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Virginia Cooperative Extension -
 Knowledge for the CommonWealth

Viticulture Notes

Volume 14, Number 1 -- March-April 1998

Dr. Tony K. Wolf, Viticulture Extension Specialist

Table of Contents

I. Current situation

II. Frost protection

III. Early season pest management

IV. Upcoming events

I. Current Situation:

Originally I had planned to comment on the cold weather of 10-13 March and to indicate that we appeared to squeak by without cold injury. That still seems to be the case, but with the warm (hot) weather of this last week of March, the ability of buds to supercool, and their associated cold hardiness, has been rapidly lost. While we had been on track for a somewhat normal bud break date, the recent temperatures in the eighties have advanced that stage. In fact, unless temperatures cool, we appear to be close to a three-week advance in bud break. Dr. Imed Dami reviews frost protection strategies on page 2.

I call your attention once more to the 20 April Pest Management Seminar in Charlottesville. If you plan to attend, please register by 10 April to avoid increased registration fees.

Virginia grape acreage and production, 1997: Virginia's commercial grape acreage and grape production data are annually surveyed by the Virginia Agricultural Statistics Service of the Virginia Department of Agriculture and Consumer Services (VDACS). Acreage and crop production data for 1997 were recently released and are shown in condensed form in Table 1. Total grape production in 1997 approximated 3,000 tons, up 68% from the short 1996 crop, but still below the 3,200 tons produced in 1995. Many vineyards, especially those of the Piedmont region, are still recovering from significant damage caused by a February 1996 freeze. Chardonnay comprises 40% of Virginia's grape acreage and retains popularity with new acreage. Total acreage increased by over 100 acres and was reported close to 1600 in 1997. In addition to Chardonnay, Cabernet Franc, Cabernet Sauvignon, and an assortment of other white and red vinifera saw significant increases in 1997 acreage. The VDACS report also provided a breakdown of regions and counties where grapes are produced. According to the report, Virginia is currently ranked 11th in terms of bearing grape acreage (all grapes). Virginia counties with the greatest grape acreage in 1997 were Orange (250), Fauquier (230), and Albemarle (164). You may obtain a complete report by writing the VA Agricultural Statistics Service, VDACS, PO Box 1659, Richmond, VA 23218-1659. Also, if you grow grapes for commercial sale (one or more acres), and you did not receive a grape acreage/production survey during the 1997-98 winter, you should contact the Agricultural Statistics office so that your data can be included in future years.

Viticulture training programs: As Virginia's grape and wine industry continues to expand, a recurring question arises about the availability of trained vineyardists to serve the industry. Individuals with both training and vineyard experience are in short supply in Virginia. One proposal to remedy the shortage of trained individuals is to offer training programs through community colleges or continuing education programs such as Virginia Cooperative Extension. Developing a course curriculum and providing the instructional support, however, requires a major commitment. To succeed, there must be demonstrated interest on the part of prospective students, and interest within the industry to hire students who complete the course. An alternative, and certainly less expensive approach, is to offer a multi-day program that provides in-depth training without the collegiate structure. I'm interested in hearing from prospective students as well as industry members about the potential for either route of vineyardist training: option "A" being the formal multi-week course under the sponsorship of a community college, Virginia Tech, or Virginia Cooperative Extension; option "B" being a multi-day (3 to 4 days, 8 hours per day) program offered in a less formal setting. Please let me know, by way of a short letter or e-mail message, whether you're interested in enrolling as a student in either training option, or if you're interested in hiring a student who has completed the training. The latter also applies to readers who are aspiring to commercially grow grapes but are reluctant to do so for lack of qualified employee help.

Table 1. Virginia's 1996 and 1997 grape production and grape acreage by principal variety. Data obtained from Virginia Agricultural Statistics Service, VA Dept. Agriculture and Consumer Services.

