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Virginia Cooperative Extension -
 Knowledge for the CommonWealth

Viticulture Notes

Vineyard and Winery Information Series:
Vol. 15 No. 4, July-August 2000

Dr. Tony K. Wolf, Viticulture Extension Specialist

Table of Contents

I. Current situation/pest management tips

I. Question from the field

II.Potassium deficiency and flouride toxicity

III.VVA/VSHS annual meeting talks (part III)

V.Upcoming Meetings

I. Current situation and pest management updates:

Frequent rains of the last two months have led to increased disease pressure, well above that observed during the relatively dry 1999 growing season. Grower reports of disease intensity range from "clean" to significant incidence of powdery mildew and botrytis. The following suggestions are offered to manage diseases between now and harvest. They follow on the comments provided by Dr. Wayne Wilcox in the May-June Viticulture Notes.

Downy mildew: Historically I've seen more growers stumble with downy mildew (DM) during late-July and August than at any other time of the season. In some cases, failure was due to simply not including a DM-specific fungicide in the pest management program during this period. Downy can affect fruit directly, but the greatest observed infestation usually occurs on young, unprotected leaves. Fungicidal options are reduced in the 66-day pre-harvest interval (PHI), but there are still multiple choices available. According to Dr. Wilcox in New York State, Abound has been excellent for DM, as have the older materials, Captan and copper. Mancozeb or Ridomil, which are also effective, might still be permissible (66-day PHI) with some late-harvested Cabernet or Vidal. Dr. Wilcox cautions against reliance upon Sovran or Flint for DM control, although they would continue to offer excellent powdery mildew control. Abound carries a 14- day PHI, Captan is effectively 4 days, and copper, depending upon formulation, has a one- to two-day PHI. A principal advantage of Abound over Captan or copper is that Abound is a systemic material that is absorbed by the leaf and not washed off by rain.

Botrytis bunch rot: Chardonnay, Seyval, and Sauvignon blanc lead the pack in terms of susceptibility. As in previous years, we are seeing a close association between much (but not all) of the botrytis and the occurrence of grape berry moth injury. Even without grape berry moth injury, botrytis pressure increases under conditions of repeated rains and humid conditions ­ just what we're having. Leaf pulling (three to four leaves around fruit clusters ­ see related story on leaf area requirements) helps with drying of fruit clusters and spray penetration. If you pulled leaves from a botrytis-sensitive variety earlier in the season, you may want to make a second pass now, removing any yellowing or dead leaves, or doing a bit more thinning where the leaf density does not permit good exposure of the clusters to air movement. I do not recommend totally de-leafing the fruit zone, but you should be able to see at least a portion of the majority (>80%) of fruit clusters. If you can't, chances are good that you'll have your hands full of botrytis with this year's weather. The use of botrytis-specific fungicides can also help. Recommended fungicides include Vangard, Elevate, and Rovral. Timing will be dictated by historical and immediate problems with botrytis in your vineyard, as well as whether you applied a fungicide at bloom. Vangard is only registered for up to two applications per year. If you applied Vangard at bloom and cluster-closing, you may not apply it now. Other choices would be Elevate and Rovral. Vangard and Rovral carry a 7-day PHI, Elevate is 0 days PHI. Donıt expect the fungicides to give 100% control.

Powdery mildew: A few reports of powdery mildew (PM) cropping up. Oils are a possibility for eradication, but see my discussion and various warnings in the May-June Viticulture Notes. If you're clean at this point, congratulations, and keep it up with PM fungicides. Options are numerous, and include the sterol-inhibitors (SI) such as Elite, Nova, Rubigan, and Procure, the strobilurins such as Abound, Sovran and Flint, and the old standby, sulfur. Again, keep in mind that the Si's and the strobilurins are locally systemic, not washed off by rain, and therefore need not be immediately reapplied following a rain. The same can not be said for sulfur.

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II. Question from the field:

A three-part question. I see some variation of the question each year:

1) If it takes 10 leaves to ripen a bunch of grapes on a shoot, does it take 20 leaves if there are two bunches on the shoot?

