Grape leaves turning yellow

Yellowing Leaves on a Grapevine

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Grapes make up one of the oldest crops, and humans have been growing them for thousands of years. Some species, especially those that are native to North America, are easy to grow, but wine grapes can pose a challenge. In addition to nutritional deficiencies, grapes are susceptible to many fungal and viral diseases that can cause leaves to yellow and vines to die.

Deficiencies

A deficiency in one of the essential elements can cause grape leaves to turn yellow. Where the yellowing occurs depends on which element is lacking. Overall yellowing of the leaves and other green tissues indicates that grapes aren’t receiving enough nitrogen. When the basal leaves turn yellow, grapes need more phosphorus. Potassium deficiencies appear in older leaves first. The leaves of white grape varieties turn yellow near the margin, and the yellowing then moves in toward the center of the leaf. Leaves of red-grape varieties turn red instead of yellow. When yellowing occurs between the veins of older leaves, white grape varieties are short on magnesium. Iron deficiencies show up as a yellowing of young leaves and new growth. If the deficiency is mild, the veins might stay green. A lack of manganese appears as yellowing between the main veins of older leaves.

Downy Mildew

Symptoms of downy mildew include the appearance of small, pale yellow lesions on the upper surface of the leaves and white or grayish fungal growth on the undersides of leaves. The lesions can grow larger and merge together, causing the leaves to turn brown or black and fall off the vine. Downy mildew infects grapes when the weather remains warm and wet for long periods of time. The fungus also grows on the grapes, which may shrivel or harden and fail to ripen. Control downy mildew with applications of fungicides.

Eutypa Dieback

Eutypa dieback is caused by a fungal infection that causes stunted shoots with leaves that cup upward. Shoots turn yellow or develop yellow streaks. One or more of the trunks may die, or the whole vine may die from wood rot. This disease progresses over a period of several years, but the initial infection usually occurs when the vine suffers a pruning wound. The fungus attacks the wound and releases spores whenever it rains. Control the eutypa fungus by removing and burning diseased trunks and vines.

Tomato/Tobacco Ringspot

Tomato and tobacco ringspot are viruses that infect French hybrid grapevines. The symptoms of both viruses are the same and include the appearance of small, yellow leaves and stunted vines. Ringspots are spread by the dagger nematode, a small wormlike creature that feeds on the roots of the grapevine. Control ringspot diseases by fumigating the soil before planting vines. Control in an established vineyard involves removing all infected vines and tilling the soil for one season before fumigating the soil and replanting with certified virus-tested plants.

Powdery Mildew

Symptoms of powdery mildew include the appearance of yellow spots on the upper surface of leaves, followed by a white, powdery fungus that can cover both sides of the leaf. Leaves may also dry out and drop prematurely. The white powder also appears on the fruit and dormant canes develop red blotchy areas. Fungicides can be used to control this disease, and they’re more effective when used as protectants.

Red Leaves in the Vineyard—Diagnosis and Management

Mizuho Nita, Assistant Professor and Extension Grape Pathologist, Department of Plant Pathology, Physiology, and Weed Science, AHS Jr. Agricultural Research and Extension Center, Virginia Polytechnic Institute and State University.

References Cited:

2Tony Wolf (ed.) 2008. Wine Grape Production Guide for Eastern North America, Plant and Life
Science Publishing. NRAES 145.

3Hemant Gohil, Gary Pavlis and Daniel Ward. 2015. Evaluate your planting material before planting your grapevine. Rutgers NJAES cooperative extension Factsheet #1260.

4Adib Rowhani and Deborah Golino. 2010. Grapevine Disease Testing Protocol 2010. FPS Grape Program Newsletter, October 2010.

5Stephen Vasquez and Jodi Creasap Gee. 2013. Grown Gall: in Grape Pest Management third edition, UCANR publication. Pp. 71-74.

6Bruce Perrygo, Dr. Joseph Fiola, Wade Hampton, Dean Jones, Ashley Mulloy, Ron Wates, and Bob White. 2016. A Sustainable Practices Workbook For Wine Grape Growing In Maryland, Maryland Grape Growers Association publication.

