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).
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.
- 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.
- 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
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.
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: firstname.lastname@example.org, phone: 814-865-6840) for assistance.
Managing Sour Rotted Fruit in the Cellar. Denise Gardner. Updated: May 5, 2016.
Sour Rot Stinks: Some Strategies for managing Volatile Acidity. Chris Gerling. Veraison to Harvest. Statewide Vineyard Crop Development, Update #5. Sept. 2018.
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.
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
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).
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
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!
By: Bryan Hed, Plant Pathology Research Technologist, Erie County and Dr. Michela Centinari, Assistant Professor of Viticulture, Department of Plant Science
This past growing and harvest season has been, accordingly to many growers, one of the most challenging ever not only in Pennsylvania but in many other eastern US regions. With the 2018 season behind us, we can reflect on what we did right and what we can improve to better manage, when possible, vines under the rainfall conditions experienced in many parts of the Commonwealth. In this article, we will mainly discuss disease and vine vigor/nutrition issues related to seasonal weather conditions. Other issues growers experienced, such as Spotted Lanternfly infestations will be addressed in future blog posts.
What was the major problem? Let’s start with the rain
In Figures 1 and 2, we reported monthly, seasonal (April 1 through October 31) precipitation and growing degree days (GDD; index of heat accumulation) collected by weather stations through the online network for environment and weather applications (http://newa.cornell.edu/) at two locations: Lake Erie Regional Grape Research and Extension Center (LERGREC) in North East (Erie County, northwestern PA) and in Reading (Berks County, southeast PA). We compared the 2018 data to the previous 19-year (1999-2017) average.
If you look at the monthly rainfall (Figure 1; Table1) throughout the growing season, it was as if Pennsylvania was divided into two regions during July, August, and September: the southern shore of Lake Erie, and the rest of the state. The Erie lakeshore was, indeed, relatively dry as compared to the rest of the state: rainfall from April to October was only about 4 inches higher than the long-term average. However, in other parts of the state rainfall was as much as 14 inches higher than average(Figure 1A: 2018 = 43.14 inches versus 1999-2017 = 28.68 inches). Berks County in southeastern PA started out with slightly above average rainfall for April and May, followed by a slightly drier than average June, but rainfall greatly increased in the second half of the season (Figure 1A). This happened not only in Berks County, but in many regions of the Commonwealth which recorded much higher than average rainfall in July, August, and September (Table 1).
Diseases that depended for development on regular rainfall, like black rot and downy mildew, were relatively easy to control for vineyards along the Lake Erie shore. Powdery mildew was in moderate supply; not light but certainly not of hardcore, epidemic proportions. To complete the picture, we did suffer more than a little from sour rot in some of our wine grapes due to the heat and return of rains in September (5 inches). We also suffered a fair amount of fruit cracking and damage from grape berry moth near harvest that led to some serious shelling and crop loss in many area vineyards. And then, on October 11, it all came to an end. Autumn, which was technically just beginning, was being ‘run out of town on a rail’; the weather suddenly took an entirely different turn and the sun and mild weather disappeared, never looking back.
In stark contrast, other parts of the state were dealing with way too much rain that created perfect conditions for the development of downy mildew and late-season bunch rots. Fortunately, from the rainfall data gathered from NEWA weather stations, it appears that rainfall in the early post-bloom period (second half of June – first half of July) was relatively average, with about 2.75 inches during that four-week period. This period is critical for fruit protection when the fruit of all grape varieties is most susceptible to all the major fungal diseases. However, by mid-July rainfall ramped up, and was especially abundant during the fruit ripening period; avoiding fruit rots was nearly impossible under those extremely wet conditions.
In addition to high disease pressure, wet conditions led to high vegetative growth and high to excessive uptake of nutrients such as potassium (K). In addition to the timely application of canopy management practices to keep vegetative growth under control and maintain an open fruiting zone, the planting of cover crops under the vines could help limit vine vegetative growth through water and nutrient competition (For more information please refer to: Why should we care about under-trellis cover crops?. Our extension team reviewed several plant tissue analysis reports from vineyards across the state and many of them had high, and in several cases excessive, leaf petiole K concentrations. For more information on K and how to manage it in the vineyard please refer to Assessing and managing potassium concentration in the vineyard.
What about heat accumulation?
