Viticulture Notes

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I. Current Situation:

If there ever was a spring in which we should have had major spring frost damage, 1998 was it. Vines at the Winchester AREC broke bud, on average, almost 3 weeks earlier than average. We had several close calls with frost in mid-April, but ultimately dodged the bullet. Several vineyards in the Charlottesville area did have some frost damage, and several others would have had frost damage had they not employed wind machines or helicopters on critical nights. Chardonnay is now beginning to bloom in northern Virginia and the outlook is for great weather for the next week or more. Given the absence of winter injury, the minimal frost injury, and the apparent fruitfulness of shoots and vines, we seem to be on track for a great year. Keep on top of the pest management and hope for continued good weather.

The following topics are presented as reminders - not so much in-depth review - to jog your memory on what you need to watch for at this time of year.

Canopy management: Activity of the last two weeks has centered on tucking shoots to achieve a vertically shoot-positioned canopy and thinning shoots, where necessary, to achieve 5 to 6 shoots per foot of canopy. Both practices aid canopy penetration by fungicides and both increase drying rate following rains. Fruit quality can also be enhanced if the more porous canopy is maintained for the balance of the season. Selective leaf pulling from around fruit clusters can further improve the fruit zone microclimate. If you choose to pull leaves, wait until about 2 weeks after fruit set or shortly after shoot hedging. Leaf pulling will have minimal effects if the fruit-zone canopy density is less than 3 leaf layers thick; it can have considerable benefits for fruit rot control if the fruit zone has more than 3 leaf layers. You may wish to delay leaf pulling until about 10 days after shoot hedging. Such a delay gives one the opportunity to simultaneously remove small lateral shoots that were stimulated to develop in the fruit zone by the hedging operation.

Diseases: Generally, the pre-bloom through second post-bloom sprays are the most important for a successful, season-long disease management program. The reason relates to the abundance of inoculum as well as the acute susceptibility of vines to the principal diseases (black rot, downy mildew, and powdery mildew) at this stage of development. The importance of choosing appropriate fungicides for each of the principal diseases was reviewed in the last newsletter. Spray every row middle, drive slowly, and apply at least 50 gallons of spray material per acre to ensure good fungicide coverage. We tend to opt for Nova for black rot and powdery mildew in the last pre-bloom spray and in the bloom/post-bloom spray, partly because it has locally systemic activity. Don't rely on captan or copper for black rot control in this period. Mancozeb can be tank-mixed to extend the control to downy mildew. Alternatively, one of the Ridomil formulations would be recommended for downy if extended wetting periods are forecast. Following bloom, we will alternate one of the sterol-inhibiting fungicides (e.g., Nova or Bayleton) with either Abound or sulfur for powdery, and either Abound or mancozeb for black rot and downy. If you've not spent much time walking the vineyard yet, do so immediately. Scout the canopy interiors for signs and symptoms of disease. Powdery mildew usually shows up on fruit clusters that are within canopy interiors. If you catch a powdery mildew outbreak in time, you may be able to arrest it with a combination of sulfur and full-rate of Nova or Abound. For sulfur-sensitive varieties, or where the powdery is out of control, I would opt for JMS Stylet oil or one of the other registered summer oils. However, be advised that it is much easier to prevent powdery mildew from becoming established than it is to eradicate an existing disease outbreak.

Grape Berry moths: Grape berry moth (GBM) adults emerge before bloom in Virginia, mate, and deposit eggs on blossom clusters or immature berries, depending on stage of vine development. The larvae that emerge from eggs feed on blossoms and young berries and form webbing in the flower cluster which is a key indicator of infestation. This initial feeding may not appreciably reduce yields, but experience suggests that untreated first generation larval feeding leads to increased pressure later in the season. Dr. Doug Pfeiffer has found that up to four generations of GBM may occur per season. The larvae of second and subsequent generations feed inside berries producing dark, irregularly shaped streaks beneath the skin of the green berries. Affected berries may exhibit a small hole where the larva entered (or exited) the berry, although this hole may only be visible once the berry is removed from the cluster. Individual larva may destroy 5 to 10 berries on a given cluster before pupating. After veraison, damaged berries are prone to Botrytis and other opportunistic pathogens that can lead to bunch rot and sour bunch rot. It is for this reason that good GBM control is important for quality fruit production.