To print this article (pdf format) click the “download document” below…

Timely Viticulture is designed to give those in the Maryland grape industry a timely reminder on procedures or topics they should be considering in the vineyard. To view other topics you can go to the Timely Viticulture page that is located on the Grapes and Fruit website.

Larry Bettiga, Viticulture Farm Advisor, UC Cooperative Extension, Monterey, San Benito and Santa Cruz Counties

Grapevine leafroll and red blotch disease are two virus-associated diseases that should be on the radar of all grape growers. The following article will hopefully provide you an update on these virus diseases base on our current knowledge. Surveying vineyards during harvest is a great time to assess vineyard blocks for the presence of disease symptoms.

Grapevine Leafroll Disease

Leafroll is one of the more important virus diseases of grapevines. It occurs in every major grape growing area of the world. There are five grapevine leafroll associated viruses (GLRaVs) that are serologically distinct. These single stranded RNA viruses are placed in a family called Closteroviridae. The majority of these are grouped in the genus Ampelovirus (GLRaV-1, -3, and -4), most of the viruses in this genus have been demonstrated to be vectored by mealybugs and scale insects in vineyards. GLRav-2 is in the genus Closterovirus, and GLRaV-7 is in the genus Velarivirus, there is no known vector of these two genera.

These viruses can cause similar symptoms in infected grapevines. All the GLRaVs can be transmitted by vegetative propagation and grafting; GLRaVs in Ampelovirus can also be transmitted by the mealybugs and soft-scale insects in vineyards. GLRaV-3 is the predominant species found in most vineyards worldwide. Recent surveys in the north coast have shown 80% of symptomatic vines sampled were infected with GLRaV-3.

To further complicate matters there are variants that have been identified for given GLRaV species. For GLRaV-3 there are several distinct variants known to exist. What needs to be better understood is the significance of these GLRaV-3 variants and their interactions with other viruses when multiple infections exist in a vine. For GLRaV-2 the “Red Globe” variant is known to cause graft incompatibility when grafted onto certain rootstocks (5BB, 5C, 3309C and 1103P) resulting in the decline and death of vines.

In the post-phylloxera infestation plantings that have occurred on the central coast during the past 20 years there has been an increased incidence of grapevine leafroll disease. The use of non-certified scion material has been a major contributor to this disease increase. The other issue has been the spread of leafroll (primarily GLRaV-3) from infected vineyards to adjacent vineyards planted with California-certified stock. UC research documented the rapid spread of leafroll into a certified planting from an adjacent infected block. During the 5 years of observation the annual rate of increase in leafroll symptomatic vines was more than 10% in a Napa Valley site.

Recognizing Leafroll

Leaf symptoms become visually apparent by early summer and generally intensify into midsummer and fall. Physical stresses to the vine may increase symptom severity and there are similar symptoms caused by other abiotic and biotic injuries. On affected vines, the margins of the leaf blades roll downward, starting with the basal leaf on the cane. Areas between the major veins turn yellow or red, depending on whether the cultivar produces white or red fruit. In some cultivars, the area adjacent to the major veins remains green until late fall.

The most important effect of leafroll disease is a reduction in the yield and quality of fruit from infected vines. Yield losses of 10 to 20% are fairly typical. Because leafroll viruses damage the phloem of infected vines, sugar accumulation is delayed and color pigment production is reduced. Fruit from infected vines can be low in sugar, poorly colored, and late in ripening.

It is important to remember that the lack of symptoms in a grapevine does not guarantee freedom from infection by the viruses that are the causal agents of leafroll disease.

Leafroll disease on Pinot noir (top) showing burgundy red between green main leaf veins accompanied by downward rolling of the leaf margins; on Chardonnay (bottom) leaves show a more generalized chlorosis and downward rolling of the leaf margins in late fall.

