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Fungicide resistance management – webinar review

by Michelle Moyer, Viticulture Extension Specialist, Washington State University, and Cain Hickey, Viticulture Extension Educator, Penn State University

On June 24th, Dr. Michelle Moyer gave a webinar presentation entitled Fungicide Resistance and the Acronyms. In this webinar, Michelle discussed the nuances of managing fungicide resistance through judicious application of fungicides. Fungicide resistance management is optimized through good fungicide stewardship. Good fungicide stewardship includes rotating fungicide modes of action (within season and between seasons), timely application of  fungicides (before disease symptoms appear), using tank mixes that effectively and broadly manage a targeted fungal disease, and proper calibration and maintenance of spray application equipment to ensure adequate coverage of the target (grapevine canopy and/or clusters).

It is important to know that some fungicide classes are at greater risk of It is important to know that some fungicide classes are at greater risk of resistant development than others. For example, Fungicide Resistance Action Committee, or FRAC, code 7 (SDHI) and 11 (QoI)  fungicides are “high risk”, while FRAC code 3 (DMI) fungicides are currently considered “moderate risk”; but fungicide resistance to these classes have been found in several grape fungal pathogens. While good fungicide stewardship (see above for resistance management considerations) is important for all fungicides, it is important to be judicious when applying fungicide FRAC codes with moderate to high risk of resistance development. Please see Michelle’s slides for more information about fungicide resistance and its management:

Remember that chemical management of fungal diseases is only one part of an integrated management system. Cultural practices, such as canopy management and appropriate cultivar selection are also major contributing factors to a successful fungal disease management program.  

For additional information on fungicide resistance management in wine grapes, please visit: https://framenetworks.wsu.edu/ 

Spotted Lanternfly Management in Vineyards 2020 – Webinar Recap

by Heather Leach, Extension Associate, Penn State Entomology 

Introduction 

Spotted lanternfly (SLF) populations are expected to be high in 2020 and some growers have already reported significant populations of nymph SLF in their vineyards. Remember that SLF feed on over 70 different plant species and will be present throughout the landscape, including areas surrounding your vineyard. All life stages of SLF except for the egg masses actively feed on plant sap (phloem). To date, grapevines have been the hardest hit agricultural commodity by SLF with ~30% of growers in southeastern PA reporting vine damage (dead vines, reduced yields) from this insect.  

Summary of 2019 Data 

In 2019, we learned more about the phenology and behavior of SLF in vineyards. Some of that work has recently been published, see here: https://link.springer.com/article/10.1007/s10340-020-01233-7  

The key takeaway points:  

-SLF are present in vineyards as nymphs, but typically not very numerous. The most problematic life stage is the adults, which are very numerous and most problematic in vineyards from late August-October.  

-SLF is an edge-pest with unequal spatial distribution within a given block. The “hot spots” with SLF typically stay that way for the majority of the season. Scout your vineyard regularly and learn these “hot spots”.  

– SLF flight activity is highest in the afternoon, and populations may increase on the vine throughout the day  

-After harvest, adult SLF begin feeding more heavily on the trunk (as compared to the shoots and cordon earlier in the season). When applying an insecticide, make sure you’re hitting the target.  

-Based on preliminary data, high levels of SLF feeding (200 per vine for ~5 weeks) reduce photosynthesis, transpiration, brix values, and cold hardiness (cv. ‘Riesling’). 

2020 Research Plans 

-Feeding trials to evaluate the damage that SLF causes to vines will continue  

-Additional insecticide trials, including testing new active ingredients, evaluating residual efficacy in-field, and application methods will be looked at 

-Landscape-scale control of SLF utilizing the biopesticide containing Beauveria bassiana is being evaluated in large trials in natural areas and in smaller trials adjacent to vineyards 

-Exclusion netting, flight-intercept traps, and utilizing tree-of-heaven will also be investigated for their use in vineyards 

Management 

-Specific questions about management of SLF on your vineyard can be directed to Heather Leach, hll50@psu.edu. Additionally, please review this factsheet for more information: https://extension.psu.edu/spotted-lanternfly-management-in-vineyards  

-The best control of SLF to-date in vineyards is the use of repeated broad-spectrum insecticides. Key pre-harvest products that are often relied on by growers for SLF management include the active ingredients zeta-cypermethrin, carbaryl*, malathion, dinotefuran, and thiamethoxam. For post-harvest, the longest lasting chemical is bifenthrin (which has a pre-harvest interval of 30 days). *Note that carbaryl has been reported as ineffective against SLF by some growers – this is being investigated for 2020.  

-There are no established action thresholds for SLF. The “best guess” approximation is ~15-20 nymphs/vine and 5-10 adults/vine. Please keep in mind that this is observation-based, not science-based. This threshold likely depends on other factors including pre-existing stress of the vine (e.g. presence of disease), age of the vine, and many other factors.  

-To avoid resistance (with SLF and other important vineyard pests like fruit flies), rotate chemical classes.  

-This year, we are seeing flare-ups of secondary pests (leafhopper, mealybug, mites) which may be attributed to the increased use of broad-spectrum insecticides for SLF control. Keep an eye on other pests in your vineyard.  

Please see this link for a PDF copy of the presentation on SLF detection and management in vineyards (from the June 17th webinar):

Mid to late season control of downy and powdery mildew and bunch and sour rots in 2020

by Bryan Hed, Grape Pathology Research Technologist, Penn State, Lake Erie Regional Grape Research and Extension Center

Rainfall is always a key factor in any discussion of grape disease development in the eastern US. After all, most of the major pathogens we do battle with every year are fungal in nature, and fungi are favored by wet, humid conditions. For that reason, 2018 was a disastrous season for many grape growers in Pennsylvania, when boatloads of rain fell almost everywhere below Interstate 90. In that year, many growers suffered heavy losses to fungal disease, making it one of their worst crops ever. Last season began looking a bit like a replay of 2018, but a relatively dry harvest season renewed our faith in the possibilities for premium wine grape production in Pennsylvania. At the time of writing this post, a look at the twenty-something NEWA weather stations across PA, (newa.cornell.edu) shows it’s been shaping up to be a drier season in many places, cutting growers a much-needed break so far. In fact, rainfall was below average in many Pennsylvania locations during May, and June rainfall – though heavy in some locations – has been defined by just three rain periods (June 3-5, 10-11, and 19-20) with lots of dry weather, and opportunities for protective sprays to be applied, in between. But current rainfall amounts only tell part of the picture. Some vineyards may still harbor fair amounts of overwintering inoculum for diseases like downy mildew and black rot, requiring that growers remain vigilant with regard to their disease control sprays, particularly when invested in the ultra-susceptible varieties of Vitis vinifera in the southeastern part of the state. In those cases, fungal diseases are still a serious threat, even if conditions remain relatively dry.  

Most of us are past bloom and have already applied sprays for fruit protection at ‘immediately before bloom’ and ‘first post bloom’. If you applied these sprays diligently, not stretching intervals beyond 14 days (10 days is even better), using best materials, spraying every row with maximum coverage, you made your way through the most critical period for fruit protection. In this blog I’ll talk about sprays beyond that critical period; mid-late season, when we continue the battle to control downy and powdery mildew on leaves, and bunch and sour rot on fruit. As always, I’ll borrow information from past blogs so as not to try to reinvent the wheel.