Sounds like simple question but the answer's not necessarily straight-forward. Crop studies under a wide range of climatic conditions, cultural practices (e.g., minimal pruning vs. balanced pruning), and over a range of varieties, have shown that a desirable leaf area to crop ratio can vary from around 6 cm2 of leaf area per gram of crop, up to around 18 cm2/gram of crop. To cite one example, the work of Kaps and Cahoon (1992) demonstrated that 8 to 10 cm2 of leaf area per gram of Seyval grapes was needed to maximize berry weight and °Brix, but that total vegetative weight continued to increase up to about 15 cm2/g of crop. Dick Smart's (Smart and Robinson, 1991) use of about 12 cm2 per gram of crop is probably a good average. For the sake of argument, let's give it a range of 10 to 12 cm2/g. Now, look at Virginia's flagship cultivar, Chardonnay, much of which is high-yielding clone #4. We averaged 191-gram clusters (0.42 lbs) over an 8-year period (Wolf et al., 1999). From our own leaf area measurements, we know that these Chardonnay have leaves that average about 210 cm2 per leaf. If you do the math, that means that each leaf can ripen about 18 to 21 grams of grapes. Put another way, a cluster that weighs 191 grams would require 9 to 11 leaves to ripen it. We do not, on average, find 2 clusters per shoot; we find, on average, about 1.3 clusters per shoot. A corresponding increase in leaf area to ripen the extra "0.3 clusters" would put our required leaf area up around 12 to 14 leaves per shoot, all else being equal. But, all else is not necessarily equal. There's good evidence that increased crop load increases the photosynthetic capability of leaves ­ at least as measured by single-leaf photosynthesis measurements. The data of Edson et al. (1993), for example, illustrate this compensation effect. [This situation is complicated if you measure whole-vine photosynthesis rates, because lower crop levels are often associated with larger leaves that produce more photosynthates than do smaller leaves]. The point to remember is that the relationship between crop and leaf area requirement is not necessarily linear. If you trust the research, as I do, if you doubled crop mass per shoot, you would not need to double the leaf area per shoot to obtain the same ripening effect. In practice, your second cluster will not weigh as much as the basal cluster anyway. We try to aim for 17 nodes (primary leaves) on our Chardonnay, the point at which we generally need to hedge VSP shoots to avoid canopy shade. We also pull leaves (3 or 4 per shoot). That puts us down around 12 to 14 primary leaves retained per shoot.

2) If it takes 20 leaves to mature cluster(s) are 10 lateral leaves comparable to 10 primary leaves?

I'm unaware of any photosynthetic efficiency or productivity differences between a unit area of primary leaf (say a cm2) and the same unit area of a comparably-aged lateral leaf. A leaf is a net exporter of carbohydrates when it's about a third to one-half its full size, and generally will reach its maximum photosynthetic performance about 30 to 40 days after emerging from the shoot tip. So, 10 laterals leaves (30 or so days old) should be comparable to 10 primary leaves, on a per area basis. However, lateral leaves tend to be a somewhat smaller than primary leaves, so you may need more than 10 to equal the area of 10 primary leaves. But here's another complication: leaves show some deterioration in carbohydrate output with time. Some of the decline relates to normal leaf senescence, but it is accelerated by spray burn, mites, disease, and normal wear and tear, so to speak. Lateral leaves are viewed by some as a desirable means of refreshing the leaf area of the vine, especially if the lateral leaf area reaches photosynthetic "maturity" at about the time of veraison (see my discussion of Stefano Poni's research in this regard in Viticulture Notes Vol. 11, No. 3 (1996). The issue of leaf aging, itself, is not clear cut. Recent work by Petrie et al. (2000) in New Zealand, suggests that ³the decline in grapevine leaf photosynthesis, generally associated with advanced leaf age, is actually caused by a progressive increase in the leaf area to fruit weight (source:sink) ratio, as leaves emerge on the developing vine.

3) Assuming that 20 leaves is ideal: if the first four leaves up from the cordon are pulled to expose the bunches, do leaves #21 thru 24 serve as well as leaves #1 to 4 which were pulled? Or, does it take more leaves to ripen the grapes if they are further from the bunches and the cordon?

The simple answer is no, the distance from the fruit will not make a practical difference in this case, at least not that I'm aware of.

Literature cited:

Edson, C.E., G.S. Howell, and J.A. Flore. 1993. Influence of crop load on photosynthesis and dry matter partitioning of Seyval grapevines I. Single leaf and whole vine response pre- and post-harvest. Amer. J. Eno. Vitic. 44:139-147.

Kaps, M.L. and G.A. Cahoon. 1992. Growth and fruiting of container-grown Seyval blanc grapevines modified by changes in crop level, leaf number and position, and light exposure. Amer. J. Enol. Vitic. 43:191-199.

Petrie, P.R., M.C.T. Trought, and G.S. Howell. 2000. The influence of leaf to fruit ratio on grapevine photosynthesis, vegetative and reproductive growth. Proc. 5th Intl. Cool Climate Symp. Enol. and Vitic. Melbourne. 3 p.

