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Virginia Cooperative Extension -
 Knowledge for the CommonWealth

Viticulture Notes

Volume 13, Number 5 -- September-October, 1998

Dr. Tony K. Wolf, Viticulture Extension Specialist

Table of Contents

I. Current situation

II. Question from the field: dormant sprays

III. Upcoming Meetings

I. Current Situation:

Season recap: I feel that I could substitute "Where has the summer gone?" for "Current Situation." In a blur the season rushed headlong into harvest; a harvest which for us, ran as much as 2 weeks ahead of average. Chardonnay clone #4 was picked on 16 September (22.5° Brix and pH of 3.35) at the Winchester AREC. Besides the advanced harvest dates many areas of the state experienced moderate to severe drought conditions. Again, using Winchester AREC as an example, precipitation was above average (fortunately) from March through June, but well below average every month since (Table 1). I saw older, non-irrigated vineyards suffering drought stress as early as the first of August. We used irrigation for the first time this season on our 7- and 8-year-old vines at Winchester to avoid drought stress in our research plots. Crop quality — in general — looks good. I would characterize our own fruit, up until mid-September, as clean (little or no fruit rots), good sugar levels, with balanced pH (e.g., < 3.4), and good fruit varietal character. After mid-September, fruit pH started jumping up and our later-maturing reds (Cabernet Sauvignon, Fer, Syrah, Sangiovese, etc.) were pushing 3.6 or higher. But then, we see that almost every year.

The most frequent pest problems that we saw this year were powdery mildew, birds, and grapevine yellows. Each warrant a few comments now, and greater elaboration in future communications.

Table 1. Long-term average and 1998 monthly precipitation (inches/month) at the Winchester Agricultural Research and Extension Center.
























I’m uncertain why powdery mildew occurred with such frequency. We again had low levels of cluster infection apparent in our divided canopy Chardonnay about one month after fruit set (mid-July). It’s possible that the frequent rains of June contributed to the development of primary infections and that poor penetration/coverage of clusters in the divided canopy trellis promoted the secondary lesions. Our spray schedule was unusual this year in that we were conducting trials in the vineyard to evaluate the effects of crop oils on vine function. Because the crop oils can cause phytotoxicity if mixed with sulfur and certain other pesticides, we had to alter our normal use of sulfur. So, we may have promoted the development of powdery mildew. Powdery mildew and the use of crop oils as powdery mildew eradicant/protectant fungicides will be one topic of discussion at our pest management-research update conference in Roanoke on 11-12 January 1999 (see page 3).

Grackles and robins were the chief avian culprits that we saw in northern Virginia vineyards this fall. We had unusually early (mid-August) pressure from robins this season and ended up using a combination of netting, ReJex-iTTM olfactory repellent, scare-eye balloons, pyro-technic "clapper" shells, 2 "Bird-Gard"TM audible distress emitters, and a shotgun to discourage depredation. We were successful, but it was probably the combination of tactics that ultimately prevailed. ReJex-iTTM is formulated with methyl anthranilate, the pervasive odor-active compound in Concord grapes. It is registered for use on grapes and certain other fruit and non-fruit crops to discourage birds. Ours was not a replicated test, so I can offer no advice on efficacy. I will say that the ReJex-iTTM odor was still detectable almost a month after application — we had no rainfall during the period. Researchers at Washington State (no/low rainfall prior to harvest) apparently found an objectionable carry-over of methyl anthranilate through fermentation when it was used as a bird repellent… might not be the best additive to Chardonnay! The PBR Bird-Gards that we purchased use a 12-volt battery and can be programmed for the frequency of emission as well as one or more bird species, including grackles, starlings, robins. Again, we used them in combination with other tactics, so I cannot vouch for their efficacy. We did, however, seem to have renewed robin problems when we let the batteries go dead. Clapper shells and shotgun reports are effective scare tactics, but offer temporary protection at best.

