Viticulture Notes

Vineyard and Winery Information Series:
Vol. 16 No. 2, March-April 2001

Dr. Tony K. Wolf, Viticulture Extension Specialist

Table of Contents

III.Coming Meetings

I. Current situation:

Question: I've followed the Virginia wine industry for the last several years with a long-term interest in establishing a vineyard. Is there a need for more grapes or have I missed the boat?

Answer: You've not missed the boat, but don't be misled into thinking that the boat will take you to Avalon. The Virginia Department of Agriculture and Consumer Service's 'Agricultural Statistics Service' annually compiles grape production and acreage data. Their preliminary figures will indicate around 2100 acres of grapes (bearing and nonbearing) grown in 2000, up from about 1600 in 1998. Perhaps related to that increase, some Virginia growers have reported a softening of demand for some grapes, notably Chardonnay. In an effort to determine what the actual demand for Virginia-grown grapes is, we recently circulated a questionnaire among Virginia wineries. The questionnaire asked what the winery's desire was for purchase of grapes "above and beyond your current sourcing/production." In other words, I wanted to know what the unmet demand for crop was - how much additional crop could be grown without saturating existing markets? We also asked wineries to project their annual needs for at least a 5-year period. Survey questionnaires were sent to 62 wineries; 28 responded. Of those 28, nine indicated that they had no interest in purchasing fruit, and 19 specified one or more varieties they'd like to purchase. The results are shown in Table 1. If we presume that wineries that did not return our questionnaire were not interested in purchasing fruit, then only 30% of existing Virginia wineries are in the market for independently grown fruit. The total tonnage sought by those wineries is about 1300 tons (Table 1). That figure is very close to the figure that we obtained in a comparable survey in 1996, as well as the figure obtained by the Wine Marketing Office's (VDACS) own survey in 1998. While the demand is still there, the composition of what is being sought has definitely broadened. In 1996, wineries expressed an interest in purchasing up to 500 more tons/year of Chardonnay. Today that figure has dropped to 118 tons/year, and wineries are more selective about which clones of Chardonnay they'd like to purchase. While the relatively high-yielding clone #4 was mentioned by one winery, the others that sought Chardonnay listed lower yielding clones. Some of the varieties sought would raise eyebrows. For example, most of the 122 tons of Muscat Ottonel and all of the 123 tons of Ruby Cabernet were sought by one winery, and that winery represented 42% of all the grape tonnage sought. Another winery represents essentially all of the expressed interest in Malbec, Mourvedre, Norton, P. Manseng, Syrah, Tannat, Tinta cao, and Touriga.

The data of Table 1 could be used as a guidepost for those who are choosing what to plant, and indeed, whether or not to plant. Bear in mind that the expressed need for 82 tons of Cabernet franc could be met by a few consistently producing vineyards. It is also fair to say that the bulk of demand for independently-grown Virginia fruit arises from just three wineries.

Readers may recall the existence of an inter-agency "Virginia Grape Production Initiative Task Force", which included industry, VA Department of Agriculture and Consumer Services, and Virginia Tech personnel, including myself. Conceived at the prompting of industry, the Task Force met as a group in December 1997, and publicly in 1998 and 1999, in an effort to communicate the industry's needs for additional grapes. The Task Force included promotional as well as educational resources. Educational resources included updated economics data and varietal recommendations, vineyard suitability maps for about one-half of Virginia's counties, and the continued funding of a viticulture extension assistant, here at Winchester. One targeted goal of the Task Force was to increase Virginia grape acreage by 500 acres, a figure based on the stated tonnage sought by wineries in the 1998 VDACS survey. It would appear that that goal, at least, has been met.

