Viticulture Notes

Vineyard and Winery Information Series:
Vol. 19 No. 3, May-June 2004

Dr. Tony K. Wolf, Viticulture Extension Specialist

Table of Contents

I. REMINDERS:

• Vines are at or one or more weeks past full-bloom, depending upon location within Virginia. The pre-bloom through 4- to 6-weeks post-bloom period is THE period of greatest concern for our most common and destructive fungal diseases. These include powdery mildew, downy mildew, and blackrot. Your ability to provide season-long management of these diseases is immensely improved if you keep the vineyard free of disease in this immediate post-bloom period. Fail that task now and the balance of the season will be a very steep uphill battle for the rest of the season.
• Downy mildew and foliar black rot lesions can now be seen in vineyards that have not been appropriately protected.
• May 2004 is shaping up to be very similar May of 2003 - many wetting periods and excellent conditions for primary and repeating infections of the major diseases. Use rainfast (locally systemic) materials to extend the protective period of applied fungicides. Example, use Ridomil or phosphorous acid for downy mildew, Elite or Nova for powdery mildew and blackrot. Alternatively, use Abound or Pristine for all three of the major diseases.
• Reminder: strobilurins include Abound, Sovran, and Flint - their efficacy against pathogens is NOT the same (e.g., Flint is weak against downy mildew but superior for powdery mildew)
• Reminder: Sterol inhibitors include Nova, Procure, and Elite

Powdery mildew:

• Berries are extremely susceptible to infection from the start of bloom until about a month after fruit set. Effective management through this period is critical.
• Use best materials now (e.g., Elite, Flint, Quintec, Endura, or Pristine), but combine with sulfur on sulfur-tolerant varieties (to delay resistance development), or alternate with Rubigan on sulfur-sensitive varieties, again to lessen resistance development.
• Question from the field: "Much of the discussion about Strobie and SI resistance reiterates the importance of not relying exclusively on the same fungicides in every spray. The usual recommendation is to 'tank-mix' ones with different modes of action. I use Strobies, SIs, biofungicides (eg Serenade) and preventive/non-systemics like sulfur, copper, Captan, etc, over the course of a spray season, but while some of these are combined in the tank to deal with specific fungus diseases, I have generally ALTERNATED at least the systemic broad spectrum ones from spray to spray. Is there an advantage in mixing these items in the same tank at each spray, as opposed to simply alternating their use over several applications?"
• Answer: Our chief concerns for resistance development would be for powdery mildew, downy mildew and botrytis, each of which has the capacity to quickly develop resistance to the more specific mode-of-action fungicides, such as the sterol-inhibitors (Sis) and strobilurins (powdery mildew), Ridomil (downy mildew), or Vangard or Elevate (Botrytis). Alternating the fungicide chemistry or mode-of-action for a particular disease is not a choice; it's a requirement if you wish to be able to effectively use the more specific action materials in the future. Whether you tank-mix within a spray, or alternate between sprays is not so black-and-white. For powdery mildew, my opinion is that tank-mixing some sulfur with the other materials (e.g., SIs, strobilurins, Quintec or Pristine) might be more prudent that simply alternating chemistries between sprays. There might be occasions, however, where the sulfur may be incompatible with other materials in a tank-mix, such as oil, in which case I would not tank-mix. Another reason to mix sulfur with other fungicides when you can is that you might not have the option to use sulfur when you "planned" to use it if you followed a plan to alternate materials over time. In other words, say you had planned to use SIs and strobilurins, and maybe Quintec during the pre-bloom through post-bloom period and then rotate back to sulfur for a spray or two in July. But July comes and it's too hot or too rainy and you want something rainfast, so you go back to the SIs. The latter situation happened to us last year, and we ended up using less sulfur and more of the other fungicides than we had planned to. Your next question will be, Can you reduce the rate(s) of either the sulfur or the more specific mode-of-action fungicides in the tank-mix with the thinking that the sum of components will equal an effective single application of one or the other? I would not do this. I would use the full rate of the resistance-susceptible fungicide, and at least a moderate label rate of the particular sulfur product. Sulfur is cheap; there's not much economic sense in applying a sub-lethal dose.
• The same rationale described above for powdery mildew management might be used for downy mildew resistance, by inclusion of either captan or mancozeb in a tank-mix with Ridomil. I'm not aware of downy mildew resistance problems to phosphorous acid (PA). Tank mixing PA with a second downy mildew material would, however, extend the protective action of the tank-mix for downy.
• There are few effective materials for Botrytis, and no "broad spectrum" (low resistance potential) materials that are as effective as Vangard, Elevate, or Endura. You could tank-mix two of these three materials in a tank-mix, but I'm not sure whether you've truly accomplished much in the way of minimizing resistance development. And, a tank-mix cocktail of 6 or more fungicides targeting all diseases may have an undocumented incompatibility problem or two lurking.

