The hot, dry weather has growers thinking more about water stress on vines than plant diseases. The dry weather this spring and early summer has reduced disease pressure to some extent, but we still need to maintain a good disease management program. For diseases such as Phomopsis, black rot, downy mildew, and Botrytis bunch rot that require free water on plant surfaces for the fungi to infect, the dry weather has greatly decreased disease pressure. This all can change very quickly if it starts to rain and keeps raining. If wet weather returns, growers need to be prepared to control downy mildew and Botrytis bunch rot, especially on wine grapes. The threat of black rot and Phomopsis should be pretty much over for this year. I will discuss fungicides for downy mildew and Botrytis control later in this note.

The disease of major concern during dry weather is powdery mildew. We need to remember that the powdery mildew fungus does not require free water to infect grape tissues. In fact, it doesn’t like free water. Powdery mildew thrives under conditions of high relative humidity in the absence of free water. Even though it has been hot, it has also been humid; therefore, the threat of powdery mildew still exists, and growers, especially of wine grapes, need to maintain a good program for powdery mildew control.

The following contains some information and thoughts for consideration during the rest of the growing season.

Sovran 50WG fungicide was recently registered for use on grapes for control of Phomopsis cane and leaf spot, black rot, powdery mildew, and downy mildew. Sovran is a product of BASF Corp. and is the second fungicide in the new class of chemistry (strobilurins) to be registered for use on grapes in the U.S. Abound was the first strobilurin to be registered, and most Ohio growers are familiar with Abound. Sovran is similar to Abound in that it provides good control for most of our major grape diseases. Unlike Abound, Sovran is not phytotoxic (damaging) to McIntosh apples and other related apple varieties. Although Sovran and Abound are closely related and both are excellent fungicides, they do differ slightly in their effectiveness against certain diseases. For example, both may provide good control of downy mildew, but one may be slightly better than another. As this information becomes available through fungicide testing and use experience, we will make it available to growers.

Both Sovran and Abound have a 14 day PHI and; therefore, can be used late in the growing season for control of downy and powdery mildew if needed.

Elevate 50WDG fungicide was recently registered for control of Botrytis bunch rot on grapes. Elevate is a product of Tomen Agro, Inc. and has good activity against Botrytis. Elevate is different chemistry than Vangard, Rovral, and Benlate. With the addition of Elevate, grape growers have a good arsenal of fungicides available for control of Botrytis bunch rot.

The threat from Phomopsis should be over for this year. Although there was (still is) a good deal of inoculum present in many vineyards across the state, the dry weather this spring has resulted in very low or no detectable level of infection in most vineyards I have seen.

The dry weather has greatly reduced disease pressure for black rot this year. I have had reports of fairly severe black rot in several backyard fruit planting where the growers used overhead irrigation. Berries become resistant to black rot by the time they reach veraison. Research in New York is generating information indicating that berries may become resistant to black rot much earlier than veraison. Hopefully, we will be learning more about this research in the near future. If no black rot is present in the vineyard and you do not have a history of black rot infections last year, the threat from black rot should be over. If you had black rot in the vineyard last year and we start to get significant rains (wetness periods), fungicide protection of green berries until veraison may be wise. Effective fungicides for use at this time are Nova, Bayleton, Abound, Sovran, ziram, or ferbam.

The dry weather has greatly reduced pressure for downy mildew as well. However, I did get a call from a grower in Indiana that lost all of his Chancellor to downy mildew shortly after bloom this year. On highly susceptible varieties such as Chancellor, I don’t think that you can ever drop your guard against downy mildew. If we get rain in the last half of the season, downy could still become a significant problem, and would require a good fungicide program for control. Remember that late season downy mildew can cause premature defoliation on susceptible varieties, and this leads to serious problems with winter injury. This is especially true in southern Ohio where harvests are earlier and there is a tendency to not visit the vines quite so much once the berries are harvested. In long, wet growing seasons, post-harvest fungicide applications may be required, especially in southern Ohio.