Lab Testing

Leafroll viruses may be diagnosed using ELISA and RT-PCR tests. Virus titer levels are variable not only within the year, but also within the vine. Collect petioles in late summer and fall, or shoots/canes for cambium scrapings in fall and winter. PCR and ELISA tests are not available for all GLRaVs. Check with the commercial lab for their preferred sampling method and collection time prior to taking samples.

Mealybug Vectors

The most common mealybug found in California vineyards is the grape mealybug (Pseudococcus maritimus). Obscure mealybug (P. viburni) is present in central coast vineyards but less common than the grape mealybug. The vine mealybug (Planococcus ficus) was introduced into California in 1994 and has now been found in most production area of the state. Less common is the long-tailed mealybug (P. longispinus) found primarily in the cooler areas of the south central coast. The Gill’s mealybug (Ferrisia gilli) is the fifth species found in California but is currently very limited in distribution with populations found in the Sierra foothills, in the northern coast (Lake County) and in the southern San Joaquin Valley.

All the above species are capable of being a vector for leafroll disease. Research has shown that mealybugs can become infective after one hour of feeding on a leafroll virus infected vine and can transmit the virus to a clean host after one hour of feeding. Although all female instars can transmit the virus once infected, the first instar is the most effective vectors of the disease. The first instar or “crawler” moves to find a feeding spot and is considered to be the most common dispersal stage of a mealybug population. Wind, equipment, workers and infested nursery stock can also move mealybugs.

Movement of leafroll disease into a recently planted vineyard of certified planting stock from an infected block on the opposite side of the avenue. Note the vines showing symptoms are nearest the avenue and are not present on vines further down the rows.

Management of Grapevine Leafroll Disease

1. Plant Material.The first management strategy should be to plant certified vines that have been grown and produced by a nursery participating in the California Grapevine Registration and Certification Program. Once virus infected a vine will remain infected, there is no cure. Commercial nurseries that produce certified grapevines and participate in the California Grapevine R&C Program obtain their clean stock from the Foundation Plant Services at the University of California, Davis. UC Davis has a foundation vineyard for major grape cultivars and clones. Before being planted in the foundation vineyard, all vines are tested across biological indicators, and by ELISA and RT-PCR. The foundation vineyard is monitored by visual inspections in spring and fall, and a portion of it is retested every year by ELISA and RT-PCR for viruses known to spread naturally. This provides the highest level of confidence about the virus status of the selections.

Both the fruiting scion and the rootstock need to come from certified mother plants. A very common spread of leafroll is the use of infected bud wood from commercial vineyards. The lack of symptoms in the source vineyard cannot be relied upon as a guarantee that there is no virus; many of the major grapevine viruses show no symptoms during some or all of the season. Particularly if wood is collected during the dormant season, it is unlikely that the source vines will show distinct symptoms of virus infection. Selected grapevines should also be pre-tested for virus by a competent diagnostic laboratory if this type of material is going to be used. Even with vine testing sourcing bud wood from established vineyards carries a risk of introducing virus into a new planting.

2. Learn to recognize leafroll symptoms.Leafrollsymptomsbecome visually apparent by early summer and generally intensify into midsummer and fall as noted above. Symptoms can vary by leafroll species, multiple virus infections, and by cultivar and rootstock combination. Symptoms are generally more apparent in cultivars producing red or black fruit than in white fruiting cultivars. Remember that the lack of symptoms in a grapevine does not guarantee freedom from infection by the viruses that are the causal agents of leafroll disease.

3. Recognize and be aware of potential leafroll vectors.As discussed above mealybugs and scale insects are known vectors of some species of GLRaVs. Monitor and be aware of which insect vectors may be in your vineyards. More information on these insects is available in Grape Pest Management UCANR publication 3343 or in the online UC IPM guideline for grapes, http://www.ipm.ucdavis.edu. Know which species of mealybugs are present in your vineyards, their population dynamics are different and will influence the timing of any needed control practices. European fruit lecanium scale (Parthenolecanium corni) is a common insect found in California vineyards, it and other scale insects has been shown to transmit some GLRaV species.

