By: Michela Centinari
I imagine as winter approaches one thought on every grower’s mind is: “Is this winter going to be anything like the previous one?”
The winter of 2013/2014 was one of the most severe since 1994 and we can hope another 20 years or more pass before we must endure another of the same magnitude. The extent of damage and crop loss varied among regions, individual vineyard sites, wine grape varieties (Figure 1) and the health of the vines going into the cold season. In this regard, during a vineyard visit in Chester County (Southeast Pennsylvania) in August, a grower pointed out a block of Cabernet Franc (Vitis vinifera L.) vines with winter cold injury symptoms. The vines had a healthy green canopy but, surprisingly, no clusters. That was unusual because other Cabernet Franc vines in the area were fine. However, the grower highlighted that those vines had already experienced severe frost damage in the previous spring (2013). Frost damage may contribute to a low overwinter carbohydrate reserve and negatively affect bud cold hardiness as well as the development of shoots and inflorescences in the following spring. Concentrations of non-structural carbohydrates are closely related with cold hardiness in grapevine buds and canes .
Could delaying fruit harvest for ice wine production negatively affect vine health and compromise winter bud cold-hardiness?
A recent 5-year study conducted in Ohio reported that neither crop level (16 vs 32 clusters per hedgerow meter) or harvest date (beginning of October vs middle of December) had an impact on winter bud cold-hardiness in ‘Vidal blanc’ vines . This is very good news for growers. However, as the authors suggested, the effect of crop level on cold hardiness may depend on the variety  and its vegetative and reproductive characteristics (i.e., tendency for excessive vigor and/or over-cropping).
Ongoing research at Penn State is being conducted to assess the impact of crop load management practices on bud cold acclimation, de-acclimation, and maximum cold hardiness, as well as carbohydrate reserve storage. We plan on highlighting these developments as results are determined over the next few years.
How to assess cold injury in grapevine, and manage cold injured vines?
After budbreak, when the extent of the damage started to become more clear, many growers wondered how to assess the extent of the damage and what the best practices were for rapid vine recovery. Our grape and wine team at Penn State put together a list of resources to help growers during this difficult growing season. Here are some of those resources:
You can start reading the article published on eXtension Cold Injury in Grapevine by Mark Chien, former Penn State Viticulture Extension educator and now Program Coordinator, Oregon Wine Research Institute, and Michelle Moyer, assistant professor at Washington State University. At the end of the article you can find of comprehensive list of recommended resources that can be used to assess and manage cold damage in the vineyard. Among these resources I would like to highlight:
- Winter Injury to Grapevines and Methods of Protection by Tom Zabadal, Michigan State University;
- Assessing and Managing Cold Damage in Vineyards, Washington State University
- Evaluating bud injury prior to pruning Part 1 and Part 2; two brief video presentations from the Finger Lakes Grape Program;
Other resources that you may find useful are:
- Managing Winter-Injured Vines published on Appellation Cornell, June 2014, by Tim Martinson (Senior Extension Associate, Cornell University);.
- Managing Winter Injury published on the Lake Erie Regional Grape Program, Cornell University, Viticulture Notes, Issue # 3, June 2014, by Kevin Martin (Penn State University, LERGP Business Management Extension Associate). The article provides useful guidelines of the cost associated with re-training and re-planting a vineyard.
What did we learn?
The severe cold winter provided a good opportunity to evaluate the cold hardiness of Vitis vinifera and inter-specific hybrid wine grape varieties at the two variety evaluation plantings established in Pennsylvania (PA) in 2008, as part of the NE1020 multistate project. The two plantings are located at the Lake Erie Regional Grape Research and Extension Center (LERGREC, Northwest Pennsylvania) and at the Fruit Research and Extension Center (FREC) in the southern side of PA. For more information about the NE-1020 trial please refer to the article “NE-1020, What? The Top 5 Industry Benefits Affiliated with the NE-1020 Variety Trial” by Denise Gardner.
At the LERGREC station all the V. vinifera varieties experienced extensive winter injury. High incidence of vine mortality was recorded in Syrah, and Muscat Ottonel; trunk injury was mostly observed in Pinot Noir and Pinot Grigio. Among the V. vinifera varieties, Cabernet Franc and Grüner Veltilner vines are recovering the best; healthy suckers are growing from above the graft union and they will be used for trunk renewal next spring. For information regarding the level of bud injury observed on the 17 grapevine varieties established at the LERGREC site please refer to the article “Grape Growing in PA In Spite of the Weather” by B. Hed and M. Centinari
As expected, lower levels of winter injury were recorded at the FREC station in the Southern part of Pennsylvania. The most significant winter injury was observed in Tannat (almost 100% vine mortality). Some of the other varieties experienced cold damage, limited primarily to primary buds. Although, some of the Syrah and Malbec vines suffered conductive tissue damage (phloem and xylem) and collapsed during the summer (Figure 2).
As a consequence of primary bud damage some of the V. vinifera varieties produced low crop yield (Table 1). Specifically, average yields of Malbec, Albarino and Cabernet Sauvignon were much lower than those of the previous season (second column, Table 1). Cluster number per vine in Sangiovese and Viognier were lower than usual. Data such as “percent live buds per total buds left (% live buds/total buds)” and “shoot number per vine” were also recorded. This will provide a comprehensive picture of the differences among the genotypes and their ability to adapt to extreme environmental conditions such as the cold temperatures we experienced in the winter of 2014.
Table 1. Yield components of 20winegrape cultivars in the NE-1020 cultivar trial at Fruit Research and Extension Center (FREC) in the southern side of PA. Vines spacing is 6’ between vines and 9’ between rows.
- Jones, K.S., J. Paroschy, B.D. McKersie, and S.R. Bowley (1999). Carbohydrate composition and freezing tolerance of canes and buds in Vitis vinifera. J. Plant Physiol. 155:101-106.
- Dami I.E., S. Ennahli, and D. Scurlock (2013). A Five-year Study on the Effect of Cluster Thinning and Harvest Date on Yield, Fruit Composition, and Cold-hardiness of ‘Vidal Blanc’ (Vitis spp.) for Ice Wine Production. HortScience 48(11):1358–1362.
- Dami, I.E., D.C. Ferree, S.K. Kurtural, and B.H. Taylor (2005). Influence of cropload on ‘Chambourcin’ yield, fruit quality, and winter hardiness under midwestern United States environmental conditions. Acta Hort. 689: 203–208.
Grapevine leafroll associated virus; A brief introduction to an old disease. Should Pennsylvania grape growers be concerned?
By: Bryan Hed, Michela Centinari, and Cristina Rosa
As if wine grape growers don’t have enough challenges in this day and age, the effects of grapevine viruses have been taking on greater importance in eastern vineyards over the past several years. Studies examining grapevine leafroll-associated viruses are developing a growing body of information that will be essential for vineyard managers to continue moving the eastern wine grape industry forward. Grape growers in the eastern United States need not feel they are the only ones with this disease management challenge (as is the case with many fungal diseases of grapes); grapevine leafroll-associated viruses (GLRaVs) are found in vineyards all over the world (Compendium of Grape Diseases). This group of viruses causes a disease known as grapevine leafroll disease, and the association of symptoms with grapevine leafroll viruses was recognized over 80 years ago. As is the case with so many plant pathogens, the worldwide distribution of these viruses occurred as a result of increased movement of plant material/goods across the globe; the ever widening dissemination of infected planting stock (Compendium of grape diseases). The effects of these leafroll viruses is most severe on – you guessed it – cultivars of V. vinifera, where the disease is known to greatly reduce yield, vine vegetative growth or vigor, and cold hardiness; a factor of critical importance for these cultivars grown in the northeastern United States. Grapevine leafroll disease can also delay fruit maturity, reduce color development in red grapes, and fruit quality (decreased soluble solids, increased titratable acidity) of V. vinifera grapes (Fuchs et al. 2009), which can negatively impact perceived wine quality. The severity of the effects of leafroll viruses is dependent on a great number of factors such as grapevine cultivar, virus strain, climate, soil, cultural practices, stress factors, etc. So naturally, the severity of symptoms can vary from one season to the next (Compendium of Grape Diseases). With respect to cultivar, the effects of these viruses on Vitis interspecific hybrids and Vitis labrusca are generally considered to be less serious, but are also less well defined and studied.
Infection by leafroll viruses results in the degeneration of primary phloem tissues in grapevine shoots, leaves and clusters (Compendium of Grape Diseases). As one can imagine, this can have profound effects on all parts of the vine. Symptoms of the disease, which are generally most observable on V. vinifera, consist of cupping and discoloration of older leaves in late summer and fall. On red fruited varieties, leaves of infected vines can display a distinct red coloration of the interveinal tissue, while veins remain green (Figure 1). On white fruited varieties of V. vinifera, symptoms are less striking and leaves tend to look yellowish (chlorotic) and cupped (Figure 2). Leaf discoloration generally affects older leaves first, but these symptoms are not diagnostic of the disease, as they may be due to other causes such as nutrient deficiencies, water stress, and even crown gall. Analysis of grapevine tissues in the laboratory is the only way to confirm the presence (or absence) of these viruses.
Currently, there are about seven GLRaVs found in cultivated grapes, the most common being GLRaV-3. These viruses are easily spread over long distances through the movement of infected nursery stock, but can be spread (vectored) within the vineyard by mealybugs (Compendium of Grape Diseases). Unfortunately, there are no known sources of resistance to GLRaVs among Vitis species and they have been found in many cultivated grape varieties, including V. labrusca, Vitis interspecific hybrids, and V. vinifera. Interest in grapevine leafroll disease and the extent of its effects has been growing in the eastern United States over the past ten years or so. Surveys conducted in New York, Ohio, and Virginia (Fuchs et al. 2009, Jones et al. 2015, Han et al. 2014), have provided confirmation of the presence of GLRaVs in commercial vineyards and have yielded important information necessary to the management of grapevine leafroll disease. For example, infection by GLRaVs is permanent and infected vines must be destroyed to reduce the incidence of grapevine leafroll disease. Therefore, management of the disease would naturally include planting only stock that is free of GLRaVs. Insecticides that target mealybugs and soft scales can prevent vine to vine spread (within the vineyard) of GLRaVs that are known to be vectored by these insects (Compendium of Grape Diseases). Indeed, studies have shown that applications of insecticides like dinotefuran (Scorpion) and spirotetramat (Movento) can significantly reduce mealybug counts and result in a slowing of the progress of the disease in vineyards. One study from New York (Fuchs et al. 2015) showed that insecticide applications should target overwintered and second instar mealybug crawlers from bud swell to bloom and summer generation crawlers later in mid-summer. A study with grape phylloxera as a potential vector of these viruses showed that phylloxera can acquire the virus through phloem feeding on infected vines, but there was no evidence that phylloxera can transmit it (Wistrom et al. 2017).
As was mentioned earlier, cultivars of Vitis labrusca (Concord, Niagara) can also become infected with GLRaVs, but the infections appear to remain latent or dormant (Bahder et al. 2012) and have not been shown to result in visual symptoms of the disease (Wilcox et al. 1998). On the other hand, cultivars of V. vinifera are severely affected by GLRaVs and make up a very important and growing sector of the PA wine grape industry. Surveys conducted in New York, Ohio, and Virginia (Fuchs et al. 2009, Jones et al. 2015, Han et al. 2014) have revealed the presence of GLRaVs in commercial vineyards to the north, west, and south of Pennsylvania and have led to the development of some important guidelines for management of grapevine leafroll disease.
Given the fact that grapevine leafroll disease is common worldwide and that grapevine leafroll disease can profoundly impact wine quality and grapevine health, researchers at Penn State University are initiating a project to look for GLRaVs in Pennsylvania vineyards. As in other states, the study is targeted to help growers recognize the impact that the disease may be having on the Pennsylvania wine industry and help them to address the effects of these viruses on productivity and fruit quality, reduce their spread and impact, and thereby grow and improve the wine grape industry in Pennsylvania.
The short term, initial objectives of this project will focus on the development of an online survey to collect information from growers with regard to the presence of symptoms of grapevine leafroll disease in Pennsylvania vineyards and their interest in participating in the project. The project will then follow up with tissue sampling from participating, symptomatic and non-symptomatic vineyards throughout the state and serological analysis to determine the presence of Grapevine leafroll virus-1 and Grapevine leafroll virus-3 – the most common of the leafroll viruses – in commercial vineyards in Pennsylvania. The collection of vineyard samples across the state will map the incidence and geographical distribution of these viruses on cultivars of Vitis vinifera and Vitis interspecific hybrid grapevines. The project will also determine and compare the impact of grapevine cultivar and age on infection by Grapevine leafroll virus-1 and -3 in Pennsylvania. Once infected vines have been identified in Pennsylvania vineyards, future objectives will focus on studying the impacts of grapevine leafroll disease on grape quality and productivity in Pennsylvania, and management techniques to mitigate the economic impact of the disease on the Pennsylvania wine industry.
Vineyards will be selected from all parts of Pennsylvania, but the number of locations will favor northwestern and southeastern PA, where the majority of vineyards are located. The study will be expanded as new findings are made and the results will be made available to growers at various meetings throughout the next several years.
Bahder, B., Alabi, O., Poojari, S., Walsh, D., and Naidu, R. 2013. A Survey for Grapevine Viruses in Washington State ‘Concord’ (Vitis x labruscana L.) Vineyards. Plant Health Progress, August 5, 2013. American Phytopathological Society (online).
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.