This is not intended to discourage those who may aspire to grow grapes. I suspect that the demand for independently-grown fruit will always exist, but that the demand dynamics will favor growers with reputations for quality fruit production, and/or the growers of more obscure, but sought-after varieties. We also anticipate further winery expansion, both in terms of new wineries and increased production of some of the existing wineries. It is also fair to say that one of the state's largest buyers of independently-grown fruit failed to respond to our survey. Thus the figures of Table 1 might be understated. The bottom line with this discussion is that anyone contemplating grape production should fully understand the risks and market situation. It's difficult to gauge what our existing industry will want in three to five years, or how California and global wine supplies will impact the growth of the Virginia wine industry. Excepting the last two years, the increase in Virginia grape acreage has occurred quite slowly (Figure 1). While new growers enter the field, others, in less than ideal locations or operational situations will leave. The risks and opportunities must be weighed against what your long-term goals and ambitions are.

Figure 1 -- Virginia grape acreage (bars) and wine production from 1985 to 1999, with preliminary grape acreage shown for 2000. The dip in wine production in 1996 reflects crop loss due to winter injury on 5-6 February.

Table 1. Survey response summary from 19 Virginia wineries in response to a questionnaire about their interest in purchasing grapes from independent producers.

Variety	Annual tonnage you wish to purchase	Number of wineries seeking this variety	Clone or clones of interest
Cayuga White	11	1
Chambourcin	24	5
Chardonel	3	1
Chardonnay	118	9	96,75,76,77, 4
Cabernet Franc	82	10	214
Cabernet Sauvignon	70	8	6,8
Gewurztraminer	15	4
Leon Millet	5	1
Malbec	20	1
Malvasia bianca	3	1
Merlot	68	10
Mourvedre	32	2
Muscat Ottonel	122	2
Nebbiolo	20	1
Niagara, Concord & other Amer.	7	2
Norton	47	3
Petit Manseng	25	2
Petit Verdot	22	4
Pinot Gris	26	3	53
Pinot noir	10	2
Riesling	31	5	239
Ruby Cabernet	123	1
Sauvignon blanc	15	4
Seyval	91	3
Syrah	28	3
Tannat	20	1
Tinta cao	20	1
Touriga nacionale	23	2
Traminette	2	1
Vidal	144	5
Viognier	70	8	1
TOTAL:	1,297 tons

Number of Responses out of 62 wineries: 28
Number of Responses with no intended new purchases: 9
Number of Wineries wishing to purchase more fruit: 19

Return to Table of Contents

II. Seasonal disease control issues:

The following discussion was graciously provided by Dr. Wayne Wilcox, Professor of Plant Pathology at Cornell University's Agricultural Experiment Station in Geneva, NY. Wayne has spoken to growers in Virginia, most recently at the VA Vineyards Association meeting in Williamburg (January 2001). While Wayne's comments were aimed primarily at New York growers, the discussion is largely applicable to us as well. As usual for Wayne, this is an excellent, comprehensive review. For some, it may be too much information. In that regard, it highlights the complexity of disease management, which is probably the chief stumbling block of new and seasoned growers alike. Study it.

Time once again for the annual review of new developments and various options on the disease-control front. As always, my sincere appreciation goes out to an outstanding team of technicians (Duane Riegel, take a bow), graduate students, postdoctoral associate, and faculty colleagues (D. Gadoury, R. Seem), whose research efforts are the bases for most of the following.

FUNGICIDE CHANGES & NEWS

1. Vangard. This is shaping up to be the "go to" Botrytis fungicide, but don't over-do it. Remember that Vangard is highly prone to resistance development, and therefore is labeled for a maximum of two applications per season (one per season is better from a resistance-management standpoint). However, even if you apply "only" one or two Botrytis sprays per season, don't use Vangard as the only Botrytis fungicide year after year. This is a good way to burn it out, and you will. Fortunately, we now have several unrelated products for Botrytis control, so it's not hard to rotate compounds in a control program. Vangard is a systemic fungicide that penetrates berries and flowers (so it's rainfast) but doesn't move from berry to berry. It's not related to any other product on the market, and doesn't control any disease except Botrytis. It's been classified as a "reduced risk" compound by the EPA (good environmental and toxicology characteristics).

2. Elevate. Last year was the first season for the commercial use of Elevate in NY, and it seemed to do a good job against Botrytis. I've generally gotten good results in my own control trials, although Vangard has been a little more consistent. The resistance risk for Elevate is still a bit unclear, but it appears to be "moderate". Elevate is not related to any other fungicide on the market, so can (and should) be used in rotational programs for resistance management purposes. Like Vangard, it's been classified by the EPA as a "reduced risk" fungicide. It does not control any other grape diseases.

