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Virginia Cooperative Extension -
 Knowledge for the CommonWealth

Viticulture Notes

Volume 13, Number 4 -- July - August 1998

Dr. Tony K. Wolf, Viticulture Extension Specialist

Table of Contents

I. Current situation

II. Seasonal Tips

III. Upcoming Metings

I. Current Situation:

Hot, dry weather of the past couple of weeks (northern Virginia) has eased Botrytis pressure somewhat, but we're still seeing greater than normal amounts of "early" (pre-veraison) Botrytis in Chardonnay. Our crops at the AHS AREC are advancing nicely and we predict a 7- to 10-day advance in maturity given the earlier bloom and hot July weather. Several vineyards have reported problems with powdery mildew. No commonalties to those problems one grower admitted he was delayed in adjusting canopy density in the pre-bloom period, and probably suffered from poor fungicide penetration. Japanese beetle feeding has been very light at the Winchester vineyard, perhaps due to the dry summer of 1997 and its effect on grub survival. We've taken note of a very high incidence of grapevine yellows in several Chardonnay vineyards in the northern Virginia area. I've included a review and update of grapevine yellows in the following section.

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II. Seasonal Tips

Crop estimation: Requirements for crop estimation are: 1) a record of average cluster weights at harvest; 2) an accurate count of bearing vines per block (or acre); and 3) an accurate, representative count of the number of clusters per vine. First, why estimate crop? Growers need to know how much crop they will have for sale, while winery owners need to know how much fermentation space they need to allocate. Accurate counts benefit both parties and reduce the likelihood of unpleasant surprises when the grapes finally come in. Crop estimation can be as simple or as complicated as you'd like to make it. Berry weight, berries per cluster, and cluster weight are the most variable components of the crop estimation equation. The more detailed crop estimation approaches involve tracking cluster development at one or more stages of development, in order to more accurately predict the average cluster weight at harvest. A simple equation that can be used to estimate crop is as follows:

(VINES/BLOCK) X (CLUSTERS/VINE) X (AVERAGE CLUSTER WT. [LBS]) X (1/2000) = TONS/BLOCK

Here, vines per block is the number of bearing vines in a particular planting unit. Clusters per vine is an average number of clusters per bearing vine obtained from a sample of vines at the time of crop estimation. The more variable your counts, the more vines should be sampled. If cluster counts on 20 representative vines in a one-acre planting ranged from 42 to 50, I would stop counting you've got a very uniform population. If clusters/vine ranged from 30 to 80, you may want to double your sample number. The more vines you sample, the more likely that your estimate will approach the true average of the population. 1/2000 converts pounds to tons per acre. Average cluster weight is best obtained by taking representative cluster weights (average of 300 or more) at harvest in preceding years. The more years of data, the better. If you lack your own data, you might try using the following data, most of which were obtained from vines at the Winchester AREC vineyard:

VarietyAverage cluster
wt. (lbs)
Cabernet
Sauvignon #7/#8
0.29
Chardonnay #40.41
Muscat Ottonel0.24
Petit Verdot0.24
Sangiovese0.61
Seyval0.59
Riesling0.18
Vidal blanc0.35
Viognier0.27

Even with thorough sampling, accurate counts, and many years' experience, your actual crop tonnage at harvest can vary significantly from that which you predicted. Don't despair. Reduce variance where possible, such as by discounting crop for missing vines. Consider a good estimate one that does not vary more than 15% from actual. Again, the most variable component of the process will be the average cluster weights. Poor fruit set may reduce berries per cluster. Prolonged dry weather will reduce berry weight. Both will reduce the average cluster weight. The more experience and data you acquire, the more accurate your estimates will become. A more complete description of crop estimation is provided in the Mid-Atlantic Winegrape Grower's Guide.