Downy mildew

The pathogen that causes downy mildew is dependent on wet conditions; without a wet plant surface, no infection takes place. Fortunately, the fruit of most varieties are resistant to direct invasion by this pathogen by about 3 weeks after capfall. In other words, a developing berry is only susceptible to direct penetration of the pathogen from about the time the flower cap comes off (at the beginning of bloom) to about 3 weeks later. However, the cluster stems may remain susceptible for a couple weeks or more after fruit are resistant, and for this reason, fruit loss can continue to occur from cluster infections 4 or 5 weeks after capfall. Once we get past the critical sprays for fruit protection (which we always apply, rain or shine!), scouting for the distinctive white ‘downy’ sporulation on the undersides of leaves and on cluster stems is very important, and yields valuable information with regard to future need to spray (Figure 1). Growers of susceptible varieties do well to keep closely monitoring their vineyards for active sporulation and use that information in combination with the DMCast model on NEWA (http://www.newa.cornell.edu/) to determine if and when infection periods have occurred or will occur. 

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Figure 1. Late summer leaf symptoms of downy mildew (Niagara) showing ‘blocky’ lesion development and discoloration on the top side (above) and ‘downy’ white sporulation on the underside of a grape leaf (below). The late summer leaf blotches can differ dramatically from the yellow ‘oil spot’ symptoms that are observed in spring.
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Leaves will remain susceptible all season, though they do become less susceptible as they age. For this reason, the limiting or elimination of new shoot growth by veraison, through good nutrient and/or canopy management, can help to reduce the supply of susceptible tissue in the vineyard during ripening, and make post veraison control of this disease more manageable. I have gone into vineyards in late August-early September and observed that downy mildew was largely present on new shoot growth, but not on mature leaves at older nodes. There were two reasons for this: i) new shoot growth is more susceptible than older, mature growth, and ii) new shoot growth, unless just sprayed, is unprotected or less protected by previous fungicide applications. Symptoms on mature leaves in late summer may appear different from those on young leaves in early spring (Figure 1).  

The sight of active, white sporulation on green vine tissues means the downy mildew pathogen is capable of spreading quickly under wet conditions, and that sprays for downy mildew should continue, especially for susceptible varieties. Even humid nights that result in heavy dews by morning, can continue to fuel downy mildew development, generating fresh sporulation that can spread the disease rapidly when plant surfaces are wet. If you let downy mildew get out of control, it can strip vines of their leaves and in the worst cases, effectively end fruit ripening for the year, and shoot ripening for next year’s crop. Your grapevines go into winter dormancy in poor condition, and are more vulnerable to damage by severe cold, leading to crown gall and expensive trunk renewal the following season, with little or no crop to pay for it; all that stuff is connected, so you want to keep downy mildew under very tight control, especially on Vitis vinifera.

Chemical control: Your list of chemical control options will start to dwindle as we get within 66 (Mancozeb products, Ridomil MZ), 42 (Ridomil copper), 30 (Ranman, Reason), 21 (Ziram), and finally 14 (Revus, Revus Top, Zampro) days of harvest. In the end you’ll be left with Captan (which will also control ripe and bitter rot), copper, and phosphorous acid products (0-day pre-harvest interval), which have their own shortcomings, discussed below. 

Products like Ridomil (the mefanoxam component), Ranman, Reason, Revus/Revus Top, Phos acid products, and Zampro, are more rainfast than the surface protectants (like copper, mancozeb, ziram, and captan) but contain chemistries that are prone to the development of resistance. Therefore, they should not be used to put down an epidemic, which will only speed up the resistance development process. Even phosphorous acid products can be lost to resistance through repeated applications on a diseased vineyard, so keep downy mildew well under control. The resistance prone materials (Ridomil, Ranman, Reason, Revus/Revus Top, Zampro, Phos Acid products) are best used to maintain a clean vineyard, NOT to put down an epidemic. Conversely, the surface protectants would be least risky in terms of the development of resistance and can be an effective means of controlling downy mildew late into the growing season. Just be aware of seasonal limits, so plan ahead as best you can.  

Here are some precautions to consider with use of the ‘old standard’ protectants: 

  • Some insecticides and oils should not be applied with Captan.  
  • There is the concern for plant injury by copper applications, which will be exacerbated by application under slow drying conditions and application to wet canopies (for example, don’t make applications to dew covered canopies in the early morning). The addition of lime to the application raises the pH of the spray solution and reduces the chances for plant injury.  
  • Consider that copper is poisonous to yeasts and that excessive copper residues at harvest can interfere with fermentation, and wine stability and quality. Unfortunately it’s impossible to predict how high residues will be on fruit at harvest; that’s going to depend on the copper formulation (some of the newer coppers utilize lower copper concentrations), rate of material used, number and timing of applications made, spray coverage, and amount of rainfall from application to harvest. I am not aware of any information that establishes a nice, clean cut-off date or pre-harvest interval for avoiding excessive copper residues at harvest, but I have heard that cutting off copper use about a month before harvest may be sufficient in most cases.  
  • There is also evidence that late Captan sprays can delay fermentation and have negative effects on wine quality but the consequences seem less severe and irreversible than those associated with copper use.  For more on this, consider this online article by Dr. Annemiek Schilder, former fruit pathologist at Michigan State University: https://www.canr.msu.edu/news/late_season_fungicide_sprays_in_grapes_and_potential_effects_on_fermentatio 

If you are protecting a non-bearing, young vineyard from downy mildew (you’re not selling/harvesting a crop), you can continue to use mancozeb products to control downy mildew past the 66-day pre-harvest interval. You can also consider using mancozeb after harvest to keep canopies clean of downy mildew and ‘firing on all cylinders’ until that first frost. The longer your vines can continue to produce and store carbohydrates after harvest, the better prepared they’ll be to withstand winter cold without damage (and the crown gall that follows).  

Powdery mildew

In contrast to downy mildew, the fungus that causes powdery mildew is dependent on rainfall only for the initial release of spores in early spring. There is no requirement for plant wetness beyond that, which is why this disease is a problem even in dry climates like California. Once primary spores (ascospores) land on a susceptible grape surface, they germinate and form colonies that grow across the plant surface (Figure 2), sucking resources from the plant and producing secondary spores (called conidia) that are now spread by wind/air currents. The disease spreads rapidly under ideal conditions of high humidity, cloudy skies, and warm (but not hot) conditions. During the mid-late summer period, every day can be a powdery mildew infection period.  Fortunately, just as for downy mildew, fruit of most grape varieties becomes resistant to powdery mildew after about 3-4 weeks past capfall, although native varieties like Concord may be resistant just 2-3 weeks after capfall. Nevertheless, it’s especially important to tightly control the disease on fruit of V. vinifera and susceptible hybrids up to 4 weeks after bloom, as even tiny amounts of powdery mildew infection on fruit (amounts you can’t even see) can leave microscopic breaches in the berry skin, and increase the susceptibility of that fruit to bunch rots later near harvest.  