Fuchs, M.; Marsella-Herrick, P.; Hesler, S.; Martinson, T.; Loeb, G. M. 2015. Seasonal pattern of virus acquisition by the grape mealybug, Pseudococcus maritimus, in a leafroll-diseased vineyard. Journal of Plant Pathology Vol.97 No.3 pp.503-510
Jones, T. J., Rayapati, N. A., Nita, M. 2015. Occurrence of Grapevine leafroll associated virus-2, -3 and Grapevine fleck virus in Virginia, U.S.A., and factors affecting virus infected vines. European Journal of Plant Pathology 142:209-222.
Wistrom, C. M., G. K. Blaisdell, L. R. Wunderlich, M. Botton, Rodrigo P. P. Almeida & K. M. Daane. 2017. No evidence of transmission of grapevine leafroll-associated viruses by phylloxera (Daktulosphaira vitifoliae). European Journal of Plant Pathology. Volume 147, issue 4. pp 937–941.
By: Denise M. Gardner
The eastern U.S. growing seasons can be somewhat unpredictable. Late season rains or untimely hurricane events can be a recipe for disaster for local grape growers (http://www.pawinegrape.com/uploads/PDF%20files/Documents/Viticulture/Harvest/Rain%20at%20Harvest.pdf), and a few have been unprepared for such events in the past. These weather events can lead to higher incidences of the grey-rot form of Botrytis in addition to other rots, which may also be related to pest damage. Furthermore, these weather incidences and pest damage can ultimately impact picking decisions for growers and wineries (Osborne, 2017).
It is almost inevitable that wineries need to be prepared for end-of-season weather flops, and plan for the best possible ways to manage or maintain wine quality in light of above-average disease pressure.
One disease that winemakers can prepare for prior to harvest is Botrytis. For the purpose of this article, we’ll be using the term Botrytis to indicate the grey-mold or grey-rot form of the disease. Grey-mold, the form of Botrytis more commonly noticed in humid regions or during heavy-precipitation seasons, can ultimately affect wine quality. Peynaud (1984) has defined 4 ways in which the grey-mold can negatively affect wine quality:
- Deplete wine color (especially important in red varieties),
- Increase the risk of premature browning (through oxidative enzymes),
- Deplete varietal character (through degradation of grape skins), and
- Contribution to off-flavors developed by the mold’s presence on the fruit.
Based on a 1977 study by Loinger et al., guidelines pertaining to wine quality were developed with regards to a visual assessment of Botrytis incidence on incoming fruit:
- 5-10% Botrytis rot on clusters: noticeable reduction in wine quality; wine quality is still “good” (as opposed to very good with 0% rot on clusters)
- 20-40% Botrytis rot on clusters: marked reduction in wine quality; wine quality is “low”
- >80% Botrytis rot on clusters: wine is commercially unacceptable
With a noticeable sensory and chemical difference in Botrytis-infected clusters, it is best for wineries to develop a standard operating procedure (SOP) for assessing rot-infected fruit, as well as how the grapes should be handled and processed during production. While there is no one correct way to work with the wine, below are some suggestions or options that wineries can integrate when dealing with Botrytis-infected grapes. For a full list of possibilities, please visit: http://extension.psu.edu/food/enology/wine-production/producing-wine-with-sub-optimal-fruit/fermenting-with-botrytis-101
Some wineries will sort through all incoming grape clusters prior to the crushing/destemming process to assess for any cluster damage or presence of unwanted material. If your operation is not set up with this equipment, sorting can also take place in the vineyard. Depending on the concentration of disease and on the projected wine style or quality parameter the fruit will go towards, disease portions of clusters can be cut out in the vineyard. Or diseased fruit can be left in the vineyard to deal with after the harvest is complete. Sorting out diseased fruit from that of decent quality will reduce the impact of the mold on the wine’s aroma, flavor, and quality.
Limit Contact Time with Skins
Depending on the resource, there are various recommendations for how to handle diseased fruit. In whites, some recommend whole cluster pressing and tossing the first 10+ gallons, which are rich in Botrytis metabolites (Fugelsang and Edwards, 2007). Many recommend separating juice press fractions for white and rosé wines, as this will give the vintner more control over the chemical constituents (e.g., phenolics, enzymes, and disease-related off-flavors) in the final wine.
Depending on the desired outcome for a red wine, treating or limiting skin contact with diseased fruit may be ideal post -primary fermentation. This would include avoiding extended maceration processes. Due to the fact that the presence of Botrytis on red varieties reduces anthocyanin and phenolic extraction (Razungles, 2010) in addition to the varietal aromatics, excessive skin contact may not be ideal during primary fermentation. Whole berry fermentations, as opposed to a more aggressive crush and destem process, may help minimize extraction of Botrytis metabolites, which can also contribute to mouthfeel variations or off-flavors.
Tannin additions pre-fermentation may also be good considerations to compensate for phenolic losses associated with Botrytis infection. Pre-fermentation and post-fermentation additions may help rebuild the wine’s structure or provide constituents for color stabilization.
Flash pasteurization (i.e., flash détente) has been previously recommended for Botrysized fruit to inactive the laccase enzyme associated with Botrytis, enhance color stability in reds, as well as improve the aromatics and flavors associated with the final wine. Wines that undergo a thermovinification step tend to extract more anthocyanins and phenolics compared to traditionally fermented wines (Razungles, 2010). Additionally, this heat step helps to inactivate laccase, which can contribute to early browning or oxidation of young wines. However, commercial producers may not find this technological application easily accessible.
Therefore, in addition to minimizing skin contact time, winemakers will want to reduce contact time with the gross lees, and may also remove the wine from fine lees associated with the mold-infected fruit quickly. The integration and use of clean, fresh lees, however, is still encouraged. Removing the lees associated with mold-infected fruit can help reduce additional contact time with rot metabolites that have settled out with the lees. This inhibits further integration of those metabolites into the wine.
Inoculate with a Commercial Yeast Strain
The presence of rot is one incidence in which processing techniques (e.g., cold soak) that encourage native microflora to dominate the fermentation are probably not desired. Things like cold soak and native ferments allow ample opportunity for the mold to progress and contribute to the wine’s flavor.
Fruit that has rot or microflora issues is best inoculated with commercial yeast and malolactic bacteria strains to outcompete the native microflora (including those microorganisms that contribute to the rot), and to give the fermentation its best chance at completing the fermentation cleanly. Remember that proper yeast nutrition is important to support the yeasts’ growth and to reduce the risk of hydrogen sulfide development. For more information on determining the starting nitrogen concentrations (YAN) and how to properly treat your fermentation with added nutrients, please refer to:
Penn State Extension’s Wine Made Easy Fact Sheet: Nutrient Management During Fermentation
With high Botrytis concentrations, a more robust yeast strain may be preferred in order to quickly get through primary fermentation. A quicker fermentation may simplify the aromatics associated with the wine, but it will also ensure little opportunity for additional spoilage. Saccharomyces bayanus strains are often selected as more robust yeast strains.
Use of Sulfur Dioxide
Sulfur dioxide additions at crush will be determined based on the style of wine in which you are producing (e.g., white, rosé, red, etc.), but in general, the use of sulfur dioxide can help inhibit further spoilage of your product and retain antioxidant capacity. Sulfur dioxide additions in the juice stage will help minimize early browning, but primarily inactivate PPO.
In general, botrysized wines tend to require more sulfur dioxide as Botrytis metabolites bind with free sulfur dioxide (Goode, 2014). This is true even when processing wines with the noble rot version of Botrytis.
When primary fermentation, and malolactic fermentation (dependent on style), is complete it is a good idea to ensure that the wine has an adequate free sulfur dioxide content in order to retain its antimicrobial protection.
Some fining agents may also be applicable in the juice stage. For example, some producers find it helpful to fine juice with bentonite in order to reduce protein content, as well as help minimize rot-associated off-flavors or partially reduce laccase concentrations.
PVPP can be added to the juice to reduce potential browning pigments or their precursor forms (Van de Water, 1985).
In both of these scenarios, neither bentonite or PVPP is specific for rot-related constituents, but each could be helpful to avoid potential challenges later on in the production process.
The presence of Botrytis can also contribute glucans to the must/wine, which can cause filterability problems for heavily-infected wines. In this situation, many suppliers have beta-glucanase enzymes that can be applied either to the juice, wine, or both, to help breakdown the glucans and enhance ease of filterability.
A Word about Laccase
Both polyphenol oxidase (PPO) and laccase can cause early browning in grapes and wine. However, PPO is inhibited by the alcohol content that is developed during primary fermentation. Laccase, however, is not inhibited by the presence of alcohol, and can only be inactivated by a pasteurization step, heated to at least 60°C (140°F) (Wilker, 2010).
Grapes tend to be higher in laccase concentration when infected with Botrytis, and, thus, wines produced from grapes that had a high incidence rate of Botrytis can develop a brown hue post-primary fermentation. This oxidative activity can occur even in young wines.
If you are concerned about the prevalence of laccase in diseased-fruit, wineries can submit wine samples to a wine lab for a laccase test. Or, if you own a copy of “Monitoring the Winemaking Process from Grapes to Wine: Techniques and Concepts” by Patrick Iland et al., pg. 90 and 94 have 2 laccase test protocols that outline how wineries can assess oxidation by laccase. The results of these test will indicate if extreme treatments are required during production to avoid the rapid and early oxidation caused by laccase.
- Fermenting with Botrytis 101
- Management of Botrytis Infected Fruit
- Managing Botrytis Infected Fruit Fact Sheet
Goode, J. 2014. The Science of Wine: From Vine to Glass. (2nd Ed.) University of California Press: Berkley, California. 216 pg.
Fugelsang, K.C. and C.G. Edwards. 2007. Wine Microbiology: Practical Applications and Proceedings. (2nd Ed.) Springer: New York, NY. 393 pg.
Loinger, C., S. Cohen, N. Dror, and M.J. Berlinger. 1977. Effect of grape cluster rot on wine quality. AJEV. 28(4): 196-199.
Peynaud, E. 1984. Knowing and Making Wine. Wiley-Interscience: New York, NY. 391 pg.
Razungles, A. 2010. Extraction technologies and wine quality. In Managing Wine Quality, Vol. 2 Oenology and Wine Quality. Andrew G. Reynolds, Ed. Woodhead Publishing: Philadelphia, PA. 651 pg.
Van de Water, L. 1985. Fining Agents for Use in Wine. The Wine Lab.
Wilker, K.L. 2010. How should I treat a must from white grapes containing laccase? In Winemaking Problems Solved. CRC Press: Boca Raton, Florida. 398 pg.
Growth Regulator Herbicides Negatively Affect Grapevine Development: Identification of Herbicide Drift Damage, How to Prevent it, and What to do if it Occurs in your Vineyard
By: Michela Centinari
The Penn State Extension grape team has been receiving reports on herbicide drift damage in vineyards from a number of Pennsylvania wine grape growers this growing season, definitely many more than in previous years. All herbicides registered for grapes can potentially harm the vines if not applied in accordance to the pesticide label (e.g., glyphosate products) . However, in many of the reported cases through the 2017 growing season the damage was caused by herbicides not registered for grapes, which drifted into the vineyards from nearby fields.
Damage from herbicide drift is, unfortunately, something that grape growers across the country are too familiar with. It represents an economic threat for the grape and wine industry and should not be underestimated. Herbicide drift damage can, indeed, result in significant crop losses which may extend to multiple seasons, and in some cases it also results in vine death. Several extension web resources are available to assist grape growers in preventing and dealing with herbicide drift damage. Some of them are listed at the end of this article, including one from Andy Muza, extension educator at Penn State (Growth Regulator Herbicides and Grapes Don’t Mix).
Due to the increase in reports of herbicide drift damage in Pennsylvania vineyards it seems appropriate to discuss some key points surrounding this issue. This article will review how to identify herbicide drift symptoms, what measures grape growers and pesticide applicators can take to prevent herbicide drift, and what steps to take if the drift occurs.
Plant growth regulators (PGR) herbicides are those most likely to injure grapevines, mainly through drift.
I will only focus on the herbicides which belong to the plant growth regulators (PGR) mode of action group. Common active ingredients of PGR herbicides are 2,4-D (2,4-Dichlorophenoxyacetic acid; phenoxy family), dicamba (benzoic acid), tricolopyr or picloram (pyridine family). A partial list of common PGR herbicides as well as other herbicides that may injure grapevines can be found at Preventing Herbicide Drift and Injury to Grapes, Table 1.
PGR herbicides are widely used for controlling broadleaf weeds in many crops, such as wheat, corn, soybean, pasture, rangeland, etc. They are also frequently utilized to control unwanted broadleaf vegetation in turf, by railroads, road ditches, fence lines, and rights-of-way. These herbicides are not registered for use with grapes. However, when applied to a nearby field, they can drift into the vineyard and cause significant injury to grapevines.
Most of the herbicide drift damage reported this season by Pennsylvania grape growers were caused by drift of PGR herbicides (Figure 1). Physiological symptoms to PGR exposure is not too surprising because grapevines are extremely sensitive to PGR herbicides, including the phenoxy, benzoic, and pyridine classes of compounds . For example, herbicides containing 2,4-D can damage grapes at a concentration 100 times lower than the recommended label rate. Moreover, drift from PGR herbicides can injure grapevines located half a mile or more from the application site.
What is “drift”?
Drift is defined as “the movement of herbicides off the site where they were applied” . Non-target drift can occur either as spray drift or vapor drift. Spray drift occurs during herbicide application when small droplets move off the application site under unfavorable wind conditions. Vapor drift occurs after herbicide application as the spray material volatizes or evaporates and is carried away from the application site by wind or temperature inversions. Some PGR herbicides, such as ester formulations of 2,4-D, readily volatilize, especially when used under high temperatures and low humidity conditions (high vapor pressure) .