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Botrytis bunch rot: Humid, shaded conditions within vine canopies, retention of senescent floral debris in developing clusters, and susceptible varieties all increase Botrytis bunch rot. The Botrytis fungus typically forms a fuzzy, gray or brown gowth on affected berries. While individual berries may be affected, the fungus usually spreads and affects a group of berries on the cluster. With repeated rains, the affected berries can be invaded by other organisms which lead to sour rot or non-specific bunch rots. Varieties that are particularly prone to Botrytis include Chardonnay, Seyval, and Sauvignon blanc. Shoot positioning and modest leaf pulling from around fruit clusters can reduce Botrytis bunch rot because they speed up fruit drying, increase pesticide penetration, and increase sunlight exposure. If your vines are small (less than 0.3 pounds of pruning per foot of canopy), you probably don't need to pull leaves. Larger vines, and those with 3 or more leaf layers in the fruit zone are more likely to benefit from some selective leaf thinning. Initial leaf pulling should have been performed by mid-July; however, it is not too late for some follow-up pulling of small laterals or additional leaves before veraison. Generally, pulling leaves before veraison is less likely to result in sun-burning than is pulling leaves after veraison. Avoid excessive leaf stripping. Pull too many leaves and you will delay crop maturity and reduce fruitfulness the following year. Application of Rovral or Vangard at veraison may also reduce Botrytis incidence and severity. These materials are pricey ($35 to $40 per acre per application). Use judiciously where the block's history of Botrytis or current observations of sporulating fungus on aborted berries suggests a high pressure situation, and where crop value is great enough to warrant the material cost. Research in New York State with the variety 'Aurore' has led to a recommendation there for Rovral application at veraison, and again 2 weeks later. In Virginia, Dr. Anton Baudoin's research with Chardonnay suggested that an early July (just prior to cluster closing) Rovral application was equally effective to a veraison application, and that a veraison, plus a 12-15°Brix application, was better than a cluster closing application used alone. We have limited information on the efficacy or usage options of Vangard.

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Powdery mildew: Primary powdery mildew infections occurred at or around bloom. Secondary infections do not require rain or free moisture and can increase dramatically with a new generation occurring in as little as 5 days at temperatures of 60-80°F. Powdery lesions will cause a greyish tint to affected leaves and fruit. The lesions darken with time and produce small fruiting structures (cleistothecia) that can be seen with a magnifying lens. Photos in the Grape Disease Compendium will aid the essential distinction of powdery and downy mildews. Immature, developing berries (< 8°Brix) and shaded stems and leaves are often the first tissues affected by powdery mildew, but all green tissue is susceptible. Affected berries may crack and a heavy powdery infestation will impart an undesirable flavor in resulting wines. Protectant fungicides include sulfur, the sterol-inhibiting fungicides (Rubigan, Procure, Nova, or Bayleton), and Abound. Sulfur is the fungicide of choice if sporulating powdery mildew lesions are present in the vineyard. It is not wise to spray one of the sterol-inhibiting (SI) fungicides (such as ), or Abound on vines with active, sporulating lesions. The use of Abound or SI fungicides on actively sporulating powdery mildew lesions only hastens the development fungicide-resistant strains of powdery mildew. It is wiser to arrest the powdery development first with one or two full rate sprays of sulfur (7 to 10 days apart), then reintroduce the SI or Abound after the mildew is checked. Sulfur will burn foliage on some varieties: I have not seen such burning on vinifera at temperatures lower than 95°F; however, 'Norton', 'Concord', Chambourcin, and some of the other hybrids are extremely sensitive to sulfur. Fortunately, those varieties are relatively resistant to powdery mildew infection. Systemic fungicides, such as Nova, Bayleton, Rubigan, and Abound, are absorbed by the plant within 30 to 60 minutes. These materials provide excellent powdery mildew control for at least 14 days, but generally do not protect leaves that emerge after application. Copper formulations are only fair (or poor) fungicides for powdery mildew control and should not be relied upon with highly susceptible varieties such as Chardonnay or Cabernet Sauvignon. Both JMS Stylet Oil and Sunoco's Sun Ultra-fine do an admirable job of eradicating existing mildew infections; both are registered for use on grapes, and both carry warnings about phytotoxicity if mixed or used close in time to applications of sulfur, captan, and certain other pesticides. At this point in the summer, I would view the use of oil as a last-ditch effort to check a powdery mildew infection. If the vineyard has no or minimal cluster infections, use sulfur in combination with Abound or a sterol-inhibiting fungicide. If the mildew affects more than 15 or 20% of clusters, or if the mildew advances to foliage, or if the variety is sensitive to sulfur, consider the oil application. The oil will, however, limit the pesticide options for the balance of the season. In 1997 we produced visible phytotoxicity when oil was used within 10 days of sulfur, captan, or copper fungicides. Research by graduate student Sarah Finger in 1998 has also shown that oils (even vegetable oil) reduce leaf photosynthesis rates and decrease berry size. The oil must be used with a large volume of water (100 to 200 gallons per acre -- or by using a spray hand-gun) to ensure COMPLETE coverage of mildew-affected tissue; any mildew lesion not covered with the oil will continue to develop.