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Figure 2. Greyish-white colonies of powdery mildew on the upper surface of grape leaves.
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At four weeks post capfall the focus for powdery mildew control shifts to keeping leaves clean, especially on V. vinifera, for many of the same reasons expounded in the section about downy mildew (ensure optimal ripening of fruit and shoots/canes, ensure optimal cold hardiness, more effectively and more easily manage fungicide resistance, etc). But there is another very important reason, demonstrated by some excellent research conducted by Wayne Wilcox and others at Cornell University, who showed that controlling powdery mildew up to about Labor Day can reduce overwintering inoculum and disease pressure the following spring. Why Labor Day? When powdery mildew infected leaves die by that first hard frost in fall, the mildew on those leaves also dies…UNLESS it has had time to form fully mature, winter resistant structures called chasmothecia. These are the tiny, dark, period sized (.) structures you observe in heavily infected tissues in late summer. If the chasmothecia do not have time to fully mature before the leaf dies (as we would expect from infections that occur after Labor Day), they will not be tough enough to 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 continue their spray program up to Labor Day, to control the ‘size’ of the powdery mildew problems he/she will potentially face next spring. Once again, this is most important if you are growing Vitis vinifera and less important for growers of native varieties like Concord and Niagara.  

Chemical control:  Fungicides like Quintec, Vivando/Prolivo, Torino, Endura (note that the price of Endura is significantly lower in 2020), Luna Experience/Sensation, Miravis Prime, Cevya (V. vinifera only; read the label) and other sterol biosynthesis inhibitors (tebuconazole, tetraconazole, difenoconazole products) can be used for additional post bloom applications to control powdery in early/mid-summer in vineyards that have maintained tight control of the disease (‘clean’ vineyards). Remember to limit the use of any one FRAC group to 2 applications per season (the FRAC group designation is on the label). 

However, where disease control has been less than ideal, and especially for late summer applications (August and September), options for powdery mildew control should emphasize materials that are less risky in terms of the development of resistance, like formulations of sulfur on varieties that are not sensitive to it (which could also be tank mixed with the aforementioned synthetics to manage resistance). The more expensive, micronized formulations of sulfur will generally perform better (more effective per pound, more rainfast) than the cheaper, wettable powder formulations, especially for V. vinifera (you get what you pay for). Also, according to the 2020 New York and Pennsylvania Pest Management Guidelines for Grapes, “sulfur activity is strongly influenced by formulation, rate, frequency of application, and weather”; that is, higher rates and shorter spray intervals will provide better control than lower rates and longer spray intervals.  Do not apply sulfur within 14-21 days of an oil application.  

Sulfur residues on fruit at harvest have been correlated with increased hydrogen sulfide and sulfurous off-aroma formation during fermentation, and so growers will need to phase out sulfur applications at some point well before harvest. This is mostly a problem for wines that are fermented on the skins (reds) where most of residues at harvest are found. Work published by Dr. Misha Kwasniewski showed that “sulfur residues are likely of low concern in white wine making, especially when juice is clarified before fermentation. However, residue levels in red fermentations (fermented on skins) can exceed levels associated with increased hydrogen sulfide production when some sulfur sprays are applied within 8 weeks of harvest” (Kwasniewski et al. 2014). However, in that same study, ceasing sprays no later than 5 weeks before harvest, resulted in sulfur residues that were below a concentration consistently shown, in previous literature, to increase hydrogen sulfide production. Therefore, for reds fermented on the skins, one may need to end sulfur applications a month or two before anticipated harvest date, to avoid increased H2S production during fermentation. Another strategy can include early-mid summer sulfur applications with micronized formulations (that are longer lasting/more rainfast) and making the later sulfur applications with a wettable powder formulation that is more quickly reduced by weathering. 

Other late season options include coppers, potassium salt sprays like Nutrol, formulations of potassium bicarbonate, and horticultural oils. Keep in mind that the later oil applications are made, the greater the chance they will negatively impact ripening. Therefore, the current recommendation is to discontinue oil sprays as you near veraison. As for coppers, the same concerns that were mentioned in the section on downy mildew, apply here as well. These materials can be a good way to maintain decent control of powdery mildew on leaves, while minimizing the chances for the development of resistance to the riskier materials used earlier in summer. 

Botrytis bunch rot control; a recap

Hopefully premium wine grape growers have applied fruit-zone leaf removal to open their fruit to better sunlight and aeration and better pesticide penetration. Research has repeatedly shown that there are great benefits of this practice in our wet, humid climate. It is one of the most effective cultural treatments for reducing the susceptibility of the crop to disease of all kinds (especially bunch/sour rots (Figure 3)), and improving coverage, and therefore efficacy, of fruit protection sprays. Though the benefits of leaf removal may generally be reduced the later it is applied after fruit set, it’s not too late yet. However, there is a greater danger of sunburn on your fruit the later this leaf removal is applied. For this reason, mid-late summer leaf removal may be best confined to the east or north side of the trellis (depending on row orientation), especially in areas where very hot mid/late summer temperatures are expected. Fruit zone leaf removal can be mechanized and is probably performed most effectively on vines trained to a vertical shoot positioned (VSP) or some other two-dimensional trellis system with a relatively focused and narrow cluster zone.  

Fungicide sprays for bunch rot are mostly for Botrytis and there are many products to choose from: Vangard, Inspire Super, Switch, Rovral/Meteor, Elevate, Endura, Luna Experience/Sensation, Fracture, Miravis Prime, and the strobilurins (Flint, Pristine, Intuity). Flint and Pristine will also control ripe/bitter rot. Use them sparingly (once or twice per season) and always rotate FRAC groups with every application. Also, pay close attention to pre-harvest intervals on each label. A Botrytis specific fungicide at full bloom and pre closure, especially in varieties with very compact clusters, can be extremely important to reduce ‘latent’ Botrytis infections that continue to accumulate throughout the ‘green’ berry development period. The next fungicide application for Botrytis is made just before or at veraison, as fruit begin to soften and skins become thinner and more easily penetrated by fungal pathogens like Botrytis. After veraison, fruit are also more likely to become injured by birds, insects, excess moisture/humidity (rain cracking), 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.  

Finally, a Botrytis fungicide application about 2-3 weeks after veraison, especially under wet weather conditions, can reduce further rot development during the last stretch of ripening.  However, 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. 

Figure 3. Botrytis bunch rot (above photo) and sour bunch rot (below two photos) in Vignoles.
A close up of a fruit tree

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A group of fruit and vegetables

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Sour rot

Work conducted by Dr. Megan Hall, a former graduate student of Wayne Wilcox at Cornell University, demonstrated how additional pesticide applications during the latter stages of ripening (beginning around 15 brix) can significantly reduce the development of sour rot. Her work has shown that there is a close connection between fruit flies and sour rot development, and that 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. The best results appear to occur when weekly sprays are initiated just before sour rot symptoms are observed (preventive sprays before about 15 brix).  

Good canopy and fertility management is essential to maximizing the effectiveness of your pesticide applications: make sure shoots are tucked and spaced within catch wires and that shoots have not flopped over to block spray penetration into the fruit zone. Also, as stated above, limiting shoot growth after veraison with good fertility management will limit the supply of new green tissue that is hyper susceptible to powdery and downy mildew and will make late season management of these diseases more effective.    

For further reading on this and many other disease management topics, refer to the 2020 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!  

References:

Kwasniewski, M. T., Sacks, G. L., Wilcox, W. F. 2014. Persistence of elemental sulfur spray residue on grapes during ripening and vinification. Amer J of Enol and Viticulture 65: 453-462. 

Vineyard nutrition – webinar review

by Tony Wolf, Professor and Viticulture Extension Specialist, Virginia Tech, and Cain Hickey, Viticulture Extension Educator, Penn State Extension

For a limited time, Penn State Extension is offering free online ...