The 2018 growing season in the Lake Erie region will be remembered as a hot season. Growing degree days accumulated from May 1 to September 30 were almost 3,000 at the LERGREC located along thesouthern shore of Lake Erie (Figure 2B). In contrast, one of the coldest seasons in the last 20 years was 2003 with 2180 GDD, 800 GDD lower than 2018! In 2018 it almost seemed everything happened too fast. Concord grapes at the LERGREC went from 50% bud break to harvest in less than five months, while the growing season for Vignoles (Vitishybrid) was less than 4 months long.
Heat accumulation was close to long-term average in Berks county (Figure 2A) and other PA regions, but with extended overcast conditions (many cloudy days!) throughout the season which might lead to moderate/low sugar accumulation in the fruit. Additionally, the overcast conditions contribute to downy mildew, black rot, and other fruit rots.
Tips for next season disease management
It is important to keep detailed records of where diseases were worst; those are the areas likely to develop disease first next year. Be sure to effectively scout those areas of the vineyard next season. For example, for downy mildew, that means beginning scouting by mid to late May. The downy mildew pathogen spends the winter inside infected grape tissue, especially leaves, that fall to the vineyard soil. The first downy mildew infections can occur during rainfall (at least 0.1 inches of rain and 50 °F) a few weeks prior to bloom, when vines have developed about 5-6 leaves per shoot.
We have several very effective downy mildew fungicides, but it is important to understand the pros and cons of each one. The old standards like mancozeb (Penncozeb, Manzate, Dithane, etc) and copper formulations are effective against downy mildew, and are great for multiple, back to back applications because they pose little risk in terms of the development of resistance, but they are not as rain-fast as some of the more modern downy mildew materials like Revus, Ridomil, and Zampro, and may need to be reapplied more often under heavy and frequent rainfall conditions. And of course, with copper, there is a risk of vine injury, that is exacerbated under wet, slow drying conditions. Copper residues from late-season applications can also interfere with fermentation. On the other hand, the more rain-fast, more modern fungicides should not be used more than two or three times per season, and even though the label may permit it, we recommend you don’t make back-to-back applications of the same chemistry, among these modern materials. Also, I purposely left out mention of the strobilurins for downy mildew control (Abound, Pristine, Reason), especially for the more intensively managed wine grape areas of southern PA; downy mildew resistance to this chemistry (FRAC 11) is common and this class of fungicides should probably not be relied upon anymore for control of this disease in many parts of Pennsylvania. And then there are phosphorus acid products which have become very popular for downy mildew control. But these materials can be overused as well. They certainly are very rain-fast and effective, but they can be lost to resistance (limit their use to two or three applications per season) and they only provide about 7-10 days of protection at each application, especially under heavy disease pressure on susceptible varieties. For more information on downy mildew control please refer to Tips for late season downy mildew control
There are cultural measures you can take to help reduce the overwintering population of pathogens. These measures are not substitutes for a solid seasonal spray program, and they all have their price, but they can make your spray program more effective. The downy mildew and black rot pathogens predominantly overwinter on the soil surface. Strict control of grape seedlings and suckers under the row in spring can reduce opportunities for these pathogens to create ‘stepping stones’ from the soil into your canopies. However, this practice needs to be balanced with the need for renewals where crown gall and the threat of winter trunk damage are perennial issues. During dormant pruning, remove all clustersnot harvested and as much diseased/dead/old wood from the trellis as is practical. Throw this material into the row middle and chop it, or better yet remove it from the vineyard and burn it (if practical). This is especially effective against Phomopsis and black rot. Upright training systems (like vertical shoot position) reduce the probability that pathogen spores will be splashed upward from cordons and trunk, into the fruit zone during rain.
A wet season like 2018 could be the start of additional disease issues heretofore not yet encountered in prior years. For example, a disease called ripe rot(Colletotrichum sp.) may have gotten a fresh foothold in some vineyards in Pennsylvania in 2018. Ripe rot is somewhat of a ‘southern’ disease, it mainly occurs in southern PA vineyards, but it was also noticed in a vineyard in central Pennsylvania in 2018 (Figure 3).
Ripe rot is identified during the ripening period by pink or orange colored slimy spore masses that appear on infected fruit after a wetting period (Figure 3, left panel).
Since downy mildew and late season fruit rot management was a major challenge for many growers in 2018, Grape Disease Management in Wet Seasonswill be discussed in more detail at the Mid Atlantic Fruit and Vegetable Convention in Hershey, PA on January 30, and again at our annual Grape Disease and Insect Management workshop on March 28. We hope to see you there.
By: Bryan Hed, Plant Pathology Research Technologist, Erie County
At this time of year, it’s so important to continue scouting leaves for the distinctive white ‘downy’ sporulation of downy mildew. Growers of susceptible varieties need to keep closely monitoring their vineyards for active sporulation and use that information in combination with the DMCast model on NEWA.
