Viticulture Notes

Vineyard and Winery Information Series:
Vol. 15 No. 3, May - June 2000

Dr. Tony K. Wolf, Viticulture Extension Specialist

Table of Contents

V.Upcoming Meetings

I. Questions from the field:

Questions: I have two questions concerning shoot and fruit thinning on vines that are entering their second year this spring. I retained two trunks on 70% of these vines, with canes of about 2 feet in length extending in both directions on the cordon wire. Every bud from the graft union to the end of the cordon pushed a shoot. Should I remove all shoots from the trunks? Secondly, how much fruit should I retain? There are 2 or 3 clusters per shoot and the vines are very vigorous.

Answers: This question, or variations on it, arise every year. The vines (Cab. F., Vidal, and Chard.) obviously made excellent growth in 1999. I commend your vineyard management and your decision to install irrigation (variety and irrigation information was provided separately to me). In answer to your first question, an abbreviated discussion on young vine training appears in the Mid-Atlantic Winegrape Grower’s Guide, (page 60) which I still encourage growers to consult for basic information. Generally, I would recommend that one or two shoots be retained near the graft union, as well as those that originate from the cane that was laid down on the cordon wire to form the cordon. The other shoots on the trunk (up to the bend or "head" region) can be removed. Be careful in stripping shoots from the trunk: shoots that are only a few inches long can be "rubbed" off with a gloved hand. However, longer shoots have more extensively developed vascular connections to the parent trunk. Breaking those more mature shoots off carries a risk of stripping wood from the parent trunk, causing a wound that may not heal well. This is strictly an anecdotal observation, but I’ve seen situations were trunk/cordon failure appears to be related to the presence of an old wound such as might occur with careless stripping of larger shoots from developing trunks. In those cases, the trunk/cordon failure was not associated with typical Eutypa dieback shoot symptoms, but the cross-section of affected trunk did reveal an inclusion sector of dead/decaying wood. There are a number of wood-rotting fungi that can affect vines, and causing entry wounds can facilitate some of those pathogens. The upshot of this line of thought is that older shoots should be removed cleanly from the trunk by cutting with pruners. Why leave the one or two shoots near the graft union? One can be used to form the second trunk (I still advocate double-trunking) if needed, and the other is simply a back-up in the event that the first trunk is less than optimal in terms of the cordon quality. That said, it’s not critical to retain any shoots at the base if you’re satisfied with the trunks/cordons that you’ve started.

The second answer addresses your question about how much fruit to retain. Here I’ll deviate somewhat from the aforementioned text, in which I recommended "a few clusters" be retained in the second year. The use of irrigation, grow tubes, better weed control and other inputs can result in very vigorous growth in the first years of the vineyard. Allowing vines to bear some crop in the second year can have two benefits: one is the accelerated return on investment gained by crop income; the other is the check or brake that the crop imposes on vine vigor. How much crop to retain is difficult to pin-point; as a start, I would suggest targeting about 1.5 tons/acre (one and one-half) for second year vines if you were able to lay down 18" or 24" canes for cordons at the start of year 2. You can start with that target and always remove crop if shoots appear weak — you can’t put the clusters back on once you remove them. How do you get there? Figure about 0.40 pounds per cluster on your Chardonnay if it’s clone 4 or 5, perhaps 0.30 per cluster with the smaller-clustered Dijon clones. Vidal = 0.35 to 0.40 #/cluster, and Cab. Franc, about 0.45 #/cluster. Then figure how many clusters per vine will produce the 1.5 tons/acre. If you’ve got 622 vines per acre (7’ X 10’ spacing), you’d need about 12 clusters per vine (@0.40 #/cluster) to get 1.5 tons/acre. I would start with that, and then do some follow-up thinning if need be by mid-July. At that point, you can use shoot growth as a gauge to determine whether more clusters should be removed. For simplicity, I often recommend using the trellis foliage catch wires as a growth gauge. This will vary vineyard to vineyard, but if a shoot fails to reach the first set of catch wires by mid-summer on a VSP trellis/training system — assume the first set of wires is 8 to 18" above the cordon — then all clusters would be removed from that shoot. If a shoot extends only to the top wire (about 30 inches above the cordon) by mid-summer, I’d take all but one cluster off it. If the shoot has extended well beyond the top wire, and is in need of hedging, I’d leave two, but no more than two, clusters on it. This formula may mean that some vines are thinned to less than 12 clusters per vine, while other could probably have tolerated more than 12 clusters.

