Cantaluppi, C.J., Area Horticulture Agent, North Carolina Cooperative Extension Service

ABSTRACT

A one-acre replicated cultivar trial of seedless fresh market table grapes (Vitis labrusca) was planted to compare the yields of current cultivars to make recommendations to growers.  Yields increased until 2010, when about 8% of the vines succumbed to Armillaria root rot.  Cultivars showing the highest yields in 2009 included Mars, Marquis, Venus, Vanessa, Lakemont, and Einset and are recommended for commercial production.

INTRODUCTION

A study was initiated in 2005 to look at the possibility of growing seedless, fresh market table grapes (Vitis labrusca) in the northern Piedmont of North Carolina.  Research done on these grapes is scant and very few growers have grown these grapes on a commercial scale in the NC Piedmont.

 A local specialty crop grower, who farms north of Oxford, NC was looking for a high value horticultural crop to gain additional income.  Seedless table grapes were suggested, since no one was growing them locally.  It is a high-value horticultural crop that was added to the grower's crop mix of blackberries and blueberries.

This study was supported in part by applying for an Innovative Program Grant, from NC A&T State University.  The grant provided $15,000 to the grower, which paid for the cost of the trellis wire and electric deer fence and labor around the one-acre perimeter.  The grower's other expenses included the grapevines, trellis posts, bamboo stakes, irrigation system, grow-tubes, mulch, fertilizer, herbicides, and insecticides, which amounted to about $10,288 (Table 1.)

Oxford, NC lies in zone 7B on the USDA National Plant Hardiness Zone Map with an average growing season of 200 days.  The grapevines were planted in a clay loam soil, having excellent drainage.

 

MATERIALS AND METHODS

The following are descriptions of cultivars grown in the trial, adapted from Dr. Bruce Reisch (4).  Most are New York varieties, except for Arkansas and Canada varieties, as noted.

 White Grapes

 Marquis, a cross of Athens x Emerald Seedless, released in 1996, is a white seedless grape with excellent mild American flavor.  The berries are large, often 3.5-5.0 grams/berry, with a juicy, melting texture.  Clusters are large and attractive, while the vines are very productive.  Ripe fruit holds well on the vine, with the flavors going from a mild fruity flavor when first ripe, to a stronger labrusca flavor two weeks later.  Vines are very vigorous and productive.

 Himrod, produced from a cross between Ontario and Thompson Seedless, has become the most successful table grape since its 1952 release from the Cornell University Grape Breeding Program.  It produces large bunches of white seedless grapes with excellent, honey-like flavor and melting, juicy texture.  The clusters are loosely filled (cluster weight = 0.36 lb., berry weight = 2.1g). 

 Lakemont, was also produced from the same cross as Himrod but has a milder flavor and more compact clusters of small to medium-sized berries.  Cluster thinning prevents overcropping (cluster weight = 0.48lb., berry weight = 1.7g). 

 Interlaken is a sister seedling of Himrod (same parents) with seedless green to golden berries. The clusters are medium sized and compact with small, white berries that ripen very early.  Cluster weight = 0.27lb., berry weight = 1.5g.

Red Grapes

Einset Seedless, resulted from the cross of ‘Fredonia’ x ‘Canner’ (‘Hunisa’ x ‘Sultanina’) made in 1963 by G.W. Remaily.  The berries are oval and bright red with a light waxy bloom (powdery covering on the fruit).  The medium soft seed remnant is not usually noticeable.  Berries are medium sized (cluster weight = 0.32 lb., berry weight = 2.3g).  The skin is slightly tough and adheres to the tender flesh.   The flavor is fruity with a mild note of labrusca and sweet strawberry-like taste. 

Vanessa was developed by the Horticultural Research Institute of Ontario, Canada, and is a red dessert grape of excellent quality.  The seed remnant is usually large and soft when noticeable.  Berries are medium in size on medium, well-filed clusters.  The flavor is mild and fruity, and berry texture is firm to crisp.  The fruit quality is among the best of the red seedless types. 

Canadice produces medium, excessively compact clusters with small red berries (cluster weight = 0.50lb., berry weight = 1.6g). 

Reliance comes from the University of Arkansas, and produces large clusters of round, red, medium-sized berries.  The skin is tender, and the flesh is melting in texture, with a sweet labrusca flavor.  Cold hardiness is among the highest of the seedless varieties (cluster weight = 0.62lb., berry weight = 2.3 grams). 