The presence of active white sporulation on the undersides of leaves means the downy mildew pathogen is capable of spreading quickly under wet conditions and can spiral out of control, strip vines of their leaves and effectively end the season (and the ripening of canes for next year’s crop).
If you find yourself trying to control this disease well into the ripening period, be aware that your list of chemical control options will start to become shorter as we get within 30 (Ranman, Reason), then 21 (Ziram, Presidio (only older stocks; can’t purchase new material anymore)), then 14 (Revus, Revus Top, Zampro) days of harvest, until in the end you’ll be left with some formulations of Captan, copper, and phosphorous acid products (0 day pre-harvest interval).
Its also important to remember that materials like Ranman, Reason, Revus/Revus Top, and Zampro contain chemistries that are prone to the development of resistance. These materials should not be used to put down an epidemic, which will speed up the resistance development process. And, although phosphorous acid products are less prone to resistance development, you will enhance the chances of losing this technology to resistance as well, by using these materials on a heavily diseased vineyard.
Also, limit your use of phosphorous acid products to three applications per season. On the other hand, fungicides like Captan or copper formulations would be least risky in terms of the development of resistance and can be an effective means of controlling downy mildew late into the growing season.
Just be mindful of varieties that may be injured by copper applications, and that copper injury will be exacerbated by application under slow drying conditions and application to wet canopies (for example, don’t make applications to dew covered canopies in the early morning). If you are protecting a non-bearing, young vineyard from downy mildew (you’re not selling/harvesting a crop), you can continue to use mancozeb products past the 66-day pre-harvest interval.
In this week’s blog, you will find updates and information from several of our authors with an emphasis on disease and insect management and vine nutrient status.
Bloom and early fruit set disease management
By Bryan Hed, Department of Plant Pathology and Environmental Microbiology, Penn State Extension
Well, the 2018 season has gone from 0 to 100 mph over the past four weeks, and grapevine shoots are currently growing at a rate of at least an inch a day. Trying to keep grape tissue protected with pesticide sprays can be a bit of a challenge when canopies double or triple in size each week. However, now it’s time for the most critical fungicide applications of the season; the immediate pre and post-bloom sprays. This is your annual reminder. Fruit ($$) of all grape varieties are most vulnerable to infection from all the major fungal diseases at this time (black rot, Phomopsis, powdery and downy mildew), and in many places across Pennsylvania the previous 4 weeks have been warmer and wetter than average; the perfect setup for fungal disease development on fruit. There’s no more critical time to “spare no expense” than immediately before bloom to about 2 weeks (juice grapes) to 4 weeks (wine grapes) after bloom. Use best materials, apply for best coverage, and allow no more than 10-14 days between these next 2 to 3 sprays. At this time, do not rely on materials that we know are slipping in efficacy, or have already slipped in efficacy, due to the development of resistance in many parts of the East (ie, strobilurins and sterol inhibitors).
When I hear from growers that have experienced problems with fungal fruit infection in the past, breaches in disease control are most often traced to the period of grapevine development around bloom. Some common mistakes include: i) use of the wrong materials (there was resistance to what they used, their mix didn’t cover all diseases, their choice of materials wasn’t very effective, etc), ii) stretching of spray intervals (more than 10-14 days between the immediate pre and post bloom spray), iii) less than optimal coverage (canopies were too dense, canopy management was lacking, sprayers weren’t adjusted for maximum coverage, etc), iv) taking a vacation from farming during this period of time (all of the above?).
If you’re growing bunch rot susceptible wine varieties, fruit-zone leaf removal around or shortly after bloom, can improve coverage and create a fruit-zone environment that is less favorable for the growth of fungal pathogens (For more detailed information see: Early season grapevine canopy management, Part II: Early leaf removal). Strict pre-bloom sucker control can delay the rise of diseases like downy mildew and black rot that emanate from the vineyard floor. Pre-bloom shoot thinning, while shoots can be easily removed by hand, will not only balance canopies with yield but also improve the efficacy and value of fruit protection sprays. Proper weed control/maintenance of row middles and cover crop height can reduce humidity in the vineyard and improve drying time of plant surfaces after rainfall. Integrating these cultural practices into your pre-bloom crop management plan will greatly assist your fungicide applications toward maximizing fruit disease control during bloom.
