Fundamental Considerations for Managing Fungal Diseases of Grapevines

Vineyard pests involve weeds, insects, and diseases/pathogens. This publication focuses on diseases, specifically those caused by fungal pathogens. Grapevines are sensitive to many pathogens, such as viruses, bacteria, and phytoplasmas. However, most seasonal management inputs are focused on management of fungal pathogens. In fact, effective fungal disease management is the hallmark of successful vineyard management; most cultural and chemical management strategies are aimed at reducing fungal disease pressure. Fungal diseases can infect all grapevines tissues. If left unmanaged, seasonal grapevine productivity and perennial health can be greatly limited by the numerous fungal pathogens that are pests to grapevines. However, as always, context and refinement are important in this case. And "it depends" can be used in reference to the relative pestilence the fungal pathogens have. For example, the disease severity caused by fungal pathogens in arid growing regions is of a lesser magnitude than in humid growing regions.

The following information will review basic considerations and steps for the development of an effective fungal disease management program in vineyards. This article is not intended to go deeply into the biology, etiology, life cycle, resistance development, and other details regarding specific grapevine fungal diseases; external links with supplemental information and recommended reading are included where appropriate. Many state and regional viticulture/pathology Extension collaborators develop, and regularly update, pest management guides, such as the 2025 New York and Pennsylvania Pest Management Guidelines for Grapes ; note – for future editions of the pest management guide, please visit New York and Pennsylvania Pest Management Guidelines for Grapes. It is good practice to read those guides and use them as resources for specific pesticide updates and any changes to pest management best practices.

Step one

Understand how your climate affects fungal pathogen/disease development.

If you are reading this, you may be in Pennsylvania, surrounding states, or in the eastern US. Most grape growing regions in the US that are east of the Rocky Mountain range are characterized by various climate types; many of these climate types include "humid" in the description (Figure 1).

For example, some regions in Pennsylvania are considered "humid continental" while others are considered "humid subtropical" (Figure 2). In general, humid growing regions are characterized by high relative air humidity and rainfall during the growing season (between April and October in the US). Because fungal pathogens generally thrive in warm and wet conditions, rainfall and humidity intensify their ability to infect host plants such as grapevines. For example, Pinot noir grown in Sonoma County, California will generally be subject to lower fungal disease pressure compared to when it is grown in Berks County, Pennsylvania. Thus, if you are growing grapes in a region that experiences high relative humidity and rainfall throughout the growing season, there is a high likelihood that fungal pathogens will causes disease issues in your vineyard.

Step two

Know the genetics (Vitis species) of the grape cultivars ("varieties") you are growing.

All wild and cultivated grapevines are in the genus Vitis; it is the Vitis species that differentiates the grapevine cultivar's susceptibility to certain fungal pathogens. If you know the species of grapevines you are growing (Table 1), you might already have an idea of their relative susceptibility to fungal diseases. For example, grapevine cultivars (called "varieties" in Tables 2 and 3, below) that are dominated by Vitis labrusca genetics (e.g., Concord, Catawba, Niagara) are mostly "native" to humid growing regions and are generally less susceptible to diseases caused by fungal pathogens (Figure 3). Note – these cultivars are less susceptible to fungal diseases but are not resistant; as you will learn, fungal disease management is still required even in commercial V. labrusca production systems. In general, and relatively speaking, "American/native cultivars," are the most disease resistant/tolerant, hybrid species (Vitis spp.) have intermediate disease resistance/tolerance (Figure 4), and European cultivars (Vitis vinifera) have the least resistance/tolerance to diseases (Figure 5). Note that, while this comparison across grapevine species generally applies, specific fungal pathogens can infect and cause as much disease in hybrid species as they can in European species. For example, even though Vignoles is a hybrid cultivar, it could be considered as susceptible to bunch rots as Riesling, a cultivar with a 100% European genetic background.

Table 1. Common commercially produced grapevine species and some popular cultivar examples of each.

American (V. labrusca)

• Catawba
• Concord
• Delaware
• Fredonia
• Niagara

Hybrid (V. spp. x V. vinifera)

• Aravelle
• Chambourcin
• Chardonel
• Vidal blanc
• Vignoles

European (V. vinifera)

• Cabernet Franc
• Chardonnay
• Merlot
• Pinot noir
• Riesling

For a list of commonly grown grapevine cultivars in Pennsylvania, where they are grown, and their relative susceptibility to common fungal pathogens (as informed by summarized survey feedback commercial growers in Pennsylvania), please visit our Cultivars in the Commonwealth web application.

Step three

Know the fungal pathogens that pose infection risk to the grapevines you are growing.