Downy mildew:

• Wet weather with temperatures in the 65 - 77 ƒF range set the stage for infections - typical night-time conditions now.
• Use best materials now (Ridomil would be my choice given precipitation patterns of last few weeks, but Abound, mancozeb and phosphorous acid products (good eradicant quality) would also serve. Switch later to captan or copper or a phosphorous acid product (e.g., ProPhyte), particularly during the 66-day pre-harvest interval when Ridomil and mancozeb are disallowed.
• Question from the field: "Would the amount of mancozeb in Ridomil Gold MZ be sufficient to provide dual control of black rot?"
• Answer: Ridomild Gold MZ contains 64% mancozeb. Sprayed at full label rate (2.5 pounds/acre), you'd only be applying 1.6 pounds of mancozeb per acre. I think that's a low rate for black rot control; particularly during this critical time of the season; particularly with highly susceptible varieties. We use 2.25 to 3.0 pounds of mancozeb per acre, or we use an SI such as Elite, to ensure adequate black rot control on highly susceptible varieties.

Black rot:

• Again, critical time is now, fruit develop resistance as they mature, but that's some time off.
• Strobilurins (Abound, Soveran or Flint) or SIs (Nova or Elite) are all locally systemic (rainfast) materials, and good choices for this time of year. They also provide powdery mildew control (if resistance has not become an issue). Mancozeb is excellent and provides dual control of downy, but is not locally systemic.

Botrytis:

• Depend primarily on your good canopy management to combat botrytis (It is good, isn't it!")
• Use botrytis-specific fungicides only on botrytis-susceptible cultivars. Vangard, Elevate or Endura are currently effective fungicides, but each has limitations on the number of applications that can be made per year.
• Apply a fungicide at bloom if rains are frequent during bloom. Or, use at cluster closing. Assess late-season (post-veraison) weather conditions and botrytis incidence in deciding whether additional sprays are necessary.

Question about the use of spreader-stickers:
Questions about the efficacy of spreader/stickers recur annually. Dr. Wayne Wilcox, Cornell University, provides the following, slightly edited question and answer discussion on this topic:

Question: "Given the rain that inevitably falls right after a spray, isn't it a good idea to use Nu-Film 17, Cohere, or one of the other adjuvants?"

Reply (Wilcox): This is probably the most frequently-asked question that I get, and the one for which I have no single good answer. In classic university-speak, "It all depends". Many products (e.g., most of the mancozeb and captan products) are already formulated with surfactants. A few (Rovral comes to mind) have been shown to benefit from the addition of surfactants. For others, experimental data shows no benefit or there is simply little experimental data to draw upon. Adjuvants are not the same. People always think they're getting a "spreader-sticker" when they add an adjuvant, but Rovral, Phostrol, and the SI fungicides need to be *absorbed* in order to work, so you don't want them to stick (e.g., the benefit for adding a surfactant with Rovral has been to increase absorption). In contrast, you want mancozeb, captan, and sulfur to stick, whereas adjuvants that promote absorption may also promote phytotoxicity. For example, when Flint first came out, I know that the company was discouraging the use of organosilicate adjuvants (e.g., Kinetic) for this very reason.

My approach has been to tell growers some version of the above, and suggest that if the label recommends use of a surfactant, it's a good idea. But given the uncertainties, if it makes somebody feel better to include the surfactant, I won't try to talk them out of it. And as a consultant, I'd be doubly hesitant to talk somebody out of it, because any ensuing problem would be ascribed to that very recommendation, regardless of the real reason.

Like I said, no single good answer. I can't, in good conscience, aggressively push the general use of surfactants or other spray adjuvants. I think that they're probably a waste of money much of the time, but I don't feel confident in defining such times. So, the easy answer is, if local experience shows no problem with a particular surfactant/product combination, you "might" help yourself, and the additional cost is relatively marginal.