For more details on the various diseases and how to deal with them during this critical fruit protection period, you may find it convenient to check out previous posts from April 7 and June 16, 2017:
Insect updates on Grape Berry Moth and Spotted Lanternfly
By Jody Timer, Entomology, Lake Erie Grape Research and Extension Station
Grape Berry Moth (GBM): The first grape berry moth for the season usually appear at about 150 degree days from January 1st. This year, in the Lake Erie Grape growing region, we had a late spring which resulted in a later-than-usual emergence of GBM (around May 15th). The emergence occurred much earlier for the growers in the Southeastern portion of the state. The research we have done in the past indicates that spraying for GBM prior to the first full generation (not this emerging generation) is more effective and will not adversely affect yields at harvest. So this generation, which starts to peak at wild grape bloom and continues for about 10 days, does not in most cases need to be sprayed. Wild grape bloom in the Lake Erie Grape growing region occurred around May 30th, it was as early as May 13th in the southeastern regions of PA. Wild grape bloom is used as the biofix for the NEWA system to start accumulating degree days. This system uses the GBM phenology model to recommend optimal spray timings for GBM http://newa.cornell.edu. It is important that you keep track of when wild bloom occurred in your area to allow the model to precisely track the GBM phenology. If you missed the wild bloom date, the NEWA system will calculate wild bloom for your area based on historical data. The best way to determine infestation of your vineyard is to scout for damage. This generation of GBM produces webbing on the flowers and clusters. This webbing, although harder to scout for than later berry damage, is a good indication of severity in the ensuing generations. If your vineyard has high GBM consider spraying more often during the upcoming generations. Grape berry moth can cause considerable damage to vineyards through berry damage and late season rots.
Spotted Lanternfly (Lycorma delicatula): This new invasive insect was first discovered in Bucks County in 2014, the affected area was placed under quarantine to prevent the movement of the insect and its egg masses. Prior to its discovery in the fall of 2014, the spotted lanternfly had not been found in the United States. This fall, when the adults were flying and laying eggs, the quarantine area saw considerable increases and movements of the population. As a result, the quarantine area has been expanded to include all of the counties in southeastern PA. There has also been a colony found in Virginia. Spotted lanternfly host plants including fruit trees, ornamentals, hardwood trees, and grapevines. These insects are exhibiting a preference for tree of heaven (Ailanthus altissima) and vines including grapevines. Spotted lanternfly has the potential to cause substantial damage. Some have estimated potential crop losses, which includes Pennsylvania apples, grapes, and hardwoods, at $18 billion dollars. While feeding on and damaging their host plants, spotted lanternfly also ejects a liquid called honeydew which causes sooty mold and attracts secondary insect pests. Spotted lanternfly overwinter as egg masses, which are small (about 1-4”) and greyish white. They somewhat resemble a dirt splatter.
The first nymphs began to hatch in late April or May and complete four instars. These nymphs are 4-9 mm long and wingless with black with white spots. The fourth instar develops red patches, and then emerge into adults in late summer. This time of the season it is important to scout for egg masses, which although hatched, would indicate an infestation in your area. The black and white nymph stage will be present now.
There is a team of state, federal, and local public officials, academic researchers, and extension personnel working on the problems dealing with this insect. It is important to report findings of spotted lanternfly is you are not in the quarantine area. The website: https://extension.psu.edu/spotted-lanternfly as well as the PDA website has important information on this insect and includes numbers to call if you find insects outside of the quarantine area.
Assessing vine nutrient status
By Dr. Michela Centinari, Assistant Professor of Viticulture, Department of Plant Science
Proper vine nutrient management is crucial for the vineyard longevity, as it helps ensure adequate vegetative growth, fruit set and growth, and optimum wine quality. While some nutrients up-taken by the vine are recycled through fallen-leaves decomposition, the majority of nutrients leave the vineyard in harvested fruit, pruned-wood material (if the brushes are not chopped and left in the vineyard), or through leaching and runoff. Assessing vine nutrient status should be a routine practice and used not just to confirm a suspected nutrient deficiency.
To determine vine nutrient status in an established vineyard, plant tissue nutrient concentration should be analyzed at bloom and/or later in the season around véraison. A soil test is useful and can provide clarification, but has limited benefit. It will indicate relative nutrient availability, but it does not tell what and how much the vines absorb.
What type of tissue to collect for nutrient analyses
There is a long-standing debate about what leaf tissue (blade, petiole, or the whole leaf) best reflects vine nutrient status and correlates to nutrient requirements for optimum vine growth, yield, and fruit composition. However, in the eastern US, the sufficiency range (or target value) of each nutrient concentration is only defined for petiole tissue.
