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Virginia Cooperative Extension -
 Knowledge for the CommonWealth

Viticulture Notes

Vol. 14 No.5, September - October, 1999

Dr. Tony K. Wolf, Viticulture Extension Specialist

Table of Contents

I. Current situation

II. Grape prices

III. Upcoming meeting

I. Current Situation

Pre-harvest crop conditions in Virginia were among the best in memory. True, the extended drought in most parts of the state were slowing grape ripening with water-stressed vines, especially those in over-crop conditions, and vineyards on droughty soils that did not have irrigation. If there was a season that illustrated the value of irrigation, it was 1999 (see related story). The long, dry summer abruptly ended in early September with back-to-back visits by Hurricanes Dennis and Floyd. Hurricane Dennis first worked up the coast and out to sea, only to return and hammer the SE part of state and dump up to eight inches of rain over the Labor Day weekend. Hurricane Floyd moved quickly through the state on 17 September after causing historic flooding in eastern NC. At Winchester, we measured 12.7 inches of rain from April through August, approximately 6 inches below the average for that period. By contrast, we received 8.7 inches of rain during September (Winchester averages 3.2 inches of rain in September). The Winchester area had more rain during the summer, and less during September than many areas of the state, so we can't complain. Some less fortunate producers were forced to pick early, in advance of the rains, and ended with relatively clean fruit, if not fully ripe - lots of Chardonnay brought in around 20.5 to 21.5°Brix. Riesling was Riesling; it does not graciously accept lots of rain near harvest. There is still a lot of Cabernet hanging at this point, and it seems to be holding up reasonably well to the rain. But with daytime highs in the sixties and seventies, we are starting to run out of heat to mature it.

Some observations of harvest: (1) Total grape production will likely set a state high record, by virtue of larger crops with mature vineyards, as well as new vineyards coming on line. The Department of Agriculture and Consumer Service's Agricultural Statistics Service will again conduct a census of grape acreage and production next month. On that note, if you do not receive a grape acreage/grape production survey from the VA Agricultural Statistics Service by 30 November 1999, please contact their office at 804-771-2493. This is the only means we have of knowing what Virginia's grape acreage and production is. (2) Canopy management still works! The best fruit that I saw this fall, even after 5 or more inches of rain, was found in canopies that were relatively sparse, and that had good ventilation. Leaf-pulled Chardonnay had less Botrytis bunch rot than did Chardonnay buried deep in shaded canopy interiors. (3) Overcropping compounded drought problems and led to slow fruit maturation in some vineyards.

