Vineyard and Winery Information Series:
Vol. 17 No. 4, July-August 2002
Dr. Tony K. Wolf, Viticulture Extension Specialist
II.Question from the field
Researchers at Virginia Commonwealth University (VCU), working in conjunction with the Virginia Winegrowers Advisory Board, are conducting a survey of all vineyards and wineries in the state. The results of this survey will be used by VCU to estimate the economic importance of Virginia's wine industry and to develop an industry profile. This survey is coming at a time when there is heightened interest in further stimulating the Virginia grape and wine industry. As such, the survey results could lend additional support to the State's efforts on your behalf. It is very important that each of the state's vineyards be included in this study. A survey was mailed to the owners (or a key contact) at each vineyard on July 17. If your site has not received a survey, or if you are unsure, please contact Mr. Billy Kinsey at VCU. You may reach him at (804) 278-0961 or by e-mail at firstname.lastname@example.org.
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A. I suspect that the problem is the sulfur you applied. Sulfur can damage grape tissues if air temperature exceeds 95F or so under field conditions, even with 'tolerant' varieties such as most of the vinifera. It was probably cool enough without the tubes, but putting the tubes back on could have elevated the interior air temp by 10 or more degrees, sufficient to cause the damage. I've had other growers comment on similar injury when they simply sprayed a pesticide cocktail down into the tubes. Consider this in the future - it's typically too warm in the tubes to favor fungal growth. However, you will see jap beetles. If you need to control the beetles, spray a dilute spray of Sevin or Imidan down the tube, but don't include any spray adjuvants, and don't use any fungicide (or use something relatively safe, such as Abound or Elite.
As a reminder to anyone using grow tubes, the tubes should be removed from vines by 1 September to allow vines to normally acclimate to fall conditions. DO NOT leave the tubes on over winter. We have seen ample evidence that vines can be severely damaged by winter temperatures if the vines remain in tubes over winter.
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With the passing of veraison we can look ahead towards harvest and begin to accept that we're onto the last stretch - the final approach - leading up to harvest. It's not an opportunity to let your guard down, even if it's a time when we can begin to ease up a bit on the canopy management and, hopefully, some of the disease issues. Here's a brief reminder of some things to be aware of:
Drought stress: Parts of Virginia are currently experiencing extreme drought, a condition that is exacerbated by the sustained, chronic nature of our rainfall shortage. In particular, the eastern and western Piedmont and parts of Southside Virginia, along the North Carolina border are showing substantial departures from average rainfall ( http://www.deq.state.va.us/pdf/drought_july2002.pdf. Northern Virginia received slightly above average rainfall during the first two weeks of July, whereas the Eastern Piedmont received less than 50% of normal rainfall for the same period. As of early July, 19 Virginia localities had submitted requests to the Governor for federal drought disaster designation. The US Secretary of Agriculture approved disaster designations for Goodchland and Prince Edward Counties, with designations pending for a swath of 17 other counties through the central Piedmont. The Virginia State Climatology office also notes that El Niņo conditions in the Pacific are statistically associated with a reduced probability of tropical storm and hurricane rainfall in eastern Virginia. That is consistent with the Climate Prediction Center's precipitation forecast for the period August-October 2002 (Fgure 1), and NOAA's prediction that drought severity will tend to increase over the majority of the state before the situation improves.