4. Be aware of potential spread from leafroll infected blocks.Leafroll infected blocks can be a source for vector and disease spread into adjacent clean plantings. Consider if plant removal is a viable option to reduce further spread for both the source and clean blocks. Vector control may be a management decision to consider. Recent research suggests the rate of disease spread of GLRaV-3 is greater when higher mealybug population levels are present. Treatment of virus source blocks should minimize the infective vectors leaving the block; the treatment of clean blocks should be targeted to kill infective vectors quickly upon entering the block and to reduce secondary spread to adjacent vines.

5. Area-wide management.When both mealybug populations and the virus causing leafroll disease are present in an area, cooperation between neighboring vineyard owners will be necessary to improve on reducing the spread of disease from infected source blocks to non-infected vineyards.

Grapevine leafroll disease is actively being studied both here in the US and internationally. Improvements in identification techniques and better understanding of disease epidemiology in vineyards will hopefully improve our ability to develop management practices to reduce economic impacts.

Red Blotch Disease

Grapevine red blotch disease was suspected as a concern on vines growing in the Napa Valley in 2008. In 2011 a DNA virus was identified in independent studies in California and New York and shown to be associated with the symptoms on infected vines. Since the initial identification of Grapevine red blotch-associated virus (GRBaV), it has been found to be widespread in vineyard producing areas of the United States and Canada. A recent survey of a grape herbarium collection at UC Davis has shown one plant specimen collected by Harold Olmo in 1940 from a Sonoma County vineyard to be positive for GRBaV.

Recognizing Red Blotch

In red wine cultivars, irregular red blotches form on the leaf blades on the basal parts of shoots. Veins on affected leaves can turn pink to red in color. Symptoms can vary between cultivars and the severity may also vary between years. In white cultivars the symptoms are not as dramatic. Interveinal chlorosis is most common followed by irregular chlorotic blotches. These symptoms can begin to appear as early as July and as late as September. In comparing red blotch to leafroll disease, leafroll symptoms are generally more uniform across the leaf blade, the veins remain green, and the there can be a downward rolling of the leaf margin. For more pictures of red blotch symptoms on different cultivars got to: GRBaV symptoms

Late summer symptoms on Chardonnay, red blotch on the upper photo and leafroll on the bottom.

Lab Testing

The identification of GRBaV can be difficult to determine by visual observation due to the similarity of the symptoms to leafroll disease and other nutrient deficiencies. This is especially true in the case of white cultivars. Co-infections with other viruses can also affect symptom expression. Suspected infections should be confirmed by having samples assayed by a PCR test by a commercial diagnostic lab. Check with the commercial lab for their preferred sampling method and collection time prior to taking samples.

Disease Spread

GRBaV is spread by the propagation of planting stockor grafting non-infected vines using infected budwood. The widespread occurrence of red blotch disease would suggest this type of spread has occurred. Since the identification of the virus and the availability of the PCR testing in 2012, grapevine nurseries have been testing their increase blocks and removing infected vines to eliminate this type of spread. The recently established Russell Ranch Foundation Vineyard at UC Davis has been tested and all vines are free from GRBaV. Each vine planted at the Russell Ranch has undergone extensive virus testing following a process known as Protocol 2010. For nurseries participating in the CDFA R&C Program this will provide a source for future increase blocks to supply certified vines for vineyard plantings.

GRBaV is a DNA virus and is closely related to a family of viruses called Geminiviridae. Insect such as leafhoppers and whiteflies can vector other virus diseases within this family. Researchers are currently testing potential insect vectors of GRBaV. Although there was a report of Virginia creeper leafhopper being a vector in a greenhouse study other researchers have been unable to duplicate that study. The evaluations of other potential insect vectors have not yet identified one that can successfully acquire and transmit the virus in the field. Although there is anecdotal information that there is spread within some vineyards to date there is insufficient data to support that claim.