On June 10, 2020, Dr. Tony Wolf presented Assessing and Managing Vine Nutrient Status in Mature Vineyards as part of the PSU Wine and Grape Team’s weekly webinar series. Tony discussed perspectives on why vineyard nutrition is important, how vineyard nutrition can be assessed, ways to optimize vine nutrient status. Tony reviewed nitrogen management considerations in vineyards that maintain cover crops on the entire vineyard floor and also discussed the popular topic of potassium nutrition (as it relates to wine pH issues). What follows is a brief review of the points discussed. Use this blog post, the information in Tony’s slides, and the Wine Grape Production Guide for Eastern North America as information resources to guide nutrient management in your own vineyard. Here are Tony’s slides from his presentation on June 10:

Assessing vine nutrient status. Soil tests reveal mineral nutrients status of the soil, which may be available for vine uptake. Plant tissue tests reveal mineral nutrient status of the vines themselves and are indicative of the mineral nutrients that are, or are not, effectively taken up from the soil. While plant tissue analysis is most revealing of actual vine nutrient status, both soil and plant tissue tests are important to assess in order to understand and effectively manage vineyard nutrition. Visual observations can also be used to help diagnose mineral nutrient imbalances; however, plant tissue tests should be used to objectively confirm those visual diagnoses. As an extension publication from Rutgers points out, leaf reddening can be caused by numerous issues, including nutrient imbalance or systemic infections. Note that it is not uncommon for young vines to display foliar mineral nutrient deficiency symptoms as their root systems are shallow and small and are thus ineffective at accessing some of the soil nutrients, particularly during drought conditions. Similarly, foliar mineral nutrient deficiency symptoms may also be more common in vines planted on vineyard sections with “lean, rocky soils” (e.g. on highly sloped hillsides, or at the apex of a convex landform).

The two common growth stages to sample grapevine tissues for nutrient analyses are at bloom and “mid-summer,” or veraison. Assessment of vine nutrient status is timely right now as many PA vineyards are at bloom, or will be at bloom, in the near future. It is important to notify the analytical laboratory about the stage at which tissues were sampled as tissue nutrient concentrations change over the course of the season. For example, petioles at bloom generally contain greater nitrogen concentration compared to petioles at veraison.

Bloom (top) and veraison (bottom) are two common growth stages at which grapevine tissues are sampled for nutrient analysis.

Petioles (leaf stems), leaf blades (lamina), or whole leaves (petioles + blades) are all examples of grapevines tissues that can be sampled and submitted for mineral nutrient analysis. It is thus also important to notify the analytical laboratory about the specific tissues (e.g. petioles, blades, whole leaves) being submitted as sufficiency ranges vary between tissues. Historically, petioles have been the most common grapevine tissue used for nutrient analyses in the United States; thus, interpretation of petiole analyses are based on a comparatively larger database relative to leaf blades or whole leaves (petioles + blades). There are several analytical laboratories that will quantify tissue mineral nutrient contents, including the Penn State Agricultural Analytical Services Lab.

Wholes leaves (top left), petioles (top right), and blades (bottom) are grapevine tissues that can be sampled and submitted for nutrient analysis. Note: petioles have historically been the most common grapevine tissues submitted for nutrient analysis in the United States.

Correcting vineyard nutrient imbalances. Optimal soil pH for grapevines ranges from 5.5 to 6.5, which corresponds to the soil pH at which many soil macronutrients and micronutrients are available for plant uptake. Correction of soil pH is more effective before planting, when amendments such as lime can be disked and incorporated into the soil. After a vineyard is established, several commercial fertilizers, lime, and other amendments are available to correct grapevine nutrient imbalances. Soil mineral nutrient analysis, grapevine tissue mineral nutrient analysis, soil type, and vine age should all be taken into consideration when developing a plan to correct vineyard nutrient imbalances.

Nitrogen and under-trellis cover crops. The use of cover crops and grasses in vineyard alleyways is a common practice in order to prevent soil erosion and accommodate tractor and ATV traffic. However, more recently, growing cover crops underneath the vine trellis is becoming common in an attempt to combat vine vigor in humid regions that promote vine vigor through supra optimal water and nutrient availability. Further, as vineyards are established on steeply sloped sites (15 to 20%), under-trellis cover crops provide a means to prevent soil erosion on these particularly prone sites. One potential drawback to under-trellis cover crops is their competition with vines for available nitrogen, and potentially other soil mineral nutrients. Too much resource competition could result in greater vigor reduction than desired, which could ultimately result in poor perennial vine health, decreased crop yields, and premature vine decline. To be brief, the importance of monitoring vine nutrition may be heightened when under-trellis cover crops are used; while nitrogen may be particularly important to monitor, cover crops may also compete with other essential mineral nutrients such as phosphorous. Find more details on cover crops and nitrogen nutrition in Tony’s slides (attached above in this post).

Under-trellis cover crops in a Cabernet Sauvignon vineyard in Virginia. Under-trellis cover crops can help regulate vine vigor. However, under-trellis cover crops may increase the importance of monitoring vineyard nutrition as they can compete with vines for mineral nutrients such as nitrogen.

Potassium and wine pH. With some exceptions (e.g. young vineyards, high pH soils), soil potassium is generally in sufficient quantities and readily available for uptake in eastern US vineyards. Potassium is an important macronutrient and is needed for many physiological and metabolic processes in plants. Thus, potassium deficiency should be avoided. Potassium has a (somewhat weak) positive correlation to grape, must, and wine pH. Due to potential drawbacks of high wine pH (color and microbial instability), excessive vine potassium concentration is undesirable. Limited management tools are available to moderate potassium uptake. However, using rootstocks with V. berlandieri heritage (e.g. 420-A, 100-R), limiting canopy self-shading, and avoiding planting on sites with excessive soil potassium are a few ways to limit potassium concentrations in vine tissues, including harvested grapes. See Tony’s slides (above) for more detail on potassium nutrition. Also, see previous outreach literature on potassium nutrition from Tony Wolf and Michela Centinari.

Please contact Tony (vitis@vt.edu) or Cain (viticulture@psu.edu) if you have further questions about vineyard nutrition. Best wishes for dry and warm weather during bloom and fruit set… and beyond!

Canopy fruit zone management – fundamentals and webinar review

by Cain Hickey, Viticulture Extension Educator, Penn State Extension and Michela Centinari, Assistant Professor of Viticulture, Penn State Department of Plant Science and Penn State Extension, and

For a limited time, Penn State Extension is offering free online ...

On June 3, Cain Hickey and Michela Centinari reviewed the fundamentals of canopy fruit zone management as part of the PSU Wine and Grape Team’s weekly webinar series. Here are the slides from that webinar.

Bloom has started in southeast PA which means bloom will commence in northwesterly PA regions in the coming week or so. Fruit zone leaf removal is timely when implemented during late bloom into the BB-size or pea-size berry growth stages. Below is just a brief review of fruit zone management fundamentals. Use the words below in tandem with the attached slides for a review on how fruit zone management can be effectively implemented in your own vineyard management program.

Well-exposed Merlot clusters at pre-harvest.