What is the impact on grapes and grapevines? From an agricultural perspective, the current drought conditions have their greatest impact on relatively shallow-rooted agronomic plants and on pastures. Corn, soybeans and hay are severely affected and some farmers are feeding hay or selling stock where pastures no longer support grazing. Established vineyards are somewhat more buffered from normal summer droughts by virtue of their deeper root systems. Nevertheless, a mature vine can transpire more than 40 gallons of water per week under the hot, dry conditions of July and August weather. If the moisture is not available from precipitation or irrigation, drought stress symptoms will develop. Symptoms vary, but include a perceptible heating (above air temperature) of leaves in the heat of the day. The heating is due to a lack of transpirational cooling, and it can be detected by pressing leaves between your hands. Simply put, if leaves feel warm (greater than your body temperature), they're not transpiring enough water to remain cool. If leaves are not transpiring, their stomates are closed. If the stomates are closed, no CO2 is entering the leaves and therefore carbohydrate production is either not occurring, or is occurring at reduced rates. With increased duration and intensity of drought, additional symptoms will occur, including a shedding of tendrils, "flagging" or wilting of leaves, abortion of shoot tips, yellowing and eventual shedding of basal leaves of the shoot, premature periderm formation on shoots, berry shrivel, and eventual defoliation of the vine. Dry years have tended to promote higher grape and wine quality in Virginia than have the wet years, but the trick is to find a balance. Irrigation provides the option of regulating the extent of drought stress to favor grape quality without overly stressing the vines. We want to apply enough water to keep the leaves optimally functioning, without applying so much that the vine is diverting resources to continued shoot extension. Our research vineyard at Winchester is planted on deep Frederick/Poplimento, limestone-derived clays. Roots can be found 4 to 5 feet deep. Shoots are still elongating. These vines do not need additional moisture. Your vineyard, on the other hand, might be showing one or more of the above drought symptoms, in which case you may need to increase supplemental irrigation.
Canopy management: This will depend upon the level of drought stress and what your aims are for cluster exposure. For reds, increased cluster exposure to sun is desirable for color development; however, the beneficial response is not linear. Excessive, direct exposure can lead to decreased fruit color, bitterness of the fruit/wine, and physical sunburning/ raisining. For north/south oriented rows, I would advocate some leaf removal on the eastern sides of the canopy, but a retention of about one leaf layer on western sides to avoid the potential for burning.
Disease issues: If you've done a good job with powdery mildew (PM ) control, you can "coast" through harvest; if not, you may still have a fight on your hands. Berries are less susceptible to PM infection once they attain about 8° Brix. They may, however, continue to show lesion development from infections that occurred up to one month ago. Also, recent research in New York State illustrates that low levels of PM may exist on fruit, even with apparent "good" prevention programs. The "inconspicuous" mildew can increase fruit susceptibility to botrytis and other rots later in the season. So, when I say "coast' I mean you should continue to maintain a prudent mildew prevention program. Good options at this time of year are sulfur, on sulfur-tolerant varieties (fits nicely with cooler weather forecast after 5 August), sterol-inhibitors such as Elite or Rubigan, and possibly a strobilurin (e.g., Flint), if you've not used the strobilurins too much earlier in the season. Watch the label preharvest intervals (PHI) Rubigan for example has a 30-day restricted PHI; most of the others vary from 7 to 14 days. Consult your grape buyer (winery) regarding their wishes on pre-harvest use of sulfur. Many prefer that sulfur not be applied in the month preceding anticipated harvest. Other alternatives are Nutrol (monopotassium phosphate) and Armicarb 100 (potassium bicarbonate). These are very short-lived materials once applied. Work in New York State points to these products being more effective as post-infection materials than as protectants. Used on a weekly (7-day) basis, they appear to effectively control powdery. Oils, such as JMS Stylet oil, offer good protection IF used with sufficient gallonage (at least 100 gallons of water/acre). The downside of oils, as shown by former grad student Sarah Finger's work here in Virginia, is a delay of sugar accumulation in treated fruit. Post-harvest oil use might be an acceptable proposition though, and oil lends itself to disease resistance management by introducing a different mode of action to that of the sterol-inhibitors and the strobilurins. Other post-harvest fungicide options for PM are sulfur or copper fungicides. Copper is only fair for PM control, but if the vineyard is clean, it has the advantage of offering excellent downy mildew control.
