I’m uncertain why powdery mildew occurred with such frequency. We again had low levels of cluster infection apparent in our divided canopy Chardonnay about one month after fruit set (mid-July). It’s possible that the frequent rains of June contributed to the development of primary infections and that poor penetration/coverage of clusters in the divided canopy trellis promoted the secondary lesions. Our spray schedule was unusual this year in that we were conducting trials in the vineyard to evaluate the effects of crop oils on vine function. Because the crop oils can cause phytotoxicity if mixed with sulfur and certain other pesticides, we had to alter our normal use of sulfur. So, we may have promoted the development of powdery mildew. Powdery mildew and the use of crop oils as powdery mildew eradicant/protectant fungicides will be one topic of discussion at our pest management-research update conference in Roanoke on 11-12 January 1999 (see page 3).

Grackles and robins were the chief avian culprits that we saw in northern Virginia vineyards this fall. We had unusually early (mid-August) pressure from robins this season and ended up using a combination of netting, ReJex-iT^TM olfactory repellent, scare-eye balloons, pyro-technic "clapper" shells, 2 "Bird-Gard"^TM audible distress emitters, and a shotgun to discourage depredation. We were successful, but it was probably the combination of tactics that ultimately prevailed. ReJex-iT^TM is formulated with methyl anthranilate, the pervasive odor-active compound in Concord grapes. It is registered for use on grapes and certain other fruit and non-fruit crops to discourage birds. Ours was not a replicated test, so I can offer no advice on efficacy. I will say that the ReJex-iT^TM odor was still detectable almost a month after application — we had no rainfall during the period. Researchers at Washington State (no/low rainfall prior to harvest) apparently found an objectionable carry-over of methyl anthranilate through fermentation when it was used as a bird repellent… might not be the best additive to Chardonnay! The PBR Bird-Gards that we purchased use a 12-volt battery and can be programmed for the frequency of emission as well as one or more bird species, including grackles, starlings, robins. Again, we used them in combination with other tactics, so I cannot vouch for their efficacy. We did, however, seem to have renewed robin problems when we let the batteries go dead. Clapper shells and shotgun reports are effective scare tactics, but offer temporary protection at best.

Grapevine yellows (GY) is a destructive disease caused by a bacteria-like organism called a phytoplasma. We observed a substantial increase in GY incidence among some vineyards in 1998, but are uncertain of the reasons. Chardonnay is the principal variety affected by GY; however, Riesling, and to a lesser extent, Cabernet Franc and Sauvignon blanc, have also been affected by GY in Virginia. Our surveys since the early nineties show a widespread distribution of yellows among Chardonnay vineyards along the Blue Ridge. Three symptoms, appearing together, are useful in diagnosing yellows: (1) abortion of fruit clusters anytime after fruit set, (2) downward rolling and yellowing of leaves, and (3) failure of bark or periderm to mature on affected shoots. Other things to look for include shoot-tip dieback, general vine weakness, and a "brittle" texture to affected leaves. This disease generally kills vines within two to three years of symptom onset. While we now know more about the GY pathogens and alternative hosts, we still don’t know what insect vectors are involved with transmission. Affected vines or vine parts (e.g., an affected cordon) should be removed from the vineyard as soon as symptoms become apparent. Retention of affected vines in the vineyard may contribute to further spread of the disease as long as foliage remains on the affected vine. We have had limited success in cutting affected vines off above the graft union and restructuring the training system with renewal shoots. The alternative is to pull the affected vine and replant, or extend cordons from adjacent vines to fill the resulting gap. The Sept./Oct. 1995 issue of Vineyard and Winery Management (1995) has a somewhat dated but more detailed description of GY with color photos. For those interested, Agdia (Elkhart, IN; 219-264-2014; ask for Andrea) has an assay for grapevine phytoplasmas that costs $175 per sample.

Simplified temperature recording: Here’s a good idea and a blatant commercial endorsement. Spectrum Technologies’ (1-800-248-8873) Hobo data logger is about the size of a small box of stick matches, but will record over 4 months of temperature data on an hourly basis. The units are programmed, and the stored data are downloaded, via your PC’s serial port. We used several of the temperature/relative humidity recording devices in vineyards this summer and I was impressed with the ease of operation and reliability. Who would use these? Anyone interested in maintaining a record of temperature at an existing or potential vineyard site. Because they automatically record data, there is no need to manually check and reset "min/max" thermometers. What’s the cost? Recorders with 8K of memory and an internal sensor cost $59 each. You’ll also need the software ($59) and you should buy the radiation shield ($44 each) to avoid radiant heating and cooling of the recorder. Of course, you need a PC with Windows operating system. The software plots the downloaded data and allows exporting to spreadsheets for further data analysis.

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II. Question from the field: dormant sprays

"I am interested in what sprays, if any, would be effective on powdery mildew overwintering on canes. My Cabernet Sauvignon was hit hard with powdery. I obtained good control with a couple of sulfur applications, but would like to continue treatment through the winter if possible. Any thoughts?" The question of dormant sprays for powdery, phomopsis, and other fungal diseases surfaces each year about this time, especially from growers who have just fought an uphill battle with powdery mildew. There is not a lot of data on the subject, but I’ll relate what pathologists have recommended on the subject. In the case of powdery mildew, the fungus overwinters here in the East primarily as sexually produced spores (cleistothecia). Many of the cleistothecia that are washed into crevices of bark of trunks and cordons survive the winter and initiate primary infections in the spring with the advent of favorable weather and shoot growth. Cleistothecia that remain on foliage, berries and canes show very poor winter survival. For this reason, the removal of pruned canes from the vineyard is of little value for disease sanitation. The most important spores are those that survive the winter lodged in the rough bark of trunks and cordons. Our task in dormant spraying, then, is to find materials that are lethal to the spores and apply them in a manner that allows of all the nooks and crannies of the rough bark. This, in the final analysis, is a tall order. Pathologists David Gadoury and others at Cornell University examined a range of fungicides for their efficacy against cleistothecia (Gadoury, 1991). In field trials conducted in 1988, dormant sprays of copper sulfate, Bordeaux mixture (copper sulfate and lime), copper and lime sulfur all delayed the onset of powdery mildew. The applications were made just before bud break and were made at 300 gallons of spray material per acre. The copper sulfate was applied at 12 pounds per acre while the lime-sulfur was applied at 36 gallons/acre (again, in 300 gallons of water). It is important to point out that "lime-sulfur" (calcium polysulfide) is NOT a mixture of lime and sulfur. Furthermore, the only 1998 label (UAP) that I found for "lime-sulfur" does not include grapes on the label. The initial success at reducing powdery mildew with dormant sprays in 1988 was not observed in 1989 or 1990. The New York State researchers used a hooded boom sprayer to thoroughly drench the vines (300 gal/acre). This was the only sure means of penetrating the rough bark of vines. Given the high material cost of the application (about $90/acre), the need for high gallonage (300 gallons/acre), and the mediocre control, Gadoury has not recommended dormant sprays of either copper compounds or lime-sulfur. Instead, Dr. Gadoury has recommended that a more intensive program be followed in the period from bud break to bloom. The current Virginia Tech grape Pest Management recommendations lists only one dormant spray recommendation. That is for Bordeaux mixture, applied only where anthracnose (bird’s eye rot) has been a problem.

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III. Upcoming Meetings

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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

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