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Downy mildew: Downy mildew symptoms appear first as a chlorosis (yellowing) and eventual browning of portions of leaves. Sporulating structures that appear as a white, cottony mass appear on the underside of affected leaves soon after the chlorotic tissue becomes apparent. The signature spores of downy mildew are much less obvious during dry weather, which can lead to some confusion in diagnosing this disease. If in doubt, put some symptomatic leaves in a plastic zip-loc bag with a piece of moist paper towel. If downy's a factor you should soon see renewed sporulation occurring on the viable tissue. Downy fungicides include of mancozeb, Captan, various copper fungicides, Abound, and at least two formulations of Ridomil. Ridomil also offers up to 4 days of post-infection activity. Mancozeb and Ridomil are disallowed in the 66 days prior to harvest. Therefore, Captan, Abound and copper formulations are the remaining alternatives for most Virginia producers at this time of the year. Pre-harvest intervals for other fungicides are: Captan (0, but a 4-day restricted reentry period) copper (0 to 14 days, depending upon formulation) and Abound (14). Check with your crop purchaser to determine if they have any restrictions on fungicide usage in the pre-harvest period. Some of the broad spectrum fungicides may retard yeast metabolism resulting in sluggish or stuck fermentation.

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Grape berry moth: Pheromone-baited traps help monitor adult grape berry moth flights, but we rely more heavily upon cluster checks for timing of insecticide applications. Look for individual berries darkening within a cluster of otherwise green berries. We've used an incidence of about 5% affected clusters as an action threshold for spraying, especially with compact-clustered varieties that are prone to bunch rot. The restricted-use insecticides, azinphosmethyl (Guthion) and micro-encapsulated methyl parathion (Penncap-M) offer rapid control of GBM, but two applications may be necessary for control once larvae have entered berries. Non-restricted use insecticides registered for GBM include carbaryl (Sevin), methoxychlor (Marlate), and phosmet (Imidan). Check the label of these pesticides for relevant pre-harvest intervals and specific usage instructions.

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Grapevine yellows: Grapevine yellows disease was reviewed in-depth in Viticulture Notes, Vol. 8, No. 6 (1993). Chardonnay and Riesling have been the most commonly affected varieties in Virginia, but recently we have seen unconfirmed cases of yellows in Cabernet Sauvignon and Sauvignon blanc. Diseased vines may appear at random in the vineyard or more abundantly along edges that border woods or fence rows. Once affected vines are present in the vineyard, the vine-to-vine spread appears to be significant. Three symptoms, all of which must be present to eliminate other causes, are useful in diagnosing yellows: (1) abortion of fruit clusters anytime from fruit set to maturity, (2) downward rolling and yellowing of leaves, and (3) failure of bark or periderm to mature on affected shoots. Other symptoms include shoot-tip die-back, general vine weakness, and a "brittle" texture to affected leaves. Grapevine yellows typically kills vines within two to three years of symptom onset. The causal agent of grapevine yellows is a phytoplasma. Phytoplasmas are extremely small, bacteria-like organisms. Grapevine yellows occurs in vineyards worldwide, but the specific phytoplasma that causes the disease can differ. Recent research by the USDA has provided evidence of two different phytoplasmas responsible for yellows in commercial Virginia vineyards. One of those phytoplasmas has a wide host range that includes wild grapevines (V. riparia), other woody plants, as well as certain herbaceous annuals. The other, thus, far, has only been found in cultivated vines. Grapevine yellows is somewhat like Pierce's Disease in that for disease to occur, an insect vector must transmit the phytoplasma to our cultivated grapevines. Unfortunately, other than suspecting certain leafhoppers, we are unclear about which insect species are responsible for transmitting the causal agent from vine-to-vine, or from alternative host to cultivated grapevines. Effective control measures for grapevine yellows are elusive. Removal of affected portions of affected vines may slow the spread within the vineyard. Where this has been tried (e.g., removing one affected trunk from a multiply-trunked vine), some vines appear to have been salvaged. I have not observed affected vines recover in the absence of such radical pruning. Another option is to completely remove affected vines and fill in the trellis gap using cordon extensions from adjacent vines. Insecticides are available and registered for leafhopper control on grapes. But lacking specific knowledge of the responsible leafhoppers, one would have to spray insecticides all season in hopes of intercepting the infective insects - not an attractive option. The solution to the grapevine yellows problem will require fundamental research on insect vector biology, as well as an exploration of alternative hosts for the phytoplasmas that infect our cultivated vines.