What happens if PM gets out of hand in your vineyard? Yours would not be the first casualty. I'm aware of at least three PM outbreaks in Virginia vineyards this season. For what it's worth to others, two of the cases may arguably have been due to using insufficient spray gallonage (30 to 50 gallons/acre in lyre-trained vines). We have flirted with powdery in our own lyre-trained Chardonnay and, for peace-of-mind, we've adopted several practices that thus far have avoided PM showing up: we use the best fungicides for PM control immediately prior to bloom through bloom. This year, that amounted to consecutive sprays of Abound on 28 May ("pre-bloom" and 7 June ("fruit set"). The subsequent spray was of Elite and Penncozeb on 18 June. Secondly, we sloooowww the tractor down and put on 95 to 100 gallons of spray material after bloom (with the divided canopy vines); third, we do not exceed 14 days between consecutive sprays in the period from two weeks before to six weeks after bloom. So much for proselytizing, what about the epidemic on hand? There are several options. Oil, such as Sun Ultrafine or JMS stylet oil, is an excellent eradicant. You must, however, ensure complete coverage of infected tissues (at least 100 gallons/acre spray). Oils, however, have the undesirable effect of retarding sugar accumulation. The retarded sugar accumulation may be a small penalty (1-3°Brix) to pay to avoid further or complete loss of crop. Perhaps a better option would be to use sulfur or Armicarb 100, or a combination of sulfur and Armicarb. Virginia Tech's pathologist, Dr. Anton Baudoin, had good results arresting PM in a Chardonnay vineyard last year by using a combination of sulfur and Armicarb, both at 5 lbs/acre. You must, however, use sufficient spray gallonage to completely wet the affected tissue (i.e., at least 100 gallons/acre). The least attractive option, short of doing nothing, would be to apply a sterol-inhibitor or a strobilurin directly on sporulating PM colonies. That is a certain way to hasten the development of fungicide-resistant strains of mildew.
Botrytis: Botrytis incidence varies from year-to-year, but we tend to have greatest problems in our old, lyre-trained Chardonnay. Culturally, the incidence of botrytis can be reduced by removing leaves that are directly touching clusters, and opening the eastern side of N/S-oriented rows to aid air movement and spray coverage. It's certainly not too late to do some follow-up leafing in botrytis-prone cultivars, but avoid pulling too many leaves that could result in sunburning of fruit (see comments above under canopy management). Fungicide options, specific for botrytis, are Rovral, Elevate or Vangard. Vangard is limited to two applications per year. Last year, we obtained excellent season-long control of botrytis (in a high-pressure situation) by applying Vangard at cluster-closing followed by a veraison application. Details are in the Sept.-October 2001 Viticulture Notes ( http://www.vaes.vt.edu/winchester/grape/newsletter.html). New York State researchers have found that the veraison and post-veraison fungicide applications gave more consistent control than did the bloom and cluster-closing applications. Vangard should be rotated with Rovral and Elevate on a seasonal basis to slow the development of botrytis resistance to any one of the fungicides. Should you apply a botrytis fungicide now if you're starting to see botrytis? I'd offer a qualified "yes", simply to slow new infections. Once botrytis starts affecting multiple berries, it seems to progress quickly to adjacent, touching berries, and this is nearly impossible to control, short of getting some dry weather.
Downy: I've heard a report or two of downy mildew (DM) occurrences in Virginia vineyards, but the generally hot and dry conditions in many areas of the state since mid-June have not favored the development of this disease. Conditions that favor the spread of DM are temperatures of 65 to 77°F and free moisture. A summer shower followed by a cool evening creates the perfect scenario for a downy infection. Fruit becomes resistant to infection as it develops; however, young leaves (such as on laterals) are quite susceptible, and this is often where I see late-summer problems develop. To avoid a potential defoliation, continue a DM protection program through harvest or mid-October, whichever is later. Fungicide options once you are within 66 days of harvest, are captan, copper formulations, Abound, and the phosphorous acid compounds such as ProPhyt and Aliette. Dr. Wayne Wilcox of Cornell University indicated that he has obtained good DM control using phosphorous acid fungicides on a 14-day interval (see the May-June, 2002 Viticulture Notes). Captan provides excellent DM protection as well as providing control of the fruit phase of Phomopsis, and perhaps some of the other late-season rots (e.g., bitter rot [Melanconium spp.], ripe rot [Glomerella spp.]) that we occasionally observe. Captan does, however, carry a four-day restricted reentry constraint. The various copper formulations also offer excellent DM control, and give some protection against powdery. Although effective against both downy and powdery mildew, I would tend not to use Abound at this point in the season for reasons of cost and for conservation for the more critical timing around bloomtime. Mancozeb and Ridomil are excellent materials for DM, but are no longer allowed at this time of year due to the 66-day pre-harvest interval usage restriction. One could, however, continue to use mancozeb materials (e.g., Penncozeb, Manzate, etc.) on young or otherwise non-fruiting vines, or as a post-harvest treatment on vines harvested early in the fall.
