Vineyard and Winery Information Series:
Vol. 17 No. 3, May-June 2002
Dr. Tony K. Wolf, Viticulture Extension Specialist
II.Plant tissue analysis
III.Grape disease management: 2002
Late frosts: Widespread frosts associated with a cold Canadian high pressure system affected the state during the week of 20 May, particularly the morning of 22 May. For some, these frosts follow on the heels of frosts approximately one month earlier. Reports of vineyard frost injury were received from points in the central Shenandoah Valley, both northern and southern Fauquier County, near Fredericksburg, and in the southwest portion of the state near Abingdon and near the Parkway. Most, but not all, of the reports were from vineyard sites that had relatively low absolute or relative elevation. The temperatures in affected vineyards ranged from about 28ƒF in Augusta County to around 31¯F. The unusual feature of these recent frosts was the seasonal lateness. Shoot growth in some cases exceeded 24 inches. Low temperature records were broken in many areas on the mornings of 20 and 22 May. A quick review of monthly records at Winchester, however, revealed that the corresponding days in 1992 were colder for that station.
What can be expected with frost-injured vines? Frost will produce variable levels of injury to vines, depending upon the degree and extent of injury, as well as the variety. Longer shoots might only be affected near their distal ends, and regrowth by lateral shoots can, in time, compensate for the loss of the primary shoot tip. There is no guarantee, however, that the flower clusters on such shoots are undamaged, or that they will set a normal complement of berries. But if the clusters remain turgid and are well below the point of apparent shoot damage, there's cause for optimism that some of this crop will ripen. In other cases, some shoots are damaged while others escape. Secondary buds will develop from frosted canes or cordons, but the net effect is two or more populations of shoots, each ripening their crop at different rates. Much of the variability in cluster development that is apparent now will translate into variability in fruit maturation. Unfortunately, the solution to this problem is to sequentially harvest the grapes as they ripen, meaning two or more harvest dates in the affected blocks, with pickers who are trained to visually recognize the differences in stage of fruit maturity.
Even when all shoots are completely frosted, vines will normally produce a second canopy from latent buds (this includes vines that were planted this spring). Depending upon variety, the secondary shoots may bear a partial crop, but rarely more than 25% of what the primary crop would have been. Varieties with extremely fruitful secondary buds, such as Seyval, may do a bit better.
Management of the vines during the course of the growing season may need to be adjusted in response to frost injury. The loss of crop is demoralizing of course and one might be disinclined to exercise the same level of pest management and canopy management that he/she would expend with fruitful vines. Remember though that the light environment and carbohydrate status of this year's shoots will determine bud fruitfulness in the following year. Shoot thinning and shoot positioning may still be necessary. The pest management schedule can be modified, depending upon the presence or absence of crop. Lacking crop, one could justifiable cut back on black rot and botrytis fungicides, as well as the grape berry moth sprays. It would still be important, however, to keep foliage free of the mildews and to avoid excessive japanese beetle feeding. Unfortunately, a partial crop, if you wish to harvest it, will still require a full pest management program. New growers, experiencing their first episode of frost, may be concerned about the long-term welfare of the frosted vine. There is no point in attempting to remove frost-damaged tissues from vines; the affected tissues will be shed in time. And, unless the temperatures were very cold, it is unlikely that damage to the canes or cordons will have occurred. Be patient. But if you find that spring (or early fall) frosts become a regular feature of your vineyard, you may need to consider one or more avoidance measures in the future, such as discussed in previous Viticulture Notes (Vol 13, No. 2 and 3).
As a corollary to above discussion, a grower recently asked what equipment we use for automated weather recording. Automated weather recording instruments provide a record of temperature, wind speed, precipitation, light and other environmental events, and some can be accessed for real-time viewing, but they are incapable of accurately forecasting the weather. If you want the record, your options are varied. We've used a solar-powered Easylogger in our research vineyard to record temperature, leaf wetness, and sunlight on an hourly basis. We bought the unit from a company called Omnidata, but the datalogging division of Omnidata has since been sold to Wescor (www.wescor.com/environmental/index.phtml) or 435-752-6011 ext. 1310. The Easylogger has served us well, but requires some time to program. With standard memory, hourly data can be collected for about nine months before the need to download.
We also use a Watchdog Weather Station sold by Spectrum Technologies, Inc. (www.specmeters.com) or (800) 248-8873 / (815) 436-4440. For a little over $1,000 you can acquire wind speed/direction, temperature, RH, and precipitation data. If your interest is primarily to record temperature events, I would suggest Spectrum's 100 series dataloggers. These matchbox-sized loggers cost as little as $60 each and will record up to nine months of hourly temperature data before the need to download. The associated software is easy to install and use, but a note of caution on all of the above dataloggers: there's no point in purchasing this equipment if you don't make the commitment to download the data and do something with it. We have a series of Watchdogs deployed at different elevations across the Blue Ridge Mountain and we've used the collected data to validate certain features of our vineyard site suitability maps. I should point out that the companies listed above are not the sole distributors of weather monitoring equipment; they are simply the ones that I've had direct experience with. Another company that specializes in agricultural weather monitoring (especially for irrigation scheduling) is Automata, Inc., based in California www.automata-inc.com/ (530) 478-5882; (800) 994-0380 (US only).
Weather forecasts: If your interest is getting a better fix on the weather forecast, the options are again varied. I start with the morning news or the paper, and work from there if I'm concerned. Most if not all of these forecasts are derived from National Weather Service-generated predictive models. Inexpensive (<$100) VHF "marine band" and AM/FM radios are available for local weather forecast reception; those with Specific Area Message Encoding "SAME") capability can be programmed to receive only locally-important weather information.