Suffolk Red produces medium to large clusters of mild-flavored red berries.  The clusters are loose (cluster weight = 0.32lb., berry weight = 2.7g). 

Blue Grapes

Mars is a release from the University of Arkansas, and is a vigorous, blue seedless grape.  The flavor is mildly labrusca and the berries are slipskin (having a tough skin which separates readily from the pulpy flesh).  Clusters are medium-sized, cylindrical, and well filled.  A very high-yielding cultivar (cluster weight = 0.40lb., berry weight = 3g. 

Venus, also from the University of Arkansas, is a vigorous and productive blue-black grape.  The medium-large clusters produce large berries with mild labrusca flavors.  Cluster weight = 0.60 lb.  Berry weight = 2.9g.  Seed traces may be noticeable. 

Glenora produces medium-sized blue berries.   The clusters are extremely loose. The taste is very bland and not as flavorful as the other varieties. 

Jupiter was released from the University of Arkansas in 1998.  It is an early maturing reddish-blue to blue variety when mature.  It has large, firm, non-slipskin berries on medium-sized clusters.  Fruit has a distinct Muscat flavor.  Cluster weight = 0.5lb., berry weight = 5g. 

Concord Seedless is similar in flavor and texture to Concord.  The clusters and berries are much smaller than those of Concord.  Productivity is erratic, due to its uneven ripening under hot temperatures.  When grown in hot climates, the berries produce seeds, hence, it is not seedless.

 A replicated cultivar trial was established on the farm, consisting of the 14 above mentioned seedless grape cultivars on one acre.  The objective was to identify which cultivars performed the best in the northern Piedmont.  The cultivars came from the breeding programs at Cornell University, the University of Arkansas, and the University of Ontario.  A randomized complete block design with 5 plants per plot and 5 replications was used.  Vines were spaced 10 feet between vines in the row and 10 feet between rows and were planted on May 18, 2005 in a clay loam soil. 

During 2005 and 2006, the vines were trained and pruned to prepare for a first harvest in 2007.  Despite a freeze on Easter weekend in 2007, which killed the primary buds, the secondary buds emerged and produced a good crop.  In 2008, hail destroyed most of the grape crop so yield data was not taken.  In 2009, a much larger crop was harvested.

 

RESULTS AND DISCUSSION

Table 1.  Vineyard Establishment Costs Per Acre , First Year

 

Installation of deer fence, trellis, & labor	$15,000
Bamboo stakes	121
Fiberglass stakes	462
Drip Irrigation injector, piping, faucets	2,340
Grape Vines	2,460
Snap and Grow Tubes	1,462
Tapener guns (2) to tie vines to trellis	133
Insecticides, fungicides, herbicides	500
Kasco Respirator	750
Grape lugs for harvesting	308
Fertilizer	234
Diesel fuel	200
Gasoline for lawn mower	210
Reflective tape for bird exclusion	108
Other irrigation installation help	1,000
Total	$25,288

 

Table 1 shows the costs associated with planting one acre of seedless table grapes based on this study.

 

Table 2.  Seedless Table Grape Trial, Angels Nest Farm, Oxford, NC

                                

                                    Yield(lbs./Acre)¹

Cultivar                                       2007      2009      2010            %Sugar                                    Harvest Dates

Mars	4329a  11954a  3818a	17	7/27 – 8/10
Marquis	4295a    4341b  2645b	18	8/2 – 8/10
Venus	1972b    4344b  1623c	18	7/20 – 8/3
Jupiter	1686b    1795b    411d	19	7/20 – 7/26
Lakemont	970b    4256b   545d	20	7/26 – 8/3
Glenora	705b    2450b  739cd	19	7/20 – 7/27
Einset	668b    3228b  347  d	17	7/20 – 7/26
Canadice	559b   1847b 1579c	18	7/26
Vanessa	503b   3668b  1126cd	21	7/20 – 7/27
Concord Seedless	341b   --------   ---------	19	8/10
Suffolk Red	250b   1064b     222  d	22	8/10
Himrod	241b   1536b     486  d	17	7/20 - 27
Reliance	-----------------------	----	------------
Interlaken	-----------------------	----	------------

 ¹Yields with the same letter within columns are not statistically significant, Duncan’s Multiple Range Test, .05 level. 