Tons producedAcreage*
Variety1996199719961997
Vinifera
Chardonnay404.5837.0413.1439.2
Cabernet Sauvignon238.5357.7192.3210.2
Cabernet Franc105.6190.081.3102.6
Gewurztraminer4.419.317.615.8
Merlot70.5124.282.5 93.4
Pinot Noir24.843.632.530.4
Sauvignon Blanc9.422.014.616.9
Riesling99.4225.0134.0126.8
Other white vinifera48.9145.985.0100.4
Other red vinifera32.4134.541.064.0
Hybrid
Seyval200.0206.287.4 83.3
Vidal Blanc213.5285.093.0108.7
Chambourcin52.463.041.641.6
Other white hybrids37.241.632.529.8
Other red hybrids25.757.533.635.5
American
Concord106.5103.128.128.5
Seedless table (all)4.44.36.33.4
Other red/black American37.673.4 13.417.0
Other white American47.824.416.612.6
State total1,763.52,957.71,450.81,565.4

* Bearing and non-bearing, combined. Column sums may not equate with column totals due to omission of individual operation data; omitted data are, however, included in state totals.

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II. Frost protection

(contributed by Dr. Imed Dami, Viticulture Extension Assistant, VA Tech):

The winter of 1997-1998 in Virginia, like much of the country, was one of the warmest on record. The good news is that grapevines seem to have escaped winter cold injury. However, spring is here early, and with spring comes the potential for spring frost. Bud break normally occurs from late-March through mid-May, depending on the variety and vineyard location. The new green shoots are very sensitive to temperatures below 32° F. The specific temperature that may cause injury to buds or shoots varies with the stage of bud development and upon meteorological conditions such as the dewpoint. Although a spring frost should not kill established vines, reduction in crop can be significant.

In spring, bud or shoot injury typically occurs during a radiational frost event. Clear skies, calm winds (less than 5 mph), and temperature inversions characterize a radiational frost. During the day, the sun warms the soil and solid objects, e.g. grapevines. The heat captured by the soil and grapevines is lost on a clear night to the atmosphere by radiational cooling. Thus, temperatures at the ground level keep dropping at night and reach a low just before sunrise. This creates a layer of warm air floating over a layer of cold air next to the ground surface. In other words, air is warmer rather than cooler with increasing height. This phenomenon is called temperature inversion. Frost protection using wind machines (discussed below) takes advantage of this phenomenon.

One or more Virginia vineyards experience crop reduction due to spring frost almost every season. Some of the problems are due to inappropriate site selection. But our continental climate with significant and rapid shifts in air temperature also increases the risk of spring frost. The following summarizes the techniques and methods used for frost protection. First, almost all frost protection methods aim to keep the plant tissues above a critical, lethal temperature. Second, growers should realize that there is no perfect method for frost protection (unless grapes are grown in a greenhouse!). Third, cost-effectiveness is usually the dominant factor that dictates whether frost protection can be practiced. In this issue, frost protection techniques and practices currently used in Virginia vineyards are discussed. The next Viticulture Notes issue will cover methods used elsewhere.

Site selection: Following centuries of research and practice we must admit that the most efficient frost protection rests with "location, location, location"; the best frost protection technique available today is good site selection. Under radiative frost conditions, low areas are much colder than hilltops due to the drainage of cold air. Because cold air is heavier than warm air, it flows downhill much like water. Thus low spots, or "frost pockets" where cold air would collect and settle should be avoided. Also, avoid low areas where cold air is trapped by natural topography, trees, or buildings that inhibit cold air drainage. More information is available on site selection in the references listed at the end of this discussion.

Wind machines and helicopters: Wind machines are basically large propellers that pull warmer air down from above their 40-foot towers, and mix it with cold air in the vineyard. Wind machines are only effective if there is an inversion of warm air above the vineyard. The difference between the air temperature at 5 feet and 40 or 50 feet above the ground is a common way to measure or describe a temperature inversion. The larger the difference, the stronger the inversion and the more potential for protecting vines. Temperature in the vineyard could be increased up to 50% of the temperature difference. For example, if there is a difference of 8F between the air temperature at 5 and 50 feet, you can get up to 4F temperature rise in the vineyard. One wind machine could affect an area of 8 to 12 acres, depending on the strength of the inversion and the performance of the wind machine. If several degrees of warming are required, an area of only 4 to 5 acres may be protected. If you are planning on installing a wind machine, you will need detailed information on inversions in your vineyard site. Temperature sensors should be mounted on a frost pole or tower to measure temperatures at different heights during springtime inversions. Wind machines are not very effective if the inversion strength is small (2F or less). Also they require calm winds to ensure safe mechanical fan operation. Helicopters, which use the same principle for frost protection as wind machines, have been effectively used in Virginia vineyards. Helicopters have the advantage over wind machines in eliminating the initial cost of installation, and growers pay for them only when they are needed. However, growers should weigh the initial and annual operating costs of these two systems in frost-prone areas.