Not everyone will have vines that can ripen 1.5 tons per acre in the second year, and some may argue that 1.5 acres is unreasonably low if their initial vine vigor is great. I emphasized above that the 1.5 t/a target might be reasonable if canes are already on the cordon wire. If not, concentrate on vegetative growth. Don’t automatically double the yield (3 ton/acre) in year 3. A more modest crop of 2 t/a in the third year could be attempted if you had both good fruit maturity and good cane "ripening" in the second year. Also, this answer is directed specifically at persons growing grafted grapevines. I would not, for example, attempt 1.5 t/a with non-grafted Seyval or other non-grafted hybrids.

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Plant tissue analysis:

Tissue analysis is a cheap, easy means of monitoring plant nutritional needs and avoiding nutrient deficiency symptoms. Bloom-time (or close to bloom) is the recommended time for collecting grape tissue samples in Virginia. An in-depth discussion is provided in the Mid-Atlantic Winegrape Grower’s Guide (http://www.ces.ncsu.edu/resources/winegrape/), and in a 1998 Viticulture Notes (http://www.ext.vt.edu/news/periodicals/viticulture/98mayjun.html) . Leaf petioles (75 to 100) are collected, dried and submitted to either a commercial or university lab for mineral analysis. The diagnostic sample concentrations are compared to standard concentrations associated with nutrient adequacy. On the basis of that comparison, the lab can indicate whether your vines are at deficient, adequate, or surplus levels for each of the tested elements. Tissue analysis is ideally used in combination with a visual assessment of vine growth, which is particularly important when determining the vine's nitrogen needs. Besides the routine bloom-time sampling, tissue sampling would also be recommended to help diagnose potential nutrient deficiency symptoms that develop late in the season. This has been particularly helpful with identification of potassium deficiency in young, drought-stressed vines over the past two years. I have no strong recommendations on labs to submit samples to. At $18 per sample, the Penn State service is still about the best bargain, but may not be quite as rapid as a commercial lab. If you wish to use the Penn State lab, give us a call and we’ll send you the submission kits (one kit per sample). The three labs listed below are three that we’ve used; however, there are others available. Readers in North Carolina should check with North Carolina State University for in-state service.

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III. Seasonal grape disease control issues:

The following discussion is provided by Dr. Wayne Wilcox, Department of Plant Pathology at Cornell University’s NY State Agricultural Experiment Station in Geneva, NY. While the comments apply principally to grape producers in the Finger Lakes Region of New York State, they also generally apply to Virginia conditions.

Recent fungicide registrations:

1. Vangard (cyprodinil). The federal label specifically calls for one application at early bloom and a second application at either berry touch, veraison, or preharvest. More discussion on the timing of sprays under the Botrytis section later on. Last year was the first season for commercial use of Vangard in NY, and it looked very good. In fact, Alice Wise on Long Island compared various two-spray programs of Vangard with programs incorporating up to four sprays of Rovral. Bottom line: Vangard provided excellent control, Rovral provided little or no control (probably due to fungicide resistance). (Resistance to Rovral may or may not be an issue in Virginia). Vangard is highly prone to botrytis resistance development, and therefore is labeled for a maximum of two applications per season. If you’re applying "only" two Botrytis sprays per season, I’d rather see Vangard used just once in rotation with something else (i.e., don’t use Vangard as the only Botrytis fungicide year after year, this is a good way to burn it out). Fortunately, we’re starting to get new Botrytis fungicides, so rotation is more feasible. And backing off on Rovral use may even bring it back to life where it’s having problems (discussed later).

2. Elevate (fenhexamid). Elevate is a new Botrytis fungicide that received federal registration late last year. Like Vangard, it has been classified by the EPA as a "reduced risk" fungicide (good environmental and toxicology characteristics). It is not related to any other fungicide on the market, so can be used in rotational programs for resistance management purposes once it’s registered here. Elevate has provided generally good control of Botrytis in our Finger Lakes tests, but not quite as good as Vangard. It does not control any other grape diseases.

3. Elite (tebuconazole). Elite now has NY registration. Recall that it’s a sterol inhibitor fungicide in the same chemical family as Nova. In repeated trials, Elite at 4 oz/A (the only labeled rate) and Nova at 4 oz/A have given us equal control of both black rot and powdery mildew. I’d choose one over the other on the basis of price. Although the company has data showing some suppression of Botrytis by Elite, we saw no activity in our trial last year (the only time we’ve looked at Botrytis control with this material).