3. Elite. Elite is a sterol inhibitor fungicide in the same chemical family as Nova, and has given virtually identical control of powdery mildew and black rot in repeated trials over the years (using both at 4 oz/A). I'd choose one over the other on the basis of price. The label claims some activity against Botrytis, but we saw no activity in the one trial where we examined the material for this use; in contrast, the three strobilurin fungicides all provided significant Botrytis activity in the same trial.

4. Strobilurin fungicides. The strobilurin fungicides (Abound, Flint, Sovran) were discussed at length in last year's version of this treatise. They're an important and unique group of fungicides, and it's worth reviewing a few basics about them.

   How they work. The "strobies" are not classical surface protectants (e.g., mancozeb, captan, ferbam, and ziram), the old warhorses that don't face resistance problems. Neither are they true systemics (sterol inhibitors, Ridomil, Benlate), thus they lack the scope of physical properties that this characteristic gives to such fungicides (rapid movement within tissues, good post-infection activity). Rather, their characteristics lie somewhere between these two groups, and they should be thought of this way.

   All are excellent inhibitors of spore germination; thus, they are excellent protectant fungicides, providing their best activity when they are present on the foliage or fruit before a spore lands and tries to germinate and infect. They are retained primarily within the outer waxy cuticle of leaves and fruit, which means that they are more rainfast than traditional protectants like mancozeb and captan.

   However, some of the strobie fungicide does "leak" from the cuticle into the sprayed organs. For pathogens like black rot, which establishes itself just beneath the cuticle, or powdery mildew (lives on the surface and one cell deep), there is enough leakage to provide significant postinfection control for several days, although not as much as Nova and Elite provide. In contrast, for pathogens like downy mildew which establish themselves further within the tissues (where, presumably, less of the leakage reaches them), the postinfection control is weak. In contrast, Ridomil's is pronounced.

   In addition, a small portion of the "leakage" can slowly move from treated leaf surfaces to the untreated surface on the opposite side of the leaf, where it accumulates to the point that it can protect against new infections (so-called "translaminar" activity). For instance, when we treated only the top surface of 'Riesling' leaves with Abound and then inoculated the underside with downy mildew spores 1 day later, we got approximately 50% control (versus 100% control for Ridomil). In contrast, we got nearly complete control when we inoculated after allowing 7 days of "leakage".

   Finally, the strobies show significant "antisporulant" activity. That is, when applied after infection has occurred but before symptoms develop, they often allow lesions to form but inhibits the production of a new round of secondary spores from those lesions. (This probably happens when fungus within the tissues tries to grow back through the surface and contacts the fungicide). Regardless of mechanism, this is a particularly significant property, since economic losses from all major grape diseases except Phomopsis result from repeated infection cycles caused by rounds of secondary spores produced on newly-infected tissues.

   Bottom line: The strobies will work best when you use them as "super protectants" that don't wash off. But the premium price you pay in excess of the standard protectants also provides you with some (incomplete) postinfection activity (depending on the disease), time-dependent translaminar activity, and significant antisporulant activity. It's a package deal. Resistance risk. New cases of resistance to the strobilurins continue to be reported internationally, already compromising the utility of these materials for control of certain diseases on other crops. Various pathogens appear to behave differently, and the absolute risk for individual grape diseases is still being determined. Nevertheless, I've heard rumors of confirmed cases of resistance with both powdery and downy mildew on grapes overseas, so this risk must be taken very seriously.

   To date, strobilurin resistance appears to most closely follow the "Benlate model". That is, although there are some important exceptions and unknowns, most resistant isolates are virtually immune to the fungicides and multiply with impunity 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 strobies have identical resistance-management label restrictions: 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; on juice grapes (or those for other purposes), do not make more than three applications per season. Remember, these are legal maxima. As with so many other things in life, somewhat less than the absolute maximum is often prudent.

