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/
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.
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.
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.
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.
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
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.
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!
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.
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 ).
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 ).
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
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
Planning for the 2020 Season: Resistance Management Guidelines for Fungicides Used for Downy Mildew of Grape
By Andy Muza, Penn State Extension – Erie County
Downy mildew has been a major problem for many grape growers in Pennsylvania (outside of Erie County) over the last few years. This is no surprise, considering the amount of rainfall that has occurred throughout areas of PA during the past few seasons. As a result, downy mildew inoculum levels may be high in many vineyards at the start of the 2020 growing season.
Therefore, in preparation for planning your downy mildew management program (and reducing the risk of fungicide resistance) for the 2020 season, the following information from the 2019 New York and Pennsylvania Pest Management Guidelines for Grapes is provided (1).
Fungicide Resistance Risks
Fungicides that have similar chemical structures and share common modes of action are classified together into Groups. Resistance risk for each fungicide group is considered as either: LOW, MEDIUM, HIGH or Resistance not known (2). “The likelihood and speed of resistance development largely depends upon whether the fungicide affects a single metabolic site (single-site) within the fungus or multiple sites (multi-site). High-risk products have a single site of action or those for which disease resistance populations have been discovered. Medium-risk products are associated with fungicides where resistance is seen with the mutation of more than one target site or resistance formation is less frequent than that of high risk. Low-risk fungicides are characterized by a very rare or undocumented occurrence of resistance after many years of use” (3).
FRAC Codes
The Fungicide Resistance Action Committee (FRAC) developed a Code, consisting of letters and/or numbers, to distinguish different fungicide groups based on their mode of action (2). Each fungicide product includes a FRAC Code on the fungicide label.
Eleven different modes of action groups [FRAC Codes – M 01, M 03, M 04, 4, 11, 21, 22, 33, 40, 43, 45] are included in Tables 3.2.1 and 3.2.2 on pages 46 – 48 of the 2019 New York and Pennsylvania Pest Management Guidelines for Grapes that are rated excellent (++++) to good (+++) for management of downy mildew (1).
NOTE: PRESIDIO (fluopicolide – FRAC Code 43) is not included in the information below. The manufacturer has pulled the grape use from the PRESIDIO label, and any new product will not be legal for use on grapes. However, grape growers will be able to legally use up old stock of PRESIDIO with the grape use pattern on the label.
Multi-Site Fungicides
- FRAC Code M 01 – The common name of the active ingredient in this group is copper.
- FRAC Code M 03 – The common names of active ingredients in this group include mancozeb and ziram.
- FRAC Code M 04 – The common name of an active ingredient in this group includes captan.
Resistance Risk: LOW. No signs of resistance developing.
Fungicide Products containing active ingredients listed within FRAC Codes: M 01, M 03, M 04
- COPPER products (several formulations) – copper
- DITHANE, MANZATE and PENNCOZEB products – mancozeb
- ZIRAM – ziram
- CAPTAN products – captan
Resistance Management Guideline: Multi-site fungicides are important tools in a resistance management program (4). Copper, mancozeb and captan products provide good control of downy mildew while ziram provides moderate control. These fungicides can also be used, as either a tank mix partner or as a co-formulation product, with fungicides that are designated as HIGH or MEDIUM risk for downy mildew resistance. Use of multi-site fungicides, as either a co-formulation product or as a tank mix partner, can: improve disease control; reduce the risk of resistance development; or provide a measure of control if resistance is already present in a vineyard (5).
Be sure to read the label of the products used for information such as: maximum allowable rates/A/season, compatibility and phytotoxicity precautions, preharvest and reentry intervals.
FRAC Code 4 – The common name of an active ingredient in this group includes mefenoxam.
Resistance Risk: HIGH
Fungicide Products containing an active ingredient listed within FRAC Code 4
- RIDOMIL GOLD/COPPER – a co-formulation product containing mefanoxam + copper hydroxide.
- RIDOMIL GOLD MZ WG – a co-formulation product containing mefanoxam + mancozeb.