How PGR damage occurs in grapevines
PGR herbicides mimic auxins, plant hormones that regulate growth and development. Applications of PGR herbicides disrupt plant hormone balance causing growth abnormalities. PGR herbicides can be absorbed by both roots and leaves, however grapevines are usually injured through foliar absorption.
How to tell if the vines have been damaged by PGR herbicide drift
Damage from PGR herbicides typically appears within 2 days of the drift occurrence. Herbicide drift can damage leaves, shoots, flowers, and fruit. Leaf symptoms are often easy to recognize, but sometimes can be mistaken with those of fanleaf degeneration, a viral disease . Growers can send pictures of damaged vines to a local extension specialist for confirmation.
Typical symptoms include:
- Distorted leaf appearance: Symptoms are typically more severe on the youngest leaves and shoot tips. Affected leaves are “smaller, narrow, deformed, and they have closely packed, thick veins that lack of chlorophyll” . They may also have a distinct fan-shape appearance, and depending on the herbicide’s active ingredient, they can bend downward or cup upward (Figures 2, 3). Leaves may or may not outgrow the symptoms, it largely depends on the severity of the injury and other factors listed in the following section (“Factors affecting the severity of injury”). It is also common to see regrowth of deformed leaves after drift exposure .
- Shoot growth: Damaged shoot tips rarely resume growth, but lateral shoots can keep growing giving in some cases a “bushy” appearance to the vine resulting in a highly shaded canopy and poor fruit sun exposure.
- Flower clusters (inflorescences): symptoms can include aborted or failed flowers, and poor fruit set (Figure 4). If the injury is severe enough it can cause reduced yield at harvest and poor fruit quality, in addition to potentially illegal residues of herbicide on the exposed crop.
In some cases, depending on the timing and level of drift exposure, floral symptoms may be much more pronounced than those on the leaves making the diagnosis more difficult (i.e., growers may relate poor fruit set or dead flowers to other causes rather than herbicide drift) (Figure 5).
If the damage occurs early in the season, between bud burst and bloom, as it usually does, a significant reduction in healthy leaf area during the period of rapid shoot growth may affect vine photosynthetic capacity, lowering vine ability to fully ripen the crop and possibly its ability to survive cold winters.
Unfortunately there is no guarantee that the vines will fully and rapidly recover from herbicide drift damage. Carry-over effects into the following years, such as reduction in vine vigor, yield, fruit quality, and increased susceptibility to diseases, are common if the damage is extensive and/or the vines have been repeatedly exposed to PGR-herbicide drift. Finally, vines may die as a consequence of their weakened condition .
What factors affect the severity of PGR-herbicide drift damage?
Some of the most important factors affecting the severity of drift damage are:
- Vine growth stage at the time of exposure. Grapevines are always sensitive to PGR herbicides, but they are most susceptible during the early part of the growing season, from bud burst through bloom. While dependent on the growing season and site, in Pennsylvania this usually occurs around April through June. Early in the growing season shoots are rapidly growing and PGR herbicides are quickly translocated to the shoot tip, where the natural concentration of auxins is greatest inside the grapevine. If exposure occurs later in the season, vines typically outgrow the damage and still produce good yield .
- Vine age: Younger plants are more vulnerable and they have a lower ability to recover from the PGR herbicide damage than mature vines. Young vines may be killed even at low exposures .
- Level of exposure: Higher concentration and/or repeated exposures will result in higher disruption of the vine’s physiology and lower ability of the vines to rapidly and fully recover from the damage .
- Grapevine variety. All grapevine varieties are sensitive to PGR herbicides, but some may show more visual and physiological symptoms than others (see for example Table 1, Questions and Answers about Vineyard Injury from Herbicide Drift)
- Other factors include herbicide concentration and formulation (for example ester formulations of 2,4-D are more volatile than amine formulations, thus ester formulations of 2,4-D are more prone to move off-target as vapor), weather conditions (temperature, humidity, and most importantly wind speed) at the time of herbicide application.
What is the best strategy to protect vines from herbicide drift injury?
Prevention is undoubtedly the best strategy for grapevine growers to avoid herbicide damage. To reduce the risk of herbicide drifting into their vineyard, vineyard managers and/or owners should be proactive. Some prevention steps both grape growers and nearby growers of other crops can take are listed below:
- Maintain good relations with neighbors. Vineyard owners and managers should make sure their neighbors within approximately a half-mile to 1 mile radius, are aware that vines are extremely sensitive to PGR herbicides . It is also recommended to encourage neighbors to “use drift-reduction spray nozzles (nozzles that produce large droplets) and to select herbicides that are less likely to injure grapes” . If growers of other crops are unaware of damage to grapevines, collecting information such as this blog post, may be an important educational tool to share. Mike White, viticulture extension specialist at Iowa State University, suggests to share an aerial map of the property showing the vineyard location with neighbors and commercial pesticide applicators to increase their awareness. It is also recommended to communicate the presence of the vineyard to state and county highway departments.
- Windbreak (shrubs, trees, physical barriers) and a buffer area between the vineyard and the edge of the field being sprayed are always a good idea. Penn State offers a free publication or pdf print-out regarding windbreaks: http://extension.psu.edu/publications/uh172/view
- For those states where the service is available, growers can register the location of their vineyard on https://driftwatch.org/. This online service is not available in Pennsylvania, but in many Midwestern states growers and pesticide applicators can use this web resource free of charge to report (growers) and locate (applicators) potential drift hazards.
Taking all these steps may not guarantee that herbicide drift will not occur in your vineyard, but increasing pesticide applicators awareness of grape sensitivity to PGR herbicides, the resulting economic loss, and potential litigation risks may very well serve the purpose.
Applicators should always follow all the measures available to minimize the risk of herbicide drift into a nearby vineyard or to other sensitive crops. Legal complaints may result in expensive settlements. In an extreme example, an owner of a 150-acre vineyard in Australia was awarded AUS$ 7M in damages over pesticide drift (Grape grower Awarded $7M in damages over spraying) that occurred from 2013 to 2015.
If PGR herbicides are applied after vine bud burst, applicators should consider eliminating volatile compounds and apply only non-volatile products.
Extension personnel could also facilitate communication between grape and crop field growers as it happens in Long Island, NY. Extension personnel from Cornell University-Long Island, including Alice Wise and Andy Senesac, organized a meeting with local grape and sod growers to tackle the herbicide drift issue which was affecting local grape growers without having to resort to regulatory restrictions. The result of that meeting was a ‘gentleman’s agreement’ not to spray herbicides containing 2,4-D after April 15, around bud burst for the earliest grapevine varieties in Long Island. To keep all parties informed, extension sends out a weekly reminder about this issue.
What to do if the drift occur
Here some key steps Mike White put together on what to do right after a drift incident :
- Identify area affected.
- Document the date, time and growth stage of the grapes.
- If possible, identify the source of the drift and make a determination if you want to settle the problem amongst your neighbors.
- Contact your state department of agriculture (Pennsylvania Department of Agriculture, PDA) as soon as possible if you cannot determine the source of the drift and/or you want to formalize the complaint (30 – 45 day deadline in many states).
- Flag both affected and unaffected plants, take high resolution pictures weekly until symptoms subside and measure final yields per plant.
- Severe injury settlements should be delayed until after next season’s harvest. Photo and yield documentation should be continued. Unless the settlement offered seems exceptionally lucrative, I would suggest delaying any settlements until after next season’s harvest to assess for potential carry-over vine damage.
For information on where to find a drift consultant please refer to Need Help? Pesticide Drift Consultants
How to estimate the loss in revenue
Tim Martinson, viticulture extension specialist at Cornell University, provided useful examples on how to estimate the economic loss associated with herbicide drift damage under different scenarios. Scenarios include vine recovery across multiple years, with and without the need of vines replacement. Please refer to: Diagnosis, Economics, Management of Grape Injury from 2,4D and other Growth Regulator Herbicides.
How to manage damaged vines
There is limited information available on best management practices for vines affected by herbicide drift damage. To favor a full and a rapid recovery it is recommended to still implement good management practices and avoid further stress to damaged vines, as for example over cropping (assuming damaged vines have fruit). Fungicide applications made to protect the fruit should not be necessary if the fruit has been removed . It is also recommended to adjust pruning strategies to smaller vines, with the intent of regaining full vine size .
- Growth regulator herbicides and grapes don’t mix. Penn State. https://psuwineandgrapes.wordpress.com/2015/10/16/growth-regulator-herbicides-and-grapes-dont-mix/
- Watch out for: Grapes. Purdue University. DW-10-W. https://www.extension.purdue.edu/extmedia/ho/dw-10-w.pdf
- Preventing herbicide drift and injury to grapes. Oregon State University. EM 8860. http://extension.oregonstate.edu/yamhill/sites/default/files/spray_drift/documents/3-preventing_herbicide_drift_to_grapes_osu_8660.pdf
- Avoid phenoxy herbicide damage to grapevines. Texas Cooperative Extension. http://winegrapes.tamu.edu/files/2015/11/phenoxy1.pdf
- Avoiding 2,4-D injury to grapevines. Colorado State University. http://webdoc.agsci.colostate.edu/cepep/FactSheets/Avoiding%202,4-D%20Injury%20to%20Grapevines.pdf
- Questions and answers about vineyard injury from herbicide drift. Kansas State University. MF-2588. https://www.bookstore.ksre.ksu.edu/pubs/MF2588.pdf
- Need Help? Pesticide drift consultant. Northern Grapes Project. http://northerngrapesproject.org/wp-content/uploads/2013/01/11-3-NE-Find-Drift-Consultant.pdf
- Top 10 questions about herbicide drift into vineyards. Iowa State University. https://www.extension.iastate.edu/wine/growersnews/243-may-29-2013#Top
- The view from New York: Diagnosis, economics, management of grape injury from2,4‐D and other growth regulator herbicides. Northern Grapes Project. http://northerngrapesproject.org/wp-content/uploads/2013/01/Martinson-2-4D-Presentation.pdf
By: Denise M. Gardner
It’s that time of year again: bottling time! The past year’s vintage is slowly starting to take up too much room in the cellar and now is the time for decision making in terms of preparing for the pending vintage. Finalizing a good bottling schedule before harvest starts is an essential good winemaking practice, but bottling comes with its own set of challenges.
It is not uncommon for winemakers to express feelings of “not being able to sleep at night” when wines get bottled, as they are worried about possible re-fermentation issues. As wine naturally changes through its maturity, it is easy to feel insecure about bottling wines, especially those wines that may have had challenges associated with it throughout production.
However, there are several analytical tests that winemakers can add to their record books every year to ensure they are bottling a sound product. The following briefly describes a series of analytical tests that provide information to the winemaker about stability and potential risks associated with the product when it goes in bottle.
Basic Wine Analysis Pre-Bottling:
This first list is the bare minimum data that should be measured and recorded for each wine getting bottled, regardless of the wine’s variety or style. Keeping accurate records of these chemistries is also helpful in case something goes wrong while the bottle is in storage or after it is purchased by a customer.
pH is essential to know as it gives an indication for the wine’s stability in relation to many chemical factors including sulfur dioxide, color, and tannin. For example, high pH (>3.70) wines provide an indication that more free sulfur dioxide is needed to obtain a 0.85 ppm molecular free sulfur dioxide content. At the 0.85 ppm molecular level, growth of any residual yeast and bacteria in the wine should be adequately inhibited.
High pH wines tend to have issues with color stability. At this point, color stability can be addressed by blending or with use of color concentrates (e.g., Mega Purple). Keep in mind that if the wine is blended with another wine, all chemical analyses, including pH, should be completed on the blend (as opposed to average individual parts) prior to bottling.
Free and Total Sulfur Dioxide Concentration
In the United States, total sulfur dioxide is regulated and must fall under 350 mg/L for all table wines (CFR: https://www.ecfr.gov/cgi-bin/text-idx?SID=eddaa2648775eb9b2423247641bf5758&mc=true&node=pt27.1.24&rgn=div5#sp27.1.24.a).
However, the free sulfur dioxide concentration provides an indication to the winemaker regarding antioxidant strength and perceived antimicrobial protection. To inhibit growth of yeast and bacteria during bottle storage, a 0.85 ppm molecular free sulfur dioxide concentration must be obtained. The free sulfur dioxide concentration required to meet the molecular level is dependent on pH. Therefore, free sulfur dioxide additions should be altered and based on a wine’s pH for optimal antimicrobial protection.
Analytically, it can be daunting to measure free sulfur dioxide as the wet chemistry set up looks intimidating. However, many small commercial wineries have benefited from the integration of a modified aeration-oxidation (AO) system, and with a little practice, have been relatively successful at monitoring free sulfur dioxide concentrations. A few wineries have worked to validate use of Vinmetrica’s analyzer (https://vinmetrica.com/), and found results comparable to those obtained by use of the AO system.
Residual (or Added) Sugar
Any remaining sugar in the bottle, whether through an arrested fermentation or direct addition, can pose a risk for re-fermentation post-bottling. This is especially true if the winery lacks good cleaning and sanitation practices. Nonetheless, it is a good idea to assess the sugar content pre-bottling to record a baseline value of the sugar concentration going into bottle. If bottles were to start re-fermenting, a sugar concentration could be analyzed and used to compare against the baseline value in order to assess the potential of yeast re-fermentation.
For wineries with minimal residual sugar concentrations, a glucose-fructose analysis (often abbreviated glu-fru) is often used to help determine accurate sugar content. For wines with added sugar an inverted glucose-fructose analysis may be required.
If you are concerned about potential risk for Brettanomyces (Brett) bloom post-bottling, it is usually encouraged to reduce the sugar content in the finished wine below 1% (<10 g/L sugar) in the bottle.