   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. So, even though a Concord grower could legally apply three strobie sprays each year and nothing else, s/he would be asking for trouble due to the lack of rotation with unrelated chemistries.

   THE STROBIES ARE IMPORTANT TOOLS FOR GRAPE DISEASE MANAGEMENT, AND THERE'S NOTHING SIMILAR IN THE IMMEDIATE PIPELINE TO TAKE THEIR PLACE. USE THEM WISELY AND DON'T BURN THEM OUT!

   Phytotoxicity. The phytotoxicity picture with the strobies is a bit complex. As most grape growers know, Abound is extremely phytotoxic to some apple varieties, but not others. Flint is registered for use on grapes in general, but it's phytotoxic on (and not labeled for) Concords. Sovran is phytotoxic to certain sweet cherry varieties, not others. (As a follow-up to last year's article, the Sovran representative has informed me that spray drift indeed can cause injury on nearby sensitive cherry varieties, so appropriate care must be taken when spraying in such a situation).

   However, in addition to these "black and white" situations, all of which are stated on product labels, there are several "gray" areas with at least some potential risks. Remember that the strobies are held primarily in the outer waxy cuticle of the plant, and that only a fraction of the total dose "leaks" through to the inside of the leaves and berries. Most plants (with the exceptions noted above) can tolerate these levels of the compounds inside their tissues. However, when higher doses are "forced" across the waxy cuticle, damage can occur under certain circumstances. What might force these compounds into the leaves and fruit? Oils, organosilicate surfactants, and liquid insecticide formulations, i.e., the same types of materials that move captan from the surface (where it's harmless) to the inside of the plant, where it causes phytotoxicity.

   Any potential danger from these "gray" areas will probably depend on specific fungicide/plant species and variety/solvent combinations. For instance, the Flint label advises not to use it on apples (a labeled crop) with organosilicate surfactants. I've received a report from Virginia regarding injury on Chardonnay vines treated with a tank mix of JMS Stylet Oil and Abound (other potentially mitigating factors are not known, and the JMS rep tells me they've had no problems mixing it with Abound on a variety of crops internationally). Most tank-mix combinations with the strobies will pose no problem, and any potential risk should not be overstated. Nevertheless, the prudent approach would be to use caution in mixing the strobies with any material that you wouldn't combine with captan, until you know that it's safe on your particular varieties.

   Variable spectra of activities. In my experience, the three labeled strobies are equivalent against black rot (very good) and Phomopsis (only fair, although others have had significantly better results with them than I have). All three have significant activity against Botrytis, it's still not clear to me how they compare. In head-to-head trials, Flint has shown the strongest activity against powdery mildew, with Sovran second and Abound third; for context, however, note that most growers have been very satisfied with the control that Abound has provided. Abound is clearly superior to Sovran for control of downy mildew, and Flint is weak against this disease.

5. Nutrol (monopotassium phosphate). Last year, we continued greenhouse tests to find out the basics of how this "dual purpose" material (foliar nutrient plus powdery mildew fungicide) works. The results confirmed our earlier tests, showing that it provides little protective activity (no significant control when applied before inoculation with powdery mildew spores), but that it has significant activity when applied within 3-5 days after exposure to the spores.

   This scenario suggests that Nutrol should be more effective when applied relatively frequently (repeated knock-downs), rather than relying on long periods of protective activity between sprays. So for the second year, 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 more "hits"). Sure enough, the 7-day schedule was significantly more effective. Control was even better with 8 lb/A every 7 days, but there are economic limits.

   Powdery mildew is an unusual disease, since the fungus that causes it lives almost entirely on the surface of leaves and berries (the powdery stuff you see). Thus, it is "naked" and subject to (temporary) eradication following topical treatment with a range of products that don't affect other diseases. Thus, I strongly suspect that the same general principle we've shown for Nutrol will apply to any of the "alternative" PM control products, e.g., salts such as monopotassium phosphate or potassium bicarbonate (Kaligreen, Armicarb), oils such as Stylet Oil or Trilogy, dilute solutions of hydrogen peroxide (Oxidate).