Not all species of grapevines are susceptible to infection by all grapevine fungal pathogens. Through scientific trials and observations, the common fungal diseases of grapevine species have been documented (Table 2, taken from the New York and Pennsylvania Pest Management Guidelines for Grapes). As with any plant production system, the interaction of genetics and environment can impact the prevalence of certain fungal diseases on grapevines. For example, even though most, if not all, European grape cultivars are susceptible to downy mildew (caused by Plasmopara viticola) (Figure 6) and botrytis bunch rot (caused by Botrytis cinerea) (Figure 7), these disease are rarely an issue in vineyards located in arid/dry climates (such as many regions of California and eastern Washington); however, powdery mildew (caused by Erysiphe necator) (Figure 8) is still an issue in vineyards in arid/dry regions.

Key:
+ Slightly susceptible or sensitive
++ Moderately susceptible or sensitive
+++ Highly susceptible or sensitive
No = Not sensitive
? = Relative susceptibility or sensitivity not established

¹The relative ratings in this chart apply to an average growing season in NY and PA. Under conditions favorable for disease development, any given variety may be more severely affected.
a.    BR=Black rot, DM=Downy mildew, PM=Powdery mildew, Bot=Botrytis, Phom=Phomopsis, Eu=Eutypa, CG=Crown gall, ALS=Angular Leaf Scorch, S=Sulfur, C=Copper
b. Berries only weakly susceptible
c. Slight to moderate sulfur injury may occur even on tolerant varieties when temperatures are 85°F or higher during or immediately following the application
d. Copper is most likely to cause injury when applied under slow-drying conditions (cool or very humid).

Step four

Know the stages of the grapevine life cycle during which the fungal pathogens pose greatest risk of infection.

Fungal pathogens can infect actively growing grapevine tissues throughout the growing season. However, not every fungal pathogen species needs to be managed throughout the entire season. Since growing seasons vary in weather patterns, the timing of bud break (the initial green tissue growth after dormancy) and subsequent rate of grapevine growth can vary. Thus, while they can guide and approximate fungal disease management, calendar dates are not reliable to use as a guide for management implementation. Further, after specific growth stages, certain grapevine tissues (like grape berries) are no longer susceptible to certain fungal pathogens. For example, as you will learn below, grape berries are initially susceptible to powdery and downy mildew infection (Figures), but become resistant to them at approximately 3 to 4 weeks after capfall (start of bloom, or grape flowering). Like many aspects of management of agricultural crops, the key to effective fungal disease management in vineyards is timeliness. Timely implementation of strategies to control the pathogens is necessary; implementation of cultural and/or chemical control measures that are too early or too late will miss the optimal window of opportunity to keep grapevines free of diseases. These are a couple of online resources that highlight the timely management of grapevine disease through the growing season, as based on grapevine growth stage: Virginia Grape Disease Updates; Viticulture Management (field report) - University of Georgia/.

Step five. Develop an integrated pest management plan to manage the fungal pathogens that pose a threat to the grapevines you are growing.

Fungal disease management in vineyards should be an integrated approach, which does not solely rely on the use of chemicals for pathogen control. The term "integrated pest management" (IPM) applies to management of fungal diseases much like it applies to management of insects, weeds, and other pests. Management of fungal diseases in vineyards truly starts with site and cultivar selection. From there, "integrated disease management" refers to the integration of cultural and chemical management strategies.

Cultural disease management strategies involve management of the vineyard and grapevine canopy to create an environment that is less favorable to fungal pathogen persistence. Such environments that are less favorable to fungal pathogen persistence are those that receive maximum amounts of sunlight and maximize air movement and, as such, limit humidity in vineyards and rapidly dry wet grapevine tissues after dew and/or rainfall. Most, if not all, viticulture/pathology extension personnel and experienced growers would agree that cultural management practices are necessary to limit fungal disease pressure, as fungicides alone are not effective enough in most situations. Planting the vineyard on a convex landform with high relative elevation to surrounding land will maximize sunlight and air movement, which hasten tissue drying (Figure 9).

Planting the vineyard away from tree lines and other tall objects that create shade and limit air movement is good practice; so is removing trees or hedgerows that cast shade during parts of the day. Keeping the vineyard floor managed so that it is growing close to the ground (and separate from grapevine canopies) is a simple step to limiting humidity and improving air movement through the vineyard (Figure 10).