Smart, R. and M. Robinson. 1991. Sunlight into Wine. Winetitles, Adelaide. 88 p.

Wolf, T.K., I.E. Dami, B.W. Zoecklein, and M.K. Warren. 1999. Commercial Grape Varieties for Virginia. VCE Public. 463-019. 42 p.

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III. Potassium deficiency and fluoride toxicity:

Here are two observations from the pack of unusual 2000 season observations.

The first observation involved several cases of potassium deficiency in young vines (2 or 3 years old). In two Roanoke area vineyards, the potassium deficiency was observed with Cabernet franc, but we also observed an Eastern Shore vineyard with potassium deficiency in Merlot and Chardonnay. Symptoms in the red-fruited varieties were striking with mid-shoot leaves, in particular, showing marginal leaf reddening and scorching, as described in the Mid-Atlantic Winegrape Grower's Guide. Petiole analyses from the two Cabernet franc vineyards showed petiole potassium levels of less than 0.30% (bloom-time sufficiency range in Virginia is 1.50 to 2.50%). Nitrogen levels were also low, and corrective recommendations included immediate application of potassium nitrate, followed by additional potassium chloride. The occurrence of potassium deficiency in two-year-old vines raises the suggestion for doing a plant analysis test at some point during the first year to assess the potassium level in vines, rather than waiting until the 2nd or 3rd season.
The second case was a "first" in my experience. A grower whose vineyard is just north of Roanoke reported marginal leaf burning and shoot tip abortion of all varieties in his 12-acre, two- year-old vineyard. Problem first appeared last year, intensified this year. Marginal burning affected over 50% of leaf area with some vines, much less so on others. Unlike the potassium deficiency, necrosis was confined to specific areas, and showed sharp transitions between necrotic and healthy tissue. We ruled out possible pesticide spray burn on basis of grower's records, especially in light of symptom expression before spraying commenced. Symptoms were also unlike familiar nutrient deficiency or disease symptoms. Herbicide uptake ruled out on basis of generally uniform occurrence throughout entire vineyard. Observation of vegetation outside the vineyard revealed same symptoms on certain plants species, including black cherry, wild grape (Vitis riparia), and certain herbs, such as lambsquarter. Symptoms compared positively to those of fluoride toxicity depicted in Grape Disease Compendium, with awareness of one potential hydrogen fluoride-emitting source in local area of vineyard. Plant tissue samples from affected vines, and other affected plant species were analyzed by Brookside Farm Labs in Ohio, and revealed fluoride levels of 60 to 100 parts per million (ppm) in cultivated vines, with 35 to 40 ppm considered the threshold for injury (cf Grape Disease Compendium). Cause determined, the next step is to explore means of mitigating the problem.

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IV. VVA/VSHS 2000 annual meeting talks:

Transcripts from the January 2000 annual meeting of the Virginia Vineyards Association and VA State Horticultural Society have been presented in previous Viticulture Notes. Continuing the "Grower experiences" theme, the comments of Jennifer McCloud, of Chrysalis Vineyards in Middleburg are presented in this issue.