Internet-accessible weather forecasting services are abundant. One of many web sites worth checking out is the National Weather Service's regional forecast office, which offers a range of interesting and useful forecast and other weather information. The following web site is for the Southeast Regional Climate Center, which includes Virginia: http://www.dnr.state.sc.us/climate/sercc/products/nws_cwa.html
From this page you can enter more specific forecast offices, such as the Baltimore/Washington office in Sterling Virginia. Under the "experimental" heading of the local forecast office one can generate a 24-hr to 7-day forecast of low and high temperatures, precipitation forecast, and view sky conditions, all on a regional, graphic display. As with other "regional" forecasts, the resolution leaves a great deal of interpretation as to whether YOUR site is at risk of frost.
WWW.weather.com provides more localized weather and I routinely use the Winchester site to view current satellite imagery (very good for judging the onset of thunderstorms). Temperature forecasts are good, but imperfect.
Due to topographical variation, the best predictor of frost, low winter temperatures, and other temperature events will be your own record for your vineyard site. Most of us have had the occasion to witness how a 50- to 100-foot variation in elevation can translate into a five-degree (F) or more variation in temperature on a still, cold morning. We've used a faxed (can be emailed) forecasting service for the last five years offered by Skybit, Inc. of Bellefonte, PA (www.skybit.com) or 1-800-454-2266. The service runs about $50/month and includes a daily faxed summary of the 1- to 7-day weather forecast, including max and min temp, precipitation probability, RH and wind speed. An 8-10 day "outlook" covers the same variables. The data are specific for your site, and are arrived at by interpolating available National Weather Service data, adjusted for elevation. How good are the data? We've seen a fairly close correspondence between the predicted temperature and precipitation probability and our own data, with some notable exceptions (it's an imperfect world, folks). For example, some extreme low temperature events over the past couple of months were recorded as (Skybit 24-hour advance forecast/actual temperature recorded, all in °F): 22 May (36/35), 20 May (37/37), 24 April (33/37), 7 April (23/27), 23 March (19/25), and 5 March (14/12). The largest error here was the forecast for 19°F on 23 March, when the low only attained 25°F. The advance forecast is reasonably good, as well. For example, on 19 April, Skybit forecast a low of 34° for our site for the 24th of April. We recorded 37° on the 24th. Again, it's not perfect, but the forecasts are sufficient to prompt action (e.g., line up helicopters) or to allay fears. Unrelated to this discussion, but a point of interest, the 12°F that was recorded on 5 March was our lowest temperature of this past winter.
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Labs conducting grape tissue analysis:
[A comprehensive listing of plant and soil labs, some focusing on biological and organic matter analyses, can be found at www.attra.org/attra-pub/soil-lab.html]
|A & L Eastern Agric. Labs, Inc.||Agric. Analytical Services||Brookside Analytical Lab.|
|Richmond, VA||The Penn. State University||New Knoxville OH|
|(804) 743-9401||University Park, PA||419-753-2448|
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Contributed by Dr. Wayne Wilcox, Dept. Plant Pathology, Cornell University, NY State Agr. Expt. Sta., Geneva, New York
The following grape disease management summary was written primarily for New York grape producers. The text has been slightly edited and is applicable to our situation in Virginia. Our collective "thanks" to Wayne for providing this annual summary.
2. ProPhyt, Aliette, and phosphorous acid. ProPhyt (potassium phosphite) is a formulation of phosphorous acid (PA) that is now labeled by the EPA to control downy mildew on grapes. It does not control any other major grape disease. Various formulations of PA have been used for approximately 15 years to control downy mildew in Australia, and I repeatedly have gotten excellent results with several different formulations (including ProPhyt) in my own trials, even under very high pressure.
PA provides good post-infection control of downy mildew, but because it is highly mobile in the plant, the Aussies contend that it has only a few days' worth of residual (protective) activity before it gets shipped down into the roots. Thus, they tend to spray it after an infection period has occurred, tank-mixing with a traditional protectant (such as mancozeb or copper) to provide forward protection against the next one. In my own trials, I've applied it at 14-day intervals without any sort of tank mix and obtained virtually complete control every year, even in very wet seasons such as 2000, where nearly 70% of the berries on unsprayed vines became diseased. However, I haven't scrutinized these trials to determine just when the various infection periods occurred with respect to the timing of applications.
ProPhyt (sold by Helena) costs about $5 to $10/acre in material cost, depending on rate of application, so it is attractive from a cost standpoint. A note on rates: The ProPhyt label that I've seen specifies a concentration of 0.3%, but this assumes a sufficient water volume for complete coverage. Thus, we've used 1.2 pints per acre prebloom [assuming a spray volume of 50 gal/A for complete coverage] and 2.4 pints per acre postbloom [assuming 100 gal/A spray volume]).
Aliette is a product that has been around for many years, but just received registration on grapes last summer. It breaks down into PA once sprays have entered the plant, so basically does the same thing as PA products but at a much higher cost (about $30-50 per acre at the recommended rate for grapes). Patent issues protected Aliette against cheaper PA products in the past, but the patent has now expired.
Nationally, there are additional products containing PA that are being sold as nutritional supplements or "plant conditioners", without claims for their disease control activities. Of course, they're effective nevertheless. One such product that we worked with last year is Prudent Plus, a mixture of PA, monopotassium phosphate (which is labeled for powdery mildew control as Nutrol), and various organic compounds that are claimed to improve plant growth and health. In our trials last year, treated vines were virtually free of downy mildew and powdery mildew control was fair to good (better than Nutrol, worse than conventional fungicides).