Resistance management (this is an annual reminder)
The development of powdery mildew, downy mildew, or botrytis strains that are resistant to some of our newer fungicides is a reality. Once resistant strains appear, the fungicides will exhibit reduced efficacy, or no efficacy. To slow the development of resistant fungal strains, adhere to the following recommendations:

• Ensure thorough canopy coverage (use 75 to 100 gallons water/acre). Slow the groundspeed, increase nozzle orifice size, and make more frequent refills if necessary, but don't cut corners on coverage. Use water-sensitive spray cards in the canopy to ensure that sprayer is providing good coverage, especially in the cluster zone of "dense" canopies.
• Use full rates of fungicide when the label specifies a range.
• Avoid using strobilurins more than 2 times per season.
• Alternate strobilurins with other fungicide chemistries from spray-to-spray, or tank-mix with sulfur. Ditto with sterol inhibitors, Quintec and Endura
• Shorten the spray interval to no more than 12 days for powdery mildew control.
• Use an eradicant such as Armicarb-100, sulfur, or horticultural oil (e.g., JMS Stylet oil) IF you have a powdery mildew outbreak. DO NOT simply treat such an outbreak with a strobilurin or a sterol inhibitor.

Spray program at the research vineyard at Winchester:
We've made four fungicide applications to-date at the research vineyard at Winchester (Table 1). As with past presentations of our spray schedule, this is not intended to recommend one product over another, or to say that the same program should be used in your vineyard. We do not have a specific, pre-planned "schedule" that we follow for spraying. We consider the growth stage of vines, the environmental conditions since the last spray, the products previously used, the products that can currently be used, resistance management (note the use of three applications of sulfur thus far in 2004 in Table 1), and our need to do canopy management in the vineyard.

Table 1. Fungicides and insecticides, and stage of growth at each application, used in the AHS AREC research vineyard in April-May 2004. "Precip." is the amount of rainfall that was recorded since the last spray (e.g., 0.43 inches of rain was measured between 6 and 13 May).

Date	Pesticides used	Growth stage	Precip.
27 April	Penncozeb 75DF, Nova 40W, Microthiol Disperss (sulfur)	3 -5" shoots
7-May	Penncozeb 75DF, Microthiol Disperss (sulfur)	6 - 8" shoots	0.43
17-May	Pro-phyt, Elite 45DF, Microthiol Disperss (sulfur)	16-36" shoots	1.30
21-May	Ridomil Gold MZ, Elite 45DF, Microthiol Disperss (sulfur)	pre-bloom	0.51

Let me remind you of the comprehensive discussion, "Grape Disease Control, 2004", that Dr. Wayne Wilcox provided (and which I sent out on my listserv) in April. It's well worth picking that document back up and re-reading it now. I refer back to my own copy on a regular basis as I think about the fungicide options and how to structure a spray schedule.

Winter-injured vines: No or very little crop, just leavesŠ do you abandon your spray program? Absolutely not. You can lighten up on the black rot and berry moth sprays, but keep the foliage free of powdery and downy mildew, at least through September. It's important that these vines be given a good opportunity in 2004 to develop reserve carbohydrates for the 2005 season. They won't do that if mildew destroys the canopy by mid-summer.

Canopy management tips:

• Shoot positioning (downward with GDC and Smart-Dyson or Scott Henry) to start at or around bloom (too early = more shoot breakage; too late = tendrils latched and shoots break at a different place).
• Leaf pulling: for botrytis-sensitive cultivars or where more fruit exposure warranted. Wait until fruit set, then complete within 6 weeks. Pull leaves on East side of N/S-oriented rows. Follow-up leaf pulling may be warranted later in summer if increased fruit exposure needed.
• Shoot hedging (after fruit set) if needed - try to retain at least 12 leaves per shoot as the shoots are hedged.
• Desired canopy characteristics: 1.5 to 2.0 leaf layers, 25 to 40% canopy gaps (in leaf-thinned fruit zone), > 50% of clusters to receive some direct sunlight in the course of day.
• Let the weeds under the trellis grow a bit if your vines are overly vigorous.