Question from the field: Should I "hill-up" my vines this fall for winter injury avoidance? This question surfaces annually, and the following answer was formerly provided in the Sept-Oct 1997 VN. Mounding or "hilling" of soil over graft unions of grafted, cold-tender varieties is one means of avoiding potential vine loss due to cold injury. In practice, soil is ploughed up against the trunks of vines with a tractor-mounted blade in the fall, before the advent of severe cold weather. The soil must be mounded high enough to protect a 6- to 12-inch portion of the vines' trunks. This soil conducts heat from the earth and insulates the covered portion of the trunks. In the event of catastrophic cold damage to the above-ground structure, the vine can be retrained using buds that had been protected by the layer of soil. The extreme example of this practice is the complete burial of vines practiced in very harsh environments. The fall hilling operation is followed in the spring by a "de-hilling" of the trunks, ostensibly to prevent scion rooting. The "scion" (pronounced "sign") is the horticultural term applied to the upper, or fruiting portion of a rootstock/scion combination (e.g., the Chardonnay part of a grafted, Chardonnay vine). What are the pros and cons of hilling (and dehilling)? Benefits include the protection offered in the event of extreme weather. Vinifera trunks, depending upon variety and time of season, can be injured by temperatures above 0°F, although injury is more common at temperatures below -10°F. Symptoms of cold injury can include poor shoot growth in the following season, development of crown gall, and death and splitting of affected trunks. Another possible benefit of hilling and dehilling is the destruction of weeds, overwintering insect pests, and reduction of certain disease inoculum caused by the mechanical cultivation. The costs of hilling and dehilling must also be considered. First is the capital cost of equipment and annual operating costs. Grape hoes can cost from $1,500 to over $5,000, while operating (machinery and labor) costs run from $20 to $25 per acre. Annual hilling and dehilling has led to severe soil erosion problems in some older vineyards. The soil in some of these vineyards has eroded many inches below the graft union and the practice of hilling is no longer effective. Furthermore, the loss of top soil is associated with reduced vine vigor, lack of trellis fill, and unprofitable crop yields. One means of reducing soil erosion on hilly sites (aside from keeping rows oriented perpendicular to the prevailing slope) is to leave undisturbed soil "dams" every 30 feet or so along the row. Simply pull the plow out of the soil at regular intervals to avoid creating a continuous channel or trench down a row. Another potential negative consequence of hilling and dehilling is the mechanical damage to vines. This can range from the overt collisions with trunks to the less obvious damage to roots near the soil surface. An additional negative is the cost of equipment ($1K to $4K) and operational cost of hilling and dehilling. Each grower must weigh the pros and cons of hilling and decide for one's self if this is a justifiable practice. Your own experience will determine whether hilling of graft unions is good insurance or a wasteful practice. A grower may conclude, after 5 to 10 years without trunk cold injury, that the "insurance" is unnecessary. The most recent severe cold event in Virginia (February 1996) would have been much more destructive had it not been for the snow cover that blanketed most of the Piedmont vineyards. The snow did essentially the same thing that our mounding of soil did - it provided a thermal continuum between the earth and vine trunks. What about sawdust, grow tubes, white paint, etc? Sawdust and finely milled bark mulch would probably work, provided it retained sufficient moisture to conduct heat; however, the mechanics and cost of application must also be considered. Anecdotally, we have noticed that the use of organic mulches may lead to increased climbing cut-worm populations in the subsequent spring. Grow tubes provide no cold protection, and can even cause increased winter injury. Painting of trunks with white paint is intended to reflect sunlight and limit radiational warming of the trunks. I am unaware of this practice being used successfully in Virginia vineyards. Nurserymen generally recommend the hilling-up of young vines for the first few years in the vineyard, even with excellent sites. The occasional observation that trunks of young vines sustain greater cold injury than do the trunks of older, established vines probably relates more to cropping stress on the young vines, rather than direct age effects on cold hardiness. I do, however, recommend that you follow the advice of your grapevine supplier with respect to hilling of graft unions. It's usually easier to obtain recompense from a nursery for failed vines if you've followed the nursery's planting and care recommendations. Be careful when mounding soil against young vines. The young trunks and graft unions may not withstand the impact of heavy clods of soil. For first-year vines, we find that it's safer to turn the soil near the trunk with a grape-hoe and then use a hand-hoe to move the loosened soil against the trunks.

Some growers have found that hilling does not guarantee vine renewal in the event of trunk injury. Repeated episodes of vine kill generally dictate the need for more radical measures. If the problem is confined to a small area of the vineyard, study the area to see if it's associated with poor soil conditions, lower topography, or other features that may be contributing to vine failure. It may be best to remove these "problem" areas from production if there are site-specific limitations.

Timing: Fall hilling can be done at any time before the ground freezes, typically after harvest and before mid-December in VA. De-hilling in the late-winter or spring occurs after the threat of extreme weather, and before the application of pre-emergence herbicides; the period from late-February until mid-March is convenient.

The following is a non-exhaustive listing of vendors of "grape hoes" or other implements for hilling and dehilling of grapevines.

Grape hoe suppliers*:
The Green Hoe Co., Inc. (NY) Green grape hoe
716-792-9433

Weed Badger (ND) Hoes and tillers
1-800-437-3392

The Grower's Supply Center (MD)
Retailers of Clemens-Radius grape hoes and tillers
410-931-3111 or 410-333-2856

* The listing of commercial products is for the reader's convenience and does not constitute endorsement by Virginia Cooperative Extension or Virginia Tech, nor does it imply discrimination against similar products not mentioned

Thanks: Appreciation is extended to the Virginia Vineyards Association for two recent grant-in-aid donations to the viticulture effort here. A gift of $3,000 was provided to me for the purchase of a new lap-top computer. A second gift of $1,000 was made to partially cover the printing cost ($4,800) of our new "Commercial Grape Varieties for Virginia" extension publication. The added printing cost reflects our desire to include color plates of most of the recommended varieties. The extension publication is at the print shop, and should be available ($10/copy) from the distribution center in Blacksburg by mid- to late-October. More details in the November-December VN.