When to collect grapevine petiole samples for nutrient analyses
Collecting a petiole sample at both bloom and véraison and having it analyzed will provide meaningful insight when developing a nutrient management plan. For example, if you noticed visual symptoms of nutrient deficiency in the previous growing season (Figure 1), a nutrient test at bloom will help determine if there is an actual deficiency, and you will be able to correct it in a timely manner (1). Nutrient concentrations in leaf tissue tend to be more stable as the season progresses, so taking a sample at véraison is typically recommended compared to taking samples at bloom, especially for routine analysis (1).
How to collect grape leaf tissues for nutrient analyses
A comprehensive and illustrated guideline on how to collect whole leaf samples (which can also be used for petiole sampling) is on page 12 of the Vineyard nutrient management in Washington State extension bulletin. Be sure to sample each variety separately and to collect 50 large petioles or 100 small ones per variety.
Where to send the samples
Use a reliable lab in your area that has experience in vineyard tissue testing, and use the same lab each year so that the analysis is consistent. If you are in Pennsylvania you can send your plant tissue sample to the Penn State Agricultural Analytical Services Lab. Please be sure to provide all the information required to interpret the lab results (e.g., type of tissue, time of the year the sample was collected). Lab results will report the concentration of each nutrient analyzed and if its level is low/deficient, sufficient, or too high/excessive. If you need assistance with interpreting your report, contact your local extension for further assistance. You can find the contact information for your local Penn State Country Office by entering your zip code in the search field on this site: bit.ly/2J9yCPr
- Moyer M., Singer S., Hoheisel G., and Davenport J. – Vineyard Nutrient Management in Washington State, EM111e (Bulletin) Washington State University
Comments concerning insect and disease management at this time of the season (Immediate Prebloom – Early Postbloom period)
By Andy Muza, Penn State Extension – Erie County
I’ll begin by stating that every commercial grape grower in Pennsylvania should have a copy of the 2018 New York and Pennsylvania Pest Management Guidelines for Grapes: https://store.cornell.edu/p-201631-2018-new-york-and-pennsylvania-pest-management-guidelines-for-grapes.aspx This guideline provides a wealth of information on insect, disease and weed management with pesticide options, rates, and schedules, as well as, a chapter on sprayer technology.
Also, monitoring your vineyard(s) at least weekly throughout the season is critical for managing pests. Frequent scouting will alert you to problems developing in the vineyard and provide the information needed to make informed decisions concerning pesticide applications. (You won’t know what’s out there if you’re not).
Diseases – When thinking about disease management the first thing that commonly comes to mind are fungicide applications. However, cultural practices (e.g. shoot thinning, leaf removal in the fruit zone, etc.) are integral components of a disease management strategy and should be used whenever applicable.
As Bryan Hed mentions and deserves repeating, The Immediate Prebloom (just before blossoms open) through early post-bloom/fruit set period is a critical time for managing fruit infections caused by phomopsis, black rot, powdery mildew and downy mildew. Fungicide protection for botrytis on tight – clustered varieties at bloom (when 80 – 90% of caps have fallen) can also be important in wet seasons.
Insects – Two important insect pests that Jody Timer is covering are grape berry moth and spotted lanternfly. (For additional information on grape berry moth see: Three Phases to Managing Grape Berry Moth https://psuwineandgrapes.wordpress.com/2017/04/28/three-phases-to-managing-grape-berry-moth/ and Grape Berry Moth: Answers to questions you should be asking about this native pest https://psuwineandgrapes.wordpress.com/2015/05/15/grape-berry-moth-answers-to-questions-you-should-be-asking-about-this-native-pest/ ).
I will briefly mention 2 of the more widespread, leaf-feeding pests that you are likely to see sometime this season which are grape leafhopper and Japanese beetle.
Grape Leafhopper – There are several species of leafhoppers in the genus Erythroneura that feed on grape foliage. Regardless of which of these species is prevalent, their life cycles are similar and the injury caused by these leafhoppers and their management is the same. The greatest risk for economic losses due to grape leafhopper feeding occurs during hot, dry years in vineyards with heavy crop loads and high leafhopper populations. In most years, the majority of vineyards in Pennsylvania should not require an insecticide treatment specifically for management of grape leafhopper. However, the decision to apply an insecticide should be based on scouting information and threshold levels. (For more detailed information see: Grape Leafhoppers https://psuwineandgrapes.wordpress.com/2017/06/09/grape-leafhoppers/ ).