Varietal choice: Grape varieties commonly grown in Virginia break bud over a span of 7 to 14 days: Chardonnay is one of the earliest to break bud, whereas Cabernet Sauvignon is one of the latest, about 10 days later. The span can be shortened or lengthened depending upon the particulars of the preceding and intervening temperatures. Nevertheless, varieties that break bud early should be planted in areas least susceptible to frost. I could not advocate planting any variety in a known frost pocket, but for a given vineyard, I would plant Vidal blanc (late budding and relatively cold hardy), for example, lower on a slope and reserve the higher ground for Chardonnay (early budding and relatively cold tender).

Cultural practices: A frequently asked question is: "Do grapevines lose hardiness if I prune early in the dormant season?" Research data suggest no significant effect of pruning time on cold hardiness of buds and canes of grapevines. The application of such findings is that growers may prune vines anytime during the dormant period. 'Double pruning', however, is often used in Virginia as a frost protection practice. On spur-pruned vines, canes are first cut back or "pre-pruned" to leave about 5 to 8 buds on each spur. The more distal buds on these long spurs break and begin growth first, whereas the buds towards the base of the spur are delayed. A second pruning is realized to leave the desired number of buds per spur. This practice can delay bud break by up to a week, but more labor is involved. Delaying pruning altogether until bud swell is not recommended because pulling pruned canes from the trellis would be apt to injure swollen buds, which become fragile and break off.

Planting cover crops between vine rows in Virginia vineyards is a common practice that is beneficial for various purposes, but not for frost protection. In fact, bare soils absorb more heat and thus are warmer than soils with a cover crop. To minimize this dilemma, cover crops should be kept short by mowing during the spring frost period to maximize heat absorption during the day.

Selected References:

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

Wolf T. 1989. Site Selection for Commercial Vineyards. VCE publication # 463-016.

Wolf T. and EB Poling. 1996. The Mid-Atlantic Winegrape Grower's Guide. NCCES publication # AG-535.

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III. Early season pest considerations:

The following pests are briefly reviewed with descriptions of currently registered materials for their management. The reader is reminded that pesticides registered for grape in Virginia are listed in the 1998 Virginia Cooperative Extension publication #456-017, "Pest Management Guide for Horticultural and Forest Crops." Other resources include the Grape Disease Compendium and the Mid-Atlantic Winegrape Growers Guide. Information on these references can be obtained through our office. See, also, the information on the Pest Management Workshop planned for 20 April (page 8).

A. Powdery mildew

Essentially all hybrid and vinifera wine grape varieties in Virginia are either moderately or highly susceptible to the powdery mildew (PM) fungus. Chardonnay is, perhaps, the most susceptible of the commonly grown varieties. Once PM is present in a vineyard, it is difficult to bring under control, and it can seriously affect grape and wine quality, as well as yields. Management requires a thorough understanding of the organism's biology, and a knowledge of effective management strategies. Primary PM infections result from inoculum that overwinters on the vine as cleistothecia. Cleistothecia release spores starting at about 10 inches of shoot growth through the post-bloom period. Primary infections require at least 0.1" of rain and temperatures above 50° F. All green tissues are susceptible to infection. Berries are susceptible until they attain about 8° Brix, and may be particularly susceptible at and shortly after fruit set. Primary infections soon produce the whitish lesions which give the disease its common name. Those lesions produce an abundance of conidial spores which are wind-blown to other susceptible tissue. Secondary infections by conidia do not require the presence of free moisture; however, high relative humidity favors disease development. Repeating cycles of infection, disease and conidial generation occur every 6 to 8 days at temperatures of 60 to 80° F. The rapid generation cycle accounts for PM's destructive, wildfire-like spread.