4. Strobilurin fungicides. Strobilurins are the group of fungicides first represented by Abound. Two new "strobies", Sovran and Flint, will be available this season. Strobilurins are by far the most important group of fungicides to come along since the SIs, so let’s review how they work and compare them.

a. General characteristics. Recognize that Abound, Sovran, and Flint have their own individual strengths and weaknesses, but they also share a number of general characteristics. All are excellent inhibitors of spore germination; thus, they are excellent protectant fungicides. They are retained primarily within the waxy cuticle of leaves and fruit, which means that they are more rainfast than traditional protectants like mancozeb and captan. The fungicides diffuse throughout this waxy layer to provide a relatively uniform dose across the surface. Also, a small portion of the total dose diffuses through the leaf from the sprayed surface and, after a few days, enough accumulates on the other side so that it offers fungicidal protection on that side even if it was unsprayed. (We’ve done our own greenhouse tests to support this claim of the manufacturers). This combined "package" of fungicide retention and movement is unique to the strobilurins, and different manufacturers have made up their own trademarked names to describe it, e.g., "surface systemic" for Sovran and "mesosystemic" for Flint.

Because the strobies are primarily retained in the waxy surfaces, they are not good postinfection fungicides. That is, they do not get down into the body of the leaves and fruit where most fungi do their dirty work after they establish an infection. However, the strobies are powerful antisporulants. That is, when applied beyond their period of true postinfection activity, they allow lesions to develop but inhibit the production of a new round of secondary spores from the lesions. This is particularly significant for powdery mildew, downy mildew, and black rot, where most disease losses result from repeated infection cycles caused by the secondary spores produced on infected tissues during a single season.

b. Resistance risk. Resistance to strobilurins has already appeared in powdery mildews of cereal grains and cucurbit crops in Europe and Asia, as well as in Botrytis of greenhouse crops. Thus, resistance is a very real concern, and resistance management must be taken seriously.

To date, strobilurin resistance appears to follow the "Benlate model", that is, resistant isolates are virtually immune to the fungicides and multiply rapidly if they are not controlled by some other material. Furthermore, a fungal strain that is resistant to one of the strobies will be resistant to all of the others. Therefore, all three companies have agreed on identical labeling which requires use patterns that incorporate basic resistance-management principles: Do not make more than four sprays per season of any strobilurin on wine or table grapes, with a maximum of three applications in a row. NOTE THAT THESE RESTRICTIONS ARE DIFFERENT FROM THOSE ON THE PREVIOUS ABOUND LABEL (which allowed six seasonal sprays, but no more than two in a row).

These restrictions are designed to (i) minimize the selection of resistant strains, by limiting the number of selection events (sprays); and (ii) limit the opportunity for resistant strains to multiply, by using unrelated fungicides in rotation. Pricing will discourage the reckless overuse of these materials, but use some common sense as well to help prolong their useful lives.

c. Sovran (kresoxim-methyl). Sovran received federal registration last season. We’ve tested Sovran pretty intensively since 1995 and Flint since 1998. Based on our experience and what I’ve seen from other locations, I view all three strobies as equal versus (i) black rot (very good, a bit better than mancozeb/ferbam/ziram but not quite as good as Nova/Elite); (ii) Phomopsis (only fair); and (iii) Botrytis (none are labeled for this disease, but they’ve provided fair to good control in our limited tests under moderate pressure).

The differences among the three materials come with respect to control of powdery and downy mildews. At commercial rates, Sovran (3.2 - 4.0 oz/A) has been a little stronger than Abound (11-12 fl oz/A) versus powdery, but not as strong versus downy. Note that the company recommends a rate of 4.0 - 6.4 oz/A for downy control by Sovran, which is not cost competitive with Abound above the 4.0 oz rate. Commercial experience will tell the tale, but my feeling is that the 3.2 - 4.0 oz/A rate of Sovran should provide adequate downy protection on moderately resistant varieties (e.g., Concord) and even on susceptible varieties under moderate pressure; however, I wouldn’t count on it for viniferas under pressure.

Sovran is phytotoxic to a select group of sweet cherry varieties when sprayed directly onto the foliage; however, manufacturer representatives have stated that concentrations resulting from drift or spray tank residues will not cause damage. Sovran is not known to have any other phyto problems. It is registered for use on apples.

d. Flint (trifloxystrobin). Flint is the newest of the strobies, seemingly coming from out of nowhere only 2 yr before it gained federal registration last fall. Although experience is limited, Flint at commercial rates (1.5 - 2.0 oz/A) appears to be the strongest of the three strobies versus powdery but the weakest versus downy. In fact, Flint is labeled only for "suppression" of downy, and at the economically-prohibitive rate of 4 oz/A. Bottom line: If using Flint, boost it by tank mixing with an effective downy fungicide (e.g., a half-rate of mancozeb) where control of this disease is needed.