Grapevine yellows (GY) is a destructive disease caused by a bacteria-like organism called a phytoplasma. We observed a substantial increase in GY incidence among some vineyards in 1998, but are uncertain of the reasons. Chardonnay is the principal variety affected by GY; however, Riesling, and to a lesser extent, Cabernet Franc and Sauvignon blanc, have also been affected by GY in Virginia. Our surveys since the early nineties show a widespread distribution of yellows among Chardonnay vineyards along the Blue Ridge. Three symptoms, appearing together, are useful in diagnosing yellows: (1) abortion of fruit clusters anytime after fruit set, (2) downward rolling and yellowing of leaves, and (3) failure of bark or periderm to mature on affected shoots. Other things to look for include shoot-tip dieback, general vine weakness, and a "brittle" texture to affected leaves. This disease generally kills vines within two to three years of symptom onset. While we now know more about the GY pathogens and alternative hosts, we still don’t know what insect vectors are involved with transmission. Affected vines or vine parts (e.g., an affected cordon) should be removed from the vineyard as soon as symptoms become apparent. Retention of affected vines in the vineyard may contribute to further spread of the disease as long as foliage remains on the affected vine. We have had limited success in cutting affected vines off above the graft union and restructuring the training system with renewal shoots. The alternative is to pull the affected vine and replant, or extend cordons from adjacent vines to fill the resulting gap. The Sept./Oct. 1995 issue of Vineyard and Winery Management (1995) has a somewhat dated but more detailed description of GY with color photos. For those interested, Agdia (Elkhart, IN; 219-264-2014; ask for Andrea) has an assay for grapevine phytoplasmas that costs $175 per sample.

Simplified temperature recording: Here’s a good idea and a blatant commercial endorsement. Spectrum Technologies’ (1-800-248-8873) Hobo data logger is about the size of a small box of stick matches, but will record over 4 months of temperature data on an hourly basis. The units are programmed, and the stored data are downloaded, via your PC’s serial port. We used several of the temperature/relative humidity recording devices in vineyards this summer and I was impressed with the ease of operation and reliability. Who would use these? Anyone interested in maintaining a record of temperature at an existing or potential vineyard site. Because they automatically record data, there is no need to manually check and reset "min/max" thermometers. What’s the cost? Recorders with 8K of memory and an internal sensor cost $59 each. You’ll also need the software ($59) and you should buy the radiation shield ($44 each) to avoid radiant heating and cooling of the recorder. Of course, you need a PC with Windows operating system. The software plots the downloaded data and allows exporting to spreadsheets for further data analysis.

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II. Question from the field: dormant sprays

"I am interested in what sprays, if any, would be effective on powdery mildew overwintering on canes. My Cabernet Sauvignon was hit hard with powdery. I obtained good control with a couple of sulfur applications, but would like to continue treatment through the winter if possible. Any thoughts?" The question of dormant sprays for powdery, phomopsis, and other fungal diseases surfaces each year about this time, especially from growers who have just fought an uphill battle with powdery mildew. There is not a lot of data on the subject, but I’ll relate what pathologists have recommended on the subject. In the case of powdery mildew, the fungus overwinters here in the East primarily as sexually produced spores (cleistothecia). Many of the cleistothecia that are washed into crevices of bark of trunks and cordons survive the winter and initiate primary infections in the spring with the advent of favorable weather and shoot growth. Cleistothecia that remain on foliage, berries and canes show very poor winter survival. For this reason, the removal of pruned canes from the vineyard is of little value for disease sanitation. The most important spores are those that survive the winter lodged in the rough bark of trunks and cordons. Our task in dormant spraying, then, is to find materials that are lethal to the spores and apply them in a manner that allows of all the nooks and crannies of the rough bark. This, in the final analysis, is a tall order. Pathologists David Gadoury and others at Cornell University examined a range of fungicides for their efficacy against cleistothecia (Gadoury, 1991). In field trials conducted in 1988, dormant sprays of copper sulfate, Bordeaux mixture (copper sulfate and lime), copper and lime sulfur all delayed the onset of powdery mildew. The applications were made just before bud break and were made at 300 gallons of spray material per acre. The copper sulfate was applied at 12 pounds per acre while the lime-sulfur was applied at 36 gallons/acre (again, in 300 gallons of water). It is important to point out that "lime-sulfur" (calcium polysulfide) is NOT a mixture of lime and sulfur. Furthermore, the only 1998 label (UAP) that I found for "lime-sulfur" does not include grapes on the label. The initial success at reducing powdery mildew with dormant sprays in 1988 was not observed in 1989 or 1990. The New York State researchers used a hooded boom sprayer to thoroughly drench the vines (300 gal/acre). This was the only sure means of penetrating the rough bark of vines. Given the high material cost of the application (about $90/acre), the need for high gallonage (300 gallons/acre), and the mediocre control, Gadoury has not recommended dormant sprays of either copper compounds or lime-sulfur. Instead, Dr. Gadoury has recommended that a more intensive program be followed in the period from bud break to bloom. The current Virginia Tech grape Pest Management recommendations lists only one dormant spray recommendation. That is for Bordeaux mixture, applied only where anthracnose (bird’s eye rot) has been a problem.