Following recommended canopy management practices is another necessity to effectively managing fungal diseases. "Canopy management" is a suite of practices with the common goals of maximizing crop quantity and quality and maximizing sunlight interception by the leaves and grape clusters (Figure 11); these practices consist of shoot thinning, shoot positioning, summer shoot hedging, and fruit-zone leaf removal. See these sources for more on shoot thinning and fruit zone leaf removal:

Grapevine fruit zone leaf removal

A brief review of fruit zone management principles

Mechanized grapevine fruit zone leaf removal

Shoot thinning considerations in bunch grape vineyards

Early season grapevine canopy management shoot thinning

For control of fungal pathogens, chemical disease management strategies involve the use of fungicides. Below is a table of fungicide effectiveness, taken from the New York and Pennsylvania Pest Management Guidelines for Grapes (Table 3). The list may appear bewildering due to the abundance of fungicide options available. However, it is imperative to understand that the timing and methods of fungicide application can be just as important as what you use.

First, here are the basics:

1. Early season/budbreak to bloom (approximately 4-6 weeks of time). Disease pressure is relatively low, so it's easier (and important) to maintain tight control of fungal diseases to make fruit protection (the next, most important phase of disease control) as effective as possible: take advantage of that! Your focus, initially, is Phomopsis cane and leaf spot (Figure 12), shortly after budbreak (from approximately 1-5" shoots). Just beyond this stage, black rot (Figure 13) and powdery mildew can become important, and finally downy mildew (the last of the major diseases to "kick in" in the spring) becomes an active threat at about the time vines have attained 5-6 leaves per shoot (approx. mid May/early June in PA). Make good use of old standard fungicides when you can: mancozeb and captan will control downy mildew, black rot, and Phomopsis, with little concern for resistance development (see more on "fungicide resistance" below). Sulfur formulations are effective for powdery mildew control (for grape cultivars that are not injured by sulfur). This is also a time when some alternatives can be effectively used: JMS stylet oil (and other horticultural oils) can be used for powdery mildew control (in the absence of sulfur use).

2. Bloom through early fruit development (approximately 3-6 weeks of time). This is the most critical time for disease management. Fruit of all varieties are most susceptible to the major diseases from the time bloom begins (beginning of capfall) through about 3-4 weeks later…depending on varietal susceptibility.

• • The fruit of most varieties lose their susceptibility to powdery and downy mildew after about 3-4 weeks from capfall (see Figure 14 for powdery mildew infection on fruit).
  • However, some varieties (all vinifera and most hybrids and natives?) can retain some susceptibility to downy mildew of the cluster stem tissue, for an additional 2 weeks, or so (Figure 15).
  • Fruit of most varieties retain susceptibility to black rot for about 6 weeks after the beginning of bloom (capfall). However, fruit of vinifera can retain some black rot susceptibility through 7-8 weeks after capfall (Figure 16).
  • Fruit susceptibility to Phomopsis may remain for many weeks after bloom. However, in most seasons, the threat of Phomopsis typically wanes or expires about 2-4 weeks after bloom due to the absence of available inoculum for disease initiation: no inoculum available = no threat of disease
  • Botrytis management begins with a Botrytis specific fungicide spray at late bloom, on varieties that are susceptible to late season bunch rots.

3. Post fruit susceptibility to veraison (approximately 4-6 weeks of time). After the end of fruit susceptibility to certain diseases, growers should focus on leaf protection, to ensure the maintenance of a fully functional canopy for fruit ripening. The bigger the crop, the more critical this is, even for native varieties like Concord and Niagara. The good news is that management of black rot and Phomopsis are not important issues at this time, and growers can focus on protecting leaves from powdery and downy mildew. Synthetic fungicides can continue to be used for powdery and downy mildew to maintain a clean canopy. However, sulfur and copper can also be used for powdery and downy mildew control, respectively, especially if a fair amount of these diseases have developed. Botrytis management continues with a Botrytis specific fungicide at "just before cluster closure".

4. Fruit ripening period (approximately 6-8 weeks of time). If canopies are relatively clean, fungicide sprays for powdery mildew can be terminated, especially on native varieties like Concord and Niagara. However, canopies of vinifera and sensitive hybrids may require continued use of fungicides for powdery mildew control. Downy mildew can also remain a threat to leaves - and may require continued management - if conditions favor disease development (heavy dews, regular rainfall). This is especially important for susceptible varieties, to avoid defoliation (Figure 17). Botrytis management continues with a Botrytis specific fungicide spray at veraison AND about 2-3 weeks later (Figure 18). Sour rot management begins on susceptible varieties at about 15 brix, with an insecticide spray targeting fruit flies (Figure 18). Sour rot control may also be improved beyond insecticides, with the use of certain "sterilant fungicides" that control yeasts and bacteria (for example, Oxidate, ProBlad Verde, etc).