FLINT IS PHYTOTOXIC TO CONCORD GRAPES AND CANNOT BE USED ON THIS VARIETY. Manufacturer representatives have stated that concentrations resulting from drift or spray tank residues will not cause damage. Flint is not known to have any other phyto problems. It is registered for use on apples.

Finally, note that--surprise!--prices for the three strobies will be "competitive" with one another within the commercial ranges given above.

6.Monopotassium phosphate (eKsPunge, Nutrol). Now labeled as a powdery mildew fungicide in NY, the trade name of "eKsPunge" is being changed to "Nutrol". We’ve been looking at this "dual purpose" material (foliar nutrient plus powdery mildew fungicide) since 1996. Last spring, we found out that it functions poorly as a protectant (when applied before inoculation with powdery mildew spores), but does a good job as a "curative" spray when applied within 3-5 days after exposure to the spores. This suggested that more frequent applications (i.e., a greater number of "curative" sprays) might be more effective than our standard 2-wk schedule, since PM spores are almost always present during the growing season. So, we compared 8 lb/A on a 14-day schedule versus 4 lb/A on a 7-day schedule (same amount of product per season, but different numbers of potentially-curative applications). Sure enough, the 7-day schedule was significantly more effective.

We’ll continue to investigate this phenomenon further. However, my guess is that the same general principle will apply to any of the "alternative" PM control products (e.g., salts such as monopotassium phosphate or potassium bicarbonate, oils such as JMS or Trilogy, dilute solutions of hydrogen peroxide), which appear to function via topical application to new or existing PM colonies. In other words, use them at fairly short intervals or to stretch out the effective period of a standard product (e.g., by controlling new infections that start to bleed through as the standard material poops out), but don’t count on long residual control after the application.

Because monopotassium phosphate is an acidifying agent (lowers pH of the spray water), it should not be used with copper products until more experience with this combination is obtained.

You’re getting tired of hearing this, but it doesn’t make it any less true. Remember that Concord berries become virtually immune within 3-4 weeks after bloom starts. Vinifera berries lose most of their susceptibility at this same time, although they do not become fully immune until considerably later. Susceptible hybrids seem to act like viniferas, e.g., on ‘Rosette’, we typically get 90% control of berry infection from just the prebloom plus first postbloom sprays, whereas we get nearly 100% control on Concords.

Leaves also lose susceptibility as they mature, but new susceptible tissue is constantly being produced so long as the shoots keep growing. On vinifera and susceptible hybrid varieties, there’s a direct relationship between control of PM on the foliage and fruit quality at harvest. Maintaining a healthy, functional canopy should also improve winterhardiness. In contrast, Concord fruit are remarkably unaffected by foliar infection at moderate cropping levels, although Brix and other quality factors are decreased by foliar PM at higher cropping levels (e.g., 10 tons/A and above).

Bottom line, one more time: The first few weeks after the start of bloom is not the time to economize on PM control programs. Use your best fungicides (generally, one of the strobilurins), spray every row, and take the time to do it right. Keep the fruit and foliage clean afterwards to an extent appropriate to the variety and crop value. See next item.

2. Failure to control inconspicuous PM infections on the berries can increase the severity of Botrytis (gray mold) at harvest. This unanticipated association was noticed by David Gadoury on Pinot noir berries in 1998 and was confirmed by him on additional vinifera varieties in 1999. In experiments designed to study how berries become more resistant to PM as they age, David noted that clean fruit inoculated with PM spores about 4 wk after the start of bloom developed sparse, inconspicuous infections that were barely visible to the naked eye. He also noted that these same fruit had much higher levels of gray mold at harvest than did berries on which such infections were controlled. Seeing such things happen in one vineyard in one year is "interesting"; seeing it happen two years in a row, in different vineyards and on different varieties, convinces me that something real is going on.

The "why" of this phenomenon is being investigated. What to do is simple: on the fruit of varieties susceptible to Botrytis, be sure to maintain an excellent PM control program at least through bunch closure.

3. The SI fungicides don’t work like they used to, but they’re not dead. Those of you for whom the SI fungicides still do work like they used to are lucky, but you’re still bound by the same laws of nature as everyone else. The efficacy of these materials will erode over time. The question is not "if", but rather, "when". And it’s the "when" part that we have some control over.

If using the SIs, a primary objective (after disease control!) should be to maintain the effectiveness that they still have. Ideally, we can continue to use these materials as effective components in rotational programs with the strobilurins, thereby helping to keep both groups alive.

Below are the annual reminders with respect to SI resistance management:

(i) Limit SI use, preferably a maximum of three sprays per year, and rotate with unrelated fungicides.