Malic Acid Concentration
While using paper chromatography to monitor malolactic fermentation (MLF) is useful, it does not give an accurate reflection of residual malic acid concentration. In fact, some winemakers find that a paper chromatogram may show a MLF has been “completed,” but would prefer to have lower residual malic acid concentrations remaining in the wine.
During my time at an analytical company, 0.3 g/L of malic acid and below was considered “dry.” This is typically a safe level of residual malic acid to avoid post-bottling MLF.
Volatile acidity (VA) is federally regulated, and levels are indicated in the Code of Federal Regulations (CFR: https://www.ecfr.gov/cgi-bin/text-idx?SID=eddaa2648775eb9b2423247641bf5758&mc=true&node=pt27.1.24&rgn=div5#sp27.1.24.a). For most states, with California as an exception, the maximum allowable VA for red wines is 1.40 g/L acetic acid (0.14 g/100 mL acetic acid) and for white wines is 1.20 g/L acetic acid (0.12 g/100 mL acetic acid).
Monitoring VA through production is a good indicator of acetic acid bacteria spoilage. At minimum, wineries should record VA
- immediately post-primary fermentation,
- periodically through storage (e.g., every 2-3 months) and
Whiling monitoring VA, sharp increases in VA should alarm the winemaker of some sort of contamination. Typically, these increases are caused by acetic acid bacteria, which can only grow with available oxygen.
As a general rule of thumb, knowing the final alcohol concentration is a good idea. Alcohol content helps determine a tax class for the wine and is required for the label.
Titratable Acidity (TA)
All wines are acidic in nature as they fall under the pH 7.00. However, titratable acidity (TA) acts as an indicator for the sour sensory perception associated with a given wine. For example, two wines, Wines 1 and 2, with a pH of 3.40 may have different TAs. If Wine 1 has a TA of 8.03 g/L tartaric acid while Wine 2 has a TA of 6.89 g/L tartaric acid, Wine 1 would likely taste more acidic (assuming all other variables are the same).
Cold stability tests are often recommended to ensure the wine is cold stable, and will, therefore, not pose a threat of precipitating tartrate crystals during its time in bottle. Not all wines require a cold stability process (e.g., seeding and chilling). Cold stability testing can be done prior to a cold stabilization step in order to avoid extraneous processing operations, saving time and money.
For more information on cold stability processes and testing, please visit Penn State Extension’s website: http://extension.psu.edu/food/enology/analytical-services/cold-stabilization-options-for-wineries
Additionally, haze formation is a potential risk post-bottling. While hazes do not typically offer any safety threat to wine consumers, they often look unappealing. Protein hazes tend to make the wine look cloudy. Some varieties are more prone to protein hazes then others, and running a protein stability trial could minimize the risk for a protein haze in-bottle.
It is important to remember that due to the fact protein stability is influenced by pH, cold stability production steps should take place before analyzing the wine for protein stability and before going through any necessary production steps to make the wine protein stable. This is due to the fact that cold stability processes ultimately alter the wine’s pH, and the chemical properties of proteins are influenced by the pH.
Analysis for Those that May Consider Bottling Unfiltered:
Yeast and Bacteria Cultures (Brett, Yeast, Lactic Acid Bacteria, Acetic Acid Bacteria)
Having a microscope in the winery can be a great reference point in terms of scanning for potential microbiological problems. However, if the winery does not have a microscope, but knows that some microbiological issues or risks may exist in a wine, having a lab set test the wine on culture plates is a good indicator for potential growth risks during the wine’s storage.
If the wine is going to be bottled using a sterile filtration step, keep in mind that wines are not bottled sterile. Assuming the absolute filtration method is working properly, the wine has potential to become re-contaminated with yeasts and bacteria from the point of which it exits the filter. In fact, it is not uncommon for wines to pick up yeast or bacteria contamination during the bottling process.
Managing free sulfur dioxide concentrations can help inhibit any potential growth from contamination microorganisms if the proper antimicrobial levels (0.85 ppm molecular) are obtained at that wine’s pH and retained during the bottle’s storage.
4-EP and 4-EG Concentrations for Reds
For wines that may have had a Brettanomyces (Brett) bloom, knowing the concentrations of 4-EP and 4-EG in the wine going into bottle is a good result to keep on file. If a Brett bloom occurs later in the bottle, it is likely (although, not guaranteed) that the volatile concentration of 4-EP and/or 4-EG may increase and confirm the problem.
Furthermore, evaluating a wine for 4-EP and 4-EG concentrations can also help isolate a possibility of Brett existence, especially if their concentrations are below threshold. However, it should be noted that both compounds can also exist in wines that are stored in wood, even without a Brett contamination.
Double Check: PCR for Reds
Brett can be a tricky yeast to isolate and identify. It is usually recommended to run multiple analytical tests related to Brett in order to confirm its existence or removal from a wine. While culture plating identifies living populations of microorganisms, PCR cannot typically differentiate between live and dead cells as it is measuring the presence of DNA. A microorganism’s DNA can get into a wine after yeast death and through autolysis. Therefore, a positive PCR result for Brettanomyces is hard to confirm if the result includes live cells, dead cells, or a combination of both.
Culture plating can help confirm the presence of active, live cells, but the success rate of growing Brettanomyces in culture plates is variable.
Nonetheless, scanning wines by PCR for Brett can help winemakers isolate a general presence and risk of Brett in their wines.
Still Worried About Your Wine Post-Bottling?
Bottle sterility testing is helpful, especially when a winemaker wants to ensure wines have been bottled cleanly. For this type of testing, it is best to sample a few bottles
- at the beginning of a bottling run,
- immediately before any breaks,
- immediately after any breaks, and
- at the end of a bottling run.
Bottles can, again, be evaluated under a microscope and evaluated for the presence of microorganisms. Bottles can also be sent to a lab for culture plating. The growth of yeasts or bacteria from culture plates at this stage indicates a failure of the sterile filtration system or contamination of the wine post-filtration. Clean wines, obviously, should help put a winemaker’s mind at ease as it matures in bottle.
Ensuring a wine’s stability post-bottling is a challenge. However, with proper cleaning and sanitation methods coupled with the right analytical records, winemakers can reduce their worry. For information on any of these topics, please visit:
- An Overview of Winery Sanitation by Patricia Howe: https://www.umpqua.edu/images/areas-of-study/career-technical/viticulture-enology/downloads/conferences/technical-symposia/2011-march-wine-flaws/2011-ts-howe-winery-sanitation.pdf
- Making Cleaning and Sanitation Practical for the Small Commercial Winery by Denise M. Gardner: http://bit.ly/PracticalWinerySanitation
- Minimizing Spoilage of Wines in Barrel by Denise M. Gardner: http://bit.ly/WineBarrelSanitation
- Bottling Line Cleaning Protocol by Scott Labs: http://www.scottlab.com/uploads/documents/technical-documents/1191/Bottling%20Line%20Cleaning%20Protocol.pdf
- Preparing Wines for Bottling by Enartis Vinquiry: http://www.enartis.com/upload/images/03_2016/160311011309.pdf
- Starting a Lab in a Small Commercial Winery: http://extension.psu.edu/food/enology/analytical-services/setting-up-your-winerys-lab
- Wine Analytical Labs: How Your Winery Can Use Them: http://extension.psu.edu/food/enology/analytical-services/wine-analytical-labs-how-your-winery-can-use-them
By: Maria Smith and Dr. Michela Centinari, Dept. of Plant Science
In the previous post, we discussed shoot thinning as a method to achieve vine balance and improve the canopy microclimate (Part I: Shoot Thinning). In this post, we will discuss the use early leaf removal (ELR), a canopy management practice implemented around bloom. ELR primarily serves to reduce the severity of Botrytis bunch rot infection in susceptible varieties (Wines and Vines: Benefits and Costs of Early Leaf Removal), but may also be an effective practice for reducing crop yield.
ELR is currently considered an experimental canopy management practice for vineyards. While it shows great promise within the research and Extension literature (1, 2, Cornell Cooperative Extension 2016), Penn State Extension does not currently recommend implementing ELR as a replacement for traditional methods (i.e., cluster thinning, fungicide sprays) for yield and rot control. However, growers curious about the effects of ELR may find it useful as a supplementary canopy management practice, especially for disease management and crop reduction.
Throughout this post, we will discuss the effects of ELR on:
- Crop level in highly-fruitful varieties that produce a high number of clusters (3-4 per shoot) or large clusters such as vinifera cvs. Grüner Veltliner, Sangiovese, and Barbera.
- Botrytis bunch rot infection.
- Fruit and wine composition.
What is Early Leaf Removal (ELR) and how does it work?
ELR is the removal of basal leaves of the main shoots and, optionally, lateral shoots developed from the basal nodes (http://gph.is/2r3ZLc0; Figure 1).
ELR is typically performed shortly before (pre-bloom) or at the beginning of bloom (trace-bloom; Figure 2A). In some cases, however, it has been performed later during full-bloom or at the onset of fruit-set (Figure 2B).
Before and during bloom, the oldest basal leaves have a major role in providing carbohydrates (e.g., sugars) to support the growing shoot and inflorescence (i.e., flower clusters). In contrast, young leaves on the middle and top part of the shoot are still developing and not very photosynthetically ‘active’ at this time (3). Literature suggests the removal of basal leaves at bloom may starve the inflorescence for a carbohydrates food source (4). The lack of carbohydrate resources reduces fruit-set (i.e., the percentage of flowers that will develop into berries), which likely reduces the number of berries per cluster at harvest (5). When ELR is performed later, at the onset of fruit-set, removing basal leaves may induce a reduction in berry size and an increase in berry abscission due to carbohydrate limitation at the onset of fruit development (6). Therefore, yield reduction achieved with ELR is the result of reduced cluster weight (reduced number of berries per cluster and/or reduced berry weight). In contrast, yield reduction achieved by cluster thinning is the result of a reduced number of clusters per vine.
Why are ELR practices currently under research investigation?
An increased number of studies is investigating the use of ELR as a potential alternative to cluster thinning techniques used for crop yield control in highly-fruitful wine grape varieties (5, 6, 7). As opposed to traditional cluster thinning, ELR can be more easily mechanized. (Author’s note: for more information on mechanization, see Additional Resources at the bottom of the post.) ELR may additionally confer benefits such as:
- Reduced severity of Botrytis rot infection
Cluster compactness, or the tightness of berries on the cluster, has been positively related to the severity of Botrytis bunch rot infections (8). It is suggested that more compact clusters experience more rot. ELR decreases cluster compactness by reducing the number of berries per cluster and/or the berry size. Decreased cluster compactness through implementing ELR has reduced Botrytis rot infections in several tight-cluster varieties such as Pinot Noir, Riesling, Chardonnay, and Vignoles (1, 9, 10, 14). As an additional benefit, the removal of basal leaves increases sunlight penetration and air movement in the fruiting zone, which is important for improving spray penetration within the canopy (2016 Post Bloom Disease Management Review).
- Improved fruit and wine composition
ELR has consistently been reported to alter fruit composition, particularly for red Vitis vinifera varieties in Mediterranean climates (Tempranillo, Sangiovese, Barbera, etc.; 2, 5, 6, 12). In several instances, fruit harvested from ELR vines had higher levels of total soluble solids (TSS, °Brix), phenolic compounds (e.g., flavonols), and total anthocyanins compared to un-defoliated vines (2, 11, 12). ELR can also reduce methoxypyrazines, ‘herbaceous’ aromas found in higher concentrations among immature grapes at harvest, and may contribute to improved wine color intensity (13). ELR may alter three important parameters associated with berry development and ripening (2):
- Decreased berry size – Smaller berries tend to have greater skin-to-pulp ratio and higher concentrations of desirable phenolic and aroma compounds which are mainly present in the skin.
- Increased leaf area-to-yield ratio on a per shoot basis – A greater leaf area-to-yield ratio may translate into higher sugar produced per shoot. More sugar availability could contribute to better fruit ripening.
- Improved canopy microclimate – ELR, like traditional leaf removal, improves the microclimate of the fruiting zone through decreased leaf density and increased sunlight penetration to the fruit. Higher temperatures coupled with increased sunlight exposure in the fruiting zone can be especially important under cool or cloudy ripening conditions, as they may accelerate berry ripening, resulting in higher TSS, decreased malic acid, increased anthocyanin concentration, and degradation of green volatile aroma compounds such as methoxypyrazines that may mask fruity or floral aromas. Higher ultraviolet (UV) radiation in the fruiting zone in response to increased sunlight penetration may increase production of flavonols, as flavonols biologically act to protect berries from UV exposure (3, 11). Flavonol compounds along with anthocyanin influence red wine color and are used as determinants of quality in fruit (11).
It is important to keep in mind that yield reduction is not desirable in all grape varieties. The use of ELR with varieties that do not typically over-crop may result in under-cropped situations with potential negative effects on fruit quality and vine health, in addition to unnecessary yield reductions and thus revenue loss.
How many leaves should be removed to induce yield reduction?
Unfortunately, there is no “one size fits all” number of leaves to remove when implementing ELR as a vineyard management practice. The required number of leaves removed to significantly reduce yield through reduced fruit-set depends on several factors, including shoot length and the shoot leaf area at the time of removal. For example, by pulling 5 basal leaves on a shoot with only 8 leaves at trace-bloom, we would remove about 63% of the total number of leaves. The percentage of leaf area removed would be even higher as the remaining leaves at the top of the shoot are much smaller than those removed from the bottom of the shoot. In contrast, a longer shoot with 15 leaves total will only lose 33% of the leaf area when 5 basal leaves are pulled. Thus, removing 5 leaves from a short shoot would have a more severe effect of depriving the inflorescence of sugar resources than removing the same number of leaves on long shoots (Figure 3).