Japanese Beetle – Adult beetles feed on over 300 species of plants including grape. They prefer smooth, thinner types of grape leaves which are characteristic of many wine grape varieties (e.g., Chardonnay, Traminette, and Vidal Blanc). Feeding injury, depending on severity, can result in leaves having a skeletonized appearance due to consumption of the soft leaf tissues between veins. Research has shown that grapevines can tolerate a fair amount of leaf area loss without detrimental effects. However, no economic threshold level has been established for leaf injury on grapes caused by Japanese beetle. Since young vineyard blocks, vines in grow tubes and many wine varieties are vulnerable to serious leaf loss by Japanese beetle feeding consistent monitoring is important. (For more detailed information see: Japanese Beetle: A Common Pest in the Vineyard https://psuwineandgrapes.wordpress.com/2016/07/09/japanese-beetle-a-common-pest-in-the-vineyard/).
Bryan Hed, Department of Plant Pathology and Environmental Microbiology, Penn State Extension
As the new grape growing season commences, this is a good time to revisit some of the fungicide updates that were discussed at grower meetings earlier this year. While these materials are available to growers in most states, some of them have not yet cleared the extra hurdles required for legal use in New York, and in those instances, I make specific mention of that. I hope this blog will be useful for growers in the 2018 season.
FUNGICIDE CHANGES, NEWS, & REVIEWS
First, Aprovia/Aprovia Top. The active ingredient in Aprovia is solatenol (benzovindiflupyr), and while it does not represent a new chemical class for us grape growers (succinate dehydrogenase inhibitor or SDHI) it is a new and improved chemistry. The SDHI fungicides belong to FRAC Group 7, which also includes chemistries in products like Endura and Pristine (boscalid) and Luna Experience (fluopyram). Aprovia was available for use in most states last year but has now been labeled for use in New York as well. As a solo product, Aprovia is very effective for the control of powdery mildew as trials in NY over several years have shown. Trials at Penn State over the past couple of seasons have also revealed some efficacy on black rot, but I would consider it more in line with “suppression” of this disease and I cannot recommend it for black rot control, especially on susceptible varieties. Also, it should not be relied on for significant control of Botrytis, unlike other SDHIs. The label also lists control of Phomopsis and anthracnose, but I have not seen any real proof of that. Penn State has tested this product over two years on Concord, to examine it for any potential crop injury issues to that variety. in comparison to Revus Top, a standard spray program, and an untreated check, there were was no injury to Concord grape from Aprovia, while, as expected, Revus Top caused severe damage to leaves developing at the time of application.
Aprovia Top, on the other hand, is a mixture of two active ingredients: i) solatenol, the active ingredient in Aprovia and ii) difenoconazole, a DMI fungicide with very good to excellent activity against powdery mildew, black rot, and anthracnose. Aprovia Top is also labeled for control of Phomopsis, but again, local experience and published results of trials with Phomopsis is lacking. The label rate for Aprovia Top is 8.5 to 13.5 fl oz/A; 13.5 fl oz of Aprovia Top provides about the same amount of solatenol as 10.5 fl oz of Aprovia; it also provides about the same amount of difenoconazole as 18 fl oz of Inspire Super, but falls a little short of that found in 7 fl oz of Revus Top. Aprovia and Aprovia Top have a 12 hr REI and a 21-day PHI. As with all the products containing difenoconazole, Aprovia Top should not be applied to Concord grape and other varieties on which difenoconazole injury has been reported. This includes Brianna, Canadice, Concord Seedless, Frontenac (minor), Glenora, Noiret (minor), Skujinsh 675, St. Croix (minor), and Thomcord.
Intuity. The active ingredient in Intuity is mandestrobin, and if that sort of sounds familiar, it’s because this is another strobilurin fungicide (FRAC group 11). Intuity offers protectant and antisporulant activity against Botrytis, for which it is exclusively recommended, though it will provide suppression of powdery mildew, at least where strobilurin resistance has not yet developed. In limited NY and PA trials, Intuity has provided good to fair control of Botrytis equivalent to current standards like Elevate, Vangard, Scala, and Switch. The label rate is 6 fl. oz/A with a maximum number of three applications (two is recommended) and 18 fl oz per season. Do not make sequential applications; rotate with non-FRAC 11 materials (Elevate, Endura, Fracture, Inspire super, Rovral, Scala, Switch, Vangard) and allow at least 20 days between Intuity applications. Intuity is at risk for resistance development by the Botrytis fungus and it is essential that its use is limited to rotations with other, unrelated Botrytis fungicides both within and between seasons to reduce the development of resistance. Intuity is rainfast within 2 hours of application, has an REI of 12 hours and PHI of 10 days. Do not use Intuity on V. labrusca, V. labruscahybrids or other non-viniferahybrids. Avoid mixing with organosilicone surfactants. Intuity has not yet been cleared for use in New York.