(ii) Recommended rates and thorough spray coverage are CRITICAL for adequate performance and resistance management. The surest way to encourage SI resistance is to use low rates of these fungicides. The surest way to provide low rates to certain parts of the vineyard is to provide uneven spray coverage. It’s still just that simple.

(iii) The SIs will perform much better, and less resistance will develop, when they’re used to combat a small PM population rather than a large one. Position them early in the season (conveniently, not an optimal time for using the strobies) or use them to maintain a clean vineyard mid-season. You’re just asking for trouble if you try to use these materials to clean up or slow down a PM problem that’s already developed (this is true for the strobies, also).

1. As with powdery mildew, berries are highly susceptible to BR from bloom through the early fruit set period, but they become highly resistant approximately 4-6 wk after the start of bloom. We’ve seen this in all three years of a trial in which berries of Cayuga White, Chardonnay, Concord, and Riesling were inoculated at weekly intervals after bloom. Similarly, in two commercial Finger Lakes vineyards and local research plots, we’ve noted much higher BR levels in years when this period was wet versus those when it was dry. So, be extra vigilant with your BR control practices if conditions are wet in late June and early July; relax a bit if they’re dry.

2. Most, if not all, commercial control comes from the immediate prebloom and first two postbloom sprays. In fact, all of the control obtained in eight out of 10 spray timing trials that we’ve conducted since 1995 has come from these three sprays (i.e., additional sprays applied earlier and/or later provided no additional benefit). Thus, even when early leaf infections have been left uncontrolled in these vineyards, we’ve gotten complete control of berry infection with thorough coverage of the fruit during their early stages of development. This and other observations suggest that serious black rot losses are caused primarily by spread of the disease within infected clusters (i.e., from new spores produced on berries infected shortly after bloom), more so than by spores produced in early leaf infections.

However, this is not to say that leaf infections cannot be important. Trials conducted in a Finger Lakes vineyard with a history of extensive black rot losses (thus, very high inoculum levels from year to year) showed that in this case, an additional spray 2 wk before the immediate prebloom application provided an additional measure of control. Bottom line: bloom and early postbloom sprays should be adequate in relatively "clean" vineyards, but sprays may need to start earlier in blocks with significant BR the previous year.

3. Mummies retained in the canopy provide more pressure for BR development than those dropped to the ground. This should be a no-brainer, but it’s been striking to see how much such a simple practice contributed to disease control when we examined it over the last 2 years. That is, when we went into a machine-pruned vineyard where mummies had been retained in the canopy after hedging, then hand-pruned them to the ground in certain plots, we ended up with much less BR than in comparison plots where the mummies were left hanging. Don’t ignore this aspect of sanitation if you’re having trouble with BR control.

No major news with respect to BR fungicides: (i) Nova and Elite are still the "kings"; (ii) mancozeb, ferbam, and ziram will provide good control under most commercial conditions; (iii) Abound, Sovran and Flint have been equal to or better than mancozeb and ziram in our tests (they’re less likely to wash off, and probably retard secondary spread due to their antisporulant activities ). Captan, Rubigan, and Procure are fair. Copper is poor.

No real news. Recall that inoculum overwinters in last year's infected leaves on the vineyard floor. The first spores become mature about 2 to 3 weeks before bloom, and cause infection during rainy periods when temperatures are 50°F or higher. These primary infections can continue to occur until about 2 weeks after bloom (we think).

The destructive phase of the disease is caused when spores produced from primary infections blow through the vineyard and cause repeated cycles of secondary infections if humid nights are followed by rainy days. At optimum temperatures of approximately 60 to 80° F, this cycle can repeat itself every 4 or 5 days, allowing an "explosive" disease epidemic when favorable weather conditions persist. Young fruit are highly susceptible to infection, but appear to lose susceptibility quite quickly with age, much as with PM and BR. In our test block, we traditionally quit spraying ‘Chancellor’ (ridiculously susceptible fruit) 4 wk after the start of bloom, and clean fruit remain that way until harvest, even when they’re surrounded by unsprayed vines that are absolutely clobbered.

General control strategies are: (i) DM sprays should start on highly susceptible varieties about the 10-inch shoot growth stage (i.e., 2 to 3 weeks before bloom) unless the vineyard was very clean last year or you're sure it won't rain before the next spray.

(ii) All but the most resistant vineyards should receive a DM fungicide in the immediate prebloom and first postbloom sprays unless the weather is bone dry. This is the critical time to protect against fruit infection.