Jennifer McCloud, Chrysalis Vineyards, Middleburg, VA

GDC Trellising: I planted 47 acres in the last two growing seasons and now have a total of 51 acres in vines at three vineyard sites. In 1998 I used wooden posts and attached metal cross arms. The reason I chose Geneva double curtain (GDC) training was because I believe in the data that has been presented, particularly by Dr. Smart, in that split canopy trellising is an advantage in our climate to maximize the sun, open up the canopy, and to keep the grapes up high. I felt the GDC was less labor intensive in my situation. I had too many people telling me that vertically split canopies had a tendency to ripen unevenly. The GDC trellis that I use has an interesting feature; it does not converge at the end posts because we use a heavy-duty cross arm at the end posts. The split canopy goes all of the way to the end of the row, and it is secured and tied back with an earth anchor. This year we used all metal, and throughout this presentation, I will be making a case for metal. One of the things you will notice with wood is the necessity for a carriage bolt through the wood in order to secure the cross arm. That is a very time-consuming process and the bolts are expensive. With metal, the metal cross arm bolts to predrilled posts and I can use a one-inch bolt instead of an eight-inch carriage bolt. This is how it is put together, there are basically three separate supports, supporting the weight of the trellis back to the earth anchor. The center support is looped around the post and that is secured with a wire lock. I can re-tension the wire that is holding the post back with the use of a wire lock. The other supports are back up to the ends of the cross arm and they are tensioned by a S-hook (a bright idea I had), so I don't have to spend a dollar or so on a wire hook. I only spend eleven cents on a S-hook, and basically slide the S-hook towards the cross arms which tensions them as you slide. The universal cross arm and cordon wire comes into a ratchet like restrainer device, that at the top is just a square post that you can stick a crescent wrench on and crank it tight. There is a ratchet inside the device and the wire just rolls around it and tightens it up. The wire passes through an intermediate cross arm, and then terminates at the other end, at what the manufacture calls a cowboy end fastener. Again, the purpose of the device is to create a radius for the wire to go around so it doesn't crimp or chafe against the metal. Wood posts cost more than metal posts do. The bottom line is that overall the materials cost about the same, but wood is much more variable than metal. Major differences occur with labor in the vineyard. It is a lot easier to pound metal posts in the ground. If you can imagine a post having a footprint of about twenty square inches having to get pounded into the ground, as opposed to a metal post that looks like a stop sign, with a half of a hexagon, with maybe two square inches to contend with. Every time your pounder hits that metal, it is being transferred through the metal, and is not as easily absorbed as wood. Metal posts drive in much easier. My actual experience with prices has been $7.12 for each wood post driven in 1998, and $4.45 for each metal post in 1999. The cross arm installation expense has been significantly lower as well, because I don't have to drill two holes through the wood post and then secure it with a long carriage bolt. The metal is predrilled, it all fits, you just butt it up to the post and put a couple of screws in to secure it. This is a summary of costs per acre. The materials cost was roughly the same, but look at the difference in labor costs for pounding the posts and installing the cross arms. This labor savings amounted to a per acre savings of $545.00, or roughly $2,200 for a four-acre vineyard. My conclusion is that there are several advantages to metal. It is more efficient to move metal posts, they are actually lighter and smaller than wood. They are easier to pound. They are easier and less labor intensive, consequently less expensive to install GDC cross arms. Overall, the installation costs were considerably less than wood. There is a potential for them to last considerably longer than wood, particularly in our more acidic soils. In higher acid soils, the metal seemed to corrode less rapidly than in a more basic soil, so the manufacturer says, we will see.

Dogs: The fencing was buried a few inches below the surface, and the dogs wear the receiver collars, and they are trained in the vineyard. I have 13 dogs in five separate fenced areas. I have a total of 17,000 linear feet fenced, roughly 63.5 acres that cost me on average $.96 per foot. I figured out what this would cost me over a ten-year period. Each dog costs about $300 per year to care for, which includes vet bills and food. My ten-year cost per foot is $3.21, which I still think is considerably less than an effective deer fence. Some of my considerations for using dogs were the aesthetics of the property, I didn't want my property to look like a penitentiary, the costs were considerably less, and convenience. I didn't want to deal with fencing everywhere, and opening and closing gates. I had absolutely no deer in the Loxley vineyard, and only minimal damage on the periphery of the property, which abuts a wildlife preserve. The cost of the dog care versus fence maintenance and initial installation costs were my considerations and I get the added benefits of protection against groundhogs, turkeys, possibly birds, rabbits, and humans in the vineyard.

Varieties: I have a very large planting of Norton, I am very high on the variety, it is Virginia's grape, and America's grape. It has good yields with low care. I grow Petit Verdot and Tannat which I intend to blend with Norton to produce a wine of the caliber that we enjoyed last century when Norton had a reputation as a fine red wine. I have an interest in Spanish varieties, I think Albarino is a fantastic variety. It is almost like a cross between Viognier and Riesling. It has very high acids, it is very fruity, sweet and sour, and is great with food. I have Seyval blanc, Vidal blanc, and Riesling in the vineyard that I lease. I have a large planting of Viognier, and I have planted about 6 acres of Chardonnay because I think it grows well in Virginia. My largest single varietal planting, however, is Viognier.

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V. Upcoming Meetings

A. Virginia Vineyards Association annual technical conference
When: Saturday, 12 August 2000
Where: Wilson Hall, University of Virginia campus, Charlottesville, VA
Details: VVA meeting will be held in conjunction with the North American Fruit Explorers 2000 conference The entire NAFEX meeting will run from 10 ­ 12 August, and grape producers are invited to attend, using a separate registration. The North American Fruit Explorers (NAFEX) is a network of individuals throughout the US and Canada devoted to the discovery, cultivation and appreciation of superior varieties of fruits and nuts. Although the ranks of NAFEX membership include professional pomologists, nurserymen, and commercial orchardists, NAFEX members are all AMATEURS in the truest sense of the word; they are motivated by their LOVE of fine fruit.