Management of GBM starts with risk assessment. Vineyards that have chronically suffered attack should be considered at risk in 1998. Vineyard blocks that border wooded areas are particularly susceptible to attack, and the edges of the block that are closest to woods can be expected to have the greatest GBM pressure. Scouting for infestation should therefore start with the high-risk edge rows. It is possible that only vineyard edges need to be treated with an insecticide to manage GBM at or below an economic threshold. What is the economic threshold for GBM infestation? New York State researchers have used 2% berry infestation as an indicator for insecticide application. In our own vineyard, we use a threshold of 2% of clusters (2 out of 100) as a trigger for insecticide application. Due to multiple generations per year, GBM scouting should continue throughout the season up to harvest. Good control in the early part of the season does not ensure freedom from infestation in late-summer. The 1998 Virginia Tech pest management guide for grapes lists four management alternatives for GBM in the pre-bloom period: Guthion 50WP (1.5 to 2.0 lbs/acre), Imidan 70WP (2.0 lbs/acre), methoxychlor 50WP (2.0 lbs/acre), or Isomate GBM (400 dispensers/acre. Recommended post-bloom GBM sprays also include Penncap M (4 pt/acre) and Sevin 50WP (4 lbs/acre). With very high infestation levels, Imidan, methoxychlor, or Sevin may not provide adequate control. Be aware of this potential limitation and be prepared to step in with a more potent insecticide such as Guthion or Penncap-M if the GBM infestation is not managed with lower toxicity insecticides. Pheromone mating disruption (Isomate GBM) is a non-insecticidal alternative for GBM management. Mating disruption is not recommended in vineyard blocks smaller than 5 acres. Furthermore, because of the influx of mated females from vegetation surrounding the vineyard, some insecticide treatment may be required on the edge rows of blocks treated with pheromone dispensers. The interested reader is encouraged to consult with Dr. Doug Pfeiffer (540-231-4183) for more information on pheromone mating disruption.

II. Plant Tissue Analysis

Periodic soil testing is useful to monitor soil pH and assess relative availability of plant nutrients; however, plant tissue analysis is more meaningful to determine what the vine has actually absorbed from the soil. In practice, the grower collects a specific tissue sample from vines and submits the sample to a lab for analysis. The lab will analyze the sample and provide a printout of the actual concentrations of mineral elements that were in the tissue. The diagnostic sample concentrations are compared to standard concentrations associated with nutrient adequacy. On the basis of that comparison, the lab can indicate whether your vines are at deficient, adequate, or surplus levels for each of the tested elements. Tissue analysis is ideally used in combination with a visual assessment of vine growth, which is particularly important when determining the vine's nitrogen needs.

When to sample: Collect samples at full-bloom for routine nutrient assessment. Non-routine "trouble-shooting" can be done throughout the season to help identify possible nutrient deficiency symptoms that appear on foliage. For trouble-shooting, collect paired samples of leaf petioles from symptomatic leaves as well as from non-symptomatic leaves of a similar age or shoot position. Label the samples accordingly.

What to sample: Collect 100 petioles per sample (collect 150 if the petioles are less than 2 inches long). The petioles are the slender stems connecting the leaf blade to the shoot. It is important to remove the leaf blade from the petiole before submitting the sample. Collect the petioles from leaves located opposite the lowest fruit cluster on well exposed shoots. Collect the petioles into a labeled, paper bag and allow to dry before mailing. Sample varieties separately. Divide a large vineyard into sub-samples if there are obvious differences in growth within the vineyard. Label the samples as grape petioles and include a five or six character code, such as 'CAB93' (for Cabernet, planted 1993), to identify the sample. Include your name and address with each sample.

Where to send samples: Several regional labs offer tissue analysis for a fee of $18 to $21 per sample. All of these labs use comparable analytical techniques and two identical samples sent to two different labs will typically yield comparable data. Differences exist, however, in terms of the standards used for interpreting the results and in corresponding fertilizer recommendations. To avoid some confusion, I've made arrangements with the Penn State University lab to have analytical data copied directly to me. I will then provide an interpretation based on the information you supplied with the sample. Penn State's out-of-state service fee is $18.00 per year for the 1998 season. Call my office (540-869-2560 extn 20 or 23) and ask to have one or more Penn State tissue analysis kits sent to you.

Interpretation and fertilizer recommendations: If you'd like me to provide fertilizer recommendations, send a photocopy of the analysis results to me at Winchester (please do not FAX the report), or use the Penn State sampling kit described above. I will provide recommendations based on sampling procedures outlined above, and based on the sufficiency standards listed in the Mid-Atlantic Winegrape Grower's Guide.