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Please plan to attend this important meeting. In addition to the technical topics, Bruce Zoecklein and Tony Wolf will introduce plans that are underway to seek additional viticulture and enology extension support for the grape and wine industry. The Virginia Vineyards Association will conduct a short but very important business meeting, including the election of new officers. All members are encouraged to attend. Lunch will be provided and the day's activities will conclude with a wine social.
Directions: From Madison, north on Rt 231 four miles to Rt. 651. Turn left, go two miles, turn right on Rt. 652, go.1 mi., turn left on Rt. 698 and go .7 mi. to the winery, passing through a farmstead and proceeding though the winery gate.
21 Aug. Vineyard Meeting: Whitehall Vineyards, Whitehall, VA-Albemarle Co. 11:00 - 1:00 pm
Directions:From Route 29 in Charlottesville, west on Barracks Road (later becomes Garth Road) to Whitehall. Right onto Route 810, left on Breakheart (Rt. 674) continue to Sugar Ridge, winery 0.5 mile on right. From I-64: take Crozet Exit, then Rt. 250 East, left on Rt. 240, then Rt. 810 to Whitehall, continue on Rt. 810 north, , left on Breakheart (Rt. 674) continue to Sugar Ridge, winery 0.5 mile on right.
11 Sept. Vineyard meeting: Rush River Vineyard. 11:00 - 1:00 pm
Directions: 211 Business into the Town of Washington, turn left onto Rt. 622 (Harris Hollow), go 1.8 mi., turn right on Rush River Lane, cross ford and go straight up the hill after crossing ford. Parking beside the vineyard.
18 Sep. Vineyard meeting: Wintergreen Winery. 11:00 - 1:00 pm
Directions: From Charlottesville: I-64 West, exit 107, Ro250 West to Highway 151, south 14 miles to Route 664, west 0.5 mile to winery entrance on right.
11 Oct. Basic Grape Production Shortcourse
When: Friday, 11 October 2002; 8:00 am - 4:00 pm
Where: AHS, Jr. Agricultural Research and Extension Center, Virginia Tech, Winchester, VA.
Information: Tony Wolf, 540-869-2560 Extn. 20
Registration: Pre-registration required and registration is limited to first 50 persons: $75 per person, to include morning coffee/danishes, soft-drinks, catered lunch, handouts, and to cover our invited speaker expenses. Check to be made payable to "Virginia Vineyards Association", and mailed to "Grapes", Virginia Tech, 595 Laurel Grove Rd. Winchester, VA 22602. Check must be received by 1 October 2002 to guarantee lunch. Note: This course typically fills quickly. Registrants are confirmed or denied registration in the order that registrations are received.
Program : "Beginner's" grape growing seminars target individuals who are exploring winegrape growing opportunities in Virginia, or those who desire a "refresher" course. Topics covered include economics, site selection, varieties, and vineyard establishment, including materials and methods. Various aspects of established vineyard management (canopy management, pest management, pruning and training, cold injury avoidance, etc.) are discussed at an introductory level. Classroom principles are reinforced with a review of the AHS AREC research vineyard. We are pleased to again co-teach this shortcourse with colleagues from Maryland and Pennsylvania. Dr. Joseph Fiola, Associate Professor with the University of Maryland, and Mr. Mark Chien, viticulture extension specialist with Penn State University will be assisting me with a team effort.
Directions: Virginia Tech's AHS Jr. Agricultural Research and Extension Center (AREC) is located approximately 7 miles southwest of Winchester, VA in Frederick County. From Interstate-81, take the Stephens City exit on the south side of Winchester. Go west into Stephens City (200 yards off of I-81) and proceed straight through traffic light onto Rt 631. Continue west on Rt 631 approximately 3.5 miles. Turn right (north) onto Rt 628 at "T". Go 1.5
If you are a person with a disability and desire any assistive devices, services or other accommodations to participate in this activity, please contact the AHS Agricultural Research and Extension Center, at 540-869-2560 during business hours of 7:30 am to 4:00 pm weekdays, to discuss your needs at least 7 days prior to the event.
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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 would like to receive "Viticulture Notes" as well as Dr. Bruce Zoecklein's "Vinter's Corner" by mail, contact Dr. Wolf at:
Dr. Tony K. Wolf
AHS Agricultural Research and Extension Center
595 Laurel Grove Road
Winchester, VA 22602
or e-mail: email@example.com
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