at this time, providing they are still effective in your vineyard. The sterol inhibitor and strobilurin fungicides have been in use for many years in Pennsylvania vineyards and are considered at high risk for the development of resistance by the powdery mildew fungus. Research at Virginia Tech and Cornell has indicated that powdery mildew resistance to strobilurins is common in parts of those states. On the other hand, resistance appears to be less common in Pennsylvania, for the moment. If you suspect powdery mildew resistance to these materials in your vineyard and you are applying them for the other diseases they still control, apply them in a tank mix with another active ingredient for mildew (like sulfur) or discontinue their use and use an alternative active ingredient. Just because we have few documented cases of powdery and downy mildew resistance in Pennsylvania at present, be vigilant in your observations regarding potential resistance and control failure. This is even more critical for the next two fungicide application timings; the immediate pre-bloom/first post bloom sprays, where fruit protection ($$$$) is top priority.
Immediate pre bloom/first post bloom fungicide application.
The immediate pre bloom (just before the beginning of capfall) and first post bloom (7-14 days later) fungicide applications are the most important applications you’ll make all year, regardless of variety grown and disease pressure. These two sprays are designed to protect your annual investment (fruit) from all the major fungal diseases (Phomopsis, black rot, downy and powdery mildew) and cost cutting over these two sprays will often result in economic losses (unless you can reliably predict bone dry weather). There is little or nothing to be gained by doing these two sprays ‘on the cheap’, even if disease control was ‘stellar’ last year. This is because young fruit of every variety are most susceptible to all the major diseases during the period stretching from bloom (capfall) to about 2-3 weeks after bloom. I cannot overemphasize how important it is to apply your most effective materials at this time. This is generally a good time to try some of the newer active ingredients in products like Vivando or Torino (for powdery mildew only), Revus Top (for powdery and downy mildew and black rot), Inspire Super (for powdery mildew and Botrytis), Luna Experience (wine grapes only, for powdery mildew, Botrytis, and black rot) and the newer downy mildew materials (listed above). Just remember that you will need to limit the use of these materials to about two applications per season for resistance management purposes. Sulfur can also be included in a tank mix (on non-sensitive varieties) to further improve control and aid in managing powdery mildew resistance, especially in cases of high disease pressure on highly susceptible varieties. Make sure sprayers are properly calibrated and adjusted for best coverage on a bloom-period canopy, spray every row at full rates and shortest intervals, and NEVER extend the interval between these sprays beyond 14 days.
Some growers may be thinking of applying the phosphorous acid products (aka phosphites, phosphonates) for downy mildew at this time. These products are readily absorbed into plants and are rain-fast, effective, and relatively pleasant to work with. However, if you use these materials at this time, be mindful that they provide only limited protection against new infections (7-10 days under high disease pressure). They can provide excellent control of downy mildew under very high disease pressure, but that level of control can deteriorate after 10 days leaving a way in for the pathogen and potential crop loss.
Bloom may also be a time when Botrytis infections can become established in clusters. These infections do not immediately rot fruit, but remain dormant until activation during the ripening period. Though this is mainly a concern for growers of bunch rot susceptible varieties, a bloom spray for Botrytis can significantly impact fruit health and crop loss at harvest.
Figure 5. Powdery mildew symptoms on grape.
I am anticipating a new material, Aprovia, to be available for 2016, mainly for powdery mildew. This material is related chemically to Boscalid (found in Endura and Pristine) and Fluopyram (found in Luna Experience).
Finally, a shortened recap of some relevant main points from last year’s blog.
- Good overwintering inoculum control (good control last year, good trellis sanitation) will make seasonal disease control more effective and more forgiving (‘I can’t get a spray on because it won’t stop raining; good thing I controlled diseases well last year’); consider it an insurance policy.
- Early spray programs are relatively inexpensive. If disease control was lacking last year, higher overwintering inoculum levels will require that you fire up your seasonal spray program earlier this year, especially if conditions are wet.
- The bloom and early post bloom periods are the most critical for protecting your crop ($) against all diseases; it is never cost effective to cut corners during those stages of crop development.
- Scout your vineyards and develop your skills at identifying diseases. Focus on vineyard areas where disease control has been most challenging. Know what plant parts to examine for first symptoms and at what stage of plant growth to anticipate seeing them.
- Know your fungicides; their strengths, weaknesses, specific diseases they control, their tank mix partners and their rotational partners for resistance management.
- Read labels
- Make good use of the NEWA system. It will help you make pest management decisions while teaching you a little about pathogen and insect pest biology, and it’s free!
Some information in this blog was gleaned from the New York and Pennsylvania Pest Management Guidelines for Grapes. This publication is an excellent source of research based information designed to help commercial growers make important grape production decisions. Copies can be purchased at the Cornell Store at https://store.cornell.edu/p-193185-2016-new-york-and-pennsylvania-pest-management-guidelines-for-grapes.aspx
As we get closer to bloom, another article will be posted to cover important disease management concepts for the post-bloom period.