Vineyard and Winery Information Series:
Vol. 16 No. 3, May-June 2001
Dr. Tony K. Wolf, Viticulture Extension Specialist
II.Canopy modification tips
Abundant rains over the past 10 days has brought a welcome relief to the dry weather that much of Virginia has experienced since early April. Not that established vines had begun to suffer drought, but many of us had noticed parched lawns and sluggish gardens from the dearth of rain. The prolonged wetting periods, however, pose a very significant threat in terms of fungal diseases. Adding to the disease threat is the fact that we are entering a very susceptible stage of vine development, the period immediately prior to and during bloom. I encourage readers to once again review Dr. Wayne Wilcox's various tips and admonitions on disease management in the March-April Viticulture Notes. This is a prime time to bring out the most effective and "rainfast" fungicides of the season. The locally systemic materials, and those with eradicant qualities on top of their prophylactic properties might be wise choices. Metalaxyl (Ridomil), for example, would be a good choice if you were uncertain about downy mildew protection going into rainy weather. Mike Ellis, plant pathologist at Ohio State University, indicated that Ridomil can provide post-infection or curative activity if applied within 2 to 4 days of infection. Options for black rot and powdery mildew control are somewhat more varied and could include either locally systemic materials (such as the strobilurins or the sterol-inhibitors) or non-systemic protectants, such as mancozeb (black rot) or sulfur (powdery mildew). Look at the weather forecast. If prolonged periods of rain are forecast, use locally systemic materials that will not be washed off. Rainy weather during bloom and post-bloom is also conducive to botrytis bunch rot. Consider the use of Vangard or Elevate on botrytis-sensitive varieties such as Chardonnay and Sauvignon blanc. It seems redundant to say, but nevertheless bears repeating: keep your vines free of disease from now through mid-July and you will have a relatively easy time keeping them clean for the balance of the season. Screw up now, and you may very well lose a crop.
Answer: Unless you cut buds prior to pruning and examined the dormant structures for evidence of winter injury, it's not possible to rule cold injury out as a reason for your low fruitfulness. However, I suspect that the more likely reason for the barren shoots is bud necrosis. Bud necrosis (BN) results in the death of buds during the season of their initiation. Remember that the shoots that you see today started to develop as axillary buds about this time last year. I suspect that sometime during the 2000 growing season your Viognier lost many of the primary buds to BN, and that the shoots that you see now are, for the most part, secondary shoots. We are uncertain of the specific cause(s) of BN, but former PhD graduate student Lakshmi Vasudevan's work suggested that the disorder may occur as a result of localized, and apparently transient, deficiencies of carbohydrates. What would cause those deficiencies? Our best guess is cloudy weather - indeed, Dr. Vasudevan increased the incidence of BN of Riesling by application of shade cloth to vines 25 days after bud break (Vasudevan et al., 1998). The increased BN incidence was associated with a depression of carbohydrates in the buds. We are currently in the process of going back over eight years of BN data from our variety planting here at Winchester, and looking at the association of BN with rainfall and light levels during May and June of each year. Rainfall appears to be associated with BN levels, as evidenced by the data of Table 1. It doesn't matter whether we express the rainfall for the season or for just the May-June period. What does the rainfall do? It could contribute to vigor, and we do know that more vigorous shoots express a higher frequency of BN. But rainfall is also associated with cloudy weather, and we suspect that cloud conditions, especially in the bud-break to bloom period, is a contributor to the BN. If you look just at the Viognier data of Table 1, the years with rainfall of less than 5" in the May-June period (bold, italic), were associated with BN levels about 50% of those where rainfall exceeded 5". Similar patterns exist with Valdepenas and Riesling. Actually, the pattern existed with all of the varieties in our original variety planting, including Chardonnay (Table 1), which was one of the least affected varieties. The problems with BN in Viognier were mentioned in our variety publication (Wolf et al., 1999). Syrah, for you Syrah aficionados, was equally susceptible to BN.
Table 1. May-June precipitation and percent bud necrosis (BN) of three varieties at Winchester in each of eight years. The BN data are means of approximately 500 buds each.
|Precipitation (in.) May-June||6.87||3.81||4.39||12.63||9.18||4.95||10.67||3.36|
|Chardonnay #4 BN (%)||0.0||0.9||3.3||3.3||5.8||1.5||6.8|
|Valdepeñas BN (%)||58.3||21.4||33.7||69.71||51.4||17.1||40.6|
|Riesling BN (%)||7.3||49.5||38.4||18.3||10.0|
We did not examine buds for BN last year, nor do I know how much rain/cloudy weather your vines experienced last spring, so I can only speculate that this is the cause of your unfruitfulness this season. What can you do? As illustrated above, BN incidence will vary from year to year. In the future, you might want to examine buds prior to pruning. Pruning could be adjusted to compensate somewhat for primary bud loss. We found that the incidence of BN increased as you went out the cane, so spur-pruning generally retained a greater proportion of good primary buds than did cane-pruning. Cane selection was also important, even if only a spur is retained. Canes with abundant laterals and those from shaded regions of the canopy had a higher proportion of necrotic buds than did moderate-sized, well exposed canes. Keep your canopies relatively thin and well exposed during the growing season to maximize sunlight exposure of developing buds. Keep a log of cloudy days in the bud-break to bloom period and compare that log to the incidence of BN at the end of that season.