Presidio. Presidio has been with us for about 10 years now and is used for downy mildew control, for which it has been very effective. Unfortunately, Valent has pulled the grape use from the Presidio label and any new product will not be legal for use on grapes this year. However, grape growers will be able to legally use up old stock of Presidio with the grape use pattern on the label.
FLINT Extra. A new formulation of an older material, FLINT Extra is a liquid (500SC) formulation that replaces Flint 50WG. The use rate of the new product is the same (in terms of active ingredient) as the old product. In other words, 2 fl oz of FLINT Extra 500SC = 2 oz Flint 50WG. But the new product is labeled to increase the application of active ingredient per acre. For example, for powdery mildew, the new product label lists a 3-3.5 fl oz rate as opposed to the 1.5-2 oz rate on the old product label. This represents a doubling of the amount of active ingredient for powdery mildew control by the new product. For Botrytis, the old 3 oz rate is now 3.8 fl oz, and for black rot, the old 2 oz rate is now almost doubled on the new label to 3.5-3.8 fl oz. Well, what does this mean then in practical terms for grape growers in the northeast? It could mean better disease control with the new product. However, if you already have powdery mildew resistance to the strobilurins in your vineyard, then increasing the amount of active ingredient probably won’t boost efficacy against that disease, and relying on the new formulation for powdery mildew control is risky. The same goes for Botrytis control, as strobilurin resistance among Botrytis isolates becomes more common. For black rot, it could represent improved control of that disease. However, I thought the 2 oz black rot rate for the old material was pretty effective already, and to my knowledge, there have been no cases of black rot resistance to the strobilurins (though I’m not aware anyone has been looking for it). And yes, it is registered for use in New York.
That’s what new. This next section borrows from Wayne Wilcox’ fungicide updates from last year. I have updated that information with new information from some of our research trials as well.
Fracture. According to Wayne’s insights last year, “Fracture is a product whose active ingredient is a fragment of a naturally occurring plant protein, and which has been registered for use on grapes for a couple of years. It has a 4-hr REI and a 1-day PHI, and the residue of its active ingredient is exempt from tolerance by the US-EPA (i. e., it is considered safe enough to humans that there is no limit on the allowable residue level in/on food products)”. We’ve now tested it for powdery mildew control over two years in Concord and Chambourcin and consider its activity against that disease to be modest. New York trial results appear similar. Trial results for bunch rot control I think are a bit more promising; we got fair to good control of bunch rot on Vignoles with this product last year (as good as a standard Botrytis fungicide program), and we’re looking forward to testing it again for that purpose this season. New York trials with Fracture have also shown control of Botrytis as good as standard materials, as well as some activity against sour rot. Fracture is expensive but may appeal to growers looking to reduce reliance on synthetic fungicides for bunch rot control, especially if used in combination with strict sanitation and cultural controls like leaf removal. We’re hoping to look at Fracture again this season, in combination with pre-bloom mechanized leaf removal, for integrated bunch rot control on Vignoles.
Polyoxin D zinc salt. Polyoxin D zinc salt (PZS) is a relatively new fungicide active ingredient with very low mammalian toxicity that has been classified by the U.S. Environmental Protection Agency (USEPA) as a “biochemical-like” pesticide. It degrades rapidly in the environment with a soil half-life of 2-3 days. Production of PZS occurs through a fermentation process using the soil bacterium Streptomyces cacaoi var. asoensis. The active ingredient inhibits chitin synthase, an enzyme essential for the production of chitin, an important component of fungal cell walls. The product is being sold as Tovano and OSO5%SC and is marketed through Certis USA. Over the past two seasons, our results with OSO on Concord and Chambourcin grapes have shown good to modest efficacy against powdery mildew, but no practical level of activity against black rot. For powdery mildew efficacy on fruit, OSO, at the 13 fl oz rate, was equal to or better than BadgeX2 (fixed copper), and equal to a standard rotational program of Quintec/Vivando/Toledo. As with most of the biopesticide type fungicides, cost per application is generally going to be higher than that of the standard synthetic fungicides.