Sometimes the degree of ELR is severe in order to induce a yield reduction commensurate with the more traditional cluster thinning technique. For example, Pinot Noir grown in southwestern Michigan showed a reduction in yield from 6.1 tons per acre in non-defoliated vines to 3.6 tons per acre when about half (8 out of 15) of the leaves on the shoots were removed (1). This was a 40% reduction in yield. Comparatively, when 4 or 6 leaves were removed from the Pinot Noir, no significant effect was found in crop yield (1).
With the high potential for crop yield reduction, Dr. Michela Centinari’s lab has been experimenting with ELR for the past two years. We have been examining the effects of ELR at trace-bloom on Grüner Veltliner (V. vinifera) grown in Central Pennsylvania. Grüner Veltliner is highly fruitful, typically producing 2-3 large clusters per shoot. In our experimental practices, we removed 5 basal leaves at trace-bloom. Our objective was to compare the use of ELR to cluster thinning for crop yield reduction. Our first year of data found that the implementation of ELR decreased yields by only about 15% (10.7 tons per acre in the non-defoliated control to 9.3 tons per acre in defoliated vines). In comparison, vines thinned to 1 cluster per shoot had a 45-50% reduction in yield compared to the un-thinned control (10.7 tons per acre to 6.5 tons per acre).
This suggests that a greater leaf removal intensity may be needed for this variety to produce yield reduction comparable to cluster thinning, and we are currently testing different intensity levels of trace-bloom ELR to evaluate if the amount of leaf area removed correlates with reduction of fruit-set and yield at harvest.
Again, ELR is still considered an experimental canopy management technique. For those growers growing high yielding varieties and looking to reduce crop level, cluster thinning is still the recommended practice. For more information on how to implement appropriate CT techniques, please see Cornell Cooperative Extension Fruit thinning in wine grapes and Crop thinning: cluster thinning or cluster removal.
Considerations regarding ELR
Other factors to consider if you are interested in applying ELR:
- Fruit-set percentage – One of the factors facing the unpredictability of ELR is the weather conditions between bloom and fruit set. Since weather can have a large effect on the percentage of fruit-set (Fruit set in grapes 101), ELR may potentially exacerbate ‘poor’ fruit-set if extended periods of wet, cool (< 59°F), overcast, or very hot (> 90°F) weather conditions occur following leaf removal. Additionally, berry sunburn may be a potential concern with ELR when performed under chronic high light and temperature intensity.
- Bud Fruitfulness – While it is generally acknowledged that increased sunlight exposure is positive for bud development, a potential reduction in bud fruitfulness (number of clusters per shoot) may occur in the following season as a result of bud damage from ELR (14). Although still uncertain, bud damage may be the result of physical damage during leaf removal and/or reduction of carbohydrate supply during bud development.
- Carbohydrate Storage in Cool Climate Grown Vines – Carbohydrates are the main energy source for grapevine growth, stress defense, and fruit ripening. Post-harvest carbohydrate storage in perennial tissues is a determinant of vine overwinter survival and is fundamental for shoot development in the following season. Removing leaves during ELR may alter the amount of carbohydrates produced by the leaves over the season and how carbohydrates are distributed among the vine organs. Currently, limited information is available on how ELR affects carbohydrates storage in perennial tissues and how this relates to dormant tissue (buds and canes) cold hardiness. This is a point of current interest to Centinari’s lab at Penn State, with current research being conducted in vinifera and hybrid wine grape varieties.
- Crop Estimation – Yield predictions based on ELR use is currently not available. In this regard cluster thinning is a more conservative approach. Unlike ELR, which is performed very early in the season, cluster thinning severity can be decided upon estimation of final yield.
ELR holds potential as a way to reduce yield and Botrytis rot infection for some grape varieties grown in the Mid-Atlantic and other cool-climate regions. However, more research is needed to better understand the consistency of ELR practices on vine physiology, yield reductions, and fruit quality. Current efforts are on-going by the Centinari lab and Bryan Hed at the Lake Erie Grape Regional Extension Center (LEGREC) to evaluate the use of manual and mechanized ELR in hybrid and V. vinifera varieties across Pennsylvania.
PSU Wines and Grapes blogs: An Overview of Cluster-Zone Leaf Removal Strategies for Cool Climate Vineyards and 2016 Post Bloom Disease Management Review
Intrieri C, Filippetti I, Allegro G, et al. 2008. Early defoliation (hand vs mechanical) for improved crop control and grape composition in Sangiovese (Vitis vinifera L.). Aus. J. Grape Wine Res. doi: 10.1111/j.755-0238.2008.00004.x
- Acimovic D, Tozzini L, Green A, et al. 2017. Identification of a defoliation severity threshold for changing fruitset, bunch morphology and fruit composition in Pinot Noir. J. Grape Wine Res. doi: 10.1111/ajgw.12235
- Bubola M, Sivilotti P, Janjanin D, and Poni S. Early leaf removal has larger effect than cluster thinning on cv. Teran grape phenolic composition. AJEV. doi: 10.5344/ajev.2016.16071
- Illand P, Dry P, Proffit P, and Tyerman S. Photosynthesis. In The Grapevine, from the science to the practice of growing vines for wine. pp. 91-107.
- Coombe BG. The effect of removing leaves, flowers and shoot tips on fruit-set in Vitis vinifera L. J. Hortic. Sci. 37:1-15.
- Poni S, Casalini L, Bernizzoni F, et al. 2006. Effects of early defoliation on shoot photosynthesis, yield components, and grape composition. AJEV. 57: 397-407.
- Tardaguila J, Martinez de Toda F, Poni S, and Diago MP. 2010. Impact of early leaf removal on yield and fruit and wine composition of Vitis vinifera Graciano and Carignan. AJEV. 61(3):372-381.
- Silvestroni O, Lanari V, Lattanzi T, et al. Impact of crop control strategies on performance of high-yielding Sangiovese grapevines. AJEV. doi: 10.5344/ajev.2016.15093
- Vail ME and JJ Marois. 1991. Grape cluster architecture and the susceptibility of berries to Botrytis cinerea. Phytopathology 81:188-191.
- Sternad Lemut M, Sivilotti P, Butinar L, et al. Pre-flowering leaf removal alters grape microbial population and offers good potential for a more sustainable and cost-effective management of a Pinot Noir vineyard. J. Grape Wine Res. doi: 10.1111/ajgw.12148
- Hed B, Ngugi HK, and Travis JW. Short- and long-term effects of leaf removal and gibberellin on Chardonnay grapes in the Lake Erie region of Pennsylvania. AJEV. 66(1): 22-29.
- Moreno D, Vilanova M, Gamero E, et al. Effects of preflowering leaf removal on phenolic composition of Tempranillo cv. in semi-arid terroir of western Spain. AJEV. doi: 10.5344/ajev.2014.14087
- Risco D, Pérez D, Yeves A, et al. Early defoliation in a temperate warm and semi-arid Tempranillo vineyard: vine performance and grape composition. Aus J Grape and Wine Res. doi: 10.1111/ajgw.12049
- Sivilotti P, Herrera JC, Lisjak K, et al. 2016. Impact of leaf removal, applied before and after flowering, on anthocyanin, tannin, and methoxypyrazine concentrations in ‘Merlot’ (Vitis vinifera) grapes and wines. J. Agric. Food Chem. 64:4487-4496.
- Sabbatini P, and Howell GS. 2010. Effects of early defoliation on yield, fruit composition, and harvest season cluster rot complex of grapevines. HortScience 45(12):1804-1808.
Maria Smith is a viticulture PhD candidate with Dr. Michela Centinari in the Department of Plant Science. She specializes in cold stress physiology of wine grapes. She was the previous recipient of the John H. and Timothy R. Crouch Program Support Endowment, an endowment founded and funded by the Crouch brothers, original owners of Allegro Winery in Brogue, PA. She is currently funded by the Northeast Sustainable Agriculture Research and Education (NE-SARE) program, a program from the USDA National Institute of Food and Agriculture (NIFA).
By: Maria Smith and Dr. Michela Centinari, Dept. of Plant Science
This is the first of two posts on grapevine canopy management in the early growing season from bud burst to bloom. The second in the series will be post in two weeks and will focus on pre- or trace-bloom leaf removal for crop level and disease pressure control.
This week, our blog post will focus on shoot thinning, the first canopy management practice of the growing season. As seen in the pictures below, we spent last week shoot thinning Grüner Veltliner (V. vinifera) vines in a central Pennsylvania vineyard (Figure 1).
In the following sections, we will highlight the benefits and costs associated with shoot thinning while providing a few general shoot thinning guidelines for both V. vinifera and hybrid cultivars in the Mid-Atlantic region.
Benefits of Shoot Thinning Grapevines
While dormant pruning (https://psuwineandgrapes.wordpress.com/tag/dormant-pruning/) is the primary tool used by grape growers to maintain vine structure, canopy architecture and regulate crop level, shoot thinning provides an additional canopy management tool to bring vines into vegetative and fruiting balance by reducing shoot density and the number of clusters per vine. Cluster thinning later in the season may be needed in order to balance highly-fruitful vines.
In addition to improving balance between vegetative growth and fruit biomass, other benefits of shoot thinning include:
- Reduction of canopy density and fruit shading: through removal of selected shoots, shoot thinning reduces overcrowding of shoots in the canopy thus reducing the number of leaf layers and improving sunlight exposure to fruit (1).
- Reduction of disease pressure: reducing canopy density improves air circulation and sunlight penetration that promotes quicker drying of leaves and fruit, as well as increases spray penetration.
Timing of Shoot Thinning
Shoot thinning should be done early in the growing season, when shoots are approximately 5-6 inches long and not more than 10-12 inches long. Shoot thinning should be timed after the date of last ‘expected’ frost, such that secondary or non-damaged primary shoots can be retained in the event of a late spring frost.
When shoot thinning is performed before inflorescences are visible (shoots 0.8 inch to 4 inches), increased vigor of the remaining shoots and lateral shoot growth may occur as a response, negating the benefits of shade reduction (1). When performed too late (shoot longer than 10 inches), shoots become lignified at the base and difficult to remove. If performing late thinning, pruning shears should be used if there is risk of damaging the arm of the vine. It also takes longer to thin longer shoots, potentially decreasing the cost-effectiveness of this practice.
Shoot Spacing and Density Recommendations
Generally, shoot thinning on cane-pruned vines is easier, faster, and more straight-forward than spur-pruned vines, which require substantially more decisions regarding what shoots to retain or remove, and where shoots should be spaced along the cordon (2; Figure 2).
Plant genotype, soil, and climate are all factors influencing vine vigor potential and capacity to fully ripen a crop. Therefore, these factors indirectly affect the appropriate number of shoots to retain at thinning. Many Cooperative Extension websites provide recommendations on range of optimal shoot density based on cultivars grown in their region. [Author’s note: for the eastern US see the additional resources section at the bottom of the post.]
Shoot density targets for Pennsylvania regions:
- For vinifera cultivars it is recommended to leave 3 to 5 shoots per linear foot of canopy (3, 4; Figure 3). The general rule of thumb is to retain fewer shoots in red varieties and more in white varieties. However, other factors (i.e., cultivar disease susceptibility) must be taken into consideration.
- For most of the hybrid cultivars it is recommended to leave 4 to 6 shoots per linear foot of canopy (5).
- For Concord and other native cultivars, as many as 15 shoots per linear foot of canopy can be retained (4).
- In divided canopies trellis systems, the same shoot density along each cordon should be retained (Figure 4).
In addition to the number, the position of the shoots along the cordon is important. Ideally, the shoots retained should be equally spaced to promote a uniform, balanced canopy.
What types of shoots should you remove?
- Weak, non-fruitful shoots especially if they grow in crowded areas of the canopy.
- Secondary and tertiary shoots, if a primary healthy shoot has emerged.
- Shoots arising from the trunk that are not retained for renewal wood (e., new trunks and canes or cordons).
Does shoot thinning improve fruit composition and wine sensory perception?
The associated costs with manual labor and labor shortages are reasonable considerations before implementing vineyard management practices. This is also true for implementing shoot thinning techniques into a vineyard. Nonetheless, it is also important to consider the potential benefits from implementing a new practice.
The effects of shoot thinning practices on hybrid varieties are a bit unclear. A previous study on shoot thinning found that shoot thinned Marechal Foch (red interspecific hybrid of Vitis) vines exhibited higher total soluble solids (ᵒBrix) and berry anthocyanin concentrations as compared to un-thinned vines (6). The increase in berry anthocyanin, however, did not translate into higher anthocyanin concentration in the final wine, and furthermore, shoot thinning did not impact the sensory perception of “fruitiness” of the wines (6). In contrast, a study focusing on Corot noir (red interspecific hybrid of Vitis) implementation of shoot thinning provided inconsistent results in grape and wine quality across a two-year (2008-2009) evaluation, which was determined by ᵒBrix, pH, titratable acidity (TA), wine anthocyanin, berry and wine tannin content (7). Shoot thinning increased berry ᵒBrix, wine alcohol concentration and anthocyanin content only in second year of this study. While berry TA at harvest was lower (e.g., 2008, un-thinned = 8.6 g/L, shoot thinned = 7.6 g/L), there were no differences in the TA of wine in either year (7). Shoot thinning also decreased berry seed tannin in 2008 and berry skin and wine tannin in 2009, which could have negative implications for final wine, considering generally low tannin concentrations in hybrid red wines (7). In an effort to compensate for costs associated with shoot thinning and yield loss, this study on Corot Noir suggested growers increase the price of grapes by 11 to 20% per ton, depending on the average annual market price and yield loss (7).