Vine Effects

Research has shown that when comparing GRBaV infected vines to ones that have no known GRBaV, leafroll-associated viruses, vitiviruses, or Nepoviruses that Brix were lower and malic acid in the juice were higher at harvest for Cabernet Sauvignon and Chardonnay but not Zinfandel. For Chardonnay, yield was also reduced for infected vines. A study looking at the effect of dropping crop to improve quality on infected vines saw little beneficial effect from that practice. For most cultivars, there is a decrease in total phenols, tannins, and anthocyanins (for red wine cultivars) for vines infected with GRBaV.

Management of Red Blotch Disease

As with leafroll disease the first management strategy should be to use propagation material that is free from known viruses when establishing new vineyards or grafting existing sites. Meetings of the Grapevine Regulations Working Group have been recently conducted to discuss proposed changes to the Grapevine Registration & Certification Program with regards to red blotch disease. Until budwood increased from the Russell Ranch Foundation vineyard is available for use it is important that propagation material is tested to avoid virus disease.

If you have blocks that have leaf symptoms and have had delayed maturity or low crop yield have a virus panel run by a commercial lab to confirm which viruses are present. Remember symptoms are going to be more noticeable in red wine cultivars and less so with white cultivars. For confirmed GRBaV infected vineyards the management response may vary depending on the vine effects that are being observed. The difference in sugar accumulation between infected and non-infected vines in some vineyards has been as much as 5 Brix. In vineyards with a combination of infected and non-infected vines this wide variation in maturity has resulted in selective harvests to improve fruit uniformity. For infected sites that fail to meet yield and quality expectations vineyard removal is the best solution. If only a low percent of vines in a block are infected, then rogueing and replanting is an option. If vine removal and replanting is an option there is currently assistance available (see below).

Financial Assistance Available to Replant Red blotch-affected Grapevines:

The Agricultural Act of 2014 (the 2014 Farm Bill) authorized the Tree Assistance Program (TAP) to provide financial assistance to qualifying orchardists and nursery tree growers to replant or rehabilitate eligible trees, bushes and vines damaged by natural disasters.

The 2014 Farm Bill makes TAP a permanent disaster program and provides retroactive authority to cover eligible losses back to Oct. 1, 2011. In California, producers who are replanting vines affected by grapevine red blotch disease may be eligible for assistance and should contact their local Farm Service Agency Office to schedule an appointment for the required visual inspection. For more information go to: Fact Sheet

Al Rwahnih, M., et al. 2013. Association of a DNA virus with Grapevines affected by Red Blotch disease in California. Phytopathology 103:1069-1076.

Golino, D. A., et al. 2002. Grapevine leafroll disease can be spread by California mealybugs. California Agriculture 56:196-201.

Golino, D. A., et al. 2008. Leafroll disease is spreading rapidly in a Napa Valley vineyard. Calif. Agric. 62:156-160.

Krenz, B., Thompson, J., et al. 2012. Complete Genome Sequence of a New Circular DNA Virus from Grapevine. J. Virol. 86:7715.

Krenz, B., et al. 2014. Grapevine red blotch-associated virus is widespread in the United States. Phytopathology. First Look.

Oberholster, A., et al. 2015. Impact of red blotch disease on grape and wine composition and quality. American Society of Enology and Viticulture National Conference Technical Abstracts, p. 75. (2015).

Poojari, S., et al. 2013. A leafhopper transmissible DNA virus with novel evolutionary lineage in the family Geminiviridae implicated in grapevine redleaf disease by nextgeneration sequencing. Plos One 8:e64194.

Sharma, A. M. et al. 2011. Occurrence of grapevine leafroll-associated virus complex in Napa Valley. PLoS One 6(10): e26227.

Smith, R., et al. 2015. Effect of crop reduction of vines infected with grapevine red blotch-associated virus on fruit maturity. American Society of Enology and Viticulture National Conference Technical Abstracts, p. 136-137.

Tsai, C. W., et al. 2010. Mealybug transmission of grapevine leafroll viruses: Analysis of virus–vector specificity. Phytopathology 100:830-834.