3. Messenger. Messenger is a unique and interesting product now registered for control of grape diseases. It is a nontoxic protein that stimulates natural defense responses in some plants, thereby providing variable levels of resistance to disease-causing organisms. The only problem is, there is no convincing evidence that this occurs in grapevines. On the contrary, such an "induced resistance" response is notoriously difficult to elicit in grapes, although many people (including a graduate student in my own program) have tried to do so using various techniques and products. Furthermore, I have obtained poor disease control in previous grape trials where Messenger has been used without additional fungicides; however, these were conducted a few years ago and it's possible that the formulation has improved by now. Results from several grower demonstrations that I helped evaluate last year in cooperation with a juice grape processor could best be described as "inconclusive". Although my experience with the product is limited, it is not consistent with some claims in recent advertising. Those interested in the product may wish to evaluate it for themselves on a limited, trial basis.
4. Serenade. Serenade is a product whose active ingredient is a soil bacterium (Bacillus subtilis), which is registered for biological control of powdery mildew and Botrytis. In two trials last year (light disease pressure) we got fair to good control of powdery mildew when Serenade was rotated with Sovran on both the hybrid variety Rosette and on Concord. In a Botrytis trial in 2000 (moderate pressure), four applications of Serenade alone (no other fungicide) provided zero control of that disease. We're continuing to evaluate Serenade this season. Limited experience causes me to still view it as an experimental product; on a commercial crop, I'd be more comfortable experimenting to control powdery mildew rather than Botrytis.
5. Other "alternative" products for powdery mildew. As discussed last year, a number of non-traditional products have been registered recently to control powdery mildew on grapes. They work, to variable extents, but it helps to understand why. Powdery mildew (PM) is an unusual disease, since the fungus that causes it lives almost entirely on the surface of infected leaves and berries (the powdery stuff you see when control breaks down). Thus, it is "naked" and subject to (temporary) eradication following topical treatment with a range of products that don't affect other disease-causing fungi, which do their dirty work down inside the plant tissues where they're protected from such treatments. Some such products are listed below.
This scenario suggests that Nutrol should be more effective when applied relatively frequently (repeated knock-downs), rather than relying on residual protectant activity between sprays. Indeed, we've gotten significantly better control in 2 seasons of field trials when applying 4 lb/A every 7 days rather than 8 lb/A every 14 days. I strongly suspect that this same general principle (one-shot knock-down against young colonies, with little subsequent protective activity) will apply to most of the "alternative" PM control products. Thus, they may need to be applied more frequently than many traditional products.
[Note from TK Wolf: Steve Haskill, of Villa Appalachia winery in Virginia, offered the following: "I had a terrible experience with MPP 7 years ago. Bayleton will not dissolve in a MPP solution, but will stay in solution/suspension if added first. I found out the hard way in late-June when Black Rot appeared and I found the Bayleton in the bottom of the sprayer!!" . Related to this topic was our observation from several vineyards last season of foliar and fruit burn that occurred when some foliar fertilizers were applied in concert with certain fungicides under hot (>80ƒF) temperatures. As a precaution, avoid mixing nutrients and fungicides unless you're absolutely convinced that no phytotoxicity will result.
Finally, remember that the activity of these topical materials is entirely dependent upon their contact with the PM fungus. Don't waste your time and money if you can't provide thorough coverage.
6. Strobilurin fungicides. These materials (Abound, Sovran, Flint) have been discussed at length for the last 2 years. Thus, just a few updates and reminders:
7. Mancozeb and mites. This has been talked about quite a bit the last few years. Trials supervised by Jan Nyrop and Greg English-Loeb in the Entomology Department have consistently shown that fungicide programs that include regular mancozeb sprays will reduce the level of predatory mites (those that eat the spider mites), by an average of about 50% relative to programs where captan was substituted instead. In a few cases, this encouraged the buildup of spider mites, but not in the majority of trials. In an experiment last year, there was no effect on predators when mancozeb was limited to two sprays prior to bloom.
These effects are real. As with so many things, the risk (incompletely defined) and benefits (broad spectrum and economical disease control, 24 hr REI) need to be balanced. How to, specifically, is a personal decision. My feeling is that mancozeb still has a place, but that it should not be used indiscriminately. We're still working on trying to supply you more specific details than that.
2. Failure to control inconspicuous PM infections on the berries can increase the severity of berry rots (Botrytis and sour rot) at harvest. In each of the last 4 years, David Gadoury has shown that when unprotected berries of several V. vinifera cultivars were inoculated with PM spores about 4 weeks after bloom (near bunch closing), very little visible PM developed. However, such berries did develop a fine network of nearly microscopic infections and had much higher levels of rot at harvest when compared with berries that were protected against infection at that time. Furthermore, even when the inoculated berries didn't rot, they supported much higher levels of spoilage microorganisms, and wines made from these berries (by Thomas Henick-Kling's program) had noticeable off-flavors compared to the PM-free control group.
Bottom line: This isn't the only cause of berry rots and wine spoilage, but it's one that's very easy to avoid. Good PM control 4 weeks after bloom is a cheap and important safeguard of wine quality.
3. A quick review of PM biology with respect to management considerations. (i) The fungus overwinters as minute fruiting bodies (cleistothecia) that form on leaves and clusters during late summer and autumn, then wash onto the bark of the trunk where they're protectecd. Thus, the amount of fungus capable of starting disease this year is directly proportional to the amount of disease that developed last year (we even have numbers to prove the obvious). One consequence of this is that PM sprays during the first few weeks after bud break are likely to be far more important where PM was a problem last year, compared to blocks where most of the foliage remained clean through leaf fall.