Agricultural Analytical Services
The Pennsylvania State University
University Park, PA
(814) 863-6124

III. Vineyard Suitability Maps:

Recently, we have used a Geographic Information System (GIS) approach to delineate regions of Virginia that may have greater or lesser viticulture potential from physical and climatological bases. Composite maps, generated on a county basis, were produced from a series of physical, digitized databases. The individual databases included land-use classification (e.g., forest, agriculture, urban, etc.), slope (percent), aspect (north, east, etc. facing), and elevation. The digitized data were available in 30 m² resolution. This means that the highest resolution we can attain is about 100 feet. Each of the various physical features was given a scaled, numerical classification based upon experience. The individual site features were then combined to produce a "Viticulture Suitability Ranking" in the final, composite image. The composite image is based on a 0 to 100 score, 100 being potentially most suitable for a vineyard.

The individual features do not contribute equally to the composite score. Elevation and land use each contribute up to 35 points, slope contributes up to 20 points, and aspect, the least important above-ground feature, contributes a maximum of 10 points. Again, the numerical grading of each site feature was based on experience. In addition to site physical data, Mr. Boyer also plotted the occurrence of -8° F events in the last 30 years. Smoothed frequency data were generated from historical weather observations from up to 60 National Weather Service reporting stations throughout the state. A -8° F event was used because most of the [Vitis vinifera] varieties in Virginia will sustain some level of winter cold injury at or below this temperature threshold, even under the best of acclimating conditions.

What the maps can and can not do: The composite vineyard suitability maps include primary road system outlines to orient the viewer to reference points within a particular county. However, the maps are not intended to serve as a roadmap to specific sites. Rather, we consider the maps useful only as a general indicator of areas or regions of a particular county that may have greater or lesser potential for commercial grape production. The maps should be used in concert with other resources such as our site selection bulletin (VCE publication #463-016). Ultimately, vineyard site selection must involve a considerable amount of foot work to ensure that the intended site meets the criteria deemed essential for a good site.

Currently we have 46 counties available for distribution. An order form can be obtained by contacting Dr. Tony Wolf at 540-869-2560, extn 20.

IV. Publication of Interest:

V. Vangard, a New Fungicide for Botrytis:

EPA recently approved the registration of Vangard (Novartis Crop Protection, Inc., common name: cyprodinil) for use on grape, apple, peach, and several other fruit crops. The review was completed under the fast track for reduced-risk pesticides. Vangard represents a new chemical group; no other fungicide with similar activity is currently registered in the USA. For grapes, the only target disease on the label is Botrytis bunch rot, where it is expected to be at least as good or better than Rovral, but partial activity against black rot and powdery mildew has been reported in some tests. Published studies also mention activity against ripe rot, aspergillus rot, and sour rot, but it is unclear to what extent the organisms causing "sour rot" or nonspecific rots in Virginia would be affected.

Vangard may be used from early bloom until 7 days before harvest at a rate of 10 oz/acre. The maximum amount per acre per season is 20 oz, or two applications. Rates may be reduced to 5 oz per application, but only if the material is mixed with another anti-Botrytis fungicide (e.g., Rovral at 16 oz/A), and the two-limit spray should still be observed (Dr. David Laird, Novartis, personal communication). Benlate should be considered as a mixing partner only if the Botrytis strains present are known to be Benlate-sensitive (which cannot be easily determined in the field). We don't know how well captan will perform as a mixing partner: if used, it should be applied at the full rate.

The main reason for the limitation on the amount of Vangard used is the risk for resistance development in Botrytis. Botrytis strains with reduced sensitivity did develop at a trial site in Switzerland where Vangard was applied 2-4 times per season for 8 years, and disease control was compromised. In long-term monitoring plots where applications were limited to two, only a few resistant strains were detected and no increase in their number was observed. Vangard resistance is different from and unrelated to Benlate resistance and Rovral resistance. Because of the resistance risk, Swiss regulatory authorities have limited Vangard to one application per season if used by itself, or two per season if mixed with another anti-Botrytis fungicide.

For best disease control, thorough coverage of the clusters is required; an application volume of at least 100 gal/A is recommended (label). Vangard penetrates slowly into plant tissues which enhances its activity and reduces wash-off by rain. In grape berries, it is held mostly in the waxy surface layers, according to Novartis's Dr. David Laird. It has fairly low toxicity to mammals and other terrestrial organisms, but is toxic to aquatic organisms. It should be kept away from bodies of water (ponds, streams, etc.) and the label contains detailed instructions on doing so. Reentry interval is 12 hours.