A study in Fayetteville (Arkansas) on three highly-fruitful French-American hybrid cultivars (Aurore, Chancellor, and Villard noir) found that shoot thinning increased fruit sugar accumulation (ᵒBrix) only in Chancellor and without changes in pH or TA, while a more intense juice color was associated with shoot thinned vines of both red cultivars (Chancellor and Villard noir; 8). In addition, shoot thinning favorably decreased the Ravaz index (yield to pruning weight ratio) for all three cultivars, improving vine balance (8).
The results of these studies suggest that in some situations the costs of shoot thinning may not outweigh the benefits, especially for hybrids that do not command a high market value (Finger Lakes Grape Prices 2016). However, none of these studies account for potential reduction in disease infections, which may help justify the implementation of shoot thinning in a given vineyard. For example, it has been found that higher shoot density may contribute to the increased incidence of Botrytis rot infections in susceptible cultivars such as Seyval Blanc (9) and Vignoles (4).
In other cases, shoot thinning improved fruit composition in Pinot Noir and Cabernet Franc for two consecutive vintages (1), and also increased color intensity, phenolic content, and total anthocyanins of Cabernet Franc berries (1). Benefits of shoot thinning on fruit quality and wine sensory perception have been reported for other vinifera cultivars, such us Barbera (10) and Sauvginon blanc (11).
Unless your vineyard is located in a low or moderate vigor site, shoot thinning is strongly recommended for vinifera cultivars growing in the Mid-Atlantic region.
If you want to assess the effects of shoot thinning on fruit composition, plan to leave half of a row of vines un-thinned and thin the remaining half to a consistent number of shoots per foot (e.g., 4 shoots per foot). Alternatively, use two rows (of the same variety and cultivar) to assess the impact of shoot thinning in your vineyard: one row thinned and the adjacent row un-thinned. These two methods should help evaluate the effect of shoot thinning on berry composition at harvest and if possible, on wine chemistry and sensory perception assuming that the lots of berries can stay separated through wine production.
Effects of shoot thinning on vine physiology
Impacts of shoot thinning on vine physiology and performance are complex. A study conducted in Italy evaluated the whole-canopy photosynthetic response to shoot thinning using spur-pruned Barbera vines (V. vinifera; 10). Vines were thinned to 5 shoots per foot, reducing the total shoot number by 50% as compared to un-thinned control. In this study (10) shoot thinning significantly improved grape sugar content, color, and phenolics. Despite the benefits provided by shoot thinning on fruit composition, which has been already reported by other studies, what makes this study unique and interesting it that they investigated the mechanisms behind the improvement in grape quality through the measurement of whole-canopy net carbon assimilation. Although the shoot-thinned vines had initially lower photosynthesis (carbon assimilation) than un-thinned vines due to the removal of photosynthetic source (leaf), they had regained photosynthetic capacity to levels similar to the un-thinned vines within 17 days of treatment. This occurred as a result of a substantial increase in both main leaf size and amount of lateral leaves as a result of shoot thinning (10). Therefore, individual shoots of thinned-vines had a higher supply of assimilates (e.g., sugar) per unit of crop, which can increase sugar accumulation during ripening. This may explain why shoot thinning improved grape composition in Barbera under these growing conditions.
Additional Shoot Thinning Resources
- Cornell Cooperative Extension (CCE) video tutorial on shoot thinning: https://www.youtube.com/watch?v=5wyFolawc-s
- Fiola, J. 2017. Canopy Management – Shoot thinning and positioning. “Timely Vit” from UMD Extension. https://extension.umd.edu/sites/extension.umd.edu/files/_docs/programs/viticulture/TVCanopyMgmtShootThinPos.pdf
- Martinson, T and Vanden Heuvel, J. Shoot density and canopy management for hybrids. http://www.fruit.cornell.edu/grape/pdfs/Canopy%20Management%20for%20Hybrids%20-2007.pdf
- Reynolds AG., et al. 2005. Timing of shoot thinning in Vitis vinifera: impacts on yield and fruit composition variables. 56, 343-356.
- Intrieri, C and Poni, S. Integrated evolution of trellis training systems and machines to improve grape and vintage quality of mechanized Italian vineyards. AJEV. 46, 116-127.
- Fiola, J. 2017. Canopy Management – Shoot thinning and positioning. “Timely Vit” from UMD Extension.
- Walter-Peterson, H. 2013. Shoot thinning: Good for the vines, but good for the wines? Finger Lakes Vineyard Notes.
- Martinson, T and Vanden Heuvel, J. Shoot density and canopy management for hybrids. CCE. http://www.fruit.cornell.edu/grape/pdfs/Canopy%20Management%20for%20Hybrids%20-2007.pdf
- Sun Q., et al. 2011. Impact of shoot thinning and harvest date on yield components, fruit composition, and wine quality of Marechal Foch. AJEV. 62:1, 32-41.
- Sun Q., et al. 2012. Impact of shoot and cluster thinning on yield, fruit composition, and wine quality of Corot noir. AJEV. 63:1, 49-56.
- Morris, JR. et al. 2004. Flower cluster and shoot thinning for crop control in French-American hybrid grapes. AJEV. 55:4, 423-426.
- Reynolds, AG et al. 1986. Effect of shoot density and crop control on growth, yield, fruit composition, and wine quality of ‘Seyval blanc’. J. Amer. Soc. Hort. Sci. 111, 55-63.
- Bernizzoni, F. et al. 2011. Shoot thinning effects on seasonal whole-canopy photosynthesis and vine performance in Vitis vinifera L. cv. Barbera. Aus. J. Grape Wine Res. 17, 351-357.
- Naor et al. 2002. Shoot and cluster thining influence vegetative growth, fruit yield, and wine quality of ‘Sauvignon blanc’ grapevines. J. Amer. Soc. Hort. Sci. 127(4), 628-634.
Maria Smith is a viticulture PhD candidate with Dr. Michela Centinari in the Department of Plant Science. She specializes in cold stress physiology of wine grapes. She was the previous recipient of the John H. and Timothy R. Crouch Program Support Endowment, an endowment founded and funded by the Crouch brothers, original owners of Allegro Winery in Brogue, PA. She is currently funded by the Northeast Sustainable Agriculture Research and Education (NE-SARE) program, a program from the USDA National Institute of Food and Agriculture (NIFA).
By: Jody Timer, Entomology at LERGR & EC
In the colder parts of this state, we are always looking for new berries to make into wine.
Ideally, we are on a search to find berries that will stand cold winters and late frosts. As an end to this means, three years ago at Lake Erie Regional Grape Research and Extension Center (LERGR & EC) we planted an experimental patch of Haskap bushes (Lonicera caerulea).
Haskap or blue honeysuckle, is an extremely cold hardy, edible berry producing plant, resisting temperatures as low as -46°C (-50.8°F) (Thompson 2008). Even flowers can be exposed to temperatures of -7°C (19.4°F) with no detriment to fruit set. Haskap is also tolerant of a wide range of soil pH (5.5-7.5) (Retamales and Hancock 2012) allowing for production in many different soils. The bushes will survive in the wild in swamp-like conditions, but they thrive in well drained soils. The fruit development period for Haskap starts very early in spring and is very short; 6-8 weeks from bloom to harvest (Thompson 2006). In our climate, Haskap will produce fruit as early as mid-June, coinciding somewhat with the strawberry market. The small blue fruits have a fresh, somewhat tart, raspberry/blueberry to cranberry flavor. They should be purple all the way through before they are fully ripe. These plants do not sucker, need little pruning, and tend to fruit when very young. A Haskap bush can be productive for 30 years. Haskaps are native to Siberia and northeastern Asia (Bors et al. 2012), and were recently introduced to the North American market being advertised for its many claimed health benefits. Some researchers (Bors et al. 2012) believe that haskap could replace blueberries as the new ‘super fruit’. Lonicera have been used widely in folk medicine in northern Russia, China and Japan since ancient times. In recent years, phenolic compounds present in fruit crops, especially berries, have gained much attention due to the accumulating scientific evidence of their potential health benefits. Its juice has 10 to 15 times more concentrated color than cranberry juice. The fruit is high in Vitamin C, Vitamin A, fiber, and potassium.
Antioxidant levels are measured using the ORAC (oxygen radical absorbance capacity) method. A wide variety of food has been tested using this methodology, with the Haskap Berry being rated very highly in comparison with other berries. The berries’ extremely high ORAC value indicates a high anthocyanin, poly phenol, and bioflavonoid content.
In addition to fresh market potential, Haskap can be used in processed products including pastries, jams, juice, ice cream, yogurt, sauces, and candies. These berries also make a nice dark red or burgundy colored wine. The Canadian market is receives about $13.00 per pound, while the Japanese market is about $30.00 per pound of berries (LaHave Forests’ Haskap Day).
Haskap fruits obtain almost full size 4 weeks after blooming and begin to turn purple. The dark skin of the fruit is covered by a waxy coating (bloom) and resembles the outer covering of blueberries and concord grapes. At 5 weeks old they are fully purple but at 6 or 7 weeks old they are fully ripe and tasty. That is for a normal year. But some varieties do develop slower especially if not pruned to let in enough light. Though Haskap is touted as having few disease and insect pest problems, the plant can be negatively impacted by sunburn, mildew and birds.
Bob Bors of University of Saskatchewan has been the primary researcher of Haskap varieties. The following is from the research at the University of Saskatchewan (www.usask.ca/agriculture/dom_fruit/index.html):
Like many other fruit crops, haskap requires pollen from an unrelated variety in order to set fruit. Haskap does not have separate male and female plants. When two compatible haskap varieties are planted close to each other, both bushes will set fruit. But it is not enough to have compatible pollen. To pollinate each other both plants must bloom at the same time and be genetically compatible. There is overlap between nearby groups but peak bloom is usually five days different between categories. Blooming times are dependent on where the Haskap are located.
‘Tundra’ may be the variety best suited for commercial production at this time (2007).Tundra’s fruits were firm enough to withstand commercial harvesting and sorting at the University of Saskatchewan, yet tender enough to melt in the mouth. Firmness is a rather rare trait especially for large fruited blue honeysuckles. Ranking at almost the top for flavor and fruit size the shape of its fruit was deemed acceptable for the Japanese market. Its fruit is at least 50% larger than blue honeysuckles currently available in Canada and the US. Its firmness and the fact that this variety does not ‘bleed’ from the stem end when picked could make this variety especially suited for Individually Quick Frozen (IQF) processing.
‘Borealis’ has the distinction of having the best testing and largest fruit size in our breeding program as of 2007. (However, there were many good tasting haskap varieties and it was hard to decide) Its fruits were usually twice the size of any of the 35 Russian varieties in our collection of similar age. (Most varieties of haskap/blue honeysuckles seem to have larger fruit as the bushes get older). Unfortunately, this variety does not have the firmness of ‘Tundra’ and it is not suitable for IQF. It tends to get a bit mushy when handled with equipment. It may be best for home gardeners or U-pick operations who can hand pick the delicate fruit. Or if shake harvesting the fruit, the berries will be damaged and will need to be quickly processed. Not only did the breeder and a University panel choose it as having the best flavor, but its top rating for flavor was also verified by a Japanese Company that chose it as the best tasting of 43 samples!”
The Tundra is by far the hardiest and best growing of the four varieties we have planted at the research station in Erie County (PA). The Indigo Treat is also doing well. Indigo Gem and Berry Blue have both developed black leaves. We are going to determine this year if the black leaves are from sunburn, mildew, or early dominancy. Haskap can go dormant as early as mid-August which may be the cause of brown leaves.
Haskapa of Nova Scotia at www.Haskapa.com has a wide variety of products made from Haskaps. They include syrup, wine, gin, jelly, soap, dried berries, and oils to name a few. This new crop could be grown alongside existing fruit tree orchards, blueberries, raspberries, strawberries, and juice and wine grape vineyards that currently dominate the landscape. If successful, these new crops may serve to supplement the growers’ income, especially in adverse years.
- Bors, B., Thomson, J., Sawchuk, E., Reimer, P., Sawatzky, R., and Sander, T. Haskap breeding and production-final report (pp. 1-142). Saskatchewan Agriculture: Regina.
- Retamales, J.B., and Hancock, J.F. 2012. Nutrition. In J.B. Retamales and J.F. Hancock (eds.), Blueberries (pp. 103-142). Wallingford: CABI.
- Thompson, M.M. 2006. Introducing haskap, Japanese blue honeysuckle. Journal of American Pomological Society 60:4:164-168.
- Thompson, M.M. 2008. Caprifoliaceae. In J. Janick and R.E. Pauli (eds.), The Encyclopedia of fruit and nuts (pp. 232-235). Wallingford: CABI.
By: Denise M. Gardner
The use of oak in the winery offers many options from winemakers. With today’s availability of various oak products (i.e., chips, staves, powders), winemakers have more choices than ever before to integrate a wood component into their product. However, the use of oak barrels remains an intrinsic part of most winery operations. During the aging process, oak barrels have the potential to:
- integrate new aromas and flavors into the wine.
- add mouthfeel and/or aromatic complexity to the wine.
- change the wine’s style.
- add options and variation for future wine blends.
Additionally, the barrel room is often romantically viewed upon by consumers, and it is not uncommon for visitors to find barrel show cases in many tasting rooms, private tasting rooms, or while on a guided winery tour.
Nonetheless, barrels also offer challenges to wineries. One of the most inherent challenges associated with a barrel program is maintaining a sanitation program.