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Semillon, copyright BKWine Photography

Semillon, copyright BKWine Photography

Pinot Noir, copyright BKWine Photography

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Almost ripe chardonnay grapes in Chablis, copyright BKWine Photography

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Grape variety identification

Terminology note: cultivar or variety are used in viticulture

Commercial growers

If you do not have records of the plant material planted in your vineyards, there two ways to determine the cultivar and rootstock. However, the methods have different levels of accuracy.

  • Ampelography – You can use physical characteristics of the shoot tips, leaves, and fruit to identify the grape cultivar. The Vitis International Variety Catalogue can be used to search cultivars and rootstocks for images of shoot tips, leaves and fruit. Use the database search feature. This is helpful in determining the variety but is not completely definitive.
  • DNA testing — If you want to be certain about the cultivar or rootstock identification, send leaf samples for DNA testing at Foundation Plant Services. The service comes at a significant cost, but is the only way to specifically determine the cultivar. However, be aware that DNA testing cannot identify a cultivar to the clone level at this time. For rootstocks, you will need to use leaf tissue from suckers growing from below the graft union for identification.

Hobby grape growers/home garden

There are thousands of grapevine cultivars grown worldwide, and it is difficult to positively identify grapevines based on photos or plant samples. Also, having diseased or unhealthy plant tissue makes it difficult for visual identification. If you want to identify the grapevines in your home garden/landscape, you can use the resources listed above for commercial growers. However, it is often difficult to narrow down your choice of cultivars to begin searching online databases. Therefore, we suggest that you begin with the most common grape varieties sold to homeowners. Below are resources that provide details on such varieties.

  • Many grapes for the home garden are American grape varieties, largely because they are more disease resistant. These may be used for table grapes (fresh eating), juice (or wine), or jams/jellies. Some are interspecific crosses between American Vitis and Vitis vinifera. To learn more about different wine, juice and table grape varieties, check out the following online resources for descriptions and photos:
    • Table Grape Varieties for Cool Climates
    • Wine and Juice Grape Varieties for Cool Climates
    • Home Garden Grapes & Muscadines
  • Want someone to help identify your plant? Contact your local Extension () office for assistance. Specifically inquire with the Master Gardener Help Desk, as they may be able to further assist in cultivar identification based on their experience and other local resources. However, make sure that you have excellent photos that identify the plant parts (see Ampelography above). Second, make sure you have photos of your plant with ripe, disease free fruit. Having diseased or unhealthy plant tissue makes it difficult for cultivar identification.

Grapes can be broadly categorized as either table grapes or wine grapes, though many grapes can be used as both.

Table and wine grapes. Table grapes are eaten out of hand or used in baking and cooking. Wine grapes are used for making wine. Grapes can also be used for making raisins or for producing grape juice.

Grape color. After dividing grapes into table grapes and wine grapes, grapes can be further divided by color into white grapes and black grapes. White grapes—which are popularly called green grapes–include amber and yellow and green grapes, and black grapes—which are popularly called red grapes–include almost black, blue-purple, red, and pink blushed grapes.

Seeded and seedless grapes. After division by color, grapes can, once again, be divided into seeded and seedless grapes.

All of this is a lot of work for a berry fruit that is simply good eating or drinking.

But wait, grapes can be divided botanically, too.

North American and European grapes. There are two principal species in the grape family. One species is native to Europe and the other is native to North America.

The species Vitis vinifera is often called the European grape. European grapes—there are many subspecies–are characterized by tight skins and generally high heat requirement for ripening. European grapes are the most widely cultivated worldwide and produce the best grapes for winemaking as well as the most popular table grapes.

European grapes are believed to have originated in western Asia near the Caspian Sea and have been in cultivation for more than 7,000 years. These grapes were pictured in ancient Egyptian mosaics, Greek friezes, and Roman murals. There are thousands of varieties of European grapes. Two famous European table grapes are the ‘Thompson Seedless’ and the ‘Flame Seedless’. Famous European wine grapes are ‘Chardonnay’ and ‘Zinfandel’.