Bunch rots. Leaf removal is unnecessary to manage bunch rots in arid/dry regions like eastern Washington and California, but fruit zone leaf removal aids in bunch rot management in PA and other humid growing regions in the eastern US. Leaf removal is more critical to manage rots in rot-prone cultivars relative to those that are less prone (see below about “prioritization of leaf removal”). The slides provided (above) show several cases in which bunch rot was reduced in exposed relative to shaded clusters. The photo of the Cabernet Sauvignon cluster, below, was taken after harvesting that cluster from a deeply shaded canopy; this is a good visual that shows excessive shade can result in rot development.

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This Cabernet Sauvignon cluster has poor color development and Botrytis bunch rot. It was harvested from a shaded canopy. This photo summarizes the effects that shaded fruit zones can have on rot and wine quality potential in humid regions.

Fruit composition. In general, exposed clusters have enhanced “varietal character,” meaning that increased radiation and temperature enhance some of the “positive” sensory impact compounds associated with a particular cultivar. Exposed clusters can have reduced “negative” sensory compounds, such as those associated with undesirable, herbaceous aromas in some Bordeaux reds (e.g., Cabernet Franc). Well-exposed clusters also tend to have lower acidity than those ripened in shade. Thus, one must consider winemaking goals and use fruit zone management to target grape compositional attributes that can increase the chances of achieving the desired wine style. As an extreme example, acid preservation is key for sparkling wine production while color and aroma enhancement, in addition to lower acidity, may be desirable for the production of some white and red wines. In these two unique cases, fruit zone management (in tandem with harvest date) can be used to target the desired compositional attributes.

The shaded (left) and exposed (right) sides of the same two clusters. This photo exemplifies how radiation can change the color (and likely the primary and secondary metabolite profile) of grape berries. Musts composed predominantly of grapes similar to those in the left photo will likely be good for sparkling or “fresh” wine styles while those made primarily with grapes similar to those in the right photo are predicted to produce less acidic, more aromatic wines.

As with bunch rot management, leaf removal may be more critical to enhance color in red grapes grown in the eastern US compared to drier, warmer regions of California, eastern Washington, and southern Oregon. In fact, there are several cases in the attached slides (above) where exposed red grapes had greater anthocyanins and phenolics than shaded red grapes; those studies were conducted in humid growing regions. Studies conducted in hotter and drier regions in the western US have shown that well-exposed red grapes had reduced anthocyanin levels compared to shaded grapes, and this was particularly true on the “hot” or “afternoon sun-exposed” canopy side (e.g. on the west side of north/south-oriented rows). The variable cloudiness experienced in humid, eastern US growing regions attenuates the radiant heating of exposed grape clusters; clouds act as “large leaves” that preclude radiation penetration to the fruit zone. Fruit zone leaf removal thus may be considered a less “risky” practice in the eastern US, where radiation, heat, and air movement around the fruit zone can result in rot-free grapes with a desirable and balanced primary and secondary metabolite profile.

When, how, and to what extent? Common questions regarding optimal leaf removal practice are “when should I remove leaves?”, “how should I remove leaves?”, and “how many leaves should I remove?”.

When? In general, leaf removal is ideally implemented between late bloom and pea size berries. Implementing leaf removal between these growth stages will aid in spray penetration to, and air movement through, the fruit zone at the beginning of the critical period for cluster disease protection (bloom through bunch closure). Pre-bloom (or “during bloom”) leaf removal to excessive amounts (e.g. removal of greater than 4 leaves per shoot) can cause a precipitous decrease in crop yield; therefore, it is judicious to moderate the extent of leaf removal when it is implemented before or during bloom. Implementing leaf removal before pea-size berries will allow berries to acclimate to ambient radiation outside of the canopy starting at an early stage of berry development. That said, some remedial leaf thinning between bunch closure through veraison, and even after veraison, will create a microclimate that is less favorable to rot development and one that will improve wine quality potential. In many cases, a “follow-up” leaf removal pass, or two, will be needed after the initial effort in order to maintain a favorable fruit zone microclimate as lateral shoots and leaves continue to grow throughout the growing season in a humid climate.

Pea-size berries, an arbitrary the growth stage terminus for the implementation of “early season leaf removal”.

How? Leaf removal has been traditionally performed manually by removing leaf blades and petioles and lateral shoots from the fruit zone by hand. Manual leaf removal is still more common than mechanized leaf removal. However, “air pulse” and “cutting” types of tractor-mounted, mechanized leaf removal machines are becoming popular in eastern US vineyards. In fact, a few vineyard and winery enterprises in PA employ the use of a mechanical leaf removal machine. Mechanical leaf removal offers the advantage of practice efficiency, which results in leaf removal implementation across sizable acreage within a narrow time-frame. While speculative, and variable on a case-specific basis, mechanical leaf removal may be worthwhile in vineyards larger than 10 or 15 acres, as upfront cost of the machine may be offset in only a few growing seasons (assuming that leaf removal is viewed as a meaningful practice and is consequently manually implemented across the whole vineyard). It is safe to say that upfront costs will be recouped faster with increasing vineyard size; it would take several growing seasons to offset the upfront costs of a mechanized leaf removal machine in a 5-acre vineyard.

To what extent? In general, leaf removal to an average of one or two leaf layers surrounding the fruit zone should offer some rot management and fruit composition benefits relative to unmanaged fruit zones. In general, removal of two or three leaves per shoot from the fruit zone region will produce an average of one or two fruit zone leaf layers. Leaf removal to greater extents (as in the Merlot photo, below) can reduce rots, increase anthocyanins and phenolics, and reduce acidity, collective traits that may be desirable in the production of some red and white wine styles. Fruit zone leaf removal to such magnitudes (zero leaf layers) may not be commercially feasible due to the amount time and labor required to do so.

A Merlot fruit zone with zero leaf layers from a RESEARCH (not commercial) plot. While such fruit zones may improve spray penetration and rot management and produce less acidic grapes with desirable primary and secondary chemistry, commercial implementation to such extents would be difficult.

Refinement for fruit zone leaf removal prioritization. Fruit zone leaf removal is a vineyard practice used to manage cluster diseases, fruit composition, and crop yield. Like other vineyard practices, the effectiveness of fruit zone management is optimized when it is refined by region and cultivar. Since manual leaf removal (by hand) can be laborious, refining practice by prioritization may help define situations where leaf removal is most needed. Consequently, leaf removal implementation across several acres may not seem overwhelming. As an extreme example, and as mentioned above, fruit zone leaf removal should be a greater priority for fruit quality production in humid relative to arid/dry climates. The climate in southeast PA is humid, subtropical while the climate in northeast and northwestern PA is warm-summer humid, continental. Thus, while rot management is important across PA, one could make a case that rot is particularly pervasive in southeast PA and therefore leaf removal for rot management may be of greater importance in southeast PA relative to northwestern PA. However, leaf removal is still an important tool for improving fruit composition under the cooler conditions and shorter growing seasons typical of north and central PA regions.  

Leaf removal may be “high priority” in white-berried, tight-clustered, thin-skinned, vinifera cultivars, that are highly susceptible to rot. Leaf removal may be “lesser priority” in many hybrid cultivars but “greater priority” in vinifera cultivars. Leaf removal could be prioritized based on phenology. For example, Chardonnay breaks bud and blooms early; therefore, it may be judicious to perform leaf removal earlier in Chardonnay (or Merlot) relative to Petit Verdot or Cabernet Sauvignon. Leaf removal may be unnecessary in cultivars like Norton, Chambourcin, and Charodnel. This is not to say that fruit zone leaf removal should be completely avoided in “low priority” situations. But developing a plan based on cultivar rot susceptibility and/or wine quality potential “gained” will help determine where to commence seasonal leaf removal and where it may be okay to wait for a couple weeks.