   Finally, remember that eradicant activity is very dependent on thorough coverage, since you're relying on direct contact of the spray with the fungus. Don't waste your time and money if you can't provide it.

POWDERY MILDEW (PM) NEWS AND REMINDERS

1. Most berry infection occurs during the first few weeks after the start of bloom. Disease that you see on the berries later in the season usually is caused by a combination of favorable weather and problems with the spray program during that time.

   We've discussed this ad nauseum over the years, so I won't do it again. Remember: To control PM on the fruit, use best materials, full rates, and thorough spray coverage (every row!) from immediate prebloom through 2 weeks (Concords) to 4 weeks later. If you try to cheat and get caught, don't say you weren't warned.

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 3 years, David Gadoury has shown that when unprotected berries of several V. vinifera cultivars were inoculated with PM spores about 4 weeks after bloom, very little obvious PM developed. However, such berries developed a fine network of nearly microscopic infections and had much higher levels of rot at harvest than 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: Good PM control 4 wk after bloom is important to safeguard wine quality.

3. Don't overly-rely on SI fungicides, but don't abandon them. Another topic that's been beaten to death over the years. The "creeping" form or resistance characteristic of the SI fungicides has progressed to the point that these materials don't perform like they used to. However, the high risk of developing resistance to the strobies should be a clear warning that we can't rely only on those fungicides for PM control. That leaves the "alternatives" discussed previously, sulfur, and the SI fungicides. The SIs still provide significant control for many (most?) growers, so let's use them where they fit and keep them alive.

   NOTE THAT WHEN CONTROL STARTS BREAKING DOWN BECAUSE OF RESISTANCE TO SI FUNGICIDES, PROBLEMS OCCUR ON BERRIES BEFORE LEAVES. This statement (based on observations and our own research data) has two implications: (i) Be careful about relying on SIs during the bloom and early postbloom period, especially on highly susceptible varieties; and (ii) limited use of SIs may provide adequate control of foliar infections even in vineyards where fruit control is compromised.

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

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

   2. 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.

   3. 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 in full swing (this is true for the strobies, also). If PM blows up for some reason, consider an eradicant treatment (1.5-2% Stylet Oil in plenty of water would be my choice) to get the population down before coming back in with a fungicide at risk of resistance.

4. Contrary to previous indications, control of PM does appear to increase yield on Concords. We have just concluded an experiment in which the same treatments have been imposed on the same 'Concord' vines at the Vineyard Lab in Fredonia for 5 consecutive years (1996-2000). Vines have been pruned according to three systems: (1) Balance pruned; (2) 100-nodes; and (3) Minimal. Within each pruning system, vines have received one of four different PM control regimes: (i) No PM fungicide; (ii) two PM sprays (Abound immediately prebloom, Nova 2 wk later); (iii) four PM sprays (Abound/Nova/Abound/Nova @ 2-wk intervals, starting immediately prebloom); and (iv) six PM sprays (Abound/Nova/Abound/Nova/Abound/Nova @ 2-wk intervals, starting immediately prebloom). Yield increases were incremental with increasing fungicide use, leveling off at 10% (relative to the unsprayed) after four sprays in the balance-pruned and 100-node vines, but continued to increase up to 15% in the minimally-pruned vines.

   Obviously, PM is not the problem on Concords that it is on vinifera and certain hybrids, but some control is needed. These data may provide some additional basis for determining how much.

BLACK ROT (BR) NEWS AND REMINDERS

1. As fruit mature, they become increasingly resistant to infection AND infections take longer to show up. We've been talking about the period of fruit susceptibility issue for some time. After considerable experimentation, it now appears that fruit are susceptible for 1-2 wk longer than we originally had thought, but still not as long as older recommendations assumed. In experiments conducted last year, inoculated Concord fruit were highly susceptible for the first 4 wk after bloom; disease severity was reduced by approximately 70% when inoculations were made 5 wk after bloom; and no disease occurred from inoculations made 6 wk after bloom. Chardonnay and Riesling berries remained highly susceptible through 5 wk postbloom, and retained significantly-reduced levels of susceptibility through 7 wk postbloom.