(iii) By the time the first postbloom spray wears off, primary inoculum is pretty well shot and the need for additional treatments should be based on the usual array of factors: presence or absence of established disease in the vineyard, weather, and variety. Typically, DM "goes on vacation" during much of July (many of the spores that spread the disease are killed by the spate of hotter, dry weather that we usually get at that time), then it reactivates as days get shorter and nights get dewier in August.

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. Which is probably good, since resistance can develop rather quickly if the material is used heavily. In our trials, Abound has consistently been excellent, equal to mancozeb in some trials and better in others (e.g., when the first spray was applied late or in high rainfall years). As noted above, Sovran has been somewhat weaker than Abound, typically providing 80-85% control (relative to the unsprayed vines) versus 95-100% control for Abound. Flint looked very good in 1999 (dry) and pretty bad in 1998 (wet). Copper, mancozeb, and captan are old standards for a good reason: they work.

1. Rovral’s not alone anymore, but don’t throw it out just yet. After having Ronilan and then Rovral (closely related dicarboximides) as the only effective Botrytis fungicides for nearly 20 years, this picture is changing rapidly. It’s very good news to have new fungicides in the bag of tricks, but never forget that even the best Botrytis fungicide is only a complement to various cultural control practices that promote air movement around the clusters and help to expose the fruit.

First, a word about Rovral. The bad news is that resistance to the dicarboximides occurs pretty easily, and at least some anecdotal reports of inconsistent performance in commercial NY vineyards probably reflect this fact. The aforementioned failure of Rovral in a Long Island trial where Vangard provided excellent control is an even more concrete, if unproven, example. The good news is that Rovral resistance is not stable, i.e., resistant individuals of the Botrytis fungus do not survive from one season to the next as well as susceptible individuals do. Thus, there are reports that even in a resistant vineyard, the first Rovral spray of the year provides relatively good control (most of the overwintering population is susceptible), but subsequent sprays become progressively less effective as the resistant individuals selectively survive and multiply.

In practical terms, this means that we might be able to "bring Rovral back", even where it’s not working so well anymore, by (i) taking it out of the picture for a year, (ii) allowing most (?) of the resistant individuals to die out, then (iii) reintegrating it into a rotational program with other Botryticides, using a maximum of one application per year. Because our new Botryticides are also susceptible to resistance development, we need to keep all effective materials alive and in rotation with each other.

2. Infections at bloom and bunch closing can be important. Traditionally, NY recommendations for timing Botrytis sprays have emphasized the importance of the veraison and the preharvest periods. Whereas these recommendations were based on sound field data, they tended to ignore the potential importance of infections occurring during the bloom and/or bunch closure periods, which are considered to be important in many other parts of the world.

We have found a benefit from applying sprays during bloom and bunch closing in 4 of our last 6 years of field trials in the Finger Lakes; when directly compared in 1998 and 1999, these two sprays were as effective as the veraison plus preharvest combination. In the aforementioned Long Island trial, Alice Wise had only 6% infection of Chardonnay clusters when Vangard was applied at bloom plus bunch closing, versus 46% infection in unsprayed plots. (This even though there were only three rain events totaling 1.0 inch from the bloom spray through 2 weeks after the bunch closure spray, versus eight rain events totaling 9.7 inches between veraison and harvest). Furthermore, when we inoculated Pinot noir clusters in Geneva at 90% bloom, the pea-sized berry stage, or at bunch closing last year, virtually all berries developed latent (dormant) infections, and 14-20% of them activated into visible gray mold at harvest.

Collectively, these data suggest that we probably have underemphasized the importance of early-season Botrytis infections, although there is still a lot of mystery as to when and why such latent infections turn into rotten berries at harvest. Nobody wants to spray four times per year to control Botrytis, for obvious reasons. Nevertheless, it appears that fungicidal protection during the bloom through bunch closure period may be appropriate under "certain conditions" (Which ones? We’re working on it.) Currently, we’re hoping that perhaps the strobilurin fungicides might provide enough protection during this period to allow us to save the Botrytis-specific materials (Vangard, Rovral, Elevate) for the traditional period at and after veraison. See below.

3. The strobilurins appear to have significant activity against Botrytis (but how much?). Take this with a big grain of salt, because we haven’t tested the strobies in a pressure situation yet. Nevertheless, we’ve seen pretty impressive control from all three materials in both our 1998 and 1999 trials in the Finger Lakes. It would be nice if their activity turns out to be adequate during the bloom and early postbloom period (their best timing fit for control of other diseases), especially if they’re helped along with better Botryticides later on. Remember, though, this is a work in progress and may fall flat under pressure. If I had a Pinot noir block with perennial Botrytis problems and it was wet and warm during bloom or bunch closure, I’d try a shot of Vangard until I knew otherwise.