RESISTANCE WARNING: Ridomil Gold is an outstanding fungicide against downy mildew, but the causal organism (Plasmopara viticola) can develop resistance to it very quickly when the product is used intensively. This fungicide became ineffective in the humid viticultural regions of Europe soon after its introduction many years ago.
Resistance Management Guideline: To reduce the risk of developing resistance:
- DO NOT make more than two applications of RIDOMIL GOLD per season (MZ and copper formulations combined). The conservative (safer) strategy is only one application per season.
- DO NOT make two consecutive applications of RIDOMIL GOLD (MZ and/or copper formulations) per season.
- ROTATE RIDOMIL GOLD products with an unrelated fungicide (different Frac Code) having efficacy against downy mildew.
- DO NOT attempt “rescue” treatments with RIDOMIL GOLD if an epidemic is in progress.
FRAC Code 11 – Common names of active ingredients in this group include: azoxystrobin, kresoxim-methyl, mandestrobin, pyraclostrobin, trifloxystrobin and fenamidone.
Resistance Risk: HIGH
Fungicide Products containing active ingredients listed within FRAC Code 11
- ABOUND, AZAKA 2.08 SC – azoxystrobin
- QUADRIS TOP – a co-formulation product containing azoxystrobin + difenoconazole
- TOPGUARD EQ – a co-formulation product containing azoxystrobin + flutriafol
- DEXTER MAX – a co-formulation product containing azoxystrobin + mancozeb
- SOVRAN 50WG – kresoxim-methyl
- INTUITY 4SC- mandestrobin
- PRISTINE 38WG – a co-formulation product containing pyraclostrobin + boscalid
- FLINT, FLINT EXTRA – trifloxystrobin
- LUNA SENSATION – a co-formulation product containing trifloxystrobin + fluopyram
- REASON – fenamidone. Although not a strobilurin, fenamidone has the same biochemical mode of activity. Cross resistance has been shown between all FRAC Code 11 fungicides.
RESISTANCE WARNING: Downy mildew resistance to the strobilurin (FRAC Code 11) fungicides has occurred in multiple vineyards throughout New York, various mid-Atlantic regions, and probably Pennsylvania. It is now risky to rely on FRAC Code 11 fungicides for control of either downy mildew or powdery mildew. When such resistance occurs, none of the FRAC Code 11 fungicides will provide commercial control of downy mildew, and they must be combined with an effective rate of an unrelated fungicide to avoid potential crop loss.
Resistance Management Guideline:
- DO NOT make more than two applications per season of all FRAC Code 11 products (combined).
- DO NOT make two consecutive applications of a FRAC Code 11 product.
- ROTATE FRAC Code 11 products with an unrelated fungicide (different Frac Code) having efficacy against downy mildew.
FRAC Code 21 – The common name of an active ingredient in this group includes cyazofamid.
Resistance Risk: Unknown but assumed to be MEDIUM to HIGH.
Fungicide Product containing an active ingredient listed within FRAC Code 21
- RANMAN – cyazofamid
Resistance Management Guideline:
- DO NOT make more than two applications per season of RANMAN.
- DO NOT make two consecutive applications of RANMAN.
- ROTATE RANMAN with an unrelated fungicide (different Frac Code) having efficacy against downy mildew.
- Tank Mixing RANMAN with a phosphorus acid product (e.g., ProPhyt, Phostrol) has provided excellent control of downy mildew.
FRAC Code 22 – The common name of an active ingredient in this group includes zoxamide.
Resistance Risk: MEDIUM
Fungicide Product containing an active ingredient listed within FRAC Code 22.
- GAVEL 75DF – a co-formulation product containing zoxamide + mancozeb. The resistance risk for zoxamideis MEDIUM and the resistance risk for mancozeb is LOW.
This product when applied at the labeled rate of 2.0 – 2.5 lbs/A provides the same amount of mancozeb as 1.8 – 2.2 lbs of standard 75DF formulations of other mancozeb products (e.g., Dithane, Penncozeb). For control of diseases other than downy mildew, GAVEL 75DF should be applied with sufficient quantities of another mancozeb product to provide a dosage equivalent to 3 – 4 lbs/A of the 75DF formulations of a solo mancozeb product.