Control: Effective PM control starts with good canopy management to allow ventilation and permit pesticide penetration of the canopy. For most varieties, PM management will involve a season-long program of fungicides. These include the sterol-inhibiting (SI) compounds (Bayleton, Nova, Rubigan, and Procure), benomyl (Benlate), sulfur, or Abound. Copper has fair activity against powdery mildew, but should not be relied upon for PM control with highly susceptible varieties. Sulfur is relatively cheap and is highly effective, but has its limitations with sulfur-sensitive varieties or when air temperatures exceed 95° F. Bayleton, Nova, Rubigan, and Procure are highly effective PM fungicides but precautions must be taken to avoid the development of strains of PM that are resistant to those fungicides. Procure received EPA registration in 1995 and is very similar to Rubigan in terms of activity - good for powdery mildew but not for black rot. Procure is labeled at 4 to 8 oz/acre application rate and carries a 7-day pre-harvest interval. Regardless of which SI fungicide you choose to use, the SI fungicides should be alternated with sulfur in a season-long program. Do not apply the SI fungicides to sporulating PM-diseased vines without the addition of sulfur. Use the higher end of a recommended product rate per acre and do not exceed the label's recommended interval for repeat applications. PM outbreaks in Virginia have occasionally been observed when: dense canopies are sprayed with insufficient gallonage to penetrate canopy interiors; SI fungicides were used at lowest rate and excessively long intervals (21-days or more between consecutive applications); or when the spray program was suspended after harvest.

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B. Downy mildew

Downy mildew is favored by warm, wet weather. The fungus can affect all green tissues, but symptoms are usually first noticed on leaves.

Symptoms: The time from infection until the first visual symptoms varies from 4 to 12 days. Foliar symptoms initially appear on the leaf's upper surface as yellowish lesions. Soon thereafter, white, cottony or "downy" lesions will be observed on the corresponding lower side of the leaf. This downy growth is distinctive and should not be confused with the natural hairiness or pubescence found on the lower surface of some American and hybrid varieties. Evidence of downy mildew infections often first appears on young leaves of unprotected shoot tips, or on leaves hidden in dense vine canopies. Active downy mildew lesions produce additional spores which can cause repeating infections and disease cycles. Fruit infections lead to a direct loss of crop due to shelling of berries. As with most other common fungal diseases, a heavy infestation in one year can aggravate control the following season due to an increased abundance of inoculum.

Control: Significant downy mildew problems have been observed in Virginia vineyards in the post-bloom period, most frequently in late-summer. Measures to hasten drying of wetted foliage, such as maintaining a relatively thin or open canopy, will reduce downy mildew development. Acceptable control with most varieties, however, will depend upon fungicide application. Current chemical options for downy mildew include mancozeb, captan, Ridomil, copper-containing fungicides, and Abound. Mancozeb is a generic term for a several different products having ethylene bisdithiocarbamate (EBDC) chemistry. Examples include Penncozeb, Dithane F-45, and Manzate 200). All of the mancozeb products, and Ridomil, have a 66-day pre-harvest interval, during which time they may not be applied to bearing vines. Copper fungicides have the potential to burn susceptible varieties. This has generally not been a problem in Virginia with vinifera varieties, but some hybrids and American varieties are quite susceptible. First time copper users are strongly encouraged to spray a small, trial-sized area of the vineyard block and examine vines for up to a week for evidence of stippling or leaf browning. Use an alternate fungicide during the evaluation period, or if burning is observed. Prolonged wetting of copper-treated foliage is a contributing factor to copper injury. Thus, a copper trial in dry weather may not be a good predictor of burn potential. The potential for copper phytotoxicity is the reason why many, but not all, copper fungicide labels prescribe the addition of spray lime to the tank mix. Captan, too, has certain usage limitations and considerations. These include a maximum application of 24 pounds per acre, per year (50% WP formulation), and a 4-day restricted reentry period after each application.

Copper, Captan, and the mancozeb fungicides are all protective fungicides; they must be applied in advance of potential infection periods and they have no systemic activity. Ridomil, by contrast, combines both protective and eradicant qualities, and has locally systemic activity. What this means is that Ridomil applied before a rain will not be washed off once it's absorbed by the vine. Ridomil offers 14 to 21 days protection of treated foliage (it will not protect new growth that emerged after application). Ridomil also provides up to 4 days of post-infection action. That should not lull you into a false sense of security, but it does offer effective recourse if you enter a rainy period without a good protective spray, provided you can apply the Ridomil within 4 days of an infection period. There are currently three formulations of Ridomil registered for grape: Ridomil Gold Copper, Ridomil Gold MZ, and Ridomil MZ 72. It is my understanding that the manufacturer of Ridomil (Novartis) plans to focus only on Ridomil Gold formulations in the coming years; however, existing stocks of the MZ 72 can continue to be used. Rates and price per application vary somewhat depending upon formulation, but all carry a 66-day pre-harvest interval (PHI). There are seasonal limits on the per acre amount of Ridomil's active ingredient and on the amount of EBDC fungicide that can be applied, and the latter must be factored in with other applications of mancozeb. While all of the Ridomil formulations may be applied up to four times per season, my suggestion would be to try and limit Ridomil's use to no more than 2 applications per season, the first applied pre-bloom.