The growth of spoilage yeast, Brettanomyces, is often discussed amongst wineries that utilize barrel aging programs. However, additional spoilage yeast species such as Candida and Pichia have also been associated as potential contaminants in the interior of wine barrels (Guzzon et al. 2011). Brettanomyces, commonly abbreviated as Brett, was first isolated from the vineyard in 2006 (Renouf and Lonvaud-Funel 2007) and until that point had most commonly been associated with the use of oak in the winery. The growth of Brett in wine has the potential to impart several aromas as a result of volatile phenol [especially 4-ethylphenol (4-EP) and 4-ethylguaiacol (4EG)] formation in the wine. Descriptors used to describe a Bretty wine include: barnyard, horse, leather, tobacco, tar, medicinal, Band-Aid, wet dog, and smoky, amongst others. It should be noted that the presence of these aromas does not necessarily confirm that Brett is in the wine; there are other microflora, situations (e.g., smoke taint) or oak chars that can impart some of these aromas, as well.
When barrels are filled with wine, it’s important to monitor the wine regularly for off-flavors while it is aging. Wines should be regularly topped up with fresh wine to avoid surface yeast or acetic acid bacteria growth that can contribute to the volatile acidity (VA). We usually recommend topping barrels up every-other-month. Keep in mind that free sulfur dioxide concentrations can drop quicker in a barrel compared to a tank or wine bottle (MoreFlavor 2012) and free sulfur dioxide contractions should be checked (in conjunction with the wine’s pH) and altered as necessary to avoid spoilage. Finally, when using a wine thief, both the internal and external part of the thief need cleaned and sanitized in between its use for each and every barrel to avoid cross contamination. Dunking and filling the thief in a small bucket filled with cold acidulated water and potassium metabisulfite (acidulated sulfur dioxide solution) is a helpful quick-rinse sanitizer.
Barrels offer a perfect environment for microflora to flourish. Wine barrels are produced from a natural substance (wood), which has its own inherent microflora from the point of production; obviously, barrels are not a sterile environment when purchased. However, the structure of wood is rigid and porous, which provides nooks and crevices for yeast and bacteria to harbor within. The porosity of the wood also makes it difficult to clean and sanitize, especially when compared to cleaning and sanitation recommendations associated with other equipment like stainless steel tanks. Guzzon et al. (2011) found that barrels used over 3 years in production had a 1-log higher yeast concentration rate retained in the barrel compared to new and unused oak barrels. This demonstrates the ideal environment within the barrel for retaining microflora over time, even when adequate cleaning and sanitation procedures are utilized in the cellar.
Common barrel sanitizers include ozone (both gas and aqueous), steam, hot water, acidulated sulfur dioxide, and peroxyacetic acid (PAA). A study conducted by Cornell University on wine barrels used in California wineries found the use of sulfur discs, PAA at a 200 mg/L concentration, steam (5 and 10 minute treatments) to be effective sanitation treatments for wine barrels (Lourdes Alejandra Aguilar Solis et al. 2013). In this same study (Lourdes Alejandra Aguilar Solis et al. 2013) ozone (1 mg/L at a 5 and 10 minute treatment) was also evaluated and found effective in most barrels tested, but a few barrels that did not show adequate reduction with the ozone treatment. While the research conducted by Cornell indicated the potential lack of cleaning the barrel thoroughly before the ozone sanitation treatment, Guzzon et al. (2011) cited ozone’s efficacy is most likely caused by its concentration. Both are important considerations for wineries.
Barrels should always be effectively cleaned of any debris and or tartrate build up before applying a sanitation agent. This is essential to allow for maximum efficacy during the sanitation step. High pressure washers, a barrel cleaning nozzle, and the use of steam are some options available to wineries in terms of physically cleaning the interior of barrel. Additionally, some wineries use sodium carbonate (soda ash) to clean some of the debris (Knox Barrels 2016, MoreFlavor 2012) in addition to the use of a high pressure wash. Always remember to neutralize the sodium carbonate with an acidulate sulfur dioxide rinse prior to filling with wine.
Dr. Molly Kelly from Virginia Tech University has previously recommended a 3-cycle repeat of a high-pressure cold water rinse, followed by high pressure steam before re-filling a used barrel and assuming the wine that came out of that barrel was not contaminated with spoilage off-flavors (Kelly 2013). If the barrel is hot by the end of this cycle, it may be advantageous to rinse with a cold, acidulated sulfur dioxide solution before filling the barrel with new wine. If there isn’t wine available to refill the barrel, it can be stored wet with an acidulated sulfur dioxide solution or using sulfur discs (Kelly 2013).
It is not usually recommended to store used barrels dry for long periods of time, and wineries can use an acidulated sulfur dioxide solution (top off as if it had wine in it) for long-term storage. However, wineries that store their barrels dry need to rehydrate the barrels prior to filling with wine. Check the cooperage for leaks, air bubbles, and a good vacuum seal on the bung. Steam or clean water (hot or cold, overnight) are adequate rehydrating agents (Pambianchi 2002). Barrels that leak wine offer harboring sites for potential yeast, bacteria, and mold growth, which can all act as contaminants to the wine itself.
It should be noted that contaminated barrels (barrels that produce a wine with off-flavors) may need extra cleaning and sanitation steps to avoid future contamination when the barrel is refilled. It is typically recommended to discard barrels that have a recorded Brett contamination. If the barrel has picked up any other off-flavors, especially during storage, it should probably be discarded from future wine fillings.
Barrels undoubtedly offer several challenges for wineries, including proper maintenance, cleaning and sanitation. Nonetheless, engaging in good standard operating procedures for maintaining the barrel’s cleanliness can help enhance the longevity of the barrel and minimize risk of spoilage for several wine vintages.
Guzzon, R., G. Widmann, M. Malacarne, T. Nardin, G. Nicolini, and R. Larcher. 2011. Survey of the yeast population inside wine barrels and the effects of certain techniques in preventing microbiological spoilage. Eur. Food Res. Technol. 233:285-291.
Kelly, M. 2013. Winery Sanitation. Presentation at Craft Beverages Unlimited, 2013.
Knox Barrels. 2016. Barrel Maintenance.
de Lourdes Alejandra Aguilar Solis, M., C. Gerling, and R. Worobo. 2013. Sanitation of Wine Cooperage using Five Different Treatment Methods: an In Vivo Study. Appellation Cornell. Vol. 3.
MoreFlavor. 2012. Oak Barrel Care Guide.
Pambianchi, D. 2002. Barrel Care: Techniques. WineMaker Magazine. Feb/Mar 2002 edition.
Renouf, V. and A. Lonvaud-Funnel. 2007. Development of an enrichment medium to detect Dekkera/Brettanomyces bruxellensis, a spoilage wine yeast, on the surface of grape berries. Microbiol. Res. 162(2): 154-167.
By Bryan Hed
Another season of grape growing is upon us and it’s a good time to review important disease management principles and be aware of some of the tools to consider integrating into your vineyard management programs this spring.
First is your annual reminder to check out the NEWA website (Network for Environment and Weather Applications) found at http://newa.cornell.edu. On the home page is a map of the Northeastern U.S. marked with the locations of hundreds of weather stations where historical and ‘up to the hour’ weather data can be viewed. Although is provided free on the internet, it is funded through the New York State IPM program. Click on a weather station near enough to you (denoted by a leaf/rain drop icon) to get weather, insect pest, and disease information you need to make important management decisions that could save you time and money. Clicking on ‘grapes’ under ‘crop pages’ will give you access to forecasting models for all the major diseases, as well as the grape berry moth degree day model that will improve your timing of grape berry moth insecticide sprays later this summer. Each model forecast is accompanied by helpful disease management messages and explanations.
Next, let’s move our minds into the upcoming pre-bloom disease management season. It’s important to recognize that the threat of disease this spring (pre-bloom) is largely determined by the amount of overwintering inoculum in your blocks. The amount of overwintering inoculum is dependent on the amount of disease that developed in your vineyard last year or in previous years. In other words, if you have kept diseases well under control in the past, especially last year, then there will be relatively little for pathogen populations to build on and cause damage, at least initially, this year. Some very practical research by Wayne Wilcox at Cornell nicely illustrates this point with powdery mildew (pm) development in susceptible wine varieties. In blocks where pm was well controlled all season, fewer overwintering structures of the fungal pathogen (chasmothecia) were available the following spring to jump start disease cycles. Early disease pressure was relatively low and early sprays were less critical to good commercial control than in blocks where disease control was poor the previous year. Where there was poor control the previous year, more of the pathogen overwintered to start disease cycles the following spring and early sprays were critical to maintaining successful commercial control. This is not to say that a bad year of pm will automatically be followed by another bad year. But it certainly tilts the odds in favor of the pathogen, especially if for some reason, you can’t manage the timely application of your early disease control program (stuff happens). It also doesn’t mean you can slack off this year if you had good control last year. Remember, there’s the weather. The weather ALWAYS plays an important role too. A good illustration of this is an experience by an organic grape grower who, in an extremely wet season, developed a serious, economically damaging case of black rot. In conventionally managed vineyards there are several very effective chemistries to control black rot, but in organic production there are no real effective fungicides, and control of this disease in organic vineyards must rely heavily on cultural measures that reduce the pathogen’s overwintering population. Of course, the grower did everything he could to sanitize the trellis of overwintering fruit mummies and bury mummies that had fallen to the ground to reduce overwintering inoculum. But fortunately, the following year was bone dry during the fruit susceptibility period and black rot was not even an issue. Had the previous wet season been followed by another wet one, I’m quite certain, the battle for control of black rot in that organic vineyard would have required ‘the kitchen sink’ to avoid losses. Unfortunately, we have no control over the weather and accurate forecasts, especially long term, are not something to rely on. But, we can (and should) strive to control overwintering inoculum levels every year and the best way to do that is good, practical, season-long disease control.
So, begin to wrap your minds around the campaign ahead. If you had poor disease control in some blocks last season, have you reviewed your spray records where control failed AND where it worked well? Where it failed, did you use the wrong material at a critical time? I’ve had growers discuss their control failures with me only to discover that their timing was fine, but their choice of material did not cover the disease(s) they intended to control. The number of spray materials, what disease each one controls, and how well each one controls each disease, can be bewildering at times…and the list keeps growing and changing. Also, materials that used to be good choices may have become ineffective due to the development of resistance by the pathogens. For example, materials like the strobilurins (Abound, Sovran, Flint, Pristine) are no longer effective at controlling powdery and downy mildew in many parts of the east. In vineyards where this has occurred, using them during the critical fruit protection period (which used to be a great idea!) can now prove disastrous. The sterol inhibitor fungicides (Rally, Elite, Orius, Mettle, Tebusol, Tebustar, Procure, Viticure, etc) are also exhibiting the effects of resistance by the powdery mildew fungus. Though in most cases they still work on powdery to some extent, they are not appropriate for the critical fruit protection period anymore, around and shortly after bloom (products that include the more active difenoconazole are an exception on less susceptible varieties). However, they may be acceptable for maintaining a clean vineyard outside the critical period. Do you have an accurate grasp on that?
Do you have a firm grasp on the critical fruit protection period? The critical period for fruit protection from all diseases generally extends from ‘just before bloom’ to about 4 weeks later. This is the period when you need to be especially vigilant about minimizing spray intervals, using your best materials that cover all the major diseases (Phomopsis, black rot, powdery and downy mildew), focus on good coverage, etc. It is never profitable to try to cut corners during the critical period. However, if you had heavy amounts of black rot in your vineyard the year before, you should assume you have an unhealthy dose of overwintering inoculum in your vineyard this spring, and prevention of leaf lesions in the fruit zone (which would need to be addressed during the first 3-12” of shoot growth, well before the fruit protection period) would also prove to be critical. This goes for other diseases as well (refer back to the previous example with Wayne Wilcox’ powdery mildew experiment). The pre-bloom presence of visible disease in the fruit zone is a big red flag; it means you’ve got potential for serious fruit loss ahead, especially if weather conditions favor the pathogen (wet, warm, humid, calm, cloudy) during the fruit protection period that follows.
Did you record the relative levels of disease that developed in years past for each of your blocks? In order to do this, you need to be able to identify the various diseases and then scout regularly for them. This takes up valuable time but you can streamline your scouting efforts in many ways. Do you know when you would expect to first see each disease? Downy mildew doesn’t become active until about the 5-6 leaf stage. So, you know you can’t expect to see it until about that time or shortly after that. In which blocks are diseases most likely to occur first? Your block or rows next to the woods would be a good place to start, or perhaps your most susceptible variety. Blocks with the most disease last year would be a good place to start. On which parts of the vine do you expect to see diseases appear first? Can recent weather data help you to determine where to look for the disease? For example, if a black rot infection period occurred 2 weeks ago (and you can find this out easily by searching the NEWA website), would you examine the newest growth, the oldest growth, or would you look for lesions on leaves that were currently expanding and most susceptible 2 weeks ago? The answers to these questions can help you streamline your scouting efforts, save time, and improve your expertise.
Do you fully comprehend the susceptibilities of all the varieties you’re growing? You cannot spray premium Vitis vinifera like the hybrids or natives and expect the same results. What are you going to change this year to address disease control breaches in your vinifera? If you had good control last year, are you ready to do it again this year? OR, do you feel lucky and plan to back off until close to bloom to apply your first spray? I always plan for the worst when it comes to the weather and assume it’s going to be wet, cloudy, and warm; ideal for fungal disease epidemics. Consider that here in the east we are growing a highly vulnerable, susceptible host (wine grapes) on the pathogen’s ‘turf’ (the wet, humid eastern U.S.). The good news is that disease control during the pre-bloom period is generally easier (good spray coverage not a problem, low initial disease/inoculum levels, etc.) and cheaper (can use lower fungicide rates, lower spray gallonage, less expensive materials, less time, etc) than in the post bloom period, and a well prepared pre-bloom disease management program will provide extra insurance against problems during bloom and early fruit set, when your fruit ($) is most vulnerable. Now let’s review the common diseases with some of these questions and concepts in mind.