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Economics publication available: "The Economics of Wine Grape Production in Virginia" has been printed and is available, free of charge, from the Virginia Cooperative Extension Distribution Center, 112 Landsdowne St., Blacksburg, VA 24060. Ask for publication #463-008. This economic analysis of winegrape production represents a significant overhaul and expansion of our previous (1994) publication on the subject. The current publication, authored by Eric Capps, Tony Wolf, and B. Jerry Walker, compares the costs and returns for three different training systems (VSP, Lyre, and Smart-Dyson). In addition, the VSP (vertical shoot-positioned) system is compared at both a narrow (7') and wide (10') row spacing. The 34-page publication contains illustrations of the training systems, detailed cost and return tables, and summary tables for each of the systems. This is a "must" for those contemplating commercial grape production - and a good review for those with vineyards already established.

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Web sites of interest:

Pesticide labels and MSDS specimens: Want to review a pesticide label of a product that you've not used before? Curious about the reentry period for a product for which you don't have experience? You can electronically review this information from a number of Web sites without having to visit your favorite pesticide dealer. Two sites that I've occasionally browsed for product rate and usage notes are:

http://www.greenbook.net/

This site is produced by the Chemical and Pharmaceutical Press, and represents much of what is printed in their Crop Protection Reference (the "green book" that is annually updated).

A second site is: http://www.cdms.net

You will need Adobe Acrobat Reader (ver. 3.x) to read the labels or MSDS from either of these sites. Acrobat Reader can be downloaded free from their website. Some products, such as those of Bayer, are not included. Be certain to read the "terms of use" for the information that you access. These sources should only be used for general information and reference, not for actual use directions for chemical applications. For the latter, be certain to have the label of the product you are using in your possession.

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Potential hazard of Roundup (glyphosate) herbicide with waxed nursery stock: We saw two situations this spring where Roundup herbicide may have caused injury to recently planted (dormant) nursery stock. Our observations should be taken at face value (we've done no testing) and are in no way intended to discourage the use of glyphosate herbicide. However, some discretion might be called for if using glyphosate over recently planted nursery stock. By way of explanation, grafted grapevines come from the nursery either waxed, or not waxed. The wax (paraffin based) is used to reduce drying of the graft union. Some nurseries use wax, others prefer not to re-wax their stock. Glyphosate is the chemical name of the active ingredient in Roundup herbicide (Monsanto). Glyphosate is a non-selective, systemic, post-emergence herbicide. It's registered for use in vineyards and the label has precautions about drift, avoiding contact with green tissue, etc.

In one of the two situations where glyphosate injury was observed, a grower had planted waxed vines from one source, and unwaxed vines from another source on the same day in adjacent blocks. Nursery stock from both sources was dormant, and bud break did not occur for at least 10 days with either nursery source. Both blocks were subsequently over-sprayed with glyphosate at around a 1% concentration to kill grass in the row. The glyphosate was applied the day after planting. This is not the sequence we would normally recommend, but it has been done without injury as long as the vines are dormant and showing no bud swell. The interesting result was that about 5 to 15% of the waxed nursery stock suffered glyphosate injury symptoms on developing shoots. None of the unwaxed vines showed glyphosate injury symptoms. We ruled out second-year or carry-over effects with the waxed vines because the nursery had no other complaints and did not indicate that they had glyphosate problems in the nursery.