LifeGard. LifeGard is another biopesticide approved for use on grapes in all states. It has provided really good results for the control of downy mildew in New York trials. Our past two years of testing in PA were a bust due to very dry conditions and little to no downy mildew up here in Erie County, PA. However, maybe we’ll get a good test of this product this year. LifeGard works by triggering a plants’ natural defense mechanisms against pathogens so the product may perform best after the vine has been ‘primed’ by an initial spray a few days before it is challenged with the pathogen. The label states that “initial triggering of plant defense response occurs within minutes of application, but 3-5 days are required to attain maximum level of protection”. This may be the reason our greenhouse inoculation trials with LifeGard were largely unsuccessful; we applied the pathogen just a few hours after application of the material instead of allowing ample time for the vine’s natural defense mechanisms to build up. Grapevines do not generally tend to respond to efforts to induce resistance, but the results from New York trials are encouraging and testing should continue.
There are several products also worth mentioning that have recently been made available to New York (and hence all) grape growers. Here is a brief recap of those materials.
- Luna Experience: a combination product consisting of two unrelated active ingredients, tebuconazole, (a very familiar sterol-inhibitor (FRAC 3)) and fluopyram, a newer SDHI (FRAC 7). Luna Experience is labeled for powdery mildew control at 6.0–8.6 fl oz/A, and for Botrytis and black rot control at 8.0 – 8.6 fl oz/A. Trials in New York have obtained excellent control of powdery mildew with the 6 fl oz rate. For Botrytis, New York trials suggest the 6 fl oz rate works well from bloom through bunch closure but the 8 fl oz rate would be best by veraison or later, especially if there is any pressure. The higher rate is also recommended for black rot control for the first few weeks after bloom when berries are most susceptible. The fluopyram provides most of the powdery mildew control and all of the Botrytis control, while the tebuconazole provides most of the black rot activity. For resistance management, limit the number of applications of FRAC 7 materials (SDHIs) to two per season.
- Zampro: We tested Zampro a number of years ago and found it to be an excellent material for downy mildew control. More extensive New York trials have gotten similar results. Though it has been approved for use in New York, it still cannot be used on Long Island. Zampro is another combination product of dimethomorph (FRAC 40, same as mandipropamid in Revus) and a new chemistry, ametoctradin.
- Rhyme: The active ingredient in Rhyme is flutriafol (sterol inhibitor, FRAC 3) and extensive powdery mildew trials in New York have shown more consistent results at the 5 fl oz rate rather than the 4 fl oz rate: Rhyme was a little better than Rally (myclobutanil) and tebuconazole, about equal to Mettle (tetraconazole), but not as good as difenoconazole (the newer, more potent sterol inhibitor in Revus Top, Inspire Super, Quadris Top). It received a registration a couple years ago and is also available for use in New York as well (except for Long Island). Rhyme has excellent activity against black rot.
- Topguard EQ: A combination product of flutriafol (just discussed above) and azoxystrobin (the ai in Abound). Obviously, this can’t be used in Erie County, PA, but is available to New York grape growers (except Long Island). The azoxystrobin picks up downy mildew (and Phomopsis?) that the flutriafol won’t, unless of course there is a significant presence of strobilurin resistant isolates of the downy mildew pathogen in your vineyard. For powdery mildew, the azoxystrobin adds a second mode of action against that disease, unless (once again) there is a significant presence of strobilurin resistant isolates of the powdery mildew pathogen in your vineyard. So, if you’re farming grapes in areas where sterol inhibitors and strobilurins have been used for many years and downy/powdery mildew resistance is suspected/likely or known, this product may not provide adequate control of these two important diseases, especially on highly susceptible wine varieties. What this product will definitely control is black rot: the azoxystrobin has excellent protective activity and flutriafol has excellent post-infection activity against this disease.
And finally, what’s new in the pipeline?
Miravis Prime. Miravis Prime is a product with two active ingredients: a new SDHI called adepidyn (FRAC 7) and an older, unrelated active ingredient known as fludioxonil (FRAC 12). This product is not yet registered for use on grapes, but federal registration may occur later this year, which will make it available for growers in most states (New York will probably have to wait at least another year). Our tests with Miravis Prime have shown good to excellent activity on powdery mildew, Botrytis, and black rot. Adepidyn (Miravis) provided excellent control of black rot in our 2015 and 2016 trials on Concord and Niagara fruit. The fludioxonil component in Miravis Prime is an older Botrytis fungicide, (introduced about 25 years ago) that is also found in a registered product called Switch (for Botrytis control in grapes). Having two active ingredients for Botrytis control makes this product effective at controlling Botrytis bunch rot disease in wine grapes.
Part 2 of this blog post will be published next Friday, May 18, 2018.