The introduction of Abound (see Viticulture Notes, Vol. 13, No.1 for a detailed discussion) means that control of downy can be integrated with control of black rot, powdery mildew, and phomopsis cane and leaf spot using a single material. Abound is not a cheap fungicide. One quoted price in the Winchester area was $250/gallon (your price may vary somewhat). The label application rate for Abound is 11.0 to 15.4 fluid ounces per acre ($21 to $29 per acre). A moderate rate (13 oz/acre) would cost $25.39/acre. By contrast, a tank mix of mancozeb (3 pounds/acre) and Nova (4 ounces/acre), using the same Winchester source of materials, would cost $21.58/acre per application.

Choice of fungicide is only one component of an effective downy mildew management program. Be certain that you have accurately calibrated your sprayer and that you are achieving good coverage of vine foliage and fruit. Use water-sensitive spray paper (available from your chemical supplier) to ensure that foliage is being uniformly wetted. Apply at least 50 gallons of spray material per acre pre-bloom and go to 100 gallons per acre in the post-bloom period.

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C. Phomopsis cane and leaf spot

Phomopsis is a troublesome, fungal pathogen that affects all major varieties grown in the mid-Atlantic region. Like black rot, phomopsis is favored by frequent rains.

Symptoms: At pruning, phomopsis symptoms will appear as elongate, darkened lesions on apparently bleached or light colored canes and spurs. The lesions are most numerous on the basal 4 to 6 inches of canes. As shoots emerge, phomopsis symptoms will appear on the basal nodes of shoots, producing elongate, darkened lesions. The lesions are not deep, but they give the base of the shoot a crusty appearance. Lesions may also extend onto fruit cluster stems and severely affected shoots may break off. Foliar symptoms begin as numerous, small greenish-yellow lesions that darken and may drop out producing a shot-hole effect. Affected leaves are distorted, smaller than normal, and eventually drop from the shoot. Phomopsis also causes a late-season rot of ripening berries. Fruit infections occur at or before the fruit set period and are followed by a period of fungal inactivity. As fruit begins to ripen, the fungus resumes growth and causes berry rot that can easily be mistaken for bitter rot or black rot. Phomopsis can reduce crop directly from loss of affected berries, and indirectly through shoot breakage.

Control: Infected canes and spurs are the source of Phomopsis inoculum and one-year-old wood can produce infective inoculum for several seasons. To the extent possible, visibly infected wood should be removed during dormant pruning. Protectant fungicides are necessary where Phomopsis is present and either Captan or mancozeb are registered for this use. Commence sprays at bud break and follow a 7- to 10-day spray program in the pre-boom period as weather conditions dictate. During his talk at Winchester on 3 March 1997, Dr. Doug Gubler indicated that they were getting effective control of Phomopsis by using 10 pounds of sulfur per acre in California. We have no experience with this treatment in Virginia, and can not recommend its efficacy. If you are tempted to try sulfur for Phomopsis, read the sulfur label to ensure that it's a legal application. Elf Atochem's Microthiol Special (80% sulfur) does have Phomopsis on the label and does permit application rates of 3 to 10 pounds (product) per acre.

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D. Black rot

Varieties and species vary in susceptibility to the black rot fungus, but most of the commonly grown vinifera and hybrid varieties should be considered highly susceptible. All young green tissues are susceptible to infection beginning with the onset of growth. Leaves are susceptible to infection for about one week after unfolding; berries are susceptible until veraison.

Symptoms: Symptoms appear on leaves as tan, circular lesions one to two weeks after infection occurs. The lesions soon produce spore-releasing structures called pycnidia, which are visisble as tiny black dots on the surface of the dead tissue of the lesion. The pycnidia release spores upon wetting which cause repeating cycles of infection and spore discharge throughout the summer. Disease progress, from primary infections to virtual crop loss, can be rapid when frequent rains affect unprotected crops.

