Vineyard and Winery Information Series:
Vol. 18 No. 4, July-August 2003
Dr. Tony K. Wolf, Viticulture Extension Specialist
Vineyard visits within the last two weeks in northern Virginia and in the Charlottesville area have revealed some significant disease problems, particularly with powdery mildew. Some of the vineyard owners had a clear understanding of the weaknesses in their program that led to disease; others were less certain. One recurring problem is poor pesticide coverage. Poor penetration and coverage might be a greater problem this year due to the very vigorous growth in some vineyards. In scouting for disease, be certain to look at leaves and clusters that are in dense, poorly ventilated portions of your canopy. Don't depend upon a cursory observation of your vines from the seat of a tractor. The powdery mildew that I observed in two vineyards this week appeared to originate within the cluster and is now spreading out towards the cluster exterior. I suspect that cluster-closing occurred without an effective protectant fungicide on the cluster rachis or interior side of berries. Once the berries have expanded to close the cluster, it is nearly impossible to penetrate the cluster interior with fungicides. Once powdery mildew gets out of control, it is EXTREMELY difficult to arrest the disease. And, it takes very little diseased fruit (< 2 or 3%) to give wine a moldy taint. What can be done if you see that powdery mildew is present? Don't give up! You may very well lose fruit, but it is important to keep the leaf area clean and functional, even if the crop is lost. To throw in the towel at this point on a diseased vineyard is only going to compound problems next year, and it will compromise the vine's ability to acclimate and withstand winter cold. The ability to eradicate powdery mildew is greatly increased if you act quickly to arrest the development before it rages out of control. Eradicant fungicide options were reviewed in the March-April 2003 Viticulture Notes and include sulfur, Armicarb-100, OxiDate, and horticultural oils (e.g., JMS Stylet). High gallonage (100-200 gallons/acre) is necessary with any of these products to achieve eradication. Even so, we have found that eradication of powdery mildew on clusters is best achieved by using a hand-gun attachment on the sprayer and hosing down the affected clusters as if you were putting out a fire (simile intended). Dr. Anton Baudoin had some success in a trial a couple of years ago by using a combination of Armicarb-100 and sulfur. In my experience (not tested), oils have worked well if you get complete tissue coverage. If you don't obtain complete tissue coverage, you won't completely eradicate the sporulating fungus. Graduate student Sarah Finger's work [Effects of horticultural oils on the photosynthesis, fruit maturity, and crop yield of wine grapes. 2002. Amer. J. Enol. Vitic. 53:(116-124)] illustrated that oils are a double-edged sword that must be carefully used to avoid depressing vine photosynthesis and delaying harvest. Oil sprays directed only at the fruit zone is one means of limiting the negative effects of oil on vine performance.
Downy and black rot are showing up here and there too, but my sense is that most growers have kept these diseases at bay. Unfortunately, the current conditions (frequent wettings, high humidity, and temperatures in the eighties) are perfect for downy mildew development. For whites, we are within the 66-day restricted pre-harvest interval (PHI) for mancozeb and Ridomil. Other options are copper, captan and phosphorous acid. Ziram is rated as "fair" for downy, and has a 21-day PHI. Dr. Wayne Wilcox of Cornell University is obtaining encouraging data on both the protectant and eradicant activity of phosphorous acid, and we will likely see additional usage of these materials in the future, with special notes about the timing of sprays relative to infection periods.
Take a few minutes to review the season's earlier newsletters, especially the March-April Viticulture Notes, and the efficacy data presented in the Virginia Tech grape pest management guide as we head towards harvest. If you've got a clean vineyard, good on'ya; keep it that way. If you've got problems, and don't understand the reasons, I want to hear from you.
We're often asked, at the end of the season, what our spray program in our research vineyard consists of, and we often post the season's program in a fall issue of Viticulture Notes. Rather than wait that long, Table 1 shows the fungicide and insecticide program as used at the AHS AREC vineyard in 2003. Products are generally used at the highest label rate. Application rates (from pre-bloom, on) are at 95 gallons per acre, spraying with a Durand-Wayland 3P100-32, 3-pt hitch-mounted sprayer. Spreader-sticker adjuvant (Cohere) was used only in two sprays in early July. Vines are primarily vinifera, so an intensive spray program is used. Training includes open lyre, Geneva Double Curtain, VSP, Smart-Dyson. Fruit and foliage is free of disease at this writing (1 August). Our plans from here would be "maintenance" through harvest, with an increased reliance upon sulfur for foliar powdery, copper, captan or Pro-phyt for downy, and captan for late-season summer rots. Our last spray on 25 July should protect until the 7th or 8th of August, at which point we'll likely re-apply either the Tenn-cop 5E with sulfur, or do a combo of sulfur and captan. Compared to "normal" years, our 2003 program has relied less on mancozeb, and more on Ridomil for downy control -- but then, this has been a wetter than normal year. We "normally" apply around 13 sprays/year. At 11 thus far, we will be well over that mark in 2003. Expensive? Yes. But what are the alternatives? I've seen 10- to 20-acre vineyards decimated by disease this season and, at $1400 to $1500 per ton of grapes, the expense can be justified. Finally, there is nothing about the spray program in Table 1 that deviates from the printed (e.g., March-April Viticulture Notes) or verbal (various spring and summer meetings) recommendations made, with the possible exception that we have used less sulfur, to date, than might be desirable from a resistance management standpoint. With a cooler than average summer, we will have opportunities to remedy that in the coming sprays.