Cultivars that yielded the highest in 2009 are Mars, Marquis, Venus, Vanessa, Lakemont, and Einset and are recommended for commercial production.

Concord Seedless was taken out of the trial in 2009 because of the actual presence of seeds and its uneven fruit cluster ripening characteristics.  Reliance and Interlaken were removed because many vines died before becoming established.

Armillaria Root Rot Discovered

In 2010, yields were reduced due to the presence of Armillaria mellea, a soil fungus, which kills grapevine roots by killing the cambium and xylem tissue.  It can survive as a saprobe on woody host roots after the host has died.

As a result, 30 vines (8.5 percent) were dug up from the vineyard in November 2010 and the roots were examined to find the presence of a white mycelial fungal growth.  The fungal mycelium decomposes cellulose, hemicellulose, and lignin for nutrients as it grows, thereby decaying the root wood (1).  It is impractical to re-plant vines in those areas, because they will become infected with the Armillaria and die due to the longevity of the fungus in the soil.

Practical research is needed to find a fungicidal soil drench that could be applied as a theraputic treatment to kill existing Armillaria propagules in the soil surrounding the newly planted grapevines.

 Pierce's Disease Discovered

Pierce’s Disease of Grape (Xylella fastidiosa) is a very destructive bacterial disease of grapes in the south that is vectored by leafhoppers.  The bacteria reside and multiply in the xylem and eventually block water movement in the plant.  The vector does not survive cold winters at high elevations in NC but it does overwinter in the Coastal Plain.  Symptoms of Pierce's Disease were first observed in the vineyard in 2007.

Dr. Donald Hopkins, plant pathologist at the University of Florida has discovered a benign strain of the bacterium that causes Pierce’s Disease (2). He found this strain in an elderberry plant (3).  This benign, or avirulent strain of the bacterium cross-protects or “vaccinates” the plant so that it does not contact Pierce’s Disease when the virulent strain of the bacterium is transmitted by the leafhopper.  His inoculations have been done primarily on new vines before they are transplanted into the vineyard.

He came to the trial vineyard and 2008 and 2009 and inoculated the bacterium in some of the grape vine trunks.  He will be observing the vines to see if his inoculations protect symptomless vines from getting Pierce’s Disease  and also if the disease can be halted on symptomatic vines.  He has evaluated the vines in August of 2009 and has concluded that about 10% of the vines have symptoms of Pierce’s Disease.  The decreased yield in 2010 is probably due to the combination of Armillaria and Pierce’s Disease. 

 

SUMMARY

Seedless table grapes are a viable and profitable fresh-market horticultural crop that can be grown in the northern Piedmont of North Carolina.  They can be sold retail directly to the consumer, with the grower getting a high price ($4.00/lb. or more) for thin-skinned seedless grapes.  The cultivars showing the highest yields in 2009 were Mars, Marquis, Venus, Vanessa, Lakemont, and Einset and are recommended for commercial production.  It is hoped that an effective fungicide can be found and labeled to inject into the soil to protect newly-planted grapevine roots from propagules of the Armillaria root rot fungus.

Hopefully, Dr. Hopkins’ inoculations will prevent Pierce’s Disease in symptomless vines, as well as halting the disease in symptomatic vines.  it is also hoped that the avirulent strain of the bacterium can be used to inoculate new vines that are replanted in the trial. The trial will be monitored to see how the above factors are contributing to yield decline or yield stability.  In spite of having occurrences of two destructive diseases, the study showed that there are several seedless fresh market table grapes that can be grown in the Piedmont that can add a high-value horticultural crop to a direct-market retail grower's crop mix.

 

REFERENCES

1.  Gubler, W.D., et. al.  2004.  Root diseases of grapevines in California and their control. Australasian Plant Pathology,      33:   157-165.

2.   Hopkins, D.L.  2005.  Biological control of Pierce’s disease in the vineyard with strains of      Xylella fastidiosa benign to grapevine.  Plant Disease 89: 1348-1352.

3.  Hopkins, D.L., and Adlerz, W.C.  1988.  Natural hosts of Xylella fastidiosa in Florida.  Plant   Disease 72: 429-431.

4.  Reisch, B.  1993.  Table grape varieties for cool climates.  Information Bulletin 234, Cornell     University, Ithaca, NY.

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