While some PA regions are warmer than others, all are humid and are characterized by variable rainfall and cloudiness throughout the growing season. Source: https://upload.wikimedia.org/wikipedia/commons/c/c3/US_50_states_Köppen.svg

Practical “pros and cons”. A practical disadvantage to fruit zone leaf removal is that it requires labor, time, and/or money, regardless if manually or mechanically implemented. Bird and vertebrate pest pressure is variable across sites. However, when clusters are exposed, pests can easily target their bounty. Therefore, the need for pest management and bird netting may be heightened when leaf removal is implemented to the point where clusters are easily visualized. Harvesting visible clusters is much easier and efficient than harvesting clusters surrounded, and hidden, by foliage. Therefore, a benefit to leaf removal is the ability to efficiently harvest; some may make a final “leaf removal pass” nearing the harvest date for this reason.

Due to leaf removal and the subsequent ability to visualize clusters, harvest will be more efficient from the forefront fruit zone relative to the background fruit zone.
Bird netting and other pest management measures may be important to prevent depradation and crop yield loss.

Please contact us (Michela – mzc22@psu.edu; Cain – viticulture@psu.edu) if you have questions related to fruit zone management or other vineyard management practices.

Best wishes on finding a suitable and effective fruit zone management plan. And best wishes for warm and dry weather throughout bloom and fruit set… and beyond!

Grape Disease Management Reminders: Bloom Through Bunch Closure – webinar review

by Dr. Mizuho Nita, Virginia Tech Grape Pathology Extension Specialist and Cain Hickey, Penn State Viticulture Extension Educator

Clusters are within the critical period for cluster protection at the pea-size berry stage

On Wednesday, May 27, Dr. Mizuho Nita presented the Grape Disease Management Reminders: Bloom Through Bunch Closure webinar as part of the Penn State Wine and Grape Team’s weekly webinar series. The webinar focused on optimal grape fungal disease management practices between bloom and bunch closure.

It is important to manage for Botrytis bunch rot during bloom and berry touch stages

The critical period for grape cluster fungal disease protection is between bloom and bunch closure, when grape clusters are highly susceptible to many pervasive fungal diseases. Powdery mildew, downy mildew, black rot, botrytis, ripe rot, and other fungal diseases can infect flowers and young berries. Integrated management options to optimize the control of these diseases during the early grape cluster developmental stage were covered. Please find a PDF version of Mizuho’s presentation here:

And access and follow Mizuho’s grape pathology blog here: http://grapepathology.blogspot.com.

Thanks for the presentation, Mizuho!

Michela Centinari and Cain Hickey will present the Canopy Fruit Zone Management webinar on Wednesday, June 3. This webinar will outline fruit zone management fundamentals in a humid climate and share data to help growers refine their practices. Register for this webinar here: https://bit.ly/2TruM7H.

Best wishes for dry and warm weather in the coming weeks to limit fungal disease pressure and optimize fruit set and crop potential in your vineyards!

Early season insect and disease management in vineyards – webinar review

by Dr. Flor Acevedo, Assistant Professor of Entomology and Arthropod Ecology, Andy Muza, Erie County Extension Educator, and Bryan Hed, Plant Pathology Research Technologist

The Early season insect and disease management in vineyards webinar was held on Wednesday, May 13. The following is a brief recap of information that was presented in that webinar.

IPM fundamentals; phylloxera and mealybugs (Flor). This presentation describes the basis of an integrated pest management program, emphasizes the use of economic thresholds to make control decisions, stresses the importance of using diverse pest control methods to prevent insecticide resistance, and describes two early-season insects pests: Phylloxera and mealybugs. Here is the link to Flor’s presentation: Early_Season_Pest_Management_1

Early season insect management (Andy). This presentation covers nine insects that may appear in vineyards from Bud Swell – Immediate Prebloom stages with accompanying photographs of pests and injury. Also included are practices which are integral to an Integrated Insect Pest Management Program and reference sites for additional information. Here is the link to Andy’s presentation: Early Season Management of Insects in Vineyards – Webinar

Early season disease management (Bryan). This presentation delivers a review of the major diseases that affect grapes in spring and early summer, including Phomopsis cane and leaf spot, black rot, and powdery and downy mildew. The presentation will help growers to i) identify diseases in the field, ii) become familiar with the kinds of weather conditions that contribute to disease development, and iii) how to manage the major diseases during pre bloom and early post bloom stages with chemical and cultural controls. Lastly, we also present the newest chemistries available for control of the major diseases. Here is the link to Bryan’s presentation: Webinar series_Early season disease management_May 13

Dr. Mizuho Nita, Grape Pathology Extension Specialist and Assistant Professor at Virginia Tech, will present the next webinar, Grape Disease Management Reminders: Bloom Through Bunch Closure, on Wednesday May 27th. Here is a short description of the webinar: “The critical period for grape cluster fungal disease protection is between bloom and bunch closure when grape clusters are highly susceptible to many pervasive fungal diseases. Powdery mildew, downy mildew, black rot, Botrytis, ripe rot, and other fungal diseases, can infect flowers and young berries. I will cover integrated management practice options to optimize the control of these diseases during the early grape cluster developmental stage.” Here is the registration link to the webinar: https://extension.psu.edu/grape-disease-management-reminders-bloom-through-bunch-closure

Warmer temperatures have finally arrived in PA… let’s hope these weather patterns remain and we have warm and dry weather over the next several weeks. Best wishes to all!

Early season canopy management – webinar review

Cain Hickey, Viticulture Extension Educator, Penn State Extension

The Penn State Wine and Grape Team held its first webinar of the “2020 weekly webinar series” on Wednesday, May 6th. Here is a link to the slides that were presented during the “Early Season Canopy Management” webinar: Early season canopy management 6 May 2020

Shoot thinning was primary topic covered throughout the webinar. Shoot thinning is best implemented between the 5″ and 18″ shoot growth stages (as soon as inflorescences can be visualized to determine fruitful vs. unfruitful shoots but before tendrils grab neighboring shoots). However, some may wish to delay shoot thinning until the threat of frost has passed or until after the extent of frost damage can be determined (as may be the case in some vineyards this year). Optimal shoot densities are generally between 4 and 6 shoots per linear foot of row, or 24 to 36 shoots per vine in vineyards with between-vine spacing of 6 feet (see below photo for an ideal shoot density). Many will be out shoot thinning their vineyards in PA in the forthcoming weeks. For more on shoot thinning, please see the above slides from the webinar or reference this publication: https://secure.caes.uga.edu/extension/publications/files/pdf/C%201152_1.PDF

Shoot thinning density example_Merlot

Shoot positioning was a topic covered in the May 6th webinar. Shoot positioning is ideally started around bloom; shoot positioning is often needed through the pea-size berries and bunch closure growth stages. Shoot positioning is easiest before tendrils grab neighboring shoots in order to preclude shoot breakage and optimize practice efficiency. Shoot positioning improves canopy light interception and limits fruit zone congestion. While shoot positioning is important in all training systems, proper positioning is particularly critical in divided canopy systems [see below photos of well-positioned shoots in a VSP (top) and Watson (bottom) training system].