North American grapes fall mainly into the species Vitis labrusca. These grapes are known as American or North American grapes and are often called slip skin grapes because their skins slip easily from the fruit pulp. These grapes require less heat than European grapes to ripen. Slip skin grapes are often used to make jelly or unfermented grape juice. Slip skin grapes are sometimes called ‘Concord’ type grapes and include the black Concord grape, the green Niagara grape, and the red Catawba grape.

The subspecies Vitis rotundifolia is another native North American grape. Vitis routundifolia grapes are often referred to as muscadine grapes. These grapes are tolerant of greater heat and are often grown in the South. Muscadine grapes produce only half a dozen large grapes per cluster and are usually black or coppery purple colored.

American grape varieties have a distinctive grapey flavor that is often referred to as foxy—which can also be characterized as musky or earthy. The foxiness of American grapes is contrasted to the sweet and winey flavor of European grapes. American grapes can be found in most temperate regions of the northern hemisphere. These are the grapes that the Norse explorers found when they first discovered North America in about 900 A.D. and called it Vineland.

In addition to the ancient stock of European and American grapes can be added to modern hybrid grapes, which are sometimes referred to as French hybrids. Hybrids are generally human-made plant combinations.

Hybrid grapes. Modern hybrid grapes varieties originated with the European grape, Vitis vinifera. The hybrids were developed beginning in 1865 after a grape root aphid called Phylloxera vastarrix devastated more than 2½ million acres of European grapes in France. Because American grapes were generally immune to phylloxera, European grape stems were grafted to American rootstock to create the modern hybrids. Hybrid grapes allowed Italy, France, and Spain to become the largest grape-producing countries in the world.

Grapes are woody, deciduous, perennial climbing plants with coiled tendrils, large, toothed leaves and clusters of inconspicuous flowers that develop into bunches of juicy berries. Vines can grow to 55 feet or more in length and have as many as 50 clusters of fruit on one vine. Grape clusters can contain from 6 to 300 grapes each.

The juicy pulp of the grape is covered with a skin that has a thin powdery coating called the “bloom.” Individual grapes can be seedless or contain between 1 and 4 seeds. Grapevines flower in spring and the fruit is ready for harvest about three months later.

Serve. The flavor of fresh grapes eaten out of hand is difficult to beat. But, if snacking is not enough, table grapes easily combine with other fruits: try grapes in fruit cups, fruit salads, and fruit compotes.

Combine grapes with avocado, grapefruit sections, melon balls, or strawberries.

Choose. Select table grapes that are fresh, plump, and bright. “Bloom” is the velvety powdery look that you see on fresh grapes. That’s good! Grapes that are too shiny have probably been handled just a bit too much.

Fresh-harvested grapes will have stems that are green and firm. These grapes will be the most flavorful. If the stems have turned brown or black, the grapes have begun to age.

There are dozens of varieties of table grapes to choose from: green-skinned, red-skinned, and blue-skinned, seeded and seedless.

Concord grapevine, decades-old

Table Grape Varieties:

Here are some of the best-known table grape varieties you are likely to find at your farm market:

• Almeria: green-skinned, small-seeded, medium-large fruit with firm, juicy flesh, and tangy sweetness. Ripens late midseason, fall through mid-winter.

• Autumn Royal: blue-skinned, seedless, medium to large oval fruit with a crisp, sweet-tasting flesh. Ripens late mid-season, fall through early winter.

• Baresana: white, seeded, large, round-oval fruit with juicy, sweet flesh. Ripens mid-season.

• Beauty Seedless: blue-skinned, seedless, small to medium-sized, oval fruit with firm flesh and spicy flavor. Ripens early, mid-spring to summer.

• Black Corinth: purple-black, seedless, very small fruit that is crunchy and very sweet. Also known as Zante currant or champagne grape. (Zante is the name of the Greek island where these grapes were cultivated 2,000 years ago.) Ripens mid-season in summer.