Wolf, T. K. et al. 1999. Commercial Grape Varieties for Virginia. VCE Public. 463-019 42 p.
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Shoot thinning: For most varieties, our experience suggests that good canopy architecture is achieved with a shoot density of around five shoots per foot of canopy. One common exception to that rule of thumb is for Seyval, whose abundant fruitfulness dictates a shoot density of three to four shoots per foot of canopy to limit crops (often with additional cluster thinning) to five or six tons/acre with non-divided training systems. With appropriate pruning, the need for shoot thinning can be minimized; however, we still usually remove one or two shoots per foot of canopy in this process.
When: Start when shoots are 6 to 12" long and when flower clusters are apparent, and after the threat of spring frost; complete 2 weeks before bloom (about the end of May in northern VA) if possible. Shoot vascular connections to older wood become lignified at or shortly before bloom, making their removal more difficult after bloom.
What to remove: For cordon-trained, spur-pruned vines - remove the distal shoot(s) of multi-shooted spurs. In other words, try to retain shoots closer to the cordon to serve as spurs in the following year. Where the option exists, remove nonfruitful shoots in preference to fruitful shoots, unless crop reduction is part of your strategy. Retain nonfruitful shoots, however, that might be in a position to serve as a spur in the following year. An example would be a base shoot originating directly from the cordon. This strategy helps to keep the one-year-old, fruiting wood close to the cordon. The thinning can be done on a per vine basis, or per foot of canopy basis. I find it easier to simply focus on one foot of cordon at a time (5 shoots) and not worry about the number of shoots per vine.
Divided canopy vines: For GDC and lyre, hold to same concept of about 5 shoots per foot of cordon. Thin the upper 180° of the GDC cordon in preference to those shoots that are already angled down.
Young vines: Refer to training instructions in MAWGG. Remove shoots from trunks if 50% or more of cordon is developed. Unless the shoots break cleanly, use pruners to remove to avoid stripping bark of trunk.
Shoot positioning: We position shoots in an attempt to uniformly distribute the leaf area over the available trellis space and to promote the formation of our intended training system. Thus, vertically shoot-positioned (VSP) training is not VSP unless the shoots are vertically trained upright above the cordon (or cane). A combination of foliage catch wires and manual "tucking" are usually used to facilitate this operation.
When: As shoot length warrants. On VSP systems, the first set of catch wires is typically at 10 to 18" above the cordon. When the majority of shoots are at or above this point, the first round of positioning is done. Wait too long and the cordon (or cane) may rotate and shoots will be pointing down, or to the side. Trying to turn such shoots back up to a vertical plane results in a vase-shaped canopy; undesirably wide through the fruit zone, and narrowing through the catch wires. Some use movable catch wires to help position shoots. The wires are "parked" beneath the cordon during the winter, and pairs (either side of trellis posts) are brought up to a fixed position above the cordon, bringing the shoots into a vertical plane in the process. Various shoot "taping" or tying systems are commercially available to assist with keeping the shoots between or otherwise attached to trellis wires.
Divided canopy systems: GDC: it ain't GDC unless the shoots are positioned downward on both curtains. Start a week or two before bloom, raking the shoots out and down. Wait a week if significant shoot breakage occurs. Repeat the positioning about 2 weeks after the first round. If you wait too long after bloom, the tendrils will intertwine shoots, and significant shoot breakage will occur if you attempt to position the shoots. Timing is everything. For Scott-Henry, Smart-Dyson and Smart-Dyson ballerina, again, a two-stage process seems to facilitate the operation. The first stage, two weeks or so prior to bloom is aimed at getting the intended downward-oriented shoots out of their upward habit. Do not attempt to orient the shoots to the 180° degree position in one move; it's easier to move them to the 90° or 270° position now, and then come back at or just after bloom to further "encourage" them to the downward plane. Two grower tips: Lee Sandberg, Loudoun County, pointed out the need to time sprayer or other vineyard equipment traffic to avoid having to move in the vineyard when the shoots are hanging out - before shoots have been fully positioned into their downward plane. Dick Buttons et al. At Ivy Creek illustrated "fenders" that they mounted on tractors to deflect the shoots to avoid snagging or pinning by tires. Polyethylene water pipe work well for this (it bends before the tractor bends!).