(ii) Although leaf wetness isn't required for PM to spread once it's established, the first infections of the season do require rain to get started. Thus, the relative lack of spring rains last year may have contributed to the relatively low levels of PM that were observed in many vineyards throughout the region. Cluster disease severity over a number of years also has been correlated with the number of rain events during the period of maximum fruit susceptibility. Although PM is not influenced by water to the same degree as other fungal diseases, the relative need for control will be influenced by the frequency of rain events, particularly those during the first half of the season.
(iii) Once PM gets started, disease spread is influenced primarily by temperature.
Below is a table summarizing work conducted in California during the 1950's, showing how (constant) temperature affects the number of days from the time a spore lands on a leaf until it produces a PM colony with a new generation of spores to cause disease spread.
This is the "guts" of the current University of California PM model, which allows growers to back off their spray program when temps consistently stay in the 90's. In our region, these data may be most useful as a reminder that PM is relatively slow to develop when spring temps are cool, but can spread rapidly once we get warm days and nights.
(iv) Many observers have noted that PM "hot spots" often develop close to bodies of water or in other humid sites. Recently, our research (conducted under controlled conditions) has confirmed that disease severity increases significantly as the relative humidity increases. Thus, the higher average humidities associated with wet years appears to be more conducive for disease development (tighter spray program needed) than the lower humidities associated with dry years.
4. Don't overly-rely on either the strobilurin or the SI fungicides. Just another reminder of the need for resistance management, in case you missed the sermon above.
5. Fungicides. Flint is the best thing out there (A+), but is weak against downy mildew; Sovran also is excellent, more of an "A" than an "A+", but is stronger on downy; Abound is an "A-" , but is excellent against downy, significantly better than the other two under pressure situations. Everybody knows that the SI fungicides have slipped, but they still have their place in rotational schemes; most growers no longer rely on them very heavily during the critical period from the start of bloom through early berry development. Sulfur is cheap and effective. Newer non-traditional products are discussed above.
1. As fruit mature, they become increasingly resistant to infection AND infections take longer to show up. This is old news by now. Remember that berries are highly susceptible to black rot from cap fall until 3-4 weeks (Concord) or 4-5 weeks (Riesling, Chardonnay) later, then become highly resistant to immune after about 2 more weeks. Not surprisingly, this acquisition of age-related resistance happens a bit more quickly (faster by a week or so) in warm summers relative to cool ones. As often noted, we've regularly obtained excellent control with sprays applied at the start of bloom plus 2 and 4 weeks later, which provide protection during the period of peak susceptibility and most or all of the remaining susceptible time. Some growers get good control with just the first two of these sprays. Some try to and don't. Obviously, inoculum availability and weather have a lot to do with how far you can push things.
We've also found that clusters infected within a few weeks after bloom show symptoms about 13-15 days later and that disease progress is typically completed within 21 days after the infection event. In contrast, clusters infected near the end of their susceptible period showed virtually no symptoms 21 days later, and those symptoms that did develop failed to appear until 23 to 33 days after infection. Significance: Black rot that begins to show up in early- to mid-August is probably the result of infections that occurred in early- to mid-July. This fact should be considered when trying to determine "what went wrong" should such disease occur.
2. The SI fungicides are most effective in "reachback" activity, whereas the strobilurins are most effective in "forward" activity. In field experiments last year, we inoculated young berries at various intervals both before and after sprays with Nova and Abound. Nova showed greater activity when applied after the infection period, whereas Abound was the opposite. These general trends aren't surprising, but they're worth considering in certain circumstances. For instance, if the first BR spray of the season is applied after a number of potential infection periods, Nova or Elite may be the best choice if this disease is of significant concern. Conversely, the superior residual activity of the strobilurins may make them more attractive as the final BR spray of the program. No need to get too fancy here, other diseases also need controlled along with BR, but understanding how these materials work can help sometimes.
3. BR pressure is extremely dependent on overwintering inoculum levels. We, and many growers, have grown accustomed to ignoring the consequences of BR infection periods that occur before the start of bloom. Research and experience has shown that this is possible when overwintering inoculum levels are low, as they are in most commercial vineyards, since the spores produced from any early leaf infections are few and far between. Thus, they are easily controlled by the critical sprays applied as fruit begin to form. Scarce overwintering inoculum also reduces the chance that fruit will become infected from this source before such spores are depleted in the early postbloom period, thereby allowing BR sprays to stop early if the vineyard is clean. In contrast, heavy disease carryover from the previous year may require protection of the foliage 2 or more weeks before bloom along with protection of the fruit until they are highly resistant.
4. Mummies retained in the canopy provide significantly more pressure for BR development than those dropped to the ground. Once again, this concept is getting to be old history. Few growers got much black rot last year, and even fewer left their mummies in the canopy. Those that did usually had their reasons. Nevertheless, don't forget how much additional control you can provide by the simple practice of dropping mummies to the ground during hand pruning or follow-up.
5. Fungicides. Nova and Elite remain the "kings". Unfortunately, the most important time to control black rot (bloom and early postbloom) is when we're trying to substitute strobilurin fungicides to control PM. As with so many other things, there are trade-offs, it just depends which disease is more important to you. That being said, Abound, Sovran and Flint do provide very good to excellent control, equal to mancozeb, ziram, and ferbam under moderate pressure and superior to them under heavy rains (they're less likely to wash off). Of course, mancozeb, ferbam, and ziram are old standards and will provide good control under most commercial conditions. Captan, Rubigan, and Procure are fair. Copper is poor.