Table 1. Fungicides and insecticides, and stage of growth at each application, used in the AHS AREC research vineyard during 2003. "Precip." Is the amount of rainfall that was recorded since the last spray (e.g., 1.66 inches of rain was measured between 6 and 13 May).
|Date||Pesticides used||Growth stage||Precip.|
|6-May||Penncozeb 75DF, Nova 40W||8-10" shoots|
|13-May||Nova 40W, Ridomil Gold MZ||12-16" shoots||1.66"|
|20-May||Elite 45DF, Ridomil Gold MZ||16-24" shoots||1.74|
|27-May||Abound, Microthiol Disperss (sulfur)||pre-bloom||0.9|
|5-Jun||Elite 45DF, Pro-phyt||pre-bloom||1.97|
|10-Jun||Ridomil Gold MZ, Flint, Microthiol Disperss (sulfur)||bloom||0.92|
|18-Jun||Penncozeb 75DF, Rubigan EC, Microthiol Disperss (sulfur)||post bloom||2.68|
|27-Jun||Captan 50W, Rubigan EC, Intrepid 2F||pea-size berries||1.37|
|4-Jul||Abound, Intrepid 2F, Elevate 50WDG||beg. bunch closure||0.86|
|11-Jul||Nova 40W, Tenn-Cop 5E, Imidan 70W||berries hard & green||2.48|
|25-Jul||Elite 45DF, Tenn-Cop 5E, Pro-phyt, Imidan 70W||berries hard & green||0.74|
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Grape root borer: Some growers that are trapping for grape root borer this season are finding that so many adult males are being caught that traps lose their effectiveness. At times moths are seen to come in contact with the trap bottoms and fly off, rather than becoming stuck on the bottom (liner). This may occur even if captured moths are removed, because scales that cover the body remain in the sticky surface, reducing the tackiness. It will be necessary to change the liners more often while moths are very active.
Intrepid versus Confirm: For the 2001 and 2002 seasons we had Section 18 emergency registrations for Confirm (tebufenozide) for use against grape berry moth. This season, recall that we have two newly registered insecticide for GBM: Intrepid (methoxyfenozide) and SpinTor (spinosad). Intrepid and Confirm are closely related, with Intrepid considered to be a somewhat superior product. Both are molt-accelerating compounds effective against Lepidoptera and with very low toxicity against humans and beneficial arthropods in the vineyard. However, there is no Section label in effect for Confirm on grape in 2003. With the availability of Intrepid and SpinTor, an emergency registration would not have been approved. Hence, Confirm is not legal in Virginia vineyards this season.
It would be best to either return left-over product to the point of sale, or arrange for it to be used on a crop for which it is registered (bush berries, caneberries, cole crops, leafy vegetables, turnips, cotton, Christmas trees, fruiting vegetables, pome fruits, and pecans. Confirm has been used on apple for leafrollers and codling moth, although even on this crop it has mainly replaced by Intrepid because Intrepid is more effective than Confirm against oriental fruit moth.
Grapevine aphids: I had a question on the best means to control grapevine aphid. This is the most common aphid that feeds on grape. The winter host is viburnum. After several generations on viburnum in the spring, aphids migrate to grapevines. This is a common life history pattern for temperate area aphids. Dark brown to nearly black aphids may become very numerous on the shoot tips. However, the effect on vines is slight, and populations normally decline on their own from a combination of natural enemies and the lessening of shoot growth (nutrient levels are higher in growing shoot tips). Insecticidal control of grapevines is seldom needed.
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Virginia has many small vineyards - 2 or 3 acres in size - and interest in small vineyards continues, and raises the question of appropriate equipment. Obviously a one or two acre vineyard makes it difficult to justify $25,000 for a tractor and sprayer. The question is, can we really achieve effective disease control with lower power, less expensive sprayers? A quick review of prices and available sprayers suggests that the smallest, effective sprayers, still cost about $4,000. So, if we cannot reduce the sprayer cost, our only option is to see how small of a tractor we can get away with.