As stated above, these are the basics… but JUST the basics… an approximation. Every situation will be different, depending on cultivar grown, site characteristics, current weather, how much disease was allowed to develop in the previous season, etc, and disease management under the full range of circumstances is far too big a subject to address here. One must assess their growth stage and canopy health in combination with previous, current, and future weather patterns, and use this information to be nimble and plan fungicide use and spray frequency "in real-time."

¹These ratings are relative rankings, based on standard application rates, good spray coverage, and proper spray timing. Actual levels of disease control will be influenced by these factors in addition to varietal susceptibility and disease pressure.

Key:
++++ excellent
+++   good
++    moderate
+     slight
0    not effective

Notes:
a.    Note: Powdery mildew (PM) resistance to the strobilurin (Group 11) fungicides has occurred in multiple vineyards, sometimes resulting in significant crop loss. Downy mildew (DM) resistance to these fungicides also appears to be widespread, and has caused significant crop loss as well. Thus, it is now risky to rely on strobilurin fungicides for control of either powdery or downy mildew. When such resistance occurs, none of the Group 11 fungicides will provide commercial control of the affected disease if applied alone, and they must be combined with an effective rate of an unrelated fungicide to avoid potential crop loss. "Pre-mixed" strobilurin products such as Pristine, Quadris Top, †Topguard EQ, and *^NY†Luna Sensation include an unrelated active ingredient that has good activity against powdery mildew but NO activity against downy mildew.
b.    Fair control at the lower rate labeled for powdery mildew, good to excellent control at the higher rate labeled for other diseases.
c.    Refers to fixed copper formulations listed in Table 8.3. Most insecticides labeled for use on grapes are incompatible with lime, which is often mixed with these products. Check insecticide label for incompatibility with alkaline spray materials. See New York Food and Life Sciences Bulletin No. 118 for information on effects of alkaline hydrolysis on pesticides.
d.    The Ridomil MZ formulation (Ridomil + mancozeb) will give moderate control of Phomopsis and black rot, due to the partial rate of mancozeb that is provided by applying the labeled rate of this product. The Ridomil Copper formulation will provide moderate suppression of powdery mildew, particularly on moderately resistant cultivars (e.g., Concord), due to the amount of copper provided by applying it labeled rate.
e.    Sulfur activity is strongly influenced by rate and frequency of application, formulation, and by weather. It is highly effective when applied at relatively high rates and short (7-day) spray intervals, but efficacy can decline as intervals increase and/or rates decrease, especially in rainy weather. Micronized and flowable formulations are more persistent than wettable powders. "Spreader-sticker" adjuvants will increase persistence in rainy weather.

*      Federal restricted-use pesticide.
*^NY Restricted-use pesticide in New York State
† Not for use in Nassau/Suffolk Counties in New York
^ Not registered for use in New York State at press time.

Additional considerations

Fungal disease management is a proactive (not retroactive) endeavor. You cannot see fungal pathogens before they infect your grapevines. Fungal pathogens are microscopic in size and are generally ubiquitous in the environments they thrive in; their spores are in the air and on surfaces and are not visible to the human eye. When they do infect your grapevines, they will be observed primarily as symptoms that they cause. However, symptoms may not be observed for several days or even weeks after infection has occurred and the damage done. Thus, management of fungal pathogens that infect grapevines should be a planned strategy to prevent infection - that is, before infection occurs. As mentioned above, timely implementation of management strategies is key to effective fungal disease management and proactive planning is necessary to effectively manage grapevines diseases. This contrasts with management of other vineyard pests, such as insects, management of which is implemented after scouting and determination that the pest is present in amounts above the levels of concern (greater than the "economic threshold," or the level at which productivity and perennial health are threatened).

Fungal pathogens can develop resistance to fungicides. When this occurs, those fungicides become less effective, or ineffective, at controlling the fungal pathogen population and the disease it causes. A striking example of this applies to a group of fungicides known as the strobilurins. These fungicides (fungicide resistance action committee group (FRAC) 11) were introduced to grape growers in the US during the late 1990s. The first strobilurin to be introduced was Abound, and it had activity against all four major grape diseases: powdery and downy mildew, black rot, and Phomopsis. Within a few years of regular use, the powdery mildew fungus had developed resistance to the strobilurins (Abound, Sovran, Flint) and was no longer effectively controlled by them. Now, over 25 years later, research by several universities has confirmed that strobilurin resistance by the powdery mildew fungus is so widespread in the US, that we recommend that grape growers NOT rely on them for powdery mildew control. More recently, university research has confirmed that strobilurin resistance by the downy mildew pathogen has also become widespread in parts of the eastern US.