Accommodations: For those who wish to spend one or more nights in Charlottesville, please see the conference registration web site for options:

The viticulture program and tour on Saturday, 12 August will be as "Track 5" and "Tour 3" on the NAFEX program and appears on the following page

Viticulture Program

8:30 am: On-site registration (Wilson Hall, UVA Campus ­ see NAFEX web site)

8:45 am: Tony Wolf: Viticultural research programs:

1) Bunch stem necrosis: Can this disorder be avoided in your vineyard?
2) Grapevine yellows: Current research efforts aimed at identifying vectors
3) Review of current research at Winchester: Chardonnay clone evaluations, training system comparisons, crop load and growth regulator studies

10:00 am: Bruce Zoecklein: Current enological research projects

11:00 am: Tony Wolf: A snapshot of South Australian viticulture

12:00: Board buses for vineyard tour. Box lunch served on buses

12-5:00 Tour of vineyards (as follows):

12:45 ­ 2:00: Ivy Creek Vineyards, hosted by Paul Mierzejewski (vineyard manager). Review of variety pros and cons (Chardonnay, Cabernet S., Viognier, Gewurzt., Touriga nacional); review of Paul's experience with vine training, including lyre, Scott-Henry, and Geneva double curtain); examples of grapevine yellows, description of routine pest management and peculiar features of 2000 season relative to pest management program.

2:30-3:45: White Hall Vineyards, hosted by Tony Champ (owner) and Brad McCarthy (winemaker). Discussion of the fruit harvest criteria used by Brad with their own vineyard and others'. Review of cellar, with wine tasting, and vineyard at White Hall, example being Pinot gris, planted '94 and trained to bi-lateral cordon and VSP.

4:30 ­ 5:30: Cardinal Point Vineyards, hosted by Tim Gorman (owner). Points of interest include hearing Tim's experiences with varieties, and training modifications (some lyre, some modified GDC), frost and wind machine usage, irrigation pros and cons, post-harvest retrieval of grapes from vineyard and cold storage.

6:15 pm: Arrival at Mt Cove Vineyards for Vineyard & winery tour, Blue Ridge Mountain Traditional Outdoor Feast, and Live Mountain Music with the McKenzies Band.

One or more buses will depart immediately to UVA campus, for those not wishing to stay for BBQ, and other buses will depart periodically from 7:30 to 10:30 pm to return attendees to UVA campus and vehicle retrieval. Note: all attendees must use buses for tour; no private vehicle caravans on this meeting, as per request of participating vineyards.

Registration: Registration for the VVA technical program (12 August only) is $60 pp. Send check, payable to ³VVA² to: VVA Summer Meeting, 145 Durrett Town Rd., Afton, VA 22920. Registration of other aspects of the NAFEX meeting can be done separately via the NAFEX web site:

B: Virginia Cooperative Extension Vineyard Meeting
When: 13 September 2000; 11:00 am until approximately 1:30 pm
Where: Prince Michel Vineyards, Larry and Greg Morris
Details: Dr. Tony Wolf, Viticulturist, "Current situation and management strategies".
Directions: Take Rt. 29 to Leon, 9 miles south of Culpeper and 30 miles north of Charlottesville. Just north of winery, take Rt. 612 (631) west approximately 2 miles. Farm entrance is on left. Contacts: Kenner Love, Rappahannock Co. VCE (540-675-3619, or Brad Jarvis, Madison Co, VCE, (540-948-6881, Bring a bag lunch.

C: Beginners Grape Growing Seminar
When: Monday, 25 September 2000; 8:30 am - 4:00 pm
Where: AHS, Jr. Agricultural Research and Extension Center, Virginia Tech, Winchester, VA.

Information: Alison Hectus (540-869-2560, Extn. 23) or Tony Wolf (Extn. 20)

Registration1: Pre-registration required and registration is limited to first 50 persons: $20 per person, to include coffee, soft-drinks, catered lunch, and handouts. Check made payable to "Virginia Vineyards Association", and mailed to "Grapes", Virginia Tech, 595 Laurel Grove Rd. Winchester, VA 22602. Check must be received by 21 September 2000 to guarantee lunch.

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. Various aspects of established vineyard management (canopy management, pest management, pruning and training, etc.) are discussed at an introductory level. Classroom principles are reinforced with a review of the AHS AREC research vineyard.

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 miles north on Rt 628 and turn left (west) onto Rt 629. Go 0.8 miles to AREC on left.

1If you are a person with a disability and desire any assistive devices, services or other accomodations to participate in this activity, please contact the A.H. Smith 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

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