With proper resistance management and avoidance of over-use, Vangard is expected to be a valuable addition to our disease control arsenal. The Vangard label may be downloaded from http://www.cp.us.novartis.com/

VI. Frost Protection: Part II:

In the previous issue, frost protection methods used in Virginia vineyards were discussed. Other techniques and systems have been attempted in other regions with different degrees of success. First, let me remind you of criteria growers need to think about in selecting one frost protection method over another. In selecting a system to modify cold air temperatures that may occur in a vineyard, a grower must consider the prevailing climatic conditions, which take place during the cold protection season. Temperatures and expected duration, occurrence and strength of inversions, soil conditions and temperatures, wind speed and directions, cloud cover, dew point temperatures, critical bud temperatures, land contours, and cultural practices must all be evaluated. The following are methods of frost protection currently used in other parts of the country with their respective advantages and disadvantages:

Heaters: Heating has been employed for centuries (perhaps millennia by Romans to protect grapes!) as a method of freeze protection, and is still widely used throughout the world. Heating provides freeze protection by raising air temperature in the vineyard through radiant and convective heat transfer from the heaters directly to plant surfaces. Heaters are designed to burn fuels such as propane or petroleum. The disadvantages of heaters are high fuel cost, operation logistics, energy-inefficiency (only 10% of the energy is captured by plants), and environment concerns (air pollution). Nowadays, heaters are always used in conjunction with wind machines. This combination provides savings in fuel use (up to 90%), and increase in overall efficiency of both components.

Overhead-sprinklers: The principle is based on the continual freezing of applied water during a frost event. When applied, water freezes and releases heat (heat of fusion, see definition below) keeping the temperature of an ice-water mixture at about 32° F. By constantly rewetting the surfaces of the grapevine's shoots, it is possible to maintain a protective film of ice-water at 32° F, which is not injurious. The advantages of this method are that it does not rely on inversion like all other methods; the initial investment and operating costs per acre are cheaper than that of wind machines and heaters; overhead sprinklers do not require extensive labor to operate; they are clean and quiet in operation; and do not use large amounts of fuel. The disadvantages include the very large amounts of water required to cover a vineyard; over-watering may cause water-logging of heavy soils (common in Virginia) and nutrient leaching; application rate is extremely crucial and if not adequate crop loss would be more severe than without any protection; due to design and water pressure requirements, growers usually install irrigation and frost protection systems separately which add to the cost. This system is used in many California vineyards.

Evaporative cooling: like the previous system, evaporative cooling is based on the physical properties of water. When water evaporates (liquid to gas, see definition below), it absorbs or extracts heat and thus cools the surrounding environment (same principle used to cool greenhouses with swamp coolers). It has been demonstrated that during dormancy and when grapevines are maintained cool by sprinklers, buds break at a later date than normal; thus reducing the chance of frost injury. This method is often used in regions with warm winters to prevent early bud dehardening. It is also considered as a preventative or passive protection method since the sprinkler system is turned on well before a spring frost event. Although this method has been successful in delaying bud break of grapevines, evidence of protecting crop from frost injury is uncertain.

Chemical application: the use of chemicals is an attractive method because of the low cost and ease of application. Hundreds of chemical products such as growth regulators, anti-transpirants, oils and cryoprotectants have been used in order to increase cold hardiness and/or delay bud break of horticultural crops. These chemicals have been claimed to have the potential to provide freeze protection and prevent crop damage by unknown modes of action. However, inconsistent results over the last five decades have precluded the widespread use of chemical frost protection; and growers should be cautious about believing the promotional claims of these materials. During my graduate studies, I have applied a mixture of sugar and alginate (seaweed) on grapevine buds and canes few weeks before bud break. This has resulted in a gain of few degrees in freeze resistance and a delay in bud break by an average of 10 days for Chardonnay and other varieties. Although the results are promising, the cost of the material and the mode of application are limitations of this method especially in large vineyards. Also, when heavy rains follow the application, the product is washed off and becomes ineffective unless reapplied.

The following are basic descriptions of frost protection terms and physical concepts that are used in the previous and current issue.