Phomopsis cane and leaf spot is often the first disease problem we face in the pre-bloom period, particularly where trellis systems maintain lots of old and/or dead wood. That’s because old and/or dead wood is where the pathogen overwinters. Therefore, the more old wood you have in your trellis, the more inoculum you can expect to be battling with this spring. Conversely, cane pruned systems have fewer problems with Phomopsis, and cane pruning/minimizing older wood is an important cultural control for this disease. Fortunately, many areas of PA and other parts of the east experienced a relatively dry spring in 2016, helping to minimize new overwintering infections on year-old wood. But, older cordons and especially dead wood and pruning stubs, can carry overwintering inoculum into many subsequent springs. So, if there was little opportunity for new Phomopsis infections to occur last year, you can still be carrying a fair amount of overwintering inoculum in old cordons and pruning stubs.
During early spring rains, Phomopsis spores flush from lesions on wood and are splashed about to invade any new shoot, leaf, and inflorescence they land on…provided the wetting period/temperature combination falls within a minimum range for infection. The basal-most (oldest) internodes of new shoots are the most susceptible to shoot infections simply because they are closest to the inoculum source; wood. In every trial where I have rated shoot infection of Phomopsis, the most severe lesion development was ALWAYS found (on average) on the first (oldest) internode region of the shoot. Lesion development typically got less severe as my rating progressed through internodes 2, 3, 4, and 5. However, once these internodes become fully expanded after the first few weeks in the season, they are no longer susceptible to lesion development. I rarely see Phomopsis lesion development beyond the fifth internode region. That’s why this disease is best dealt with preventatively, very early, during the first few inches of shoot growth. Infections that occur on the first few internodes of new shoots are not only the most likely to occur, but also the most critical; infections of inflorescences (generally on nodes 2-5) can lead to crop loss early (parts of the inflorescence may be ‘bitten off’ by the pathogen) or later during ripening (cluster stem infections in spring move into berries and cause fruit rot and shelling after veraison). And, infections that occur on the basal-most internodes, can’t all be eliminated by judicious hand pruning during the dormant season. So, in blocks where you suspect any risk of early Phomopsis infections, applications of a fungicide (mancozeb or captan are good choices) at no later than 3-6” of shoot growth are a good investment, particularly if you are not cane pruning. Following up with fungicides at 8-12” shoots and immediate pre-bloom are also important pre-bloom applications. Below are some pics from last year’s blog (Figures 1, 2) to help you get a handle on the appearance of lesions on year-old canes. Unfortunately, determining the presence of Phomopsis on older wood generally involves more than just a visual assessment.
Figure 1. Dark brown lesions on the first few internodes on these Chancellor canes are from Phomopsis infections that occurred during early shoot growth in the previous year (when these were green shoots). The buds present are just ready to burst open with new shoot growth that will be very vulnerable to infection during subsequent rain periods.
Figure 2. Although the 1” shoot stage can be vulnerable to damage from this pathogen, the more critical stage is at 3-6” shoots, when more shoot, leaf, and cluster tissue is exposed and is highly susceptible (below). Note the inflorescence in the upper right picture from which Phomopsis has “bitten off” whole branches, dramatically limiting yield potential for that cluster.
Pre-bloom fungicide applications for Powdery mildew are also prudent during early shoot growth for Vitis vinifera cultivars and highly susceptible hybrids, especially in vineyards where control of this disease may have slipped last year (again, because of lots of overwintering inoculum). The primary inoculum for this pathogen generally comes from overwintering structures of the fungus that are lodged within cracks in the bark of cordons and trunks. Spring rain periods of at least 0.1” of precipitation and temperatures of 50 F or more, are the requirements for release of primary inoculum (ascospores) from the overwintering structures. The more mildew that was allowed to develop the year before, the larger the release of spores in early spring, the more primary infections that are likely to occur, and the more critical the need to control the disease early. Sulfur, oils, monopotassium phosphate, and potassium bicarbonate materials can be good choices for mildew management early on. All of these materials can eradicate small existing powdery mildew infections on leaves and cluster stems. Most do not generally offer any protection from future infections and therefore work best if applied often. Sulfur is an exception, and has the added benefit of providing a week or more of protection against future infections. Many of the more experienced growers like to utilize a mancozeb/sulfur combination to control all diseases during the pre-bloom period. This combination is relatively inexpensive, there are no resistance issues, and it works. Remember to read labels and be aware that you can’t mix sulfur and oils, or oils and captan. The tebuconazole products can be used during early pre-bloom to control powdery mildew as well, especially at the 8-10” shoot stage. These materials are very inexpensive and generally provide enough powdery mildew control to keep vines healthy until the immediate pre-bloom spray (they will also nicely control early black rot infections). At immediate pre-bloom and first post bloom, you want to apply your best powdery mildew chemistries like quinoxyfen (Quintec), difenoconazole (Revus Top), metrafenone (Vivando), fluopyram/tebuconazol (Luna Experience), etc. For native juice grapes, powdery mildew is rarely a concern during the early shoot growth stages, especially in the cooler Lake Erie region of Pennsylvania.
A note about fungicide resistance management and powdery mildew: It’s important to plan your powdery mildew management choices ahead of time with resistance management in mind. The easiest way to do this is to become familiar with FRAC (fungicide resistance action committee) codes listed prominently on the first page of fungicide labels. Fungicides with the same FRAC group number can be considered similar enough in their mode of action/chemistry that resistance to one is resistance to all others within that group. Therefore when you rotate fungicides for resistance management, you’re essentially rotating FRAC groups. Some good rules to remember are to avoid using the same FRAC group consecutively, or more than twice in a given season. The development of powdery mildew resistance is always a concern when using materials like the strobilurins (FRAC 11), the sterol inhibitors (FRAC 3), Quintec (FRAC 13), Vivando (FRAC U8), Luna Experience (FRAC 7, 3), Torino (FRAC U6), and Endura (FRAC 7) to name a few. Resistance is generally not a concern for uses of sulfur, oils, bicarbonates, and the potassium salts (mentioned above), or copper.
Next, black rot: One of the best ways to reduce overwintering inoculum of black rot is to scout your vineyard for old fruit mummies and eliminate them from the trellis. Black rot infected fruit mummies that have overwintered in the trellis are the most potent source of inoculum for infections the following spring. No matter how cold it gets over the winter, the pathogen survives just beautifully in colonized fruit remaining in the trellis. But, dropping this inoculum source to the soil, allows microbial degradation/weathering to reduce the potential for mummies to release spores the following spring. It also places the inoculum source much farther from new, susceptible plant tissue up in the trellis. The best time to ‘sanitize’ the trellis is during dormant pruning; weathering has already accomplished some of the removal of last season’s infected fruit from the trellis, and what remains is relatively easy to see and remove by hand. Experiments we conducted several years ago clearly showed that the earlier the mummies are knocked to the ground during the dormant period, the more time for decomposition to break them down before the next season, and the fewer spores released from the ground the following spring to start new disease cycles. Nevertheless, some inoculum on the ground will survive to release spores in spring, and burial of mummies with cultivation will go a step further to eliminate the threat. Removal of ALL old cluster material from the trellis before bud break is important to maintaining good control of this disease.
It may not be necessary to apply a fungicide for black rot at early shoot stages IF good control of this disease was achieved the previous year AND conscientious scouting and trellis sanitation has been implemented. However, the importance of early shoot infections should not be underestimated as I mentioned above, especially if they result in leaf lesions in the fruit zone. For example, inoculations we performed from early May to early June (simulating wet weather and an overwintering inoculum source (mummies) in the trellis) resulted in leaf and shoot lesions in the cluster zone (Figure 3). Those lesions went on to release spores during the critical fruit protection period, resulting in crop loss of 47-77% on those shoots with infected leaves!
An application of mancozeb, ziram, or captan for Phomopsis will also provide control of early black rot infections. The sterol inhibitor fungicides and strobilurins are also good materials for black rot that are more rainfast than mancozeb, ziram, and captan. The sterol inhibitors also provide excellent post infection activity that can be very useful at terminating an infection that has already occurred (but not yet manifested itself).
Figure 3. Early (pre-bloom) black rot leaf infections in the cluster zone provide inoculum that can add to problems with controlling fruit infection after capfall. The two small tan lesions on the leaf at node 2 are just inches from the developing inflorescence found at node 3 (picture on the right). These lesions will release spores during rainfall periods that could easily be splashed to highly susceptible cluster stems pre-bloom, and developing fruit after capfall. Resulting fruit infections will lead to crop loss.
Downy mildew and the 5-6 leaf stage: This stage marks the point at which the downy mildew pathogen first becomes active and is capable of releasing primary spores from inoculum sources that have overwintered on the ground (leaves and other plant material that was infected during the previous season). As with all other diseases, vineyards that developed a fair amount of downy mildew leaf/cluster infection last year will be at higher risk this spring than vineyards that were kept clean. However, overwintering structures of the downy mildew pathogen can survive more than one season in the soil.
Periods of rainfall with temperatures of at least 52 F meet the requirements of spore release and the first infections; plant surfaces must be wet for infection to occur. While scouting for this disease, expect to see it first in wetter areas of your acreage and pay close attention to leaves near the ground (sucker growth, grape seedlings that germinated from shelled berries last fall) which are most likely to become infected first. Therefore, keeping such low growth to a minimum in spring is a prudent control measure that can delay the development of the disease. It also suggests that if you’re planning vine trunk renewal from sucker growth, you will need to apply fungicides to protect that growth from the ground up as the pathogen becomes active.
Spring leaf infections are identified by the yellow ‘oil-spots’ seen on the tops of leaves (Figure 4), coinciding with white, downy sporulation of the pathogen on the undersides of leaves. Inflorescences can be blighted and show sporulation as well. Sporulation occurs during darkness under high relative humidity, and can typically be seen during a morning scout of the vineyard following a wet/humid night. Under optimum temperatures (70-75F), only an hour or two of plant surface wetness may be required for infection to occur, and new infections can produce their own spores with just 5 days.
Many parts of the northeast experienced drought conditions last year, which severely inhibited the development of this disease. Up in Erie County PA, the disease basically took a vacation in 2016, and I could barely find a handful of lesions on unsprayed ‘Chancellor’ leaves and fruit near the ground all summer: it was the perfect year to start renewal trunks! It wasn’t until later in August that rains finally returned and we began to see a few more infections, but for the most part the disease literally could not get off the ground in Erie county PA in 2016. What does this mean for 2017? The great lack of downy mildew in drought hit areas last year means that pre-bloom disease cycles this year will have to rely on overwintering inoculum from previous years (although spores of downy mildew can travel long distances between vineyards, the first infections will arise from inoculum within your vineyard). I have not found any detailed information as to how long the pathogen can survive in the soil, but I guarantee that if you’ve had downy mildew before, then it’s still there. Whether your area was wet or dry last spring, the principle described earlier still applies: vineyards devoid of downy mildew last year (whether from drought or just plain good control) will be easier to keep ‘clean’ in the pre-bloom period this year.
Mancozeb products are good options for the first downy mildew, Phomopsis, and black rot sprays in the pre-bloom period. Ziram and Captan have a similar spectrum of control, but Ziram is a little weaker on downy mildew, and Captan a little weak on black rot. However, these may be a viable option if these diseases are not a huge threat early on (that is if you had good control last year). These materials are all surface protectants subject to wash-off by rainfall, which means that under heavy, frequent rainfall conditions, application intervals will need to be minimized (7-10 days?) especially for highly susceptible varieties. For that more critical ‘immediate pre-bloom’ spray (and the first post bloom spray), there are other materials like Presidio, Revus, Revus Top, and Zampro that are quite rainfast, very effective, and will provide longer range protection under wet conditions (when you need the protection most and are least likely to be able to stick to shorter spray intervals). However, products like Presidio also require a second active ingredient (like mancozeb) in a tank mix for resistance management purposes (which isn’t a bad idea at this critical spray timing in any case). Other materials like the phosphonates, Ranman, and the strobies /Reason, are probably best utilized outside the critical two sprays around bloom (especially for V. vinifera and highly susceptible hybrids), unless they’re used as tank mix partners with other effective materials. They’re very good materials, but they’re just not the ‘best of the best’.
Figure 4. Yellow oil-spot symptoms of downy mildew on young spring leaves.
One more time for emphasis: the immediate pre bloom and first post bloom (7-14 days later) fungicide applications are the most important you’ll make all year, regardless of variety grown and disease pressure. These two sprays protect your fruit from all the major fungal diseases (Phomopsis, black rot, downy and powdery mildew). Make sure sprayers are properly calibrated and adjusted for best coverage on a bloom-period canopy, spray every row at full rates and shortest intervals, and NEVER extend the interval between these sprays beyond 14 days.
‘Newer’ Fungicides: Aprovia (solatenol) may be worth a try for powdery mildew control (received federal registration in 2015). The active ingredient is related (same FRAC group) to Boscalid (found in Endura and Pristine) and Fluopyram (found in Luna Experience). It also has activity against black rot, but should not be expected to control this disease under high pressure on a susceptible variety.
***Lastly, to help you with all your grape management decisions this year, you should have…
New York and Pennsylvania Pest Management Guidelines for Grapes. An inexpensive, excellent source of research based information for commercial growers; some information in this blog was gleaned from it and it is revised every year to include the newest information. Copies can be purchased at the Cornell Store at https://store.cornell.edu/c-875-pmep-guidelines.aspx. It sells for about $31.