Resistance Management Guideline:
- DO NOT make more than three applications per season of GAVEL 75DF.
- DO NOT make more than two consecutive applications of GAVEL 75DF.
- ROTATE GAVEL 75DF with an unrelated fungicide (different Frac Code) having efficacy against downy mildew.
FRAC Code 33 – The common name of an active ingredient in this group includes phosphorous acid (various formulations). A number of products containing phosphorous acid (also called “phosphite” or “phosphonate”) are sold as nutritional supplements and “plant conditioners,” but only a few are registered for disease control on grapes; two that have proven efficacy in NY spray trials are ProPhyt and Phostrol, although others (e.g., Rampart, Reveille, Fosphite) have been effective in commercial use.
Resistance Risk: MEDIUM
Fungicide Products containing active ingredients listed within FRAC Code 33
- PHOSTROL, PROPHYT, RAMPART, etc. – phosphorous acid
RESISTANCE WARNING: Downy Mildew resistance to phosphorous acid products has occurred when they have been used intensively on other crops, and a reduction in performance has been noted in several New York vineyards over the past few years, although resistance has not been proven conclusively.
Resistance Management Guideline:
- DO NOT make more than three applications per season of phosphorous acid products.
- DO NOT make more than two consecutive applications of a phosphorous acid product.
- ROTATE phosphorous acid products with an unrelated fungicide (different Frac Code) having efficacy against downy mildew.
FRAC Code 40 – Common names of active ingredients in this group include dimethomorph and mandipropamid.
Resistance Risk: MEDIUM
Fungicide Products containing active ingredients listed within FRAC Code 40.
- ZAMPRO – a co-formulation product containing dimethomorph + ametoctradin
- REVUS 2SC – mandipropamid
- REVUS TOP 4SC – a co-formulation product containing mandipropamid + difenoconazole
RESISTANCE WARNING: Downy mildew resistance to FRAC Code 40 fungicides has been found in three vineyards in Virginia and one in North Carolina in 2018.
Resistance Management Guideline:
- DO NOT make more than three applications per season of Frac 40 products (ZAMPRO, REVUS/REVUS TOP) combined.
- DO NOT make more than two consecutive applications of a Frac 40 product.
- ROTATE Frac 40 products with an unrelated fungicide (different Frac Code) having efficacy against downy mildew.
FRAC Code 45 – The common name of an active ingredient in this group includes ametoctradin.
Resistance Risk: assumed to be MEDIUM to HIGH.
Fungicide Product containing an active ingredient listed within FRAC Code 45:
Zampro – a co-formulation product containing ametoctradin + dimethomorph
Resistance Management Guideline: Same as listed for ZAMPRO under FRAC 40 above.
References:
- 2019 New York and Pennsylvania Pest Management Guidelines for Grapes. Weigle, T. H., and A. J. Muza. Cornell and Penn State Extension. 168 pp. https://cropandpestguides.cce.cornell.edu/Guidelines/2019/Grapes/index1.aspx
- Frac Code List 2019: Fungal control agents sorted by cross resistance pattern and mode of action (including FRAC Code numbering).https://www.frac.info/docs/default-source/publications/frac-code-list/frac-code-list-2019.pdf
- Raised Resistance Risks.https://pesticidestewardship.org/resistance/fungicide-resistance/raised-resistance-risks/
- Importance of multisite fungicides in managing pathogen resistance. https://www.frac.info/docs/default-source/publications/frac-recommendations-for-multisites/frac-statement-on-multisite-fungicides-2018.pdf?sfvrsn=19544b9a_2
- FRAC recommendations for fungicide mixtures designed to delay resistance evolution. https://www.frac.info/docs/default-source/publications/frac-recommendations-for-fungicide-mixtures/frac-recommendations-for-fungicide-mixtures—january-2010.pdf?sfvrsn=7e9d419a_4
A Complex Late Season Bunch Rot
By Andy Muza, Penn State Extension – Erie County
Harvest season in Pennsylvania is upon us or soon will be (depending on your varieties and where your vineyards are located), so late season bunch rots become a major concern for wine grape growers. A complex late season rot not controlled by fungicide applications is Sour Rot.