We contacted several grapevine nursery owners, none of whom had seen or heard about a problem with waxing and over-spraying glyphosate. Dave Mayonado, product development representative with Monsanto, speculated that the uncharged wax might absorb and hold the glyphosate in an active form, with injury occurring when the subtending buds broke and grew through the wax. We don't know for certain if this occurred. Most growers would typically kill out a sod strip and then plant. But the reverse order is not unreasonable with dormant vines. The observation of injury to waxed vines, however, might argue against glyphosate application to waxed nursery stock.

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III. Upcoming Meetings

A. Virginia Vineyards Association Annual Meeting

Where: Jefferson Vineyards, Charlottesville, Virginia

When: Saturday, 1 August 1998

Program: (as follows)

8:30 amRegistration
9:00 amIntroductory comments
Christopher Pearmund, President, VVA
9:15 amCurrent viticultural research and extension projects
Tony Wolf, Virginia Tech
Crop load studies
Training system comparison
Vineyard economics
Effects of summer oil sprays
Bunch stem necrosis (Eric Capps)
10:45 amMultiple Peril Crop Insurance
Steve Grant, Valley Farm Credit
11:15 amLate-season disease identification and management
Anton Baudoin, Virginia Tech
12:00Catered lunch
1:00 pmVineyard features that promote high fruit and wine quality
Andrew Reynolds, Brock University, Ontario
2:45 pmRefreshment break
3:30 pmVineyard and winery tours/discussions
4:30 pmAdjourn

Time is built into the program to visit with vendors which, to date, include:

Directions: Jefferson Vineyards is located just south of Charlottesville on Hwy 53, between Monticello and Ash Lawn. Take Interstate 64 to exit 121A towards Scottsville. Immediately past light, take left onto Highway 53. Winery entrance 3 miles on right.

Registration: At door, VVA members and spouses are free, all others at $30/person.

Information: Mr. Chris Pearmund, President VVA (540-347-3475); Tony Wolf, VVA (540-869-2560).


B. Four-day Basic grape growing training program

In the 1998 March-April Viticulture Notes newsletter, I posed a question about the format of future grape growing seminars aimed at beginners and other wishing to learn more basic aspects of vineyard establishment, management and vine function. The majority of respondents favored a multi-day format without concern for collegiate credit hours.

I have therefore planned a 4-day, in-depth training program for this fall. The goal of this course will be to provide the basic foundation for understanding how grapevines function and to instill practical knowledge of vineyard site selection, design and management. A significant portion of the course will be devoted to practical aspects of canopy management, variety review, and pest management. The course will be split between September and November to take advantage of crop and canopy conditions in September and dormant conditions for pruning in November. The course will be limited to 50 persons but will be repeated in subsequent years as interest warrants. Registrants are expected to attend all 4 days. The dates and general content of the program will be as follows:

Friday, 18 September and Saturday, 19 September: Canopy management, crop estimation, varieties, harvest contracts, pest management (two sessions - diseases and insects), site selection, economics (financing and tax considerations), equipment requirements (including sprayer calibration), grapevine physiology (two sessions)

Friday, 13 November and Saturday, 14 November: Vineyard design, trellis construction, market situation, training and pruning, pest management (weeds), grapevine physiology (two sessions), pesticide handling and safety, comprehensive exam

A more specific course content will appear in the September-October Viticulture Notes; however, the exact timing of the sections will depend upon weather. At least one-third of each 2-day event will be conducted in the vineyard. The course will be team-taught by Virginia Tech specialists, Virginia Cooperative Extension personnel, and others.

Location: the course will be held at Virginia Tech's AHS Agricultural Research and Extension Center near Winchester.

Registration: $100 per person (payable "VVA"); deadline of 10 September. Mail check to "Grape Course", c/o Virginia Tech, 595 Laurel Grove Rd., Winchester, VA 22602. Include PRINTED name of registrant(s) and phone number/mailing address with check. A registration confirmation will be mailed when check is received. Registration covers 4 lunches, publications and other hand-outs, and speaker travel expenses.

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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: vitis@vt.edu

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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