• Calmeria: green-skinned, seeded, large, elongated oval fruit with meaty, crisp flesh that is rich and tangy-sweet. Ripens late, late fall to mid-winter.

• Cardinal: red-skinned, seedless, large fruit that is round to elongate with a firm, crisp fruit with a Muscat-like flavor. Ripens early, late spring to mid-summer.

• Candice: red-skinned, seedless, small, oval fruit with juicy flesh and mild red grapey flavor. Ripens mid-season.

• Catawba: red-skinned, seeded, medium-sized, roundish fruit with sweet and rich juicy flesh. Ripens late summer through fall.

• Chasselas: red-skinned, seedless, plump, juicy fruit.

• Christmas Rose: dark red, seeded, large, oval fruit that is very crunchy with a juicy, sweet fruity flavor. Ripens late midseason, late summer to mid-winter.

• Concord: purple-black skinned medium to large, round fruit with juicy flesh, sweet near the skin and tar near the seeds. Use for dessert, juice, and jelly. Some varieties are seedless. Ripens mid-season.

• Delaware: red-skinned, seeded, small to medium-sized roundish fruit with sweet, juicy flesh. Ripens midseason, late summer through fall.

• Emperor: red-skinned, seeded, large, oval fruit with firm, crisp flesh with a mild cherry taste. Ripens midseason to late, late fall to early spring.

• Fantasy Seedless: blue-black skinned, seedless, large oval fruit that is firm and very sweet. Ripens mid-season.

• Flame Seedless: red-skinned, seedless, small to medium-sized, round fruit with crunchy bite and mild sweetness. Ripens early to mid-season, early summer through fall.

• Flame Tokay: red-skinned, seedless, large to very large, oblong fruit with crisp, juicy, sweet flesh. Ripens midseason, early fall through late fall.

• Italia Muscat: yellow green-skinned, seeded, very large fruit with tender juicy flesh with a heavy, sweet muscat flavor. Ripens midseason, late summer through late fall.

• Kishmishi: same as Thompson Seedless.

• Red Malaga: red-skinned, seeded, large fruit with crisp flesh and sweet flavor and low acidity. Ripens early mid-season.

• Marroo Seedless: blue-black, seedless, medium-sized fruit with firm, juicy flesh and sweet, mellow flavor. Ripens mid-season.

• Niabell: blue-skinned, seeded, very large round fruit that is sweet to semi-sweet. Slip-skin Concord type. Ripens mid-season.

• Niagra: green-skinned, seeded, medium to large oval fruit; the flesh is juicy, foxy and sweet. Ripens mid-season.

• Perlette: green-skinned, seedless, medium-sized round fruit with firm, juicy, sweet flesh. Use for desserts or raisins. Ripens very early, late spring through mid-summer.

• Queen: red-skinned, seeded, large fruit with firm, juicy flesh, and very mild sweetness. Ripens in midseason, late summer.

• Red Malaga: red-skinned, seeded, large, oval fruit with crisp, firm flesh and neutral flavor. Ripens in early midseason, mid-summer through early fall.

• Ribier: purple-blue skinned, seeded, large to very large, plump, round fruit with sweet juicy flesh with mildly astringent skin. Ripens mid-season.

Red seedless grapes

• Ruby Seedless: red-skinned, seedless, medium-sized, oval fruit with firm, crisp, juicy flesh that is sweet-tart taste. Ripens late mid-season, late summer to early winter.

• Steuben: blue-black skinned medium-sized fruit with rich, tangy flavor. Ripens mid-season.

• Thompson Seedless also called Sultanina: green-skinned, seedless, small to medium elongated fruit that has a crisp, juicy flesh that is sweet. Also used for raisins. Ripens early to mid-season, summer through fall.

• Tudor Premium Red: red-skinned, seedless, large fruit with sweet, crisp flavor. Ripens late mid-season, late summer through late fall.

Also of interest:

How to Plant, Grow, Prune, and Harvest Grapes

Growing Backyard Grapes

Table Grapes: Kitchen Basics

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