Question: What can you get when you combine: tight clustered varieties; yeast; acetic acid bacteria; berry injury; and fruit flies?
Answer– Sour Rot.
Over the last few years extensive research, by Wendy McFadden-Smith and her colleagues at OMAFRA in Ontario and Megan Hall, Wayne Wilcox and Greg Loeb at Cornell, has greatly increased our knowledge of the Sour Rot syndrome. The following information is a brief summary of what the research revealed.
How do you know if the rot in your clusters is sour rot?
Sour rot has been defined by Megan Hall and Wayne Wilcox as, “a specific syndrome, characterized by the oxidation of the berry skin and the smell of acetic acid (vinegar) emanating from diseased berries.”
Therefore, field diagnosis is by both sight and smell. In white varieties, berry skins turn brown and in red varieties, berries have a reddish – purple discoloration (Figure 1). Infected berries degrade and have a vinegarlike odor. This syndrome is usually associated with large populations of fruit flies.
Development of sour rot
A wide variety of yeasts and bacteria naturally occur on and in grapes in the vineyard. Yeasts, whether in the vineyard or in the wine cellar, do what they do best. That is, they convert sugars in grape juice to alcohol (i.e., ethanol). Likewise, acetic acid bacteria (e.g., Acetobacter spp, Gluconobacter spp), whether in the vineyard or in the wine cellar, do what they do best. These bacteria convert ethanol into acetic acid (i.e., vinegar) in the presence of oxygen. Injured berries provide the gateway for bacteria, oxygen and insects (most commonly fruit flies) to enter berries.
The presence of fruit flies has been discovered to be a key component in the sour rot syndrome (Figure 2). Experiments showed that without fruit flies the symptoms of sour rot did not develop. Fruit flies spp. (e.g., common fruit fly, Drosophila melanogaster; and spotted wing drosophila, Drosophila suzukii) are attracted to injured berries via the smell of acetic acid and ethanol. As fruit flies feed and deposit eggs they spread yeast and bacteria from their bodies or gut contents throughout the clusters. However, the complete role that fruit flies contribute in sour rot development is not yet fully understood. Megan Hall, now at the University of Missouri, is continuing research to determine the complete picture of the fruit fly connection in sour rot development.
Management
Cultural practices– Cultural practices play a critical role in the management of grape diseases and sour rot is no exception. Canopy management techniques, such as shoot thinning/positioning and leaf removal around clusters, provide better air flow and sun exposure thus reducing a more favorable microclimate for disease development. In addition, this opens up the canopy to better spray penetration.
Hall and Wilcox also showed that a vertical shoot position training system significantly reduced sour rot compared to a high wire trellis system. This should be taken into consideration if you are planning on planting a new vineyard with tight clustered, thin skinned varieties.
Berry Injury– The management of berry injury can be broken into 2 categories:
1) What we cannot control, and 2) What we can control.
- What we cannot control – the weather.
The most widespread cause of late season injury to berries in our region is due to rainfall events which cause berries to split or pull away from their pedicels. Tight clustered, thin skinned varieties (such as Pinot Noir, Riesling, Vignoles, etc.) are the most susceptible to this injury and to sour rot and botrytis development.
Unfortunately, tropical storms can and sometimes do occur around harvest, spreading excessive rainfall, resulting in berry splitting. The best we can hope for is that heavy rainfall events do not occur during harvest. - What we can control– injury caused by birds, diseases and insects.
Any injury can predispose berries to invasion from a variety of fungi, yeasts and bacteria that can result in bunch rots. Management of: birds (through use of netting and/or scare devices); diseases (through effective use of fungicides); and insects, particularly grape berry moth (through well timed insecticide applications) are important components in the reduction of berry injury levels.
Fruit flies, acetic acid bacteria and yeasts– Fungicides used for grape disease management are effective against filamentous fungi (e.g., Botrytis, powdery mildew, etc.) but not effective against yeasts and bacteria. Therefore, fungicides are not directly effective in sour rot management.