   For several years, we've noted that fungicide sprays applied immediately prebloom plus 2 and 4 weeks later provide excellent control of black rot in all but the worst-case scenarios. This last spray will protect Concords (and hybrids?) until the berries are no longer susceptible; vinifera berries may retain a slight degree of susceptibility by the time the last spray wears off, but fungal inoculum is gone by then unless disease has gotten established somehow. We have not seen a benefit from earlier sprays (to control early leaf infections) except under extreme disease pressure.

   One unanticipated but interesting finding to come out of last year's study concerns the length of time required for symptoms to appear after an infection period has occurred. Clusters inoculated within a few weeks after bloom first showed symptoms 13-15 days later, and disease progress was completed by 21 days after inoculation. In contrast, the V. vinifera clusters inoculated 6 and 7 wk after bloom showed virtually no symptoms 21 days later, and those symptoms that did develop didn't show until 23 to 33 days after inoculation. 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. 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 was striking to see how much influence mummies in the trellis can have. For 2 years, we worked in a machine-pruned vineyard where mummies had been retained in the canopy after hedging, then hand-pruned them to the ground in certain plots for comparison. Disease levels were considerably higher in plots where mummies were left hanging, regardless of the spray treatment. This probably was because (i) more spores were produced, and for a longer period, on mummies retained in the canopy compared to those on the ground , and (ii) it was easier for spores to spread to healthy fruit from mummies next to them in the canopy than from those on the ground. Don't ignore this aspect of sanitation if black rot develops in your vineyard.

3. Fungicides. Nova and Elite are still 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. Mancozeb, ferbam, and ziram will provide good control under most commercial conditions. Abound, Sovran and Flint have been equal to mancozeb, ziram, and ferbam under moderate pressure and superior under heavy pressure (they're less likely to wash off, and probably retard disease spread due to their antisporulant activities ). Captan, Rubigan, and Procure are fair. Copper is poor.

DOWNY MILDEW (DM) REMINDERS

Disease biology. Primary infections can occur from about 2-3 weeks before bloom until fruit set, so this is a critical time to prevent disease establishment. Once DM becomes established, it can spread rapidly by wind-blown spores. The disease is highly dependent on dewy nights followed by rainy days, and is favored by temps of about 65-77°F (no activity over 86°F). Under optimum conditions, the generation time is only 4-5 days, so this is a "compound interest" disease with explosive potential. Conversely, DM will "disappear" during hot, dry weather. It's a disease very much worth scouting for during the summer, to determine its current activity or lack thereof before making a spray decision.

This season. Significant foliar infections last season mean that overwintering inoculum levels are relatively high. When all other things are equal (they never are), sprays need to start earlier in such years than they would if such inoculum levels were low. Use common sense based on weather conditions, but be aware of that fact.

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). If in doubt this year, err on the early side. (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. Get out and look.

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. The relative efficacies of the three strobies and Penncozeb are provided above (unfortuantely, we didn't have the Dithane Rainshield formulation of mancozeb in this particular trial for comparison versus Penncozeb). Copper, mancozeb, and captan are old standards for a good reason: they generally work.

I have seen advertisements and heard rumors of at least two formulations of phosphorous acid coming to market for control of downy mildew diseases (don't confuse with phosphoric acid, the common form of P used in fertilizers). This active ingredient is quite effective, but I doubt if we will see registered products in NY this season. Consider this a heads-up on the products, more specific news will be provided as it becomes available.

BOTRYTIS NEWS AND REMINDERS

1. Overview. There is a long-running debate about the most important time to provide fungicidal protection against Botrytis. The fungus primarily attacks very young, injured, dead, or senescing (wilting, ripening) tissues. Thus, one school of thought is that most fruit rot originates early, as (i) direct infections that enter through the blossoms and remain latent (dormant) until the fruit begin to ripen, and/or (ii) infections of old blossom parts (trash), which remain within the clusters and spread to the berries as they ripen preharvest. By this thinking, sprays at bloom and bunch closure would do the job.