Irrigation observations: Ten years ago, drip irrigation systems were not commonly installed in new Virginia vineyards. Experience, our exhortations, and time have altered that situation to the point that the majority of vineyards established in 1999 were installed with irrigation. Our positive recommendations for irrigation are based on historical climate patterns of recurring drought (see VN Jan-Feb., 1999), the experience of Virginia vineyardists who have used irrigation, the relative cost of irrigation vs. the crop value, and research data generated in other states. A hurdle of sorts has been cleared, but questions remain. The most common, perhaps is how much water should be applied, and how frequently? Given the time of season, I'll provide a few comments in this newsletter, and pick up on this again in late-winter.

Irrigation scheduling in Virginia is admittedly not as sophisticated as in regions where irrigation has long been an integral part of grape production. Determining how much water to apply is based on a combination of two or more methods. Volume can be based on plant indices, soil moisture indices, or on the use of input-loss budgets. Plant indices are visual clues as to the degree or severity of plant stress. These range from slowed shoot growth, increased canopy temperature, and tendril abscission (slight stress) to defoliation (severe stress). Soil based indices are measures of available soil moisture. Soil moisture can be visually judged, or measured with tensiometers ("irrometers"), gypsum blocks, or neutron-emitting probes. A limitation with all soil moisture measurements is that the available soil moisture varies with soil physical properties. The more variable the soil, the more instrumentation must be arrayed in your vineyard to have an accurate picture of the vineyard's variability. The budgetary method requires a careful monitoring of vineyard water input (rainfall and irrigation), and is compared against expected moisture losses from crops, ground cover, gravity, and evaporation. Generally, the use of a combination of these measures, coupled with knowledge of vineyard soil properties, will provide sufficient information on how well the vines are supplied with moisture.

The amount of water that vines use varies with evaporative conditions (temperature, humidity and wind) and canopy leaf area, which varies with vine age and training system. Big vines and large canopies transpire large amounts of water. Dr. Alan Lakso and his co-horts at Cornell University produced data showing that mature Concord vines grown in western NY use from 30 to 40 gallons of water per week in July. That translates to roughly 3 acre-inches (27,154 gallons per acre-inch of water) of water per month. Adding the evapotranspiration loss, the vineyard loses up to 5.5 acre-inches of water per month. Given our higher temperatures in VA, our water loss is probably even greater for a comparable vine size/density scenario. How much water vines use, and how much water they need to optimally ripen crops are not necessarily equal volumes. Slight to moderate water stress in mid- to late-summer may be desirable to retard vegetative growth and limit berry volume. However, when soil moisture is insufficient to maintain leaf hydration, photosynthesis is impaired and leaves slow or cease exporting carbohydrates. Leaves that are warm to the touch and drooping or "flagging" are not transpiring and are not exporting sugar. The effect of prolonged stress of this severity has many implications, but the negative impact on the size and quality of the crop is relatively rapid. We do not know how much water is optimal for our cropping conditions in VA. Growers with copious amounts of irrigation water have used as much as 10 gallons of water per week. Given Dr. Lakso's calculations, that's probably a minimal amount in the absence of any background precipitation. One-year-old vines, because of their smaller leaf area, may function normally with half that amount. Again, monitoring plant and soil indicators of water status during the season will help decide whether the amount of irrigation water is sufficient.

To highlight a couple of points, I've included some data in Table 1 from an herbicide experiment that we conducted this season in 2-year-old Chardonnay vines. Herbicide treatments were a post-emergence material, compared with two pre-emergent herbicides ("A" and "B") used in combination with the post-emergence herbicide (actual brand names are irrelevant here). Herbicides were compared against an untreated control. All treatments received about 5 gallons of water per vine per week, although the irrigation was inoperative for a 2-week period in mid-summer. Weed competition in the control plots (note greater ground covered by weeds) limited the effectiveness of applied irrigation, resulting in slowed shoot growth, smaller berry size, and decreased crop. In addition, soluble solids concentration was somewhat lower. In reality, all treatments probably would have benefited from more water during the growing season. But the prime point is that the irrigation applied could not compensate for the weed competition in the control plots. The response of the control plots could be roughly compared to that seen with unirrigated vineyards of the same age in VA. In addition to the measured parameter of shoot elongation, all vines had some evidence of elevated leaf temperatures when assessed in July and August. Control vines also showed some evidence of leaf wilting on hot days.