RBG_P15,R3

IMG_3675

Fruit zone leaf and lateral removal was a topic also covered in the May 6th webinar. The first fruit zone leaf removal pass is best implemented between bloom and BB-size berries growth stages. Exposing grape clusters at early growth stages allows berries to acclimate to increased radiation levels from an early development stage and also aids fruit zone spray penetration during critical stages for cluster disease protection. Fruit zone leaf and lateral thinning near bunch closure and veraison stages can help manage late season bunch rots. Retaining fewer than an average of 1.5 fruit zone leaf layers can reduce Botrytis bunch rot relative to retaining an average of 3.0 fruit zone leaf layers (see figure in the above slides from the May 6th webinar). Fruit zone leaf removal is used to manipulate fruit composition (color, acidity, phenolics, aromatics) and therefore wine sensory characteristics. The Cabernet Sauvignon cluster (below), which was harvested from a highly shaded fruit zone, exemplifies how reduced airflow and radiation can result in rot and poor color development. For more on fruit zone management, see the above slides from the webinar and join our forthcoming webinar (by Dr. Michela Centinari and myself) on June 3rd.

poor color and rot in CS cluster

Shoot hedging was the final topic covered in the May 6th webinar. Shoot “topping” (if shoots are vertically trained) or “skirting” (if shoots are downward trained) will generally commence near the pea-size berries stage. Vigorous vineyards will require multiple hedging passes throughout the season. The goal of shoot hedging is to manage vegetative growth to limit canopy self shading (see photos, below) and prevent shoots from being damaged by tractors and ATVs. Shoot hedging improves canopy airflow and spray penetration. Lateral shoots will need trimmed as well, particularly after breaking apical dominance in primary shoots after the first hedging pass.

pre-hedgepost-hedge.tif

Here are links to publications that outline seasonal viticulture and pest management practices based on vine phenology (growth stage): https://extension.uga.edu/publications/detail.html?number=C1151 (University of Georgia, spotted lanternfly not included); https://www.pubs.ext.vt.edu/content/dam/pubs_ext_vt_edu/ENTO/ento-339/ENTO-339.pdf (Virginia Tech, spotted lanternfly included). The intention of these publications are to inform readers about timely implementation of vineyard management practices.

Best wishes for a great start to the 2020 season!

Welcome 2020 growing season

By Bryan Hed, Andy Muza, Michela Centinari, Lauren Briggs, Penn State Extension 

Well, it is that time of year again when we are poised to embark on a new grape growing season in Pennsylvania. Are you up to the challenge?

Over the past two weeks, several below freezing events have occurred in many Pennsylvania vineyards. While many grape varieties in the colder parts of the Commonwealth (e.g., Erie) are not at bud burst yet, grapevines are already at or are close to bud burst in warmer regions, like in southeast or south-central PA. It is too early to estimate the impact of these frost events on buds or shoots, which are just starting to emerge, but it is crucial to prepare in case vines sustain frost damage and require a management adjustment. Dr. Tony Wolf, Viticulture Extension Specialist at Virginia Tech, just published a thorough review of vineyard frost damage scenarios and considerations for addressing the damage in the last issue of ‘Viticulture Notes’ (April 2020). We have attached a pdf copy of ‘Viticulture Notes’ to the Penn State V & E newsletter. In case you are not a subscriber and don’t have access to Virginia Tech or Penn State newsletters, you can find important information on ‘what’s next after a frost event’ in past Viticulture Notes issues available online: 1) What can be expected with frost-injured vines?, published in May 2002, and 2) ‘Question from the field’ in the Viticulture notes May 2010 issue (page 2-5). If you are interested in learning more about frost protection strategies, here is a link to a comprehensive extension bulletin on Vineyard frost protection written by Cain Hickey, incoming Penn State viticulture extension educator, and his colleagues at the University of Georgia Extension.  We would like to hear from Pennsylvania growers if their vines sustained frost damage. Please email us at: psuwineandgrapes@psu.edu.

Commercial grape growers in Pennsylvania should obtain a copy of the 2020 New York and Pennsylvania Pest Management Guidelines for Grapes which provides up-to-date pest management information for those producing grapes in Pennsylvania and New York State. It has been designed as a practical guide for grape producers, pesticide dealers, and others who advise those involved in grape production.   The Guidelines can be purchased at TheCornellStore https://www.cornellstore.com/2020-PMEP-Guide-for-NY-and-PA-Grape-Mgmt

Early Season Disease Control.

Below we summarized recommendations for early season diseases and insect management. Recommendations will be updated soon to provide help with pest and disease management decisions for the immediate pre-bloom period and beyond. 

The first disease issue during early shoot growth is typically Phomopsis cane and leaf spot, caused by the fungus, Phomopsis viticola. Prolonged wetting/rainfall during the early shoot growth stages (late April/early May) are the conditions that favor the development of this disease. Infections can leave scabby black lesions and cankers on the first few nodes/internodes of shoots and on inflorescences (Figures 1,2,3). Infections of inflorescences can advance into berries way down the road, during ripening, and result in problems with fruit rot after veraison (months after the infection period took place!), so good early disease prevention is important. Chemical control: Phomopsis management with fungicides should start at the 3-5” shoot stage and continue through the first or second post bloom spray, after which inoculum of the fungus is generally spent. Mancozeb products, captan, and ziram are generally the most effective materials for Phomopsis control.

Figures 1, 2, 3. Numerous lesions of Phomopsis concentrated at the base of the oldest internodes result in larger scabby areas that weaken the shoot and ‘bite off’ sections of inflorescences.

Next on our list is powdery mildew. Powdery mildew is caused by a fungus Uncinula necator. which infects and grows on any green vine tissues. The first infection periods occur when we get at least a tenth (0.1) of an inch of rain and the temperature is 50°F or more. These “primary” infections in spring require rainfall for spore release, but subsequent cycles that result from primary infections, do not require rainfall. Optimum weather for this fungus is the norm through most of the summer, especially in southern Pennsylvania, and when we reach bloom, nearly every day is an infection period, rain or shine. Chemical control: Sulfur applications (on sulfur tolerant varieties) OR oils are an inexpensive, effective way to deal with early season mildew, but never mix them or apply them within two weeks of each other. Fungicide sprays can begin as early as 1” and/or 3-5” of shoot growth in vineyards of high susceptibility and with heavy disease development in the previous year. Generally speaking, the more mildew you had at the end of the season last year, the earlier you need to begin controlling it this spring. Vineyards of lesser susceptibility, and where disease was reasonably under control in the previous year, can usually wait until 8-12” shoots to commence powdery mildew sprays.

Black rot caused by the fungus Guignardia bidwellii can also require attention early in spring, especially if you saw more than a little of it last season and you did not remove all clusters from the trellis during dormant pruning. Chemical control: Chemical control can begin as early as 3-5” and again at 8-12” shoots, especially if black rot was a serious problem in the previous year. Chemical control options for early black rot control generally include a mancozeb, ziram, or captan product. So, if you’re applying one of these materials to protect shoots from phomopsis, you’ll also control black rot. Active ingredient classes like the strobilurins (azoxystrobin, kresoxim-methyl, pyraclostrobin, trifloxystrobin) and the sterol inhibitors (tebuconazole, tetraconazole, difenoconazole, myclobutanil) are also quite effective, but are generally reserved for 8-12” shoots or later in the spray program. The strobilurins and sterol inhibitors are more rainfast than the old standards and the sterol inhibitors have the capacity to stop the progress of an existing infection if applied within about 3 days after the infection period.