Leaf pulling: Selective and judicious removal of leaves in the fruit zone aids fruit drying, reduces disease incidence, and may improve fruit composition through reduced acidity and improved color. Leaf pulling can also lead to sunburning and excessive acid reductions if overdone, so "selective" is an important qualification.
When: First, don't pull leaves unless you feel your canopies will benefit from it. If leaf layer number is in excess of 2, and a majority of fruit clusters are hidden by foliage, there may be a compelling reason to pull some leaves. If so, try to accomplish the leaf pulling within the first 4 to 6 weeks after fruit set -- roughly the end of July with northern Virginia Chardonnay. Delaying leaf pulling into August increases the likelihood of causing sunburning as a result of the abrupt change in cluster light exposure.
How many: What's your goal? If you're trying to reduce acidity in a variety like Norton, then maybe pulling all leaves in the fruit zone to maximize fruit exposure is desirable. Excessive exposure of some varieties, however, can lead to undesirably increased phenolic levels. Generally, pulling 2 or at most 3 leaves per shoot, from just around the fruit clusters is sufficient to obtain a desired response. If you find that you need to pull more than 3, chances are you have an excessive shoot density. I don't think that the goal should be to completely denude the fruiting zone. Our research vineyard at Winchester has north-south oriented rows. We typically only pull leaves from the east side of the canopy. This maintains some leaf cover on the west side and reduces the potential of sunburn from intense sun during the heat of the day.
Shoot hedging: Effective with shoot positioned canopies, hedging prevents elongating shoot tops from shading the fruit zone of VSP- or lyre-trained vines. There's not much point in hedging high-trained vines, unless you're concerned about the shoot tops being caught by machinery tires and ripped off.
When: Before shoot tops begin to shade the subtending canopy. In wet years, such as 2000, you may need to top shoots 2 or 3 times. Alternatively, you might get away with a single topping in a dry year such as 1999. Heavy hedging after veraison can lead to lateral regrowth which may divert carbohydrates from fruit clusters until the lateral shoots become net exporters.
How much: Key is how many leaves to retain. I advocate retaining about 15 leaves per shoot. This may be somewhat more than needed to ripen crop; however, it allows for a few to be pulled from around fruit clusters, Japanese beetle feeding, or other loss.
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When: Saturday, 28 July 2001; 10:00 am until 4:00 pm
Where: Indian Springs Farm and Vineyard, Woodstock VA (Steven Brown)
Program: The objective of this field day is to provide an opportunity to observe vineyard equipment demonstrations and speak with equipment vendors. We anticipate 30 or more vendors of tractors, sprayers, cultivators, and other powered and manual vineyard implements will be demonstrating their wares. We are organizing a sprayer comparison where the relative performance of sprayers will be evaluated under the same spraying conditions. We will post a listing of the exhibitors on the VVA web site (www.virginiavineyardsassociation.com) on or shortly after 1 July. We will also have an opportunity to review current vineyard situations in Shenandoah County's largest vineyard, and to discuss results to date with a VA Tech crop study in this vineyard.
Registration: Registration is $25 per person for VVA members and $45 per person for non-members. Membership status (as of March 2001) can be confirmed/changed by checking the VVA web site. Mail registration fees (payable "VVA") to: Virginia Vineyards Association, PO Box 471, Ivy VA 22945. Include a note that you are registering for the "Vineyard Equipment Workshop, 28 July". Registration must be received by 20 July to ensure catered lunch.
Directions: I-81 to Woodstock exit. Left on Rt 42 approximately 3.9 miles. Right on Rt 623, go approximately 5.9 miles on Rt 623 to Alonzaville. Turn left onto Rt 604 and go 0.3 miles. Turn left onto Rt 681 and go approximately 0.2 miles to Indian Springs Farm on right. Follow signage.
When: Thursday, 2 August 2001; 10:00 am until 3:00 pm (see specifics under program)
Where: Ivy Creek Farms, Ivy Virginia.
Program: The objective of this program is to provide growers with the skills to estimate crop and to do basic lab and sensory analyses to judge crop maturity. The morning program (10:00 am until noon) is open to all and has no registration cost associated with it. Dr. Tony Wolf will lead a discussion of grape crop estimation procedures, followed by a hands-on exercise in the vineyard. We will compare two methods of crop sampling (whole cluster vs. berry sampling), and discuss various means of reducing variance between grape sampling and final harvest numbers. The afternoon program (1:00 to 3:00 pm) is strictly limited to 16 participants, and pre-registration is required to participate. Dr. Bruce Zoecklein will conduct a hands-on lab analysis of fruit pH, titratable acidity, and Brix, with sensory assessments of tannin maturity and juice aroma. The restriction to 16 participants is required due to a limitation of lab apparatus and space.