Disease biology. Recall that primary infections can occur from about 2-3 weeks before bloom until fruit set, so this is the critical time to prevent DM from getting established. The disease has a complex biology, requiring rainsplash to get the first spores from the fungus' overwintering sites in the soil up into the canopy, then humid nights followed by rainy days to get it to spread. Nothing happens unless all of these "stars are in alignment", but spread can be explosive with a 4-5 day generation time when everything is right for the fungus (or wrong for the grower). Spread is most rapid at temps of 65-77°F (no activity over 86°F), although it can occur down into the 50's. A current threshold for determining the time of the first possible infection is (i) a temperature of at least 52°F, accompanied by (ii) at least 0.1 inch of rain, after (iii) vines have reached a growth stage corresponding to 5-6 unfolded leaves with fruit clusters clearly visible.
The disease typically "goes on vacation" once warm, dry weather hits in the summer, and it can take some time for it to reactivate after this occurs. The erratic occurrence of DM coupled with its explosive and potentially devastating nature make it an ideal candidate for scouting, especially after fruit have become resistant and the consequences of incomplete control are diminished (see below). No need to spray for it when it isn't there, but don't let it get rolling if it's active. A weather-based computer model to provide guidance on such decisions is currently being refined.
Fruit susceptibility. Clusters of some varieties are highly susceptible to infection as soon as the fungus becomes active during the prebloom period. However, recent research indicates that berries become highly resistant to infection as quickly as 2 weeks after the start of bloom, although berry stems remain susceptible for a few additional weeks. For many years, the standard test protocol on Chancellor vines at Geneva has been to start spraying about 2 weeks prebloom and continue through 4 weeks postbloom. Recommended materials consistently provide excellent control of fruit and cluster stem infections using this schedule, on the worst possible variety under high inoculum pressure. Ongoing research is designed to more precisely identify the critical periods for control within this window of vulnerability.
Fungicides. Ridomil remains the best downy mildew fungicide ever developed for use on grapes, but its cost and lack of activity against other diseases limit its general usage. It's also highly prone to resistance development. Abound has provided excellent control every year since we began testing it in 1996. Phosphorous acid formulations (see beginning section) have typically been equivalent to Abound in my trials on Chancellor. Sovran is marginal, seems to be OK under moderate pressure but don't rely on it in a bad year or site. Flint is poor. Copper, mancozeb, and captan are old standards because they work.
2. Susceptibility. There is a long-running debate about when berry infection is most likely to occur, and thus, when protective sprays are most beneficial. One school of thought is that most fruit rot is simply due to the preharvest activation of early latent infections, i.e., disease symptoms at harvest are merely the expression of infections that were initiated back during bloom. By this thinking, sprays through late bloom should provide all the benefit that any fungicide program can, and later sprays would be unnecessary. This has NOT been our experience in New York, nor of colleagues in France.
A second school of thought is that early, latent infections do indeed account for some proportion of the rotten berries seen at harvest, but that berries are actually most susceptible to acquiring infections from veraison onwards. By this model, activated latent infections are perhaps most important as a source of Botrytis spores within the clusters, which can then spread the disease to other berries as they become highly susceptible during the postveraison period. Thus, sprays at or after veraison should be very important since they protect berries when the fruit are most prone to infection, although early sprays also can provide significant benefits by reducing the opportunity for the fungus to establish itself within the clusters. Our research and experience supports this second model.
Varieties and clones with tight clusters also appear to be at increased risk of developing Botrytis. In order to examine the effects of both cluster architecture and berry age on disease development, we inoculated Botrytis spores onto berries of a tight- and loose-clustered clone of Pinot Noir (PN29 and Mariafeld, respectively) at late bloom, pea-sized berry stage, bunch closure, and veraison. Also inoculated were PN29 clusters that had been thinned after fruit set to approximate the looseness of Mariafeld. Two findings stood out in both years of the experiment:
(i) Although the incidence of latent infection was similar among all three clonal treatments, significantly more berries developed gray mold in the tight PN29 clusters than in the Mariafeld or unthinned PN29 clusters. Thus, cultural, mechanical, or chemical practices that loosen clusters should aid in control of Botrytis. Unfortunately, there are no easy recommendations, although various options are being tried.
(ii) Inoculations at veraison produced significantly more disease than did inoculations at any other time. For instance, inoculations from bloom through bunch closure produced virtually no rot in Mariafeld or thinned PN29 clusters (despite the existence of latent infections), and only 4-15% of berries in the unthinned PN29 clusters became diseased. In contrast, inoculations at veraison resulted in 6, 16, and 41% berry rot within the Mariafeld, thinned-, and unthinned PN29 clusters, respectively.
In a different experiment on Chardonnay, we inoculated fruit to provide 0-5 moldy berries per cluster 2 weeks before harvest. Not surprisingly, there was a direct relationship between the number of initial infections and subsequent disease spread: 1, 10, 24, and 40% of all berries eventually became diseased following inoculation of 0, 1, 3, and 5 berries per cluster, respectively. Thus, the establishment of only a few early infections led to significant spread as the berries ripened.
Despite these theoretical issues, the real question is,What kind of spray program works? To examine this, we've conducted spray-timing trials for the last 6 years in a Finger Lakes vineyard of the susceptible hybrid 'Aurore'. Conclusions from the 4 years in which significant disease developed are:
(i) in two of the years, equivalent control was provided by applying either two early sprays (bloom, bunch closing) or two late sprays (veraison, 2 weeks later), with no additional benefit from applying all four;
(ii) in the two other years, sprays at veraison plus 2 weeks later provided good control but was improved further by adding applications at bloom and bunch closure;
(iii) in one of those years, the two early sprays provided little control by themselves, although they did improve the activity of the two late sprays when all four were applied. Thus, it appears that the late sprays always provided benefit (about 50-90% control relative to the unsprayed vines), that this control was sometimes improved when the early sprays were applied first, and that early sprays by themselves provided inconsistent results.