However, research conducted at Cornell in the Finger Lakes Region did show that applications of an antimicrobial material and insecticide applications against fruit flies are directly effective. Specifically, the most effective treatment regime consisted of weekly applications of Mustang Maxx insecticide (a.i. – zeta-cypermethrin) and OxiDate 2.0 (an antimicrobial, a.i. – includes hydrogen dioxide and peroxyacetic acid) starting when fruit reached 15 Brix and before any sour rot symptoms were evident. This regime (insecticide and antimicrobial) provided an average of 69% control of sour rot. However, the insecticide alone treatments in 2015 & 2016, still provided 57% and 40% control, respectively.
It is important to mention that in 2018 in a Finger Lakes, NY vineyard a local population of fruit flies have developed resistance to Mustang Maxx, malathion and Assail. I cannot overemphasize the importance of rotating different classes of insecticides (i.e., different modes of actions/different IRAC numbers) for fruit fly management in order to avoid the development of insecticide resistance. There are a number of registered insecticides with different modes of action and short preharvest intervals (PHI) which are effective against fruit flies. These include: Assail 30 SG (IRAC 4A, 3 days PHI); Delegate WG and Entrust SC (IRAC 5, 7 days PHI); Malathion 5EC or 57% or 8 Aquamul (IRAC 1B, 3 days PHI); and Mustang Maxx (IRAC 3A, 1 Day PHI). Greg Loeb and Hans Walter- Peterson (Cornell) suggest using a variety of different classes of insecticides in a season (refer to articles – Managing Fruit Flies for Sour Rot in 2019 and Suggested Fruit Fly Insecticide Program for 2019 under Additional Links).
Management of Sour Rot in the Winemaking Process
Like it or not, winemakers may be forced to deal with volatile acidity issues due to sour rot. Since I am not an enologist, I will suggest 2 articles below which provide information for dealing with this problem. In addition, winemakers can also contact Molly Kelly, Enology Extension Educator, Penn State at (e-mail: mxk1171@psu.edu, phone: 814-865-6840) for assistance.
Managing Sour Rotted Fruit in the Cellar. Denise Gardner. Updated: May 5, 2016.
https://extension.psu.edu/managing-sour-rotted-fruit-in-the-cellar
Sour Rot Stinks: Some Strategies for managing Volatile Acidity. Chris Gerling. Veraison to Harvest. Statewide Vineyard Crop Development, Update #5. Sept. 2018.
https://grapesandwine.cals.cornell.edu/sites/grapesandwine.cals.cornell.edu/files/shared/Veraison-To-Harvest-2018-Issue-5.pdf
Additional Links
For more comprehensive information concerning Sour Rot research and management of fruit flies, I highly recommend checking out the links below.
Defining and Developing Management Strategies for Sour Rot. Megan Hall, Gregory Loeb, and Wayne Wilcox. Appellation Cornell – Research News from Cornell’s Viticulture and Enology Program, Research Focus 2017-3.
https://grapesandwine.cals.cornell.edu/sites/grapesandwine.cals.cornell.edu/files/shared/Research%20Focus%202017-3.pdf
Managing Fruit Flies for Sour Rot in 2019. Greg Loeb and Hans Walter-Peterson. Lake Erie Regional Grape Program Newsletter, September 2019, pages 6-8. https://nygpadmin.cce.cornell.edu/pdf/newsletter_notes/pdf116_pdf.pdf
Suggested Fruit Fly Insecticide Program for 2019. Hans Walter-Peterson and Greg Loeb. Lake Erie Regional Grape Program Newsletter, September 2019, page 9. https://nygpadmin.cce.cornell.edu/pdf/newsletter_notes/pdf116_pdf.pdf
Mid and Late-Season Grape Disease Control
By: Bryan Hed, Plant Pathology Research Technologist, Erie County
2018 was a disastrous season for many grape growers in Pennsylvania. Excessive rainfall occurred almost everywhere below Interstate 90 and some growers have told me it was their worst crop, ever. Now, looking at various NEWA weather station locations across PA, it’s been shaping up to be another wet season in a lot of places, yet again. May rainfall was heavy in all but the Lake Erie region, with 6-9 inches of precipitation recorded across most of the state. Conditions lightened up a bit in June but were still wetter than average in most places (even in the Lake Erie region). But now, conditions in July actually appear to be drying up in a few (but not all) locations, giving some growers a break in terms of fungal disease management.