Fungicides available for late season control of downy mildew include: Abound, Sovran, Captan, and copper fungicides. Ziram and ferbam are also available, but are not nearly as effective as the other materials mentioned. In fact, I do not recommend them for downy mildew control under moderate disease pressure. Copper fungicides are very effective and quite cost effective (relatively inexpensive). Especially on processing juice grapes (Concord), fixed copper fungicides should provide good protection against downy mildew, and is often the fungicide of choice among growers. Copper is also a good choice for use on copper-tolerant wine grape varieties. Copper also provides moderate to good control of powdery mildew. Although fixed copper fungicides are fairly safe, especially when used later in the growing season when conditions are warmer and plants dry faster, they do present some risk of phytotoxicity (plant damage). Many wine grape growers elect not to use copper fungicides for this reason. If copper fungicides are used, they should not be applied at least within 30 days of harvest on wine grapes. I have heard reports that pre-harvest applications of copper to wine grapes may have an adverse effect on wine quality. This also applies to Captan and sulfur. I have not heard of adverse effects on wine quality from pre-harvest applications of the newer fungicides (Abound and Sovran). For this reason, they may be particularly useful for late season downy control. Ridomil is very effective but cannot be applied within 66 days of harvest.

As mentioned earlier, powdery mildew does not need free water to infect and could be a serious problem on highly susceptible wine grapes this year, even though it has been very dry. I have been emphasizing the importance of early season disease control for several years. The most important period to control all the diseases mentioned thus far is from immediate pre-bloom to 2 to 3 weeks after bloom. Good disease control during this period is critical to obtaining satisfactory disease control later in the season. This is especially true for powdery mildew. If you let powdery mildew get established during this critical period, it is very difficult to control late in the season. In fact, it may be impossible to get satisfactory control due to rachis and berry infections that occurred around the bloom period.

Even with good control during the critical period around bloom, late season control of powdery mildew will still be required, especially on highly susceptible varieties. This is because leaves and cluster stems (rachis) remain susceptible to infection throughout most of the season.

Fungicides recommended for control of late season powdery mildew include: the sterol inhibiting fungicides such as Nova and Rubigan; the strobilurin fungicides, Abound and Sovran, sulfur, and JMS stylet oil.

Botrytis bunch rot is a serious disease on tight-clustered French hybrid and vinifera wine grapes. The disease is generally less serious during dry growing seasons, but on susceptible varieties "special or specific" fungicide sprays are usually required to achieve acceptable control. Fungicides currently recommended for control of Botrytis bunch rot include: Rovral, Vangard, and Elevate. Benlate has been used for control of Botrytis in the past and is still used by some growers today; however, strains of the Botrytis fungus with resistance to Benlate have developed, and Benlate is not usually recommended for Botrytis control on grapes. The following information summarizes the current fungicide recommendation for Botrytis bunch rot.

Apply Rovral 50WP at the rate of 1.5 lbs. to 2 lbs. per acre, or Rovral 4F at the rate of 1.5 to 2 pints per acre, or Vangard 75WDG at 10 oz. per acre, or Elevate 50WDG at 1 lb. per acre. Proper timing and thorough spray coverage are essential for satisfactory control. Make two applications:

When the disease is first observed OR when the berries reach Veraison (begin to change color in ripening), which ever comes first; and 14 days after the first application. Rather than make a 14-day, calendar based spray after the first application at Veraison, many growers watch the weather and scout the vineyard for bunch rot development. They make the second application when disease appears or if weather is highly conducive to disease development (Wet). In very dry years, the second application may not be necessary. In very wet years, a third spray may be necessary on late varieties (e.g., White Riesling) if the interval between the second spray and harvest is greater than 4 weeks. Field experience suggests that effectiveness of the fungicide is reduced following a heavy, prolonged rainfall. If such conditions occur after the last intended spray has been made, an additional application may be necessary. If only one application can be made, make the application at Veraison. Direct the spray toward the fruit, and use a minimum of 100 gal/A of water.

Most growers usually try to combine or coordinate these "special sprays" for Botrytis with other "required" pesticide applications as much as possible.

Vangard fungicide (Cyprodonil) and Elevate fungicide (Fenhexamid) were recently registered for control of Botrytis bunch rot on grapes. These are welcome newcomers to our arsenal of fungicides for Botrytis control, which is actually very sparse. At present, Rovral, Benlate, Vangard, and Elevate are the fungicides recommended for bunch rot control. Many growers no longer use Benlate due to the development of fungicide resistance. Rovral has been the "Cadillac" fungicide for Botrytis control, but concerns over fungicide resistance development also exist with Rovral. This makes the registration of these new fungicide chemistries (Vangard and Elevate) especially important. Where resistance is not a problem with Rovral, the efficiency of Vangard and Elevate is similar to that of Rovral; therefore, Vangard and Elevate are good Botrytis materials.