No real news here. The incidence of Phomopsis shoot infections seemed to be increasing in the Finger Lakes region for several years, then it forgot to rain last spring (and summer) and the problem seemed to disappear. Nevertheless, inoculum is still present in blocks that have had Phomopsis recently, and over the long run it’s worth controlling this phase of the disease in many vineyards if rainy weather is forecast during the early shoot growth period.

Recall that fruit become infected by Phomopsis when intense and/or frequent rainfall occurs during the bloom through pea-sized berry period, although infected fruit do not show symptoms until near harvest (symptoms resemble those of black rot, and the two diseases are difficult to tell apart on the fruit). The most consistent economic losses from Phomopsis appear to be caused by infections of the rachises (cluster stems). Although not well studied, rachises appear to be susceptible to infection from the early period of cluster emergence until several weeks after bloom.

The risk of Phomopsis losses (and the relative need to control them) can be judged to some extent by (i) the recent history of the disease (an indication of how much inoculum is in the vineyard); (ii) the pruning and training system (shoots, rachises, and fruit that develop beneath old spurs and pruning stubs are at greatest risk, whereas those trained to grow above these spore sources are least vulnerable); and (iii) the weather (frequent and/or prolonged rains).

Mancozeb, captan, and ziram have all provided good control of the basal shoot infections in our fungicide trials. Abound, Sovran, and Flint have all been mediocre. We have had only one fair 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.

We all know that there are many good programs for controlling these diseases. Here are a few considerations. As always, just because it isn’t listed here doesn't mean it’s a bad idea. Only products currently labeled in NY State are listed. Readers in other states have the option of substituting Elevate into the mix for Botrytis control.

IMMEDIATE PREBLOOM (or very early blooom). A critical time for PM, BR, DM, and Ph (rachis and fruit infections). Also important for ALS on susceptible varieties. 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 (PM, BR, some Ph; also, variable DM [Abound, excellent; Sovran, fair to good; Flint, poor to fair]. The best choice if SIs have been for a number of years against PM, particularly if multiple disease control is needed. May provide some Botrytis control if a wet bloom period. Option B: Nova, Elite, or Rubigan + 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 if significant unprotected infection periods occurred within the previous 4 days. Rubigan is (was?) cheaper that Nova or Elite, but doesn’t provide the same BR control; however, mancozeb should be adequate if postinfection control isn’t required. 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.

BLOOM. Rovral or Vangard 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 (rachis and 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 may be needed if disease was present last year and a spray is strongly recommended if berry infections are evident this year, particularly if weather is wet. Fruit are less susceptible to PM now, but vinifera varieties (and susceptible hybrids?) still need PM protection, particularly on varieites susceptible to Botrytis. Rachises and foliage remain susceptible to PM. Avoid SI 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. Option A: Abound, Sovran, or Flint (PM, BR, some Ph; also, variable DM [Abound, excellent; Sovran, fair to good; Flint, poor to fair]. Provides good residual control of the listed diseases if used now. May provide some Botrytis control as bunch closure approaches. Option B: Nova or Elite (BR, PM) + captan or mancozeb (66-day preharvest restriction) 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) or (b) captan. In most years, lessening disease pressure makes this economical option increasingly practical as the season progresses. Option E: Copper + lime (PM, DM). Adequate for Concords, not enough PM control 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. Copper + lime will work for Concords. 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, 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 bunch closing, veraison, and preharvest.

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IV. Research update:

VT graduate student Sarah Finger has completed her two year MS degree study of the effects of horticultural oils on grapes. Sarah spoke of this work at the VVA/VSHS meeting in Williamburg in January 2000. Her work in Virginia was conducted primarily to determine what the "costs" or negative effects are associated with the use of crop oils used during the growing season. The oils can be petroleum or mineral oil-based products, or they may be vegetable in origin, such as the soybean oil used in some of Sarah’s work. Oils can be used as protectants as well as eradicants for powdery mildew (see Wayne Wilcox’s comments this newsletter); however, we know from previous work that oils can reduce crop maturation rate, and that they may also affect crop yield. The work in 1999 was a continuation of studies conducted in 1998. The objective of the main experiments of 1999 was to evaluate the effects of a single, or multiple applications of crop oil on leaf photosynthesis rates, crop yield components, and fruit maturation of Chardonnay and Cabernet Sauvignon grapevines.