3. Fungicides. Cultural procedure (especially promoting good air circulation and avoiding excessive nitrogen) are perhaps more important for controlling Botrytis than for any other fungal disease of grapes. Recognizing this, the availability of new Botrytis fungicides provides significant new tools to complement (not replace) the cultural control tools.
Vangard has been our most consistent performer. It's absorbed by the blossoms and fruit, thus should have limited reachback activity and doesn't wash off. It's highly prone to resistance development, so shouldn't be the only fungicide used over a period of time. The label allows two sprays per season, some European countries allow only one (resistance management). DO NOT rely on this single fungicide year after year.
Elevate has been a bit less consistent in our trials, although it appears to be a good fungicide and others have had better results. It is a protectant fungicide that doesn't enter the blossoms or fruit, but is quite rainfast. It should be a component in rotational strategies.
Rovral has a long and well-discussed history. Although primarily a protectant fungicide, it does enter sprayed tissues; it has some limited postinfection activity and is a good antisporulant material. Activity is improved by mixing it with an agent that improves uptake into the fruit, such as an oil or a nonionic surfactant. Because Rovral (and the related Ronilan) were the only Botrytis fungicides available for many years, their over-use led to resistance development and erratic activity in some vineyards. The good news is that, unlike other fungicides, resistance to Rovral declines over time if it is withdrawn from the spray program. Many growers have given it a "vacation" for the last couple of years, thus it is possible that Rovral might be safe to use in such situations for a maximum of one application per year. I see Rovral's place as a potential component in a rotational package, but don't think it should be the primary component in vineyards with a long history of use.
The strobies have performed well for us under moderate pressure. In limited trials, they have provided benefit when applied at bloom and bunch closing when followed with a Botrytis-specific fungicide at veraison and preharvest (we've used Vangard and Rovral). This strategy has the obvious benefit of taking resistance pressure off the other options while getting additional Botrytis control for free if using the strobies then anyway, but hasn't been tested thoroughly enough that I'm confident in recommending it. Appears promising enough that some may wish to experiment with it themselves if they're interested.
Control programs. Veraison appears to be the most important (but not only) time for fungicide applications, so near this time is when the best materials (Vangard or Elevate) should be used. Decisions about a subsequent preharvest application should be guided by weather, variety, current disease levels, and nerves.
Unless it's very dry, additional protection at bloom and/or bunch closure will probably improve the control provided by the later sprays. The negatives of doing so are cost and the desire to limit sprays to reduce the risk of developing resistance to the Botrytis fungicides. Whether to go with a strobies, one of the Botrytis-specific materials, or nothing should be influenced by weather, susceptibility and value of the particular variety/clone, and aversion to risk.
1. Early sprays control rachis infections. Although fruit infections by the Phomopsis fungus can cause serious and spectacular losses in wet years (especially on Niagaras), rachis infections are the most consistent cause of economic losses from this disease. In three different fungicide trials, we have found that the early, traditional Ph sprays (early shoot growth, as clusters first become visible) provide excellent control of these infections
2. Canopy architecture and management. Phomopsis spores are rain-splashed onto susceptible tissues from their overwintering sites within old wood, spurs, and pruning stubs in the canopy. Gravity makes them go down. Thus, we tend to see much worse problems in native American varieties (pendulous growth, usually drooping beneath these inoculum sources) rather than upright-growing V. vinifera and hybrid varieties. The latter aren't necessarily more resistant, but they do escape many of the potential infections that natives don't, particularly with training systems that cause most new growth to be above old wood (e.g., VSP). And of course, management systems that retain a lot of old canes and stubs in the canopy (e.g., mechanical hedging) increase the inoculum load and associated disease pressure within that vineyard.
3. Fungicides. Mancozeb, captan, and ziram have all provided good control of the basal shoot infections in our fungicide trials. Captan is being touted by some as far superior to the others. This hasn't been my experience, although it had a slight edge over mancozeb in one trial with extreme disease pressure. I'd consider other issues (captan is better at conserving mite predators, mancozeb doesn't have the 3-day re-entry restriction) as more important than any slight differences in activity between the two, especially in commercial vineyards that have maintained relatively good control over the years (low inoculum).
Abound, Sovran, and Flint have all been mediocre in my trials. We have had only one good test of the strobies against rachis infections; they provided significant control, but not as good as that provided by the traditional (and cheaper) protectant fungicides. Trial results from Michigan have shown good control of fruit infections by Abound. The jury's still out on the strobies, in my opinion, but there's no reason to use them early. Let's hope they're adequate during the bloom and early postbloom period (fruit rot control) when they're most likely to be used for other diseases.
4. Spray application technique. Many growers like to spray alternate rows in the very early season, assuming that sufficient spray will blow through the target row and impact on vines in the "middle" row. Last year, in cooperation with Andrew Landers, we examined this issue. A commercial 'Niagara' growers applied 25 gal/A to part of his block by spraying every row, and with another machine he sprayed 25 gal/A using alternate rows. Spray deposition was measured and disease was rated. In the forst spray (a few inches of shoot growth), both systems delivered the same average amount of fungicide to the canopy, but the alternate-row depositions were much more variable. In other words, some leaves were plastered whereas others were missed. In the second application (prebloom), vines in the middle row captured less spray than their every-row counterparts. Although dry weather limited disease development, there was some rachis infection in the alternate-row treatment but virtually none in the every-row.