All of these materials are costly and should be used correctly and only on the tight-clustered "more valuable" wine grapes.

All of these materials (Rovral, Vangard, and Elevate) have a specific mode of action against the fungus and are all at high risk for fungicide resistance development. Therefore, these materials should be alternated with each other in the spray program. Growers should not make more than 2 sprays of either material alone without alternating to a different form of chemistry (different fungicide).

Fungicide trials using mixtures of these fungicides in full or reduced rate combinations are currently being conducted and suggest that there may be some benefit in using fungicide combinations. As information becomes available, we will get it to you.

Note: This is an abstract of an article published in the October, 1998 issue of the Fruit Varieties Journal.

Concentrations of amino nitrogen and soluble carbohydrates were measured in bleeding sap collected at bud break from 'White Riesling' clone Niederhausen 378 and 'Cabernet Franc' grapevines growing on either 3309C, 101-14Mgt, S04 or 5BB rootstocks at Kingsville, OH. Amino nitrogen concentration was higher in sap collected from 'White Riesling' compared to the more vigorous 'Cabernet Franc.' The concentration of soluble carbohydrates in bleeding sap was highest on 'Cabernet Franc'/S04 vines. Differences in xylem solutes could not be related to cropping in the previous year or to scion effects on vine vigor in the current year. Rootstock did not influence vine vigor in the year of this study. Shoots on 'White Riesling' vines had less leaf area at bloom, and were more fruitful due to the presence of clusters at more basal nodes on the shoot compared to 'Cabernet Franc.'

Interaction of Crop Level and Fruit Cluster Exposure on ‘Seyval Blanc’ Fruit Composition by Ann Hummell and Dave Ferree

(Note: This is an abstract of a paper submitted to the Journal of the American Society for Horticultural Science, J. Amer. Soc. Hort. Sci. 123(5): 755-761, 1998.)

'Seyval blanc' grapevines (Vitis spp.) were cluster thinned 7 days after full bloom to 20,40, and 80 clusters per vine to create light, moderate, and heavy crop levels. Vines were also shoot positioned at veraison to create exposed, partially shaded, and densely shaded cluster microclimates to examine the interactions between crop level and light exposure on fruit composition during stage III of berry development. Clusters were harvested using one of two criteria: on the same date or at similar soluble solids concentrations. Cluster mass and berries per cluster decreased with increasing crop level regardless of harvesting criterion. When harvested on the same date, soluble solids concentration, pH and malic acid concentration of juice decreased with increasing crop level. When harvested at similar soluble solids concentrations, increasing crop level delayed harvest and reduced titratable acidity (TA), tartaric acid, and malic acid. As cluster light exposure increased, soluble solids and pH increased and TA and malic acid decreased when clusters were harvested on the same date. When harvested at similar soluble solids concentration, increasing light exposure advanced harvest date and pH, TA, tartaric acid, and malic acid decreased. If clusters were harvested on the same date, significant interactions were found between crop level and light exposure for soluble solids concentration and the hue angle of berries. Significant interactions were found for berry mass, pH, TA, and tartaric acid when clusters were harvested at similar soluble solids. When harvested on the same date in 1995, soluble solids concentration of densely shaded clusters declined as crop level increased, whereas the soluble solids of exposed and partially shaded clusters declined as cluster number increased from 20 to 40 clusters per vine but remained constant from 40 to 80 clusters. In 1995, the hue angles of exposed clusters decreased with increasing crop level, while those of partially shaded and densely shaded clusters increased. When harvested at similar soluble solids concentration, berry mass of exposed and partially shaded clusters was similar across crop levels, whereas berry mass of densely shaded clusters declined as crop levels increased. Based on contribution to treatment error, crop level influenced pH more, and TA less, than did light exposure if harvested at the same date. Conversely, light level influenced TA more, and pH less, than did crop load if harvest was done at similar soluble solids concentrations. Regardless of harvest criterion, crop level influenced yield components, and soluble solids concentration to a greater extent and hue angle to a lesser extent than did light exposure.

IS THIS A YEAR TO EXPECT BLACKLEAF? by Dave Ferree and Dave Scurlock

Growers of Concord sometimes experience blackleaf, which in the past has been related to potassium deficiency. The theory was that the ripening fruit acted as a sink and attracted potassium from the leaves. Recent work in Washington demonstrated that the disorder begins before veraision and can occur even when there are adequate potassium levels or potassium is added. The work of Russell Smithyman and others in Washington indicate that blackleaf is associated with environmental stresses, including drought or water stress, exposure to sun, high light intensity and high temperatures. Symptoms are more severe on vines carrying a heavy crop and growing on soils with low potassium. This year Ohio is experiencing several of these conditions much earlier in the season than normal.