As promised, an expanded discussion of this topic will appear in early 2000.

Table 1. Crop yield components and fruit chemistry at harvest (14 September 1999) among control and herbicide treatments of two-year-old, irrigated Chardonnay grapevines.

Herbicide
treatment

% ground covered by weeds (8/14)

Ave. shoot growth length/day (cm)

Clusters/
vine

Crop/
vine (lbs)

Berry
wt. (g)

°Brix

Control

80 a

0.24 c

5.1 a

1.3 b

1.06 b

21.8 a

Post-emergent

68 ab

0.81 b

8.5 a

3.3 a

1.38 a

22.4 a

Pre-emergent "A"
+ post-emergent

59 b

0.96 ab

8.8 a

2.9 a 1.47 a

22.2 a

Pre-emergent "B"
+ post-emergent

14 c

0.83 b

9.4 a

3.5 a 1.46 a

22.6 a

Means, within columns, followed by the same letter are not significantly different at P 0.05.

Return to Table of Contents


II. GRAPE PRICES:

The need for additional Virginia-grown grapes ranges from 1,000 to 1,200 tons per year based on 1996 and 1998 surveys of Virginia wineries. That need has generated considerable interest among those seeking alternative agricultural pursuit(s) and others with an interest in grape production. One of the stumbling blocks for those who have recently planted grapevines, as well as those exploring the potential returns, has been the lack of a comprehensive tabulation of prices being paid for grapes. Factual pricing information is necessary in any business plan. In particular, new growers benefit from the ability to compare how a winery contract offer compares to the industry average.

The compilation of industry "average" prices bears some risk. Most wineries use a sliding scale of payment wherein the price of grapes is adjusted for grape quality; grape prices vary by variety, and clones in some cases; and poor responses to this kind of survey can lead to misleading conclusions. Acknowledging these and other limitations, a comprehensive tally of grape prices would still be of benefit to those who are exploring commercial grape production. Accordingly, we sent a price survey questionnaire to 48 Virginia wineries in late-July seeking input on grape prices paid in 1998 as well as anticipated prices for 1999. Our appreciation is extended to all who participated. The results of the 21 wineries that responded are tallied in Table 2 (this information was previously sent to subscribers of my electronic newsletter).

The data are not presented in an attempt to establish a price for grapes; rather, they merely report prices that are being paid. The price range for a given variety reflects grape quality, as well as long-term relationships between some growers and their contracting wineries.

Table 2. Responses to Virginia winery questionnaire (7/99) asking winery owners what they paid for grapes in 1998, and what they anticipated paying in 1999.

Prices paid in 1998
($/ton)


 Prices anticipated in 1999
($/ton)


Variety RangeAverageNumber
of
responses
RangeAverageNumber of responses
Chardonnay1100-14701321141200-1500134812
Cabernet Sauvignon1100-14501286121150-1500130212
Cabernet Franc1200-1450135171250-145013757
Gewurztraminer140014001N/AN/AN/A
Merlot1200-1450132561200-145013256
Riesling900-11009805900-120010673
Sauvignon Blanc1100-1450122541100-130011833
Pinot Gris115011501120012001
Viognier1300-2000165021350-200016752
Pinot Meunier110011001115011501
Pinot Noir110011001110011001
Touriga200020001200020001
Petit Verdot 140014001150015001
Vidal550-70064210600-7006176
Seyval550-6505956550-6255955
Chambourcin550-60058336006003
Cayuga White60060016006001
Other (?)62562516256251
Norton100010001100010001
Concord5005002 5005002

Return to Table of Contents


III. UPCOMING MEETING:

When: January 10 12, 2000
What: The combined Virginia State Horticultural Society (VSHS) and Virginia Vineyards Association (VVA) technical program.
Where: Ft. Magruder Inn, Williamsburg, VA
Program: The VSHS/VVA meeting will be similar to that held in Roanoke last January. Program details are still being resolved; however, the preliminary program will include the following components.
Details: In November-December newsletter

Return to Table of Contents

"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: 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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