Control: Avoid primary infections! Most black rot inoculum is released in the pre-bloom period. A rigorous (7- to 14-day schedule, depending upon rainfall and fungicide) spray program in the pre-bloom through fruit-set period is important to prevent primary infections. Shoots are rapidly elongating during this portion of the season and exposing unprotected foliage to inoculum. Most black rot primary inoculum is released in the pre-bloom period. Black rot fungicides include Abound, Ferbam, mancozeb, Bayleton, Nova, and Captan. Captan has only fair activity and SHOULD NOT be solely relied upon for black rot control. Nova and Bayleton offer protectant as well as eradicant properties against black rot. For effective eradicant action, Nova or Bayleton must be applied within 72 hours of the beginning of an infection period. Once applied, Nova or Bayleton would offer as much as 21 days protection, but recently emerged shoot tips will be unprotected.

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E. Climbing cutworms

Cutworms feed on expanding grape buds resulting in a lack of shoot development from those nodes. This can be a minor problem on mature vines, but a real headache when you're trying to form new cordons. Vineyards tend to vary in their susceptibility to cutworm feeding, but if you've had previous problems, you should be alert to the potential for repeat occurrences. Injured buds appear hollowed out, which is the same appearance of buds damaged by grape flea beetles. Cutworms feed at night and shelter in debris at the base of vines by day. The larvae are smooth, brown or gray, and about a half inch long. Feeding begins in the spring when buds begin to expand. The extent of damage varies with cutworm population and on the duration of bud-break. A cool, prolonged bud break period can result in considerable damage. Vineyards should be carefully monitored for cutworm feeding, again, particularly if you've experienced previous problems. An insecticide may be warranted if feeding affects more than 2% of buds, or where special consideration is given to establishing productive cordons. Dipel (Bacillus thuringiensis) or Guthion 50WP insecticides are listed for cutworm control in the current Virginia Tech grape Pest Management Guide. Cutworm control can be improved by spraying in the late afternoon or early evening to ensure that fresh residues are present when feeding commences.

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F. European red mites (early season infestation)

Mites are insect-like animals whose feeding can cause foliar discoloration ("bronzing") at various times during the growing season. While we normally mention mites in the course of our summer pest management topics, a few words about early-season infestations are warranted. I have occasionally observed European red mite populations at extremely high densities soon after bud break. Mite numbers were high enough (20 to 30 mites per leaf) that the young leaves and shoots were severely stunted and incapable of normal growth. The first incidence was puzzling because the cause of the shoot stunting was not immediately obvious. The shoots were stunted (2 to 5 inches long), the leaves lacked the typically green color - they were faded, yellowish-green, and the leaves were easily dislodged from the shoot. The variety was Vidal blanc, but I've since seen the problem on other varieties, including vinifera. My first reaction was a nutrient deficiency or a growth problem caused by an excessive crop the previous season (one can imagine all sorts of causes until the obvious presents itself). It was not until I closely examined the affected shoots that I could see that they were swarming with mites. The feeding was severe enough to cause the leaf abscission and the severe stunting of growth, and the effects were generally uniform over a large portion of the Vidal planting. In the initial and subsequent cases of these early season mite infestations, two applications of a registered acaricide (miticide) remedied the problem and growth resumed, although fruit set appeared to be affected in one situation. Keep this description in mind as you scout your vineyards following bud break this spring.

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G. Winchester AREC vineyard spray record

