Programs

TONY K. WOLF, Professor

Grape Variety and Clone Evaluations - A replicated winegrape variety planting was established at the Winchester AREC in 1989 to evaluate the viticultural and enological suitability of 25 novel (to Virginia) varieties and clones. Data were annually collected since 1991 on vine phenology, crop yield and quality, pruning weights, and vine cold hardiness. In addition, small lots of wine were processed by B. Zoecklein (Food Science). Data and experiences with the varieties were relayed to the national industry in 1996 and 1997 via trade publications, a national conference, and several regional presentations. Project was concluded following 1998 season and summarized data were included in 42-page grape variety publication published by Virginia Cooperative Extension in June 1999 (VCE Public. #463-019)and two refereed journal papers. Ten clone of Chardonnay were established at Winchester in 1998 for similar evaluation. Crop yield and fruit chemistry data collection for the clone evaluations commenced in 2000. Substantial state and federal (USDA/CSREES) funding were obtained in spring 2001 to continue and expand this work to include detailed wine chemistry evaluations in conjunction with the Dept. of Food and Science and Technology. Finally, I sought and obtained additional funding, some from North Carolina, to develop a 19-cultivar wine grape evaluation planting at the Southern Piedmont AREC in Blackstone. With assistance from SPAREC staff, the vineyard was established in spring 2001 and is progressing well. This planting will eventually provide varietal recommendations for growers in the southern and eastern Piedmont.
Significance: The Virginia wine industry is expanding: acreage increased from 1,565 in 1997 to 2200 in 2001 (VA Agricultural Statistics Service, VDACS). Clientele are asking for detailed recommendations on suitable varieties and, more specifically, varietal clones. Data and interpretations from these studies, such as published in 1999, address those questions.

Defining Appropriate Crop Levels for Chardonnay and Cabernet Sauvigon: - This research seeks to determine with the appropriate crop level is for balancing the somewhat competitive goals of maximizing crop (and wine) quality, sustaining high crop production, and optimizing wood and bud cold acclimation and mid-winter hardiness. Begun in 1995, the studies use 3 crop levels with Chardonnay and 2 crop levels with Cabernet Sauvignon; both varieties are grown at the AHS Jr. AREC vineyard. Results to date have demonstrated that cane and bud cold hardiness can be reduced by up to 3 C in the absence of visible delays in cane maturation, or periderm development by high crop levels. We are unable to repeat the highest crop (about 10 tones/acre) in Chardonnay from 1997 through 1999 due to low fruitfulness (lower clusters/shoot and lower cluster weights). That trend was reversed, however, in 2000 when we again achieved in excess of 10 tons/acre with both the Chardonnay and Cabernet high crop treatments. The Chardonnay portion of the project was expanded during the 2000 season by adding a pruning type (spur-pruned vs. caned-pruned) factor into the treatment design. This work is being done collaboratively with Virginia Tech?s enologist (B.Zoecklein), because one goal is to understand the role of crop level on resultant wine quality. Juice and wine quality results to date suggest that croplevel has minor impact on quality at low (e.g. less than 19 Brix) sample maturity, but that the differences become more meaningful as crop maturity advances, particularly above 21.5 Brix. This was particularly evident in years with good ripening conditions, such as 1995. Lower crop attained riper fruit more rapidly than did high-cropped vines. When high cropped vines were allowed to carry crops longer, to ripen, those crops to the same SSC, the resulting wines were often inferior to those of lower-cropped vines.
Significance: The results of this work are important for assessing the impact of crop on vine size (vigor) and tissue cold hardiness. At the outset, I felt that 10 tons/acre was a sustainable yield if vine size did not suffer; however, our data suggest that sustainable yields of about 7 tons/acre are more realistic with the open lyre training system used in the experiment. Higher yields are occasionally possible, but they may not be sustainable. Preliminary results of this work have been presented in Virginia (August 2001) and out-of-state (February 2001). We have stressed in these discussions the negative delay of harvest caused by the higher crop levels. Aside from effects on cold hardiness, that has provided a compelling reason to limit crop; however we are not yet prepared to specify a ceiling, about which quality reductions become apparent.

Grapevine Yellows: - Grapevine yellows is a destructive disease of grapevines. In Virginia, GY is mainly restricted to Chardonnay and Riesling, but other varieties are occasionally affected. Affected vines typically die within two or three years of initial symptom onset. This disease is caused by one of several bacteria-like phytoplasmas, which are vectored by one or more unidentified leafhoppers or planthoppers. I have been involved with exploratory aspects of the ecology of GY in Virginia since 1988, chiefly in collaboration with USDA/ARS personnel at Beltsville, MD. Research begun in 1999 has been aimed at identification of specific leafhoppers and alternative host flora that may be involved in the Virginia disease occurrence. I have identified to species approximately 25 leafhoppers and planthoppers collected in the 1999-2001 season surveys. Based on other crops, and in one case (e.g., Scaphoideus titanus) grape, several of these leafhoppers are capable of transmitting phytoplasmas. Dr. LeAnn Beanland was hired as a Research Associate in January 2002 to devote a more concerted effort at identifying potential insect vectors.
Significance: Chardonnay represents more than 25% of grape acreage in Virginia. Some Chardonnay vineyards have by attrition, lost more than 30% of their original planting to GY. Exploration of effective control/abatement options is justified. Identifications of vector(s) and alternative hosts is a prerequisite to development of GY control strategies. We have made substantial progress in identifying potential vectors in Virginia vineyards; however, more detailed transmission studies and a more in-depth understanding of leafhopper biology (e.g., feeding preference and generations per year) are required before this information can be put to use.

Training System Comparison: - Vines are trained to different training systems due to varietal differences in growth habit, vigor or vine size differences, ease of vineyard mechanization, and grower's opinion about potential effects on fruit/wine quality. Consequently, many types of grape training systems have been devised and are in use worldwide. No two systems have had formal evaluation in Virginia. Research commences in 1998 to address that deficiency by way of multi-year field comparisons of two divided canopy systems (Geneva Double Curtain and Smart-Dyson) and a "standard", not divided, vertically shoot-positioned system. An additional factor of variety. (Traminette, Cabernet franc, and Viognier) was included in the treatment design. Data collection began with the 2000 growing season and will continue ca. 10 years. Vine vigor, ease of canopy management, crop components of yield, and fruit chemistry will be major response variables. Collaboration with B. Zoecklein (enologist) will allow examination of wine quality as well.
Significance: Virginia and other mid-Atlantic winegrape producers will benefit from this research by better understanding the cost, as well as the potential returns from several training systems options. Our monitoring of time involved with seasonal management of the different systems will ultimately permit a detailed examination of the economics of the different system.

Alson H Smith Jr AREC
595 Laurel Grove Road
Winchester, VA   22602
E-mail: emcintir@vt.edu
Phone: 540-869-2560
Fax: 540-869-0862