   A second school of thought is that most berry infections occur from veraison through harvest (from whatever original source), and that good protection during this period makes earlier sprays unnecessary. Until recently, this had been the dominant thinking in New York for many years.

   However, based on our own work and a recent, very involved study in New Zealand, I believe in a hybrid of these two concepts. That is, it appears that berries indeed are most susceptible to Botrytis infection from veraison onwards, and that is probably when most damaging levels of infection typically occur. However, it also appears that at least some rot is initiated much earlier, either as latent infections of young berries or in blossom debris. By this scenario, late sprays should provide the lion's share of control, but early sprays can provide significant benefits by reducing the "foothold" that the fungus might otherwise establish within the clusters, and from which it can spread.

   Despite these theoretical issues, the real question is, What works? To examine this, we've conducted spray-timing trials for the last 5 years in a Finger Lakes 'Aurore' vineyard, comparing (i) two late fungicide applications at veraison and harvest; (ii) two early applications at bloom and bunch closure (1998-2000 only); and (iii) applications at all four of those timings. The take-home messages are (i) in two of the years (1996 and 2000), the traditional program of sprays at veraison plus 2 weeks later was improved by adding the sprays at bloom and bunch closure; (ii) in two other years (1998 and 1999), equivalent control was provided by applying either the two early sprays, the two late sprays, or all four; and (iii) in 2000, the two early sprays provided little control by themselves, although they did improve the activity of the two late sprays.

   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 the early sprays alone worked well sometimes but not others.

2. 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. In fact, many people feel that Botrytis would have been much worse in the Finger Lakes last year without these new tools.

   Vangard and Elevate are discussed above. Note also that the strobies have continued to perform well, to the point that Flint and Sovran have added Botrytis "suppression" to their labels (Abound may follow suit). This means the companies recognize that the materials provide some control but that they have their limitations. So how do all of these materials fit?

   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, 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. Under moderate pressure, it appears that the strobies may provide adequate protection during the period between bloom and bunch closure (when they have their best fit to control other disease anyway), provided that a Botrytis-specific material is used at veraison and perhaps preharvest if weather conditions dictate. This program appears to work, but I haven't seen it under heavy pressure on the worst varieties, so still consider it somewhat experimental. Under very wet conditions (especially near the end of bloom), the "big guns" (Vangard or Elevate) may be better choices, but we just don't have the experience yet to know for sure. Strobies or Elevate applied to the caps will probably fall with the caps (Vangard should penetrate caps to reach the flower parts), so these materials may be more effective during late bloom rather than at pre- or early bloom.

PHOMOPSIS (Ph) REMINDERS

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 an experiment last year on 'Concord' vines at the Vineyard Lab in Fredonia, we obtained a 75% reduction in the number of rachises infected (relative to the unsprayed treatment) when the only Phomopsis sprays (Dithane) were applied at the 1-inch and 3- to 5-inch shoot stage. Control was increased to 87% by the addition of two additional prebloom sprays and to 97% by the further addition of two postbloom Ziram sprays. In contrast, we obtained only 10% control when we waited until the immediate prebloom stage to start spraying. A more minimal "grower-friendly" program of Dithane at 3- to 5-inch shoot growth, Rubigan + Dithane immediately prebloom, and Abound in the 1st postbloom spray provided 72% control. Bottom line: In a wet year, apply at least one early spray to control rachis infections.

2. Fungicides. 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 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.

PUTTING IT ALL TOGETHER

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°F), less important if cool. BR control is seldom justified unless you're 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 usually isn't an issue this early). 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°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: 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 >50°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 [Abound, excellent; Sovran, fair to good; Flint, poor to fair]. Legal, but not the most efficient time to apply these expensive and limited-use materials. 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). No BR 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 because 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 at low temperatures is still an issue at this time of year. Option G: Nutrol (PM). Short residual activity, but has eradicative activity against recent infections. Same need for thorough coverage as JMS Stylet Oil. Option H: 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 (PM, BR, some Ph; also, variable DM [Abound, excellent; Sovran, fair to good; Flint, poor to fair]. 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 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. 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 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 (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. Should provide some Botrytis control. 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 D: Copper + lime (some 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. 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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III. Coming meetings:

Virginia Cooperative Extension agents Brad Jarvis (Madison Co.) and Kenner Love (Rappahannock Co.) have again organized a series of vineyard meetings for the coming season. These are informative meetings and anyone may attend. Meetings are scheduled for the following dates from 11:00 am - 1:00 pm. The first hour will be a tour of the vineyard, followed by a lunch discussion. Everyone is asked to bring a bag lunch.