Downy mildew does not become active until about the 5-6 leaf stage of grapevine development, which is generally about 3 weeks before bloom. The first infections on leaves appear as yellowish ‘oil spots’ on the top of the leaf that coincide with a white, fluffy or downy patch of sporulation on the lower surface. On young shoots and clusters, early symptoms may first cause cluster rachises and shoots to thicken and curl.  Inflorescences and fruit clusters are most susceptible from about 2 weeks pre-bloom to about 2 weeks post bloom. Chemical control: Starting out with a fungicide application just before the 5-6 leaf stage. Mancozeb is very effective on downy mildew (more effective than captan and ziram), there are no concerns with the development of resistance (so you’ll save the ‘big guns’ until the critical bloom period), and mancozeb is safe for most (all?) grape varieties. Mancozeb products, captan, and ziram are strictly surface protectants and are subject to removal by rainfall, so if you are relying on them, you may have to reapply them every 7-10 days under high rainfall conditions to maintain good control. Fortunately, there are no worries about resistance to these.

Cultural control to help reduce all fungal diseases: Maintaining an open canopy will help fruit and other susceptible tissues dry out as quickly as possible after a rainfall and will also improve fungicide penetration and coverage of the fruit. Also, the first downy mildew infections in spring often occur on shoots and sucker growth near or on the ground, and prompt elimination of this tissue can delay disease in the canopy.

Insects of Concern in the Vineyard During Bud Swell to Bud Burst.

It is hard to believe that I am talking about preparing to scout for insects in the vineyard when I look out my window and see snow falling today (4/20/20) in Erie County, PA. But buds are starting to swell in Erie county, and this means that the first insects of economic concern will start to appear in vineyards. Both grape flea beetle and climbing cutworms feed on grape buds during the bud swell stage. Depending on variety, some vineyards in parts of Pennsylvania may be past the bud swell stage, while in other regions already passed bud burst. If vine growth is at the 1-inch stage, then concern of economic injury from these pests is over.

Grape flea beetle (GFB). These insects overwinter as adults and emerge in the spring to feed on buds of grapevines and Virginia creeper. Adult beetles are small (about 3/16”) and described as metallic blue in coloration (Figure 4). Beetles are most active on warm, sunny days and will jump like a flea when disturbed. Populations of grape flea beetle are usually localized around their overwintering sites (e.g., wooded or overgrown areas) around the edges of vineyards. Feeding by GFB adults can result in entire buds being eaten or enough tissue consumed that the developing bud is destroyed (Figure 5). Control. Scout vineyard rows bordering wooded or overgrown areas throughout the bud swell stage. Examine canes for injured buds and/or presence of adult beetles. If bud injury levels of 2% or greater are recorded then an insecticide treatment is advised. Insecticides listed in the 2020 New York and Pennsylvania Pest Management Guidelines for Grapes which are labeled for grape flea beetle include: Sevin 80 Solupak, Sevin 4F, Sevin XLR Plus; Danitol 2EC; Baythroid XL; and Leverage 360. (Grape Flea Beetle fact sheet available at:  https://ecommons.cornell.edu/handle/1813/43101 ).

Figure 4. Adult Grape Flea Beetle. Photo: https://ecommons.cornell. edu/handle/1813/43101
Figure 5. Flea beetle injured grape bud. Photo: https://ecommons.cornell.edu/han-dle/ 1813/43101

Climbing Cutworm – about a dozen species of cutworm larvae have been documented in vineyards. These larvae are immature stages of noctuid moths. Climbing cutworm larvae feed on grape buds during the swell stage. A common climbing cutworm found in Pennsylvania vineyards is the spotted cutworm (Figure 6). These larvae have a brown to gray coloration with darker stripes along the body. During the day cutworm larvae hide under stones or weeds beneath vines. Larvae climb vines during the night to feed on buds. Vineyards with weed cover under the trellis and areas with sandy soils are at greater risk for injury. Be aware that bud feeding by cutworm larvae can be confused with grape flea beetle injury. Control. Scout frequently during the bud swell stage. Examine canes for injured buds and if injury is detected then examine weeds/soil beneath vines for presence of larvae. If bud injury levels of 2% or greater are recorded, then an insecticide treatment is advised.  Some of the insecticides listed in the 2020 New York and Pennsylvania Pest Management Guidelines for Grapes which are labeled for climbing cutworm include: Sevin 80 Solupak, Sevin 4F, Sevin XLR Plus; Danitol 2EC; Baythroid XL; and Leverage 360 (Climbing Cutworm fact sheet available at:  https://ecommons.cornell.edu/handle/1813/43085 ).

Figure 6. Spotted Cutworm Larva. Photo: https://ecommons.cornell.edu/han-dle/ 1813/43085

Spotted Lanternfly Emergence.

Penn State researchers estimate that spotted lanternfly emergence will begin around the first week of May in southeast Pennsylvania this spring. Populations are predicted to be high this season based on the large number of egg masses laid last fall and the warmth of the winter. Several insecticides are effective against nymphs and labeled for spotted lanternfly (see the table from PSU Extension’s publication below. Note: Some of the insecticides tested are not labeled for SLF on grapes in PA). It is likely that standard early season applications of insecticides for other vineyard pests (e.g. Japanese beetle) will also kill any SLF nymphs present. Ultimately, early season spotted lanternfly treatments may reduce spring nymph populations but may not affect infestation by adults later in the season, as adult populations are quite mobile. See a larger version of the below table in this document: https://extension.psu.edu/spotted-lanternfly-management-in-vineyards.

Enough for now, with everything growers have on their plates at this time. As we stated earlier, pest and disease recommendations will be updated soon to help with later stages of grapevine development, so stay tuned. 

The Penn State Wine & Grape Team is hosting an online “office hour” session

The Penn State Wine & Grape Team is hosting an online “office hour” session on Tuesday, April 14, from 3 p.m. to 4:30 p.m., to answer any questions you have about your vineyard, winery, and tasting room. 

As we explore additional ways to connect with the industry members, the team’s Extension educators and faculty are hosting this Zoom session to answer questions you might have. For example, timely questions related to vineyard management, issues you are experiencing in your winery cellar, marketing strategies for your tasting room, and related. 

We look forward to meeting and talking with you.

Sincerely,

The Penn State Wine & Grape Team

How can you join the Zoom meeting? Please note that for all of these options you will need to enter this password to proceed: 370146. See the attached PDF, below, for screenshots to lead you through the process when accessing the meeting using a web browser. 

To access these Zoom meetings with a PC, Mac, Linux, iOS or Android go to:  https://psu.zoom.us/s/229078158

If using an iPhone one-tap (US Toll):  +13126266799,,229078158# or +16468769923,,229078158#

Or to call in dial:
    +1 646 876 9923 (US Toll)
    Meeting ID: 229 078 158

International numbers available: https://psu.zoom.us/u/aWuWELGMj

Meeting ID: 229 078 158


SIP: 229078158@zoomcrc.com

Password: 370146

Please click on the following website to access instructions on how to join a meeting:  https://support.zoom.us/hc/en-us/articles/201362193-Joining-a-Meeting

If you are having difficulties accessing these meetings, please contact the Penn State Wine & Grape Team at psuwineandgrapes@psu.edu