Hopefully, most premium wine grape growers have already applied fruit-zone leaf removal to open their fruit to better sunlight and aeration and better pesticide penetration. The benefits of this practice cannot be overemphasized, and in our wet, humid climate, it is one of the most effective cultural treatments we know of for reducing the susceptibility of the crop to disease of all kinds (especially bunch/sour rots), and improving coverage, and therefore efficacy, of fruit protection sprays. If you haven’t yet applied this treatment, it is not too late, though the benefits of leaf removal may be reduced the later it is applied. There is also a greater danger of sunburn on your fruit the later it is applied, and for that reason you may want to confine your leaf removal at this time 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.
And with that, let’s talk about diseases and their control for the remainder of the season. Much of this information has already been covered in previous blogs in previous years, and I have borrowed some information from those blogs here (no need to reinvent the wheel).
Downy mildew
As you know all too well, wet years are ideal for downy mildew. At about this time, the fruit of most grape varieties are resistant to this disease, but cluster stems may remain susceptible for a couple of weeks after fruit are resistant, and leaves will remain susceptible all season. If the weather remains wet or wet weather returns, downy mildew can be a serious threat to grape canopies and ripening, until harvest. Continue scouting for the distinctive white ‘downy’ sporulation on the undersides of leaves. Growers of susceptible varieties need to keep closely monitoring their vineyards for active sporulation and use that information in combination with the DMCast model on NEWA (http://www.newa.cornell.edu/) to determine if and when infection periods occurred.
If you see active, white sporulation on the undersides of leaves, the downy mildew pathogen is capable of spreading quickly under wet conditions. Even humid nights that result in heavy dews by morning, can continue to fuel downy mildew development. Once out of control, it can strip vines of their leaves and effectively end fruit ripening for this year and shoot ripening for next year’s crop. It could also mean your grapevines will go into winter dormancy at less than optimal hardiness and more vulnerable to damage by severe cold, leading to another bout with crown gall and trunk renewal to have to deal with for years to come. All these issues are connected, and this is definitely a disease you want to keep under very tight control, especially on Vitis vinifera.
If you find yourself trying to control this disease well into the ripening period, be aware that your list of chemical control options will start to dwindle as we get within 30 (Ranman, Reason), then 21 (Ziram), then 14 (Revus, Revus Top, Zampro) days of harvest, until in the end you’ll be left with Captan, copper, and phosphorous acid products (0 day pre-harvest interval), which have their shortcomings, discussed below.
Another reason to keep this disease well under control is that products like Ranman, Reason, Revus/Revus Top, and Zampro, all contain chemistries that are prone to the development of resistance, and should not be used to put down an epidemic, which will speed up the resistance development process. Even phosphorous acid products, which are less prone to resistance development, can be lost to resistance through repeated applications on a heavily diseased vineyard. I know this is probably the last thing on your mind when your vineyard is under an attack of epidemic proportions, but still another good reason to keep downy mildew well in hand.
Conversely, Captan or copper fungicides 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 that formulations of Captan have seasonal limits, so plan ahead if you can. There are also some insecticides that should not be applied with Captan. Also, keep in mind the risk for injury by copper applications, and that copper injury will be exacerbated by application under slow drying conditions and application to wet canopies (for example, don’t make applications to dew covered canopies in the early morning). It’s also important to 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 (fortunately some of the newer coppers utilize lower copper concentrations), rate of material used, 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. There is also some evidence that late Captan sprays can cause problems in the winemaking process, in terms of delaying fermentation and negative effects on wine quality but the consequences seem less severe and irreversible. For more on this, consider this online article by Dr. Annemiek Schilder, former fruit pathologist at Michigan State University.
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.