When looking into canopy sprayers, penetration and coverage, especially in the fruit zone, is critical. The bottom line here is a sprayer with enough wind to actually circulate the spray in the fruit zone and provide thorough coverage of clusters. Windspeed and the ability to get the spray to optimal coverage is a function of power, specifically horsepower (HP). For standard air blast sprayers, we find a general lower end of about 18 HP required at the PTO for ideal windspeed and circulation for disease management. This is evident by the smaller CIMA (available from BDI at 800-808-0454), John Bean (http://www.johnbeansprayers.com/ or 800 241-2308), and similar sprayers with tanks down to 80 or even 50 gallons. To find anything that effectively controls disease, and yet requires less than 18 PTO HP, takes a bit of searching.
Eugene Canales at Ferrari Tractors in California (530-846-6401) has a nice image on his website http://www.ferrari-tractors.com/specialpurpose.htm of a small 16-HP tractor with a well- matched, 3-point hitch sprayer that requires 14 HP at the PTO, and can have tanks ranging from 25 to 50 gallons. Eugene is familiar with many manufacturers of similar sprayers in Italy, and is aware of several units at 14-HP with small tanks, which are understood to offer disease control similar to standard 18-HP air blast sprayers, yet are only appropriate for relatively narrow row spacings. Examples of these 14-HP sprayers are the Fort at $4,000 to $5,000, and the Multyme starting at $4,700 with a tank up to 80 gallons.
Speaking with Andrew Landers of Cornell (315-787-2429), one option for a small power sprayer is the "Major" by Turbo Mist of Slim Line Manufacturing. This sprayer starts at $5,500, and has been implemented down to a 15 PTO HP tractor. While 15 HP has been done, salesman Doug Newman (North East representative at 519-878-1199) comments that 18 to 20 HP at the PTO is more appropriate. This machine is gaining respect in New York, and operates on a smaller 14" turbine. It is important to note that these 3-point hitch sprayers require a Category 1 hitch, not a category zero as may occur on some very small and narrow "garden" tractors.
I found no "air blast" sprayers that operate at less than 14 PTO HP. There are, however, several sprayers that have dedicated engines or that operate from the tractor's 12-volt electrical system. The "Li'l Squirt" by PBM (http://www.pbmsprayers.com/literature.htm) costs approximately $5,000 and operates off its own power supply which generates between 5 and 11 HP. I could not find anyone who had actually used such a sprayer in the field to offer testimony, and I hate to say it but upon asking the dealer I was not directed to any such reference person. Similar sprayers (e.g., Solo and Berthoud) with dedicated power supplies exist; however, the engines used to power these machines are no longer allowed to be sold in the United States due to emission issues.
The general concept is that a certain amount of horsepower is required to get enough air movement to offer the necessary coverage for optimal disease control. Backpack and small mister sprayers are available, but the performance of these units is degraded by wind, and they have the disadvantage of exposing the user to the mist that he or she is applying.
In sum, there is a tradeoff between efficacy/performance, and the sprayer power plant. Lower power requirement sprayers may be somewhat less expensive than their big brothers, but if the sprayer isn't controlling disease, then a decreased investment really didn't save you anything.
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Michigan State University extension specialists and Tim Weigle of Cornell University have produced a guide book for grape growers in the east and midwest called A Pocket Guide for Grape IPM Scouting in the North Central and Eastern U.S. The pocket guide was developed to help grape growers identify nutritional disorders, herbicide damage, grape diseases and insect pests and their natural enemies. At over 100 pages, the guide contains hundreds of photographs and descriptions and has a scouting calendar for pests and diseases. The Guide is a bargain at $13.00 (S&H are included), and can be ordered (MC and Visa accepted) by calling the Michigan State University Extension Distribution Center at: 517-353-6740. Ask for publication # E2889. You may also send a check to MSU Distribution Center, Rm 117, Central Services Bldg., MSU, East Lansing, MI 48824-1001.
b) New Dean for Virginia Tech's College of Agriculture and Life Sciences
Many in our grape/vine community know that Dr. Andy Swiger retired as dean of Virginia Tech's College of Agriculture and Life Sciences in January of 2003. Dr. Swiger served as dean since 1992, and was the longest-serving agriculture dean in the Southern region of the US. Dr. Sharron Quisenberry starts as the new dean of the College on August 1. Dr. Quisenberry comes to Virginia Tech as the former dean of the College of Agriculture at Montana State University. In her role as dean, Dr. Quisenberry will oversee the College's programs for instruction, the Virginia Agricultural Experiment Station, and Virginia Cooperative Extension. Dr. Quisenberry holds four degrees, including two master's degrees. She received a Ph.D. and Master of Science, both in entomology, from the University of Missouri-Columbia; a Master of Arts in environmental biology from Hood College, and a B.S. Ed. in biology from Truman State University.
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Directions: Virginia Tech's AHS Jr. Agricultural Research and Extension Center (AREC) is located approximately 7 miles southwest of Winchester, VA in Frederick County. 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.
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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: firstname.lastname@example.org
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