April 11th Quaker Run Vineyard, Tom and Debbi Flynn

• Topics - Weed Control Strategies and Products, VA Tech Weed Specialist, Dr. Jeff Derr
• Current situation: Alison Hectus

Directions: From Rappahannock - Rt. 231 S to Banco, VA, in Banco turn right on Rt. 670 to Criglersville, VA. Just beyond Criglersville turn left on Rt. 649 and bear right. Go approximately 2 miles and vineyard is on right.

May 23th Linden Vineyard, Jim Law

• Topics - Current Situation and Management Strategies, VA Tech Viticulturist Dr. Tony Wolf
• Fruit Maturity Evaluation, VA Tech Enologist, Dr. Bruce Zoecklein
• Insect Update, VA Tech Entomologist, Dr. Doug Pfeiffer

Directions: From Flint Hill - 522 N 4 miles, turn right on Rt. 635 for 2 miles, turn left on Rt. 726 for 4 miles, left on Rt. 638 for .5 miles to Linden Vineyard

June 13th Horton Vineyard, Dennis and Sharon Horton

• Topics - Insect Problems and Controls, VA Tech Entomologist Dr. Doug Pfeiffer
• Current situation: Dr. Tony Wolf and Alison Hectus

Directions: From Orange VA, South on Rt 15 Business, turn left on Rt. 647 (Old Gordonsville Rd), cross railroad track go 100 feet and turn left on Berry Hill Lane. Inclement Weather Alternate Site: From Ruckersville take 33 east approximately 8 miles; the winery is on the left.

August 8th Gray Ghost, Al and Cheryl Kellart

• Topics-Current Situation and Management Strategies VA Tech Viticulturist Dr. Tony Wolf

Directions: From Washington VA, 211(Lee Hwy) travel East for 12 miles to Amissville VA, the Vineyard is on the right (across from the Amissville Fire Department)

Sept 12th Prince Michel Vineyard, Larry and Greg Morris

• Topic: Harvesting Demonstration and Current Situation, VA Tech Viticulturist, Dr. Tony Wolf.

Directions: Take Rt. 29 to Leon VA, which is 9 miles south of Culpeper and 30 miles north of Charlottesville. Just north of the winery take Rt. 612 (631) west approximately 2 miles. Farm entrance is on left.

If you are a person with a disability and desire any assistive devices, services or other accommodations to participate in any of these activities, please call (540) 675-3619 between the hours of 8:00 a.m. and 4:30 p.m., Monday through Friday, two weeks prior to the event.

Out-of-state meetings:

10-13 July 2001: American Society of Enology and Viticulture - Eastern Section Annual Meeting. Niagara-on-the-Lake, Ontario, Canada. Includes a tour of vineyards and wineries on the Niagara Peninsula, space-aged grape growing symposium and technical meeting. Contact Ellen Harkness for information. 765 494-6704 or harkness@foodsci.purdue.edu.

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"Viticulture Notes" is a bi-monthly newsletter issued by Dr. Tony K. Wolf, Viticulture Extension Specialist with Virginia Tech's Alson H. Smith, Agricultural Research and Extension Center in Winchester, Virginia. If you would like to receive "Viticulture Notes" as well as Dr. Bruce Zoecklein's "Vinter's Corner" by mail, contact Dr. Wolf at:

Dr. Tony K. Wolf
AHS Agricultural Research and Extension Center
595 Laurel Grove Road
Winchester, VA 22602

or e-mail: vitis@vt.edu

Commercial products are named in this publication for informational purposes only. Virginia Cooperative Extension, Virginia Tech, and Virginia State University do not endorse these products and do not intend discrimination against other products that also may be suitable.

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