Advective Freeze: Occurs when subfreezing temperatures from an arctic or polar air mass moves into an area displacing warmer air that was present and consequently cools the vegetation and earth-bound objects. There is very little which can be done to protect against advective freezes.

Radiation Frost: Occurs when clear skies and calm winds allow an inversion to develop. Subfreezing temperatures result from the radiant heat loss from vegetation and earth-bound objects to the sky. Radiation frosts are more common and usually occur in spring. Almost all frost protection methods available today are designed to protect against radiation frost.

Advective freeze	Radiation frost
Winds >5 mph	Calm winds (<5 mph)
Clouds may exist	Clear skies
Cold air mass 500-5000 ft deep	Cold air mass 30-200 ft deep
No inversion exists	Inversion develops
No frost forms	Two types: hoar (white) and black
No cold air drainage	Cold air drainage occurs
Protection success limited	Successful frost protection likely

Radiant heat: is movement of heat energy from one object to another without the need for a connecting medium. For example, the heat that we feel when we are exposed to sunlight or when we stand by a burning fireplace is radiant heat.

Convective heat: is the transfer of heat by movement of liquids or gases (e.g. air). For example, heat is transferred by convection from a furnace that warms the air and then moves it by a fan to different rooms in a house. Conduction: is the transfer of heat within a body or from one body or fluid in direct contact with another. For example, when one end of a metal rod is warmed, heat is transfered by conduction to the other end.

Latent heat transfer: is the movement of water that carries latent heat and releases it to the surroundings when condensing, cooling, or freezing. Similarly, water removes heat from the surroundings when it melts, warms, or evaporates.

Dew point temperature: the temperature at which condensation of the water vapor in the air first occurs. In other words, it is the temperature at which relative humidity of the air equals 100%. For example, if air temperature is 40° F and the relative humidity is 100% then the dew point is 40° F; with lower relative humidities, dew points are also lower at a given temperature.

Selected References:
Dami I.E. 1997. Physiological Responses of Grapevines to Environmental Stresses. Dissertation.

Perry.1998. Basics of Frost and Freeze Protection for Horticultural Crops. HortTechnology 8:10-15

Rieger M. 1989. Freeze Protection for Horticultural Crops. Hort. Rev. 11:45-109.

VII. Crop Insurance for 1999 Virginia Grape Crop:

The written agreement is a proposed multi-peril crop insurance policy for the grower to consider for his or her 1999 crop. The grower is under no obligation to accept the coverage and would have until November 1998 to make a decision with regards to purchasing coverage for the 1999 crop. Interested growers should contact their local Farm Services Agency to determine which insurance companies are authorized by Risk Management Agency to prepare written agreements for grape coverage. In Winchester, for example, Steve Grant with Valley Farm Credit is one such insurance dealer. Some of the information which a grower would need to submit with the request for crop insurance coverage includes: (1) location map and Farm Service Agency aerial photograph of all blocks, (2) actual yields by block (five years of record required for vinifera varieties), and (3) copies of accurate pricing information (e.g., sales receipts for grapes).

VIII. Upcoming Meetings:

Where: Mica Ridge Vineyard, Unionville, PA
When: Thursday, 30 July 1998
Specifics: Program will commence at Stone Barn Restaurant in Unionville, PA at 9:00am and will feature Dr. Andrew Reynolds (Brock University, Ontario), Dr. Barbara Goulart (Penn State), and Dr. Tony Wolf (VA Tech). Discussions will focus on vineyard characteristics associated with premium wines. Following lunch, Mica Ridge Vineyard's manager, Ike Kerschner, will conduct a tour and description of vineyard where one can see mature vines trained to TK2T, Scott Henry, and Smart-Dyson training systems.
Registration: $40 per person for SEGA members ($50 for non-members) if registering before 15 July; registration increases to $50 and $60, respectively, after 15 July.
Information and directions: Call Ike Kerschner (610-486-6235) or Fred Maki (610-286-7754). Tony Wolf will have a limited amount of van space to transport interested persons (540-869-2560).

Where: Jefferson Vineyards, Charlottesville, VA
When: Saturday, 1 August 1998
Specifics: Program is currently in planning stages. Speakers will include Dr. Andrew Reynolds (Brock University, Ontario) and Dr. Tony Wolf (Virginia Tech). We plan to host an equipment demonstration similar to that arranged at Prince Michel Vineyards last June.
Information: Specific information on this meeting will appear in the July-August newsletter and in the electronic VCE-Grapenews. For now, mark your calendar.

"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

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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