Directions: Take the Ivy exit off of I-64, west of Charlottesville, onto Dick Woods Rd. Proceed approximately 0.3 miles north to Bloomfield Rd on right. Right on Bloomfield Rd. approximately 0.5 miles to Ivy Creek Farm entrance on left. Follow signage for parking.
Registration: Morning program is free. Afternoon program (lab analyses) is restricted to the first 16 registrants. To register for the afternoon program, send a check for $30.00 per person (payable "VVA") to: Virginia Vineyards Association, PO Box 471, Ivy VA 22945. Include a note that you are registering for the "Ivy Creek Workshop." The registration fee includes a box lunch. You will be mailed a confirmation of registration.
When: Friday, 3 August 2001; 10:00 am until 3:00 pm (see specifics under program)
Where: AHS Jr. Agricultural Research and Extension Center, Virginia Tech, 595 Laurel Grove Rd., Winchester VA.
Program: This program is identical to that offered on 2 August. Again, the afternoon program (1:00 to 3:00 pm) is strictly limited to 16 participants, and pre-registration is required to participate.
Directions: Take the Stephens City exit off I-81 (exit 307), south of Winchester. Go west into Stephens City (200 yards), straight through traffic signal and continue on Rt 631 approximately 3.0 miles to "T" at Rt 628 (Middle Rd.). Go north (right) on Middle Rd. approximately 1.5 miles to Rt 629 (Laurel Grove Rd.). Left on Laurel Grove Rd. 0.8 miles to VA Tech Center on left. Meet in conference room.
Registration: Morning program is free. Afternoon program (lab analyses) is restricted to the first 16 registrants. To register for the afternoon program, send a check for $30.00 per person (payable "VVA") to: Virginia Vineyards Association, PO Box 471, Ivy VA 22945. Include a note that you are registering for the "Winchester Workshop." The registration fee includes a box lunch. You will be mailed a confirmation of registration.
Three informal vineyard field meetings are scheduled. The first two (Quaker Run and Linden vineyards) featured speakers from VA Tech (Derr, Wolf, Zoecklein, and Pfeiffer) and some of these speakers will be involved in the remaining meetings. While organized by the Rappahannock and Madison County Extension units, the meetings are open to all.
June 13th -- Horton Vineyard, Dennis and Sharon Horton
Directions: From Orange VA, South on Rt 15 Business, turn left on Rt. 647 (Old Gordonsville Rd), cross railroad track go 100 feet and turn left on Berry Hill Lane. Inclement Weather Alternate Site: From Ruckersville take 33 east approximately 8 miles; the winery is on the left.
August 8th -- Gray Ghost, Al and Cheryl Kellart
Directions: From Washington VA, 211(Lee Hwy) travel East for 12 miles to Amissville VA, the Vineyard is on the right (across from the Amissville Fire Department)
Sept 12th -- Rappahannock Cellars, John Delmare
Directions: Rappahannock Cellars is located at the corner of Rt. 522 and Hume Rd., 6 miles south of Front Royal.
If you are a person with a disability and desire any assistive devices, services or other accommodations to participate in any of these activities, please call (540) 675-3619 between the hours of 8:00 a.m. and 4:30 p.m., Monday through Friday, two weeks prior to the event.
Summer Vineyard and Winery Meeting
Where: Berks County Ag Center in Leesport, PA (just north of Reading)
Time: 8 a.m. to 4:30 p.m.
Topics include: Vineyard nutrition, soil and tissue test interpretation, vineyard spray programs, new sprayer technology, canopy management, varieties, clones and rootstocks for eastern vineyards, growing and production of Chambourcin, Traminette and Vidal Blanc with a wine tasting.
Speakers are from include Dr. Andrew Landers, Cornell Ag Engineering; Dr. Peter Cousins, USDA/ARS; Dr. Gary Pavlis, Rutgers Cooperative Extension; Mr. Dennis Rak, Double A Nursery and local growers and wine makers in Pennsylvania.
Lunch is included with the $30 registration fee. For a detailed program, information, directions and registration, please see the Winegrape Network web site at http://winegrape.cas.psu.edu. Or contact Mark Chien at 717 394-6851 or email@example.com.
American Society of Enology and Viticulture Annual meeting. San Diego, CA. For information call 530 753-3142 or see www.asev.org
American Society of Enology and Viticulture - Eastern Section Annual Meeting. Niagara-on-the-Lake, Ontario, Canada. Includes a tour of vineyards and wineries on the Niagara Peninsula, space-aged grape growing symposium and technical meeting. Contact Ellen Harkness for information. 765 494-6704 or firstname.lastname@example.org.
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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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