As is previous years, I've tabulated the sprays used in our wine grape variety planting during 1997 (Table 2). The 1997 schedule was similar to those used in the previous two seasons (Viticulture Notes Vol. 12, No. 3) with some exceptions: A total of 12 sprays were used in 1997, similar to 1995 but two fewer than used in the wetter 1996 season. A single insecticide application (Guthion at 11 July) was made in 1997 for grape berry moth management. Scouting indicated no other need for either japanese beetle or grape berry moth insecticides. The pre-bloom sprays were based on mancozeb (Penncozeb) or Ridomil for downy mildew, and either Penncozeb, Nova, or Bayleton for black rot. A downy mildew fungicide was intentionally omitted from the 20 May spray due to a favorable weather forecast and the plan to use Ridomil at 30 May. The powdery mildew program used at least three different modes of action: sterol-inhibiting fungicides (Nova and Bayleton) in the early part of the season, Abound after bloom, and a reliance upon sulfur in mid- to late-summer. The inclusion of Benlate on 8 May was also targeted at powdery mildew, but this material could have been substituted with either sulfur or a sterol-inhibiting fungicide. Our 1997 program, as in previous years, follows a 10- to 14-day program in the pre-bloom period of rapid shoot growth, and lengthens, somewhat, between sprays in the post-bloom period. Note that captan was reserved for use against downy mildew within the 66-day PHI when mancozeb is not permitted. The inclusion of JMS stylet oil on 26 June was done to evaluate potential crop injury (phytotoxicity). While there was no apparent injury with the particulars of this spray, we have produced injury when the oil was applied close to the application of either sulfur, captan, or copper-containing fungicides. Spray material was applied at a rate of 75 (pre-bloom) to 100 gallons per acre. The program was effective in that crop was free of disease at harvest in September and October.

Table 2. Spray record of the Winchester Agricultural Research and Extension Center research vineyard during the 1997 season. See text for interpretation.

SprayDateGrowth stageProductAmount/acre
130 April1.5 to 3 inch shootsPenncozeb 75DF2.0 lbs
28 May3 to 6 inch shoots Penncozeb 75DF
Benlate 50DF
2.0 lbs
12.0 ozs
320 May6 to 12 inch shootsNova 40W4.0 ozs
430 MayPre-bloom Ridomil MZ72
Bayleton 50DF
2.25 lbs
4.0 ozs
513 JuneBloomRidomil MZ72
Nova 40W
2.25 lbs
4.0 ozs
626 JuneBerry setJMS Stylet oil1.5% in 100 gal.
water/acre
730 Junebb-sized berries Abound11.0 ozs
811 JulyCluster closing Penncozeb 75DF
Microthiol Special
(80% sulfur)
Guthion 50W
1.5 lbs
5.0 lbs
2.0 lbs
925 JulyMid-summer Nova 40W
Tenn-Cop 5E
5.0 ozs
4.5 pints
109 AugustPre-veraison Captan 50W
Microthiol Special
(80% sulfur)
4.0 lbs
5.0 lbs
1126 AugustVeraisonCaptan 50W
Microthiol Special
(80% sulfur)
4.0 lbs
6.0 lbs
1217 SeptemberVeraison to
pre-harvest
Captan 50W
Microthiol Special
(80% sulfur)
4.0 lbs
6.0 lbs

Disclaimer: Mention of agricultural chemicals is for the reader's convenience. The use of brand names and any mention or listing of commercial products or services here does not imply endorsement by Virginia Tech nor discrimination against similar products or services not mentioned. Agricultural chemical users are ultimately responsible for ensuring that the intended use complies with current regulations and is consistent with the product label.

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Upcoming events

A. Annual grape pest management and research topics update (see Jan.-Feb., 1998 issue)

B. Semi-annual "beginners" seminar:

When: 8:45 am to approximately 4:00 pm; Saturday, 9 May 1998
Where: VA Tech, AHS Agricultural Research and Extension Center (540-869-2560).
Details: Comprehensive classroom instruction in site selection, economics, varieties, vineyard design and establishment, and vineyard operation, followed by 1 to 2 hours in the vineyard, weather permitting.
Registration1: Pre-registration required. $20.00 per person to include refreshments, lunch, and hand-outs. Make check payable to "Virginia Vineyards Association", and mail to: Grapes, Virginia Tech, 595 Laurel Grove Rd., Winchester, VA 22602. Check must be received by 6 May to guarantee lunch. For multiple registrations, please include a list of attendees.
Directions: The AHS AREC is located approximately 7 miles southwest of Winchester, VA. 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.

1 If 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 this 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'd like to receive "Viticulture Notes" as well as Dr. Bruce Zoecklein's "Vintner's Corner" by mail, contact Dr. Wolf at:

Dr. Tony K. Wolf
AHS Agricultural Research and Extension Center
595 Laurel Grove Rd.
Winchester VA 22602

or e-mail: vitis@vt.edu

Commercial products are named in this publication for informational purposes only. Virginia Cooperative Extension, Virginia Tech, and Virginia State University do not endorse these products and do not intend discrimination against other products that also may be suitable.

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