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By: Maria Smith, HCS-OSU
This past month in the vineyard can be summarized by a few words: cool, dry, hazy. Phenological development has proceeded slowly, with early cultivars beginning bloom only 2 weeks following the last freeze event and some still moving through as recently as last 21 June (Fig 1). In part to primary shoot loss from the multiple rounds of April and May freeze, it is reasonable for there to be high variability in phenology and ripening this year – particularly among French American hybrid and Riparia (MN) cold hardy cultivars with fruitful secondary shoots. At this point in the season, it’s important to begin taking stock of yield potential and make determinations for crop adjustments. Fine-tuning crop levels can be made through cluster thinning between pea-size to bunch closer stages (Fig. 2) of those highly fruitful cultivars to aid in accelerating ripening and managing crop loads of damaged vines. For Vinifera with extensive frost injury, excessive vegetative growth in response to low yields may require adjustments to vineyard fertilization, shoot positioning, and hedging to maintain healthy vegetation and provide sunlight exposure to developing buds.
Fig 1. (Top) Bloom beginning in the cold-hardy hybrid trial block at Wooster Unit 2, 30 May 2023, (Bottom) Cabernet Franc completing bloom at Wooster Unit 2 21 June 2023.
Fig 2. Example of clusters approaching bunch closure in ‘Brianna’, Wooster Unit 2, 21 June 2023.
Growing degree days: As of yesterday (June 29), we are at 977 GDD, which is below the long-term average (1148; Fig 3) and less than where we were this same time in 2022 (1256).
Figure 3. Wooster, OH cumulative GDD (base 50F) as of June 29 = 977, historic GDD for June 29 = 1148. Chart from CFAES Weather System (https://weather.cfaes.osu.edu).
Precipitation: Dry conditions continued throughout the first half of June, with only one measurable rainfall between May 14 through June 11. Rain has been much more frequent since then, with Wooster receiving 3.05” during the last 2 weeks of June. Despite our recent rains, we are still below the 10-year average June rainfall of 4.35”. As of yesterday, much of Ohio is still registering within abnormally dry to moderate drought conditions (Fig. 3). I have yet to see any signs of drought stress from commercial vineyards with mature vines. But, as I mentioned in May, persistently dry conditions will adversely affect establishment of newly planted vines, and irrigation should be ongoing when soil is dry.
Fig 3. Ohio drought status, 27 June 2023. From https://droughtmonitor.unl.edu/
Thanks to the low precipitation and cool temperatures in May and early June, disease pressure has been low. That bodes well for clean fruit and canopies moving through bloom into early fruit set. However, with the increase in rain frequency and the forecast for warmer temperatures and humidity moving into July, we should not sleep on our spray schedules. Remember: The critical period for fruit infection is pre-bloom through 5 weeks post-fruit set. This goes for Phomopsis, anthracnose, black rot, downy mildew, and powdery mildew. Other “late season” diseases, such as Botrytis and ripe rot, can also infect during bloom (Botrytis) and berry development (ripe rot). Several resources for disease management and designing spray programs was linked in the May 2023 Vineyard Updates. There is one more addition to that set of links from Dr. Katie Gold at Cornell University: Grape Disease Control, June 2023
Fig 4. New black rot lesions following mid-June rain events, June 2023.
Regular scouting and monitoring GDD from pre-bloom through early fruit set is important for timing control sprays for grape berry moth and foliar phylloxera. These two insects can cause extensive damage if not managed.
Grape mealybug has also been reported in several vineyards over the past month. In addition to cosmetic damage, mealybugs are known vectors for grapevine leafroll virus, which is considered a major problem for Vinifera cultivars.
Minor pests, including various gall makers and grapevine aphids, are beginning to show up. These insects do not typically occur in high enough populations to represent major threats to vine health, yield, or fruit quality, thus do not require targeted control.
Japanese Beetles (Fig. 5) will begin to grace us with their presence over the next several weeks into July. I started seeing the first adult JB in NE Ohio last week.
Available chemical options and efficacy for insect control can be found in the Midwest Fruit Pest Management Guide.
Fig. 5 Japanese beetles skeletonizing leaves on 'Traminette', Wooster Unit 2, July 2021.
I never really thought I’d be talking about smoke taint in Ohio, but here we are. Air quality this past week has been awful, reaching nearly hazardous conditions of 300 in Wooster on Wednesday (Fig. 6). This is the second week in June that AQI has breached unhealthy levels, and with the ongoing wildfires in Canada, it’s projected to be an ongoing issue throughout the remainder of the summer. Does this mean that your grapes will have smoke taint? The short answer is that we don’t yet. Predicting smoke taint is difficult, and phenological timing matters with exposure being more consequential between veraision and harvest. Let’s hope that when we reach ripening the air will be clean!
Fig. 6 Air quality from 28 June 2023. Figure from www.airnow.gov