Gadoury, D.M., 1991. Dormant sprays — theory and practice. In: Integrated pest management of grape diseases: present and future strategies. p50-52. NYSAES, Geneva, NY.

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III. Upcoming Meetings

A. Pest management and research project review (and more!):

Where: Hotel Roanoke, Roanoke, Virginia

When: January 11-12, 1999

Details: Registration costs, hotel arrangements, directions, etc. will appear in the Nov.-Dec. Viticulture Notes newsletter (early November). This will be a DO NOT MISS meeting!

Program: This will be a combined meeting of the Virginia Vineyards Association and the Virginia and West Virginia State Horticultural Societies. The Society audiences are, for the most part, tree fruit producers. The viticulture-enology meeting will occur from 1:00 pm on Monday, 11 January to noon on Tuesday, 12 January. A "general" session will occur on Tuesday afternoon that will be of interest to both grape and tree fruit producers. A large trade show and a "grazing" wine/food reception will be included. Specifics of the viticulture-enology program are still being developed. At this point, the program will include the following (subject to minor content/title alterations)

Management of powdery mildew and other fungal diseases in eastern vineyards

Dr. Wayne Wilcox: Cornell University

Use of crop oils for powdery mildew, European red mites, and bud break delay

Dr. Wayne Wilcox: Cornell University; Dr. Tony Wolf, Ms. Sarah Finger, Dr. Doug Pfeiffer, Dr. Imed Dami: Virginia Tech

Analysis of viticultural suitability at the state level

Mr. John Boyer, Virginia Tech

Enology research updates

Dr. Bruce Zoecklein, Virginia Tech

Relationship of nitrogen nutrition to bunch stem necrosis of Cabernet Sauvignon

Mr. Eric Capps, Virginia Tech

Climatological and economic considerations for vineyard irrigation

Dr. Tony Wolf, Virginia Tech

Mr. Joseph Davidson, Berry Hill Irrigation

We are also making arrangements to host Dr. Peter Dry, of the University of Adelaide, South Australia for this meeting. Dr. Dry would speak on general aspects of the Australian wine industry (degree of mechanization, variety picture, Vision 2025 marketing plan, etc.), and provide a more specific talk on flavor manipulation in the vineyard via canopy management, irrigation scheduling, crop control, etc.

I would strongly encourage all serious grape producers to attend this meeting.


B. Full-day "Beginners" Grape production shortcourse

Where: Hotel Roanoke, Roanoke, Virginia

When: January 13, 1999 (the day following the two-day technical program

Program: Comprehensive discussion of current Virginia market situation, vineyard site requirements, costs and returns of grape production, varietal recommendations, vineyard design and establishment, and basic aspects of vineyard operation. Attendees are encouraged to register for and attend the technical program on 11-12 January; however, there will be a separate registration fee for this "beginners" program.

Details: Registration costs, hotel arrangements, directions, etc. will be provided with the November-December Viticulture Notes newsletter in early November.


C. Maryland Grape Growers Association Annual Meeting

Where: Howard County Fairgrounds, Clarkesville, MD

When: Saturday, 24 October 1998

Program: Program topics will include "climate and moisture balance for Maryland winegrowing, new varieties for the East, regional sampling of grapes and resultant wines." Sparkling wine reception and awards dinner to follow. Registration information, directions, etc. obtained from Ray Brasfield, 410-374-6483.


D. South East Grape Industry Association of Pennsylvania: Intensive viticulture seminar "Perfecting winter hardiness"

Where: Lancaster, PA

When: Thursday, November 5, 1998

Program: Program will deal with challenges of growing wine grapes in regions subject to winter injury. Topics to include vine vigor management, rootstock choice, soil effects, graft union protection, and more. Speakers to include Dr. Robert Pool, Cornell University, and Dr. Imed Dami, Virginia Tech. Registration information, directions, etc. obtained from Tom Webb, RD 4 Box 1, Sunbury, PA (610-760-9371).


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"Viticulture Notes" is a bi-monthly newsletter issued by Dr. Tony K. Wolf, Viticulture Extension Specialist with Virginia Tech's Alson H. Smith Agricultural Research and Extension Center in Winchester, Virginia. If you'd like to receive "Viticulture Notes" as well as Dr. Bruce Zoecklein's "Vintner's Corner" by mail, contact Dr. Wolf at:

Dr. Tony K. Wolf
AHS Agricultural Research and Extension Center
595 Laurel Grove Rd.
Winchester VA 22602

or e-mail:

Commercial products are named in this publication for informational purposes only. Virginia Cooperative Extension, Virginia Tech, and Virginia State University do not endorse these products and do not intend discrimination against other products that also may be suitable.

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