Don't fix it if it ain't broke, but if you're having trouble controlling Ph and are using alternate-row spraying, the suggested remedy is obvious.
1-INCH SHOOT GROWTH. A Ph spray may be warranted if wet weather is forecast and the training system or recent block history suggests high risk. Option A: Nothing. Option B: Captan or mancozeb.
3-5 INCH SHOOT GROWTH. A traditional time to control Ph shoot infections. Perhaps more importantly, our recent evidence indicates that this also is an important time to control rachis infections, which can occur once clusters emerge. Since the late 1980's, we've considered this the time to start control of PM on vinifera varieties if temperatures consistently remain above 50°F. It's a hard thing to prove, but I'm not so sure this spray is that important in vineyards that were "clean" last year (little overwintering inoculum). If you're spraying anyway for Ph, it won't hurt to add something for PM, but this is probably the least important PM spray of the season. More likely to be important under relatively warm conditions (>65#176;F), less important if cool. BR control is seldom justified unless you¹re trying to clean up a real problem block AND weather is wet. Option A: Nothing. Option B: Mancozeb (BR, Ph). Option C: Captan (Ph). Easier on predator mites than mancozeb (or ziram), but not as effective against BR (which seldom matters at this time). Option D: Nova or Elite (PM, BR). Use 3 oz/A for economy with so little foliage now, but remember that coverage becomes even more important when you're working with lower tank rates. Option E: Rubigan (PM). At 2 fl oz/A (minimal labeled rate), cost is only about $4. Cheaper than Nova and Elite, especially if BR control isn't an issue. Option F: Sulfur (PM). Not very active at temps below 60#176;F, but neither is the PM fungus. Doesn't control other diseases. Option G: JMS Stylet Oil (PM). Should eradicate young infections IF thorough coverage is provided. Can use with mancozeb (or ziram), but not with captan (phytotoxicity). Option H: Nutrol (PM). Should eradicate young infections IF thorough coverage is provided. Option I: Serenade, if you want to experiment with minimal risk. Otion J: One of the PM products plus mancozeb or captan for Ph.
10-INCH SHOOT GROWTH. Traditionally, we've recommended not to wait any longer to control BR. Continued experience tells us that this recommendation is conservative (the spray generally isn't needed) unless BR was a problem last year (inoculum levels are high) and weather is wet and warm. Don't wait any longer to control PM on susceptible varieties (but wait until immediate prebloom on Concords). One of the best times to use an SI, also a possible time to experiment with "alternative" materials. DM control will be needed on highly susceptible varieties if disease was prevalent last year and rains of at least 0.1 inches at temps >52#176;F occur. Rachis infections by Ph are a danger in blocks with a history of the disease. Option A: Abound, Sovran, or Flint (PM, BR, some Ph; also, variable DM). Legal, but not the most efficient time to apply these materials. Expensive and increases resistance pressure if you intend to use them later, when they're really needed. Option B: Mancozeb (BR, Ph, DM). A broad spectrum, economical choice if PM isn't a serious concern. Or tank mix with a PM material. Excessive use sometimes leads to mite problems by suppressing their predators. Option C: Nova or Elite (PM, BR). Option D: Rubigan (PM). Poor BR (usually not a problem if effective materials are applied in the next three sprays) but cheaper than Nova and Elite. Option E: JMS Stylet Oil (PM). If (and only if) coverage is thorough, this spray should eradicate early PM colonies that may be starting if previous PM sprays were omitted. At a retail cost of $11/gal, a use rate of 1% (1 gal oil /100 gal water), and 50 gal/A spray volume, cost is about $5.50/A. But don't waste your money if you can't cover thoroughly. Also may help with mites. Option F : sulfur (PM). Reduced activity (of both the sulfur and fungus) at low temperatures canh still be an issue at this time of year. Option G: Mancozeb (BR, Ph, DM) + a PM material (SI fungicide, sulfur, JMS Stylet Oil, Nutrol). Choose PM material based on previously-discussed characteristics and cost.
IMMEDIATE PREBLOOM TO EARLY BLOOM. A critical time for PM, BR, DM, and Ph (fruit infections). A good time to use a strobilurin on PM susceptible varieties. This and the first postbloom spray are the most critical sprays of the season--DON'T CHEAT ON MATERIALS, RATE, OR COVERAGE! Option A: Abound, Sovran, or Flint. Abound is very good to excellent against PM, DM, and BR, although the other two are a bit stronger against PM. Sovran is marginal against DM under pressure. Flint is outstanding against PM, inadequate against DM. All are equivalent against BR. The best choice in most Finger Lakes vineyards where SIs have been used for a number of years against PM, particularly if multiple disease control is needed. Should also provide some Botrytis control if a wet bloom period. Option B: Either Nova, Elite, or Rubigan PLUS mancozeb (PM, BR, Ph, DM). Nova and Elite are the biggest guns against BR, so might be the best choice if pressure is high and BR control is more important than PM. Nova and Elite provide postinfection activity against BR, so would be first choice if significant unprotected infection periods occurred within the previous week. Rubigan is (was?) cheaper that Nova or Elite, but doesn't provide nearly the same BR control; however, mancozeb should be adequate if postinfection control isn't required. If wet, mancozeb (or captan) should be included for control of Ph fruit infections in blocks where this has been a historical problem (processor restrictions and poor BR control with captan). Option C: Mancozeb + sulfur (PM, BR, Ph, DM). Cheap and reasonably effective but not the strongest choice at a time when the strongest choice is most justified. Potential mite problems.