The work was done with Cabernet Sauvignon grown at the Alson H. Smith Jr. AREC in Winchester, and with Chardonnay vines grown at Oaksworth Vineyard in Loudoun County, Virginia. Training, specifics of treatments, and all data related to this project can be retrieved from Sarah’s thesis http://scholar.lib.vt.edu/theses/available/etd-05262000-10430032/

Treatments: Treatment applications were made in the Cabernet Sauvignon vineyard on 21 July and 9 August. In the Chardonnay vineyard, applications were made on 20 July and 11 August. Treatments were applied using a hand held spray nozzle attached to a sprayer. The same five treatments were used in both vineyards, except that the water-only spray was not included with Cabernet Sauvignon. The oil used for all oil treatments was JMS Stylet oil. Five different treatments were compared:

Control (no applications made)

Water check — 200 gal/acre water applied to the entire canopy (only with Chardonnay)

100 gal/acre of 1.5% v/v oil in water emulsion applied only to the fruit zone

200 gal/acre of 1.5% v/v oil in water emulsion applied to the entire canopy

600 gal/acre of 1.5% v/v oil in water emulsion applied to the entire canopy

The "water" treatment was a second control — to determine whether the act of spraying had an impact on vine physiology; it did not. We would consider the 200 gal/acre rate to be the minimum effective rate to ensure complete and through coverage of leaves and fruit. Discretely spraying the fruit zone was done to see if the negative effects of oil could be minimized as in a case where powdery mildew might initially only be affecting fruit clusters. Treatment plots were protected from powdery mildew by other fungicides; however, we avoided sulfur applications for one week before and after each oil application.

Two measures of leaf photosynthesis were made after each treatment application to assess the impact of oil on leaf function. These measures were made under saturating light conditions, and with well watered vines. In other words, the vines should have been doing their thing.

Berry samples were collected from all treatment plots at both vineyards as the fruit matured. Berry weight, soluble solids concentration, titratable acidity and pH were determined. Crop yield components were determined at harvest. Pruning weights were recorded during dormant pruning. Again, other details can be found in the full thesis.

High volumes of spray (e.g., 600 gallons/acre) reduced Cabernet Sauvignon photosynthesis rates (Table 1). Even 200 gal/acre of 1.5% JMS Stylet oil reduced leaf photosynthesis relative to unsprayed vines. On the other hand, restricting the oil spray to the fruit zone (100 gal/acre) did not reduce photosynthesis relative to the unsprayed vines (Table 1). These results were similar to those observed with Chardonnay at Leesburg, where the same treatments were applied (Table 2). Again, higher spray volumes caused greater reductions in leaf photosynthesis rate. Note also that the reductions in leaf photosynthesis were greatest soon after oil application, and that leaf function recovered, or approached "control" values, with time.

Table 1. Leaf photosynthesis rates of Cabernet Sauvignon in response to 1.5% v/v JMS Stylet oil treatments applied on 21 July and 9 Aug 1999, Winchester, VA.

Photosynthesis rate (µ mol_m-2_sec-1)
Treatmentz	23 July y	3 August y	12 August y	17 August y
Water only	9.6 a	11.3	8.6 a	9.1 a
100 gal/ac.	8.7 ab	11.5	8.5 a	10.0 a
200 gal/ac.	7.8 b	10.9	7.6 a	8.8 a
600 gal/ac.	5.0 c	10.6	3.2 b	6.2 b
Days since last oil application	2	13	3	8

^zSee text for description of treatments.
^yMeans, within columns, followed by a common letter or not letter are not significantly different at P less than or equal to 0.05 using Duncan's new multiple range test.

Table 2. Leaf photosynthesis rates of Chardonnay in response to 1.5% v/v JMS Stylet oil treatments applied on 20 July and 11 August 1999, Leesburg, VA.

Fruit chemistry: Cabernet Sauvignon: The soluble solids concentration (SSC) of fruit sampled from Cabernet Sauvignon 600 gal/acre plots was lower than other treatments on the first three sample dates (Table 3). The 200 gal/acre treatment had a significantly lower SSC than the water treatment on all sample dates except 12 October. The SSC of the water treatment control and 100 gal/acre treatment were never significantly different. At harvest, there were no significant differences among the SSC of Cabernet Sauvignon fruit samples (Table 3). There were no significant differences in the pH of Cabernet Sauvignon fruit samples in 1999, except on 1 September. On that date, the pH of the 600 gal/acre treatment sample was lower than the pH of the 100 gal/acre and water control samples (Table 3). Treatment effects on titratable acidity were minimal (data not shown). Cabernet berry weights were slightly reduced at the 17 September sampling by the highest rate of oil application. In general, we did not see as pronounced a berry size reduction in 1999 as occurred with Chardonnay in 1998.