The reasons for fungicide resistance relate to basic population biology, including natural selection, genetics, and evolution. When an effective fungicide (for example, the strobilurin, Abound) is first used in a vineyard, nearly all individuals in a population of the target microorganisms (for example, the powdery mildew fungus), are killed. However, a small fraction of that pathogen population survives by chance (spray coverage is not perfect) OR because of a genetic mutation they possess that renders the fungicide ineffective at disrupting optimal pathogen physiology. Without the fungicide, those "mutants" initially make up a very small proportion of that pathogen population; they possess a mutation that’s of little survival value. The fungicide appears to control the disease very well at first, but over the span of continued use of that fungicide, the mutation becomes very valuable to the pathogen population (the mutation is being selected for) and resistant individuals continue to reproduce unchecked, as the non-mutant, susceptible portion of the population is gradually killed off. The resistant portion of the pathogen population grows, eventually making up enough of the population that the fungicide appears to no longer control the disease at a commercially acceptable level.

Poor spray coverage, excessive and consecutive use of that fungicide/fungicide class (failure to rotate with unrelated chemistries) and applying that fungicide to a large population of the pathogen (when the disease has spread and its symptoms are "easy to find" throughout the vineyard) are a few poor practices that accelerate the resistance development process. Certain characteristics of the pathogen population also contribute to the speed at which resistance develops: populations of pathogens that complete their entire life cycle (infection-colonization (symptoms)-reproduction-reinfection) in a short period of time (in less than a week for the powdery and downy mildew pathogens, for example) tend to develop resistance much faster than populations of pathogens that take weeks or months to complete their life cycle (for example, the fungi that cause black rot and Phomopsis). For this reason (varied life cycle length), strobilurins are no longer effective at controlling powdery and downy mildew but are still effective at controlling black rot and Phomopsis.

The nature of the fungicide active ingredient also plays a role in the speed at which resistance develops. For example, active ingredients that target and impair/inhibit a SINGLE biochemical process of the pathogen (thus controlling it), are much more prone to resistance development than active ingredients that target MULTIPLE biochemical processes of the pathogen. This is the reason the downy mildew pathogen has developed resistance to the strobilurins (modern, single-site inhibitors) but not "old standards" like mancozeb, copper, or captan (all multi-site inhibitors). Likewise, the powdery mildew fungus has developed resistance to the strobilurins but not sulfur (an old standard, multi-site inhibitor).

Further reading on fungal pathogen resistance development in grapevines

Fungicide Resistance Action Committee (FRAC)

Pesticide Environmental Stewardship. Raised resistance risks

Fungicide Resistance Action Committee (FRAC). Statement on multisite fungicides (PDF)

Fungicide Resistance Action Committee (FRAC). Recommendations for fungicide-mixtures (PDF)

Trunk and "wood-borne" fungal pathogens also infect grapevines and limit perennial health and productivity. However, this publication only focuses on the fungal pathogens that cause disease to actively growing ("green") grapevine tissue during the growing season.

Further reading on pathogens that infect the permanent structures of grapevines (trunks, cordons, etc.)

Vineyard Team. Grapevine Trunk Diseases, Current Management Options (PDF)

National Library of Medicine (NIH). Microbial Biological Control of Fungi Associated with Grapevine Trunk Diseases

Progressive Crop Consultant. Grapevine trunk diseases: current management strategies

International Organisation of Vine and Wine (OIV). Grapevine trunk diseases (PDF)

The Grapevine Magazine. Fungal trunk diseases, description, prevention, management, and diagnosis

Fungal pathogens are only one of several pathogen types that can infect grapevines and limit their health and productivity. Grapevines are sensitive to many pathogens that are not fungi, such as viruses, bacteria, and phytoplasmas (Figure 19). These pathogens need to be managed and scouted for but are beyond the scope and goals of this article.

Further reading on non-fungal pathogens of grapevines

2025 New York and Pennsylvania Pest Management Guidelines for Grapes. This publication, and future editions, are available through Cornell University Press and can be  ordered online

Fruit Growers News. Grapevine leafroll-associated virus addressed in pennsylvania

Compendium of Grape Diseases, Disorders, and Pests. 2nd edition, 2015. Editors Wayne F. Wilcox, Walter D. Gubler, and Jerry K. Uyemoto. The American Phytopathological Society. Pp. 118-119.

Penn State Wine and Grapes website. Crown Gall

Rutgers University Pest Advisory. Crown gall in grapevines, early symptoms and management

NIFA projects. Evaluation and investigation of biological control agents against crown gall of grape

Grape Pathology Lab (Nita Lab) at Virginia Tech. Crown Gall

Michigan State University. Managing grapevine crown gall

Answers from the vineyard winery and tasting room ("clean vine-related video" within this link)