Fluffy, white downy mildew sporulation on the underside of a grape leaf
Powdery mildew
Good control of powdery mildew is also very challenging in wet years when humidity levels remain ‘through the roof’ and cloud cover occurs for extended periods of time. Now that we are largely past the fruit protection period, our focus is on keeping leaves clean, especially on V. vinifera, for about 6-8 more weeks. I say this 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, Dave Gadoury and graduate students at Cornell University, who showed that controlling powdery mildew up to about Labor Day can also go a long way to reducing 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 stops developing and also dies…unless it has had time to form fully mature, winter resistant structures called chasmothecia. In other words, if the chasmothecia in a powdery mildew colony on a leaf, do not have time to fully mature before the leaf dies, 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 get a better handle on the ‘size’ of the powdery mildew problems he/she will potentially face next spring and the spring after that, and so on. If, for example, you had heavy powdery mildew development earlier in this season (on clusters and/or leaves), expect to have to deal with powdery mildew early next season and you’ll have to take appropriate action during early shoot growth stages with preventive fungicide sprays. Once again, this is particularly important if you are growing Vitis vinifera and much less important for growers of native varieties like Concord and Niagara.
Greyish-white colonies of powdery mildew growing across the upper surface of grape leaves
Botrytis bunch rot control
If you’re growing bunch rot susceptible wine grape varieties, you have already applied a Botrytis specific fungicide at full bloom and probably pre-closure (?) This is because Botrytis infections can occur during bloom and early fruit development under wet conditions (which most of us have had). These Botrytis infections of the clusters usually remain dormant, or ‘latent’, and do not result in active rot of the fruit…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.
In varieties with very compact clusters, the pre-closure application may be extremely important as it may be your last opportunity to get protective fungicide residues onto the interior surfaces of clusters. Along with the bloom spray, this spray will also help to reduce ‘latent’ Botrytis infections that continue to accumulate throughout the ‘green’ berry development period. The pre-closure spray may also be a good opportunity to clean clusters of bloom trash (dead cap and stamen tissue that got stuck in the clusters after bloom). Bloom trash provides a substrate for Botrytis and serves 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, which we’ve already discussed above. It is an expensive operation to add to your production costs and is most cost-effectively applied by machine (machinery costs aside). We have found that it can be mechanized most effectively if vines are trained to a vertical shoot positioned (VSP) or some other two-dimensional trellis system with a relatively focused and narrow cluster zone. One additional benefit of leaf removal that I haven’t mentioned yet is the fact that it 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).
Our 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, an application at this time, to rot prone varieties, is a good way to stave off bunch rot development. After veraison, fruit also becomes 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 the fruit of overly compact clusters, despite the application of a full Botrytis fungicide program.
And speaking of sour rot…
In case you haven’t already heard, there is some relatively new information on sour rot control that I would like to impart. It’s been included in previous blogs as well and that information was presented earlier this year at the Mid Atlantic Fruit and Vegetable Convention in Hershey PA. However, it bears repeating it here. It originated from work conducted by Dr. Megan Hall, a former graduate student of Wayne Wilcox at Cornell University, and it demonstrates how additional pesticide applications during the latter stages of ripening (beginning around 15 brix) can significantly reduce the development of sour rot, which for many premium wine grape growers in PA, is public enemy no. 1 at harvest. Her incredibly thorough work has shown a close connection between fruit flies and sour rot development. It turns out 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. 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.
Lastly, don’t forget how important good canopy and fertility management is to the efficacy of your expensive Botrytis fungicide and sour rot pesticide applications. It’s always a good idea to make sure your shoots are well tucked and spaced within the catch wires, and summer pruning has removed shoots ends that may block sprays from thoroughly penetrating the fruit zone, just before you make each Botrytis fungicide application. We like to wait as long as possible to trim shoot tips because of the effect on lateral growth stimulation, but make sure excessively long shoots have not flopped over to block spray penetration into the fruit zone. Limiting shoot growth after veraison with good canopy and fertility management will also limit the supply of new green tissue that is hyper susceptible to powdery and downy mildew and will contribute to more effective late-season management of these diseases as well.
For further reading on this and many other disease management topics, refer to the 2019 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!
2018 Growing Season Recap
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).
Disease pressure
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.
Other issues
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.
Penn State Extension Wine & Grapes U. 