Plant tissue analysis reminder:
Full bloom is the recommended time for doing routine plant tissue analysis for nutrient status determinations. Plant tissue analysis is part of a comprehensive vine nutrition management program, to be used in conjunction with soil testing and visual examination of vines. Please see the May-June 2002 Viticulture Notes http://www.ext.vt.edu/news/periodicals/viticulture/02mayjune/02mayjune.html for a more in-depth discussion of the whys, hows, and what-if questions that go along with plant tissue analysis.

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II. Wanted: Vineyard with European red mite infestation:

• a commercial vineyard, ideally within 1.5 hours of Winchester
• a developing ERM population (> 10 mites or so per leaf) by mid- to late-July. See http://www.ento.vt.edu/Fruitfiles/ERMGrape.html for details on what the ERM looks like, and what it does to the plant.
• ability to compare two rates of Acramite against a "control" (another miticide), and against an unsprayed check, where plot sizes may be as small as several panels across several rows.
• ability to have unlimited access to vineyard to collect leaf samples for mite counts and to make the treatment applications when needed (we would avoid your own restricted reentry periods caused by application of other pesticides).
• Your assistance and equipment in making the application on the treatment day

If you are interested in helping out by providing an affected vineyard for our research, please contact me at vitis@vt.edu or call 540-869-2560 x18. Thanks in advance for your consideration.

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III. Upcoming meetings:

12 Maryland Grape Growers Association Summer Field Day. Golden Run Vineyard, Hans and Jennie Schmidt (east of Chesapeake Bay, Sudlersville, MD). Tony Wolf is the invited speaker ("vineyard design and management: lessons learned and mistakes worth avoiding"). See http://www.marylandwine.com/mgga/events/main.html for detailed program and directions. Info. 410-438-3679 (Schmidt's).

19/20 Grapegrowing Seminars at Linden Vineyards June 2004. Nuts and bolts sessions for home or professional grape growers. First day covers vineyard establishment. Day 2 covers vineyard canopy management. Seminars will be held at Linden from 10:30 a.m. to 4:00 p.m. The cost is $75 per person, per day. Bread, cheese and sausage are available for purchase at Linden for lunch. Register by phone at least one week in advance. Space is limited. 540.364.1997

21-25 Seventh International Symposium on Grapevine Physiology and Biotechnology. UC Davis. Topics include photosynthesis, respiration and carbon relations, water and nutrient relations, stress physiology, temperature responses, cold hardiness physiology, fruit development, genetics and molecular biology. Tentative workshops include climate change and the vine and an update on the International Grape Genome Program. Information at http://grapevinephysiologysymposium.uckac.edu/default.htm.

30-7/2 American Society for Enology and Viticulture National Annual Meeting. Manchester Grand Hyatt Hotel. San Diego, CA. The 2004 Annual Meeting will feature a variety of presentations representing the latest in research in enology and viticulture. The program will also include invited keynote speakers from around the globe. The 55th ASEV Annual Meeting will include a full trade show and enology and viticulture poster sessions. The Annual Meeting includes a special Brett session and will be preceded by our Soil Environment and Vine Nutrition Symposium. http://www.asev.org/.

July

13-16 American Society for Enology and Viticulture Eastern Section Annual Meeting. Roanoke Hotel, Roanoke, VA. Symposium title is Grapes, Wine and the Environment. The focus will be on growing wine in a humid climate with emphasis on soils, mesoclimate and wine production. Outstanding guest speakers on the program. Technical sessions will feature regional research and projects funded by the Viticulture Consortium:East. A pre-conference tour of vineyards in southwest Virginia will be offered on 13 July. Full program description and registration information is available at: www.nysaes.cornell.edu/fst/faculty/henick/asev/

21 Virginia Summer Meeting Series. Horton Vineyard (town of Orange), Dennis and Sharon Horton. 10 a.m. to 2 p.m. First hour is tour of vineyard. Topics - Grape Root Borer and other Insect Issues: Product Labels & Environmental Precautions. VA Tech Entomologist, Dr. Doug Pfeiffer. Crop Estimation and Use of Mid-Season Average Cluster Weight Data to Refine Harvest Estimate. VA Tech Viticulturist, Dr. Tony Wolf. Bring a bag lunch. For information please contact the Rappahannock Extension Office at (540) 675-3619. Directions: From Orange, south on Rt. 15 Business, turn left on Rt. 647 (Old Gordonsville Rd.), cross RR track, go 100 feet and turn left on Berry Hill Lane.

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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: vitis@vt.edu

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