Concord is more susceptible than many French/American hybrids or vinifera grapes. Although not quantified by research, many believe that black leaf may lower yields and sugar concentration. Washington normally has 20-30% more sunlight than Ohio in the early part of the season and due to their arid climate, usually have some degree of moisture stress. Normally we have adequate soil moisture at this time of year and not as many sunny days as we are currently experiencing. The folks in Washington tested many things in an attempt to reduce black leaf, the most successful were increased irrigation early in the season and application of sunblock material (Climate, H.A. Spec Company, Helena, Montana) that reduced light transmittance by 25%. Other factors such as moderate crop load and adequate soil potassium were also important. (See Good Fruit Grower, Jan 1999, p. 27 for more details.)

Have the periodical cicadas set back Ohio’s grapevines this spring? We learned of one reported case via email about damage on two-year-old vines. This damage, called "flagging", occurs when eggs are laid on the grapevines. The female cicada’s ovipositor slices into the vine to deposit the eggs. Preferred twig size is about the diameter of a pencil or a little larger. Up to several dozen eggs can be laid in one area. Flagging is more serious on young vines, (four years or younger), since at that time more vines are the desired size for egg deposition.

The current rose chafer season is winding down. Our lab has been testing different pheromone lures with childproof dispensers from Great Lakes IPM. We’re continuing with trap height studies in Ashtabula County. Rose chafer populations there are running about the same as last year, according to our trap catches at three sites.

The grape berry moth is beginning to appear in our southern Ohio traps along the Ohio River. Earlier emergence was also noted at the Northeast Ohio Grape Branch and other sites in Conneaut.

As of last week the grape root borer, a clear wing pest in Southern Ohio, has not been captured in our pheromone traps. The main period for adult root borer activity over the past few years has been mid July to mid August.

Excerpted from the Illinois Fruit and Vegetable News Volume 5 Number 14:

Japanese beetles will continue to emerge for several weeks, and individual adults will live several days. Infestations and reinfestations may develop over an extended portion of the summer. Sevin and malathion are among the products with fairly short pre-harvest restrictions; for organic growers, rotenone provides some control. Frequent scouting is essential, and reapplication of insecticides may be necessary where reinfestations occur.

July 14-17, 1999 - ASEV-ES meeting. Oak Symposium: Oak forests, wood selection, barrel manufacture, and winemaking. Contact Ellen Harkness at fax: 765-494-7953 for details.

July 27, 1999 – Southern Ohio Vineyard and Winery Tour. Tour will begin at Painter Fork Vineyard (Mark Nissel) in Clermont county, continue onto Kinkead Ridge Vineyard (Ron Barrett) in Brown county, and conclude with winery tour and dinner at Moyer’s Vineyard, Winery, and Restaurant in Adams county. For more details contact Maurus Brown at phone:330-263-3681 or e-mail: brown.989@osu.edu.

August 6-7, 1999 - Vintage Ohio, Lake Farmpark. Contact OWPA at phone: 440-466-4417 and e-mail: winchell@knownet.net for details.

August 19, 1999 – TriCounty Grape Growers Twilight Tour. Contact Dave Marrison at phone: 440-576-9008 or e-mail: marrison.2@osu.edu for details.

January 16-20, 2000 - 5^th International Symposium on Cool Climate Viticulture and Enology, Melbourne, Australia. Contact the symposium secretary at ICMS Pty. Ltd., 84 Queensbridge St., Southbank, VIC 3006 Australia, and phone 61 3 9682 0244 or fax: 61 3 9682 0288 or web site: http://www.icms.com.au/coolclimate for details.

Disclaimer Clause

Any information provided in this newsletter regarding procedures, products or equipment are provided solely for informational purposes and are not intended for advertisement and endorsement of any procedures, products or equipment, nor criticism of procedures, products or equipment not mentioned. The authors, The Ohio State University, Ohio State University Extension, and Ohio Agricultural Research and Development Center assume no responsibility for the implementation of procedures, products or equipment mentioned in this publication. Readers should follow manufacturers label for specified directions and recommendations.