MID- to LATE BLOOM. Vangard or Elevate for Botrytis control may be beneficial in certain years, particularly in problem blocks if weather is persistently wet. Abound, Sovran, or Flint applied recently may be adequate.
FIRST POSTBLOOM (10-14 days after immediate prebloom spray). Still in the most critical period for PM, BR, DM, and Ph (fruit). Same considerations and options as detailed under IMMEDIATE PREBLOOM. Juice grape growers can substitute Ziram (very good BR and Ph, only fair DM) for mancozeb if necessary.
SECOND POSTBLOOM. BR control still advisable under wet conditions and important if infections are evident on the vine. Fruit are less susceptible to PM now, but vinifera varieties (and susceptible hybrids?) still need PM protection, particularly to guard against fruit rots and promote wine quality. New foliage remains highly susceptible to PM. Avoid SI and strobie fungicides if more than a little PM is easily visible. Ph danger is mostly over unless very wet. Primary DM should be over, but continued protection may be needed on susceptible varieties if weather is wet, especially if disease already is established (look and see) Option A: Abound, Sovran, or Flint. Provides good residual control of the listed diseases if used now, but avoid overuse to promote resistance and wallet management. Should provide some Botrytis control. Option B: Nova or Elite (BR, PM) + captan or mancozeb (66-day preharvest restriction, mites) if DM and Ph control are needed. Option C: Rubigan (PM) + either (a) mancozeb (if more than 66 days before harvest) for BR, DM, and Ph; or (b) captan (DM, Ph, some BR); or (c) ziram (BR, Ph, some DM). Option D: Sulfur (PM) + either (a) mancozeb (if still allowed, mites have been considered) or (b) captan. In most years, lessening disease pressure makes this economical option increasingly practical as the season progresses. Option D: Copper + lime (some PM, DM). Adequate PM control for Concords, not enough for vinifera and susceptible hybrid varieties.
ADDITIONAL SUMMER SPRAYS. Check the vineyard regularly to see what's needed, the main issues will be PM and DM. On vinifera and other cultivars requiring continued PM control, use sulfur as an economical choice to maintain control; SIs and strobilurins are options if they haven't been overused earlier AND little disease is evident. Both provide the advantage of longer residual activity than sulfur, especially in wet weather. For DM, copper + lime or captan are economical standards; Abound is a viable option if general disease pressure or other conveniences justify its cost; Ridomil can be used in case of emergency. BR should not be an issue after the second postbloom spray, except in unusual circumstances (disease is established in the clusters of vinifera varieties, wet weather is forecast, and it's possible to direct sprays onto the clusters). Ph should not be an issue. See previous discussion for Botrytis at veraison, and preharvest.
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12 June -- Vineyard meeting: Horton Vineyard (town of Orange). 11:00 - 1:00 pm
18 June -- New Grower Workshop: Farm and Home Center, Lancaster, PA. An intensive one-day session covering economics, vineyard development, rootstocks, varieties, equipment andmuch more. Taught by Dr. Joe Fiola (Univ. MD Coop Ext), Dr. Tony Wolf (VA Tech U) and Mark Chien (Penn State). Information and registration can be obtained at http://winegrape.cas.psu.edu/calendar/calendar_pa.html
22 June -- Vineyard Establishment class at Linden Vineyard in Linden, VA. Topics include variety and site selection, planting, trellis, early vineyard care and economics. Classes cost $75 per person and run from 10:30 to 4. Space is limited, pre-registration is required. Call 540 364-1997 or email@example.com.
23 June -- Vineyard Canopy Management class at Linden Vineyards in Linden, VA. Topics include training systems, basic vine physiology, managing vigor and quality and basic vine nutrition. Same details as previous listing.
26-28 June -- American Society for Enology and Viticulture Annual Meeting. Portland, Oregon. This is a fine technical meeting with many papers from viticulture and enology researchers around the world. A large trade show is also part of the event. You can find information at http://www.asev.org/
10-12 July -- ASEV Eastern Section American Society for Enology and Viticulture 2002 Conference, Baltimore, Maryland. Conference focus: Red Wine Varieties for the East: Merlot, Cabernet Franc, Syrah, and Chambourcin -viticultural and enological aspects of four red varieties that have become the backbone of the East. Feature presentations of international experts and commercial and academic specialists from the US, including tasting of representative wines. The conference will be held at the Sheraton Baltimore North, 903 Dulaney Valley Road, Towson, Maryland. Reservations: (410) 321-7400 or visit the hotel website at www.sheraton.com/baltimore. For conference registration and information visit the ASEV Eastern Section website at www.nysaes.cornell.edu/fst/asev or contact: Ellen Harkness, 1160 Food Science Building, Purdue University, West Lafayette, IN 47907, ph: (765) 494-6704., E-mail: firstname.lastname@example.org.
7 August -- Vienyard meeting: Christensen Ridge Vineyard and Winery. 11:00 - 1:00 pm
7-8 August -- Third Annual Eastern Pinot Noir Conference. Finger Lakes region. A technical celebration of this greatest of red wine grape varieties. Technical meeting and tasting. If you are a commercial grower or vintner of Pinot Noir, please attend. Contact Mark Chien at 717 394-6851.
21 August -- Vineyard Meeting: Whitehall Vineyards, Whitehall, VA-Albemarle Co. 11:00 - 1:00 pm
11 Sep t -- Vineyard meeting: Rush River Vineyard. 11:00 - 1:00 pm
18 Sept -- Vineyard meeting: Wintergreen Winery. 11:00 - 1:00 pm
If you are a person with a disability and desire any assistive devices, services or other accommodations to participate in this activity, please contact the AHS 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 the 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 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: email@example.com
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