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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.

Weather Update

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/

Disease management

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.

Insect management

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.

Air Quality

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

By: Maria Smith, HCS-OSU

With the frost risks largely in the rear-view of April, we are starting to see new shoot growth bolt ahead under warming temperatures of the past week (Figure 1). Keep in mind, if you did have damage from those late-April freeze events, you may just be starting to see the emergence of secondary and tertiary shoots (Figure 2).

Figure 1. Shoot growth Chardonnay 4-May 2023 (top) at E-L stages 3-4 and 16-May 2023 (bottom) at E-L stages 11-12.

Figure 2. Primary and secondary shoot emergence from single node position

Weather

Cumulative GDD in Wooster is near the historic average for this time of year (Figure 3) as warm early- and mid-April temperaturs have been buffered with a cool down in late-April through early-May. As mentioned in the last post, we saw two late spring frost events that contributed to wide-spread injury to many vineyards in the northern portions of the state.

April precipitation (4.0”) was 0.6” above the 10-year average rainfall (3.4”), but we are currently on track for a drier than average May, with only 1.3” of accumulated rainfall in the first 2 weeks of the month.

Figure 3. Wooster, OH cumulative GDD (base 50F) as of May 16 = 372, historic GDD for May 16 = 383. Chart from CFAES Weather System (https://weather.cfaes.osu.edu)

Timely vineyard management:

Below are some considerations for cultural management of your vines at this early stage of the growing season:

• New vineyard plantings: Now through early June is when we need to get our new vineyard plantings completed. If dry weather persists, new vines should be irrigated. 1 and 2-yr-old vines should receive around 0.5” to 1” of water per week through rainfall and irrigation while root systems are being established.
• 2 and 3-yr-old vines: retain the 2-3 shoots required for continued trunk and/or cordon establishment and remove the remaining shoots from the trunk. Remove inflorescences (flower clusters) from the remaining shoots. The goal of these tasks is to encourgage robust vegetative growth of young vines.
• Mature vines: Shoot thin vines when shoots are between 6-12” in growth. For details on shoot thinning and suckering mature vines, visit our blog post from May 2022 and review our video on canopy management here. *Note: shoot thinning for vines that were adjusted for bud counts following winter injury is critical, as canopies will be denser with greater bud retention.
• The process of de-hilling soil around grafted vines should be completed to prevent scion rooting

Disease management

With the rapid rate of shoot growth along with the increase of average daily temperatures, it’s important to ensure your shoots stay protected against early season diseases, including Phomopsis, Anthracnose, Black Rot, Downy Mildew, and Powdery Mildew. Remember that disease management should be preventative beginning around 1” of shoot growth and combined with best canopy management practices.  

For successful control, it’s important to understand the disease, cultivar susceptibility, and management options. There are several resources available for disease management such as the Midwest Fruit Pest Management Guide, Developing an Effective Fungicide Spray Program for Grapes in Ohio, and NY/PA Pest Management Guide. Fact sheets on important grape diseases can be found here. Read and follow all label guidelines and ensure proper fungicide rotation and sprayer coverage/calibration to reduce risks for fungicide resistance.

Vineyard insects

During the warm stretch of April, I was hearing from several growers about the prevalence of grape flea beetles in vineyards seen brazenly snacking on swollen buds. Adult beetle damage to newly developing buds can be economically damaging to yield if not adequately controlled. Flea beetles tend to be most concentrated along vineyard boarders in proximity to wood lines, so treatment may only need to be targeted in certain portions of the vineyard. Thresholds for spraying flea beetle have been suggested at 2 to 4% (or 2 to 4 injured buds per 100 buds checked), and broad-spectrum insecticides work well against flea beetles if necessary to use. Be aware that flea beetles go through one lifecycle per season and that their larvae can cause damage and skeletonization to leaves through June (though rarely in sufficient quantity to be considered economically important), and control of larvae may help reduce future populations of this insect.

Herbicide drift injury

Rapid shoot growth in vineyards generally coincides with planting time for row crops, and with that comes the risk for herbicide drift injury. The most effective way to reduce the risk for herbicide drift injury is to develop relationships with neighboring farmers and applicators and inform them about the proximity of your vineyard. However, drift injury may still happen, and it’s best to be prepared since drift events are sporadic and difficult to predict.  

An early, subtle symptom of auxinic herbicide (2,4-D, dicamba, etc.) injury is shoot epinasty, which can be mistaken for other abiotic stresses like drought (Figure 4). Other symptoms including leaf cupping, curling, and chlorosis (leaf yellowing) may take additional time to develop and depend on the amount of herbicide exposure (Figure 5).

If you suspect your vineyard has experienced an herbicide drift event, document your evidence as soon as possible and consider taking action by contacting the Ohio Department of Agriculture to file a complaint.

Figure 4. Shoot epinasty, or the downward growth of shoot tips. 48-hrs following low-concentration herbicide exposure.

Figure 5. Leaf cupping patterns 48-hrs following high-concentration dicamba exposure.

By: Maria Smith, HCS-OSU

It sure does feel like March Madness, especially with the recent arrival of Ohio’s infamous “second winter”. Thankfully, the cooldown from February’s warm, spring-inspired weather will help us keep the vines asleep a little bit longer. This cooldown should help us complete this most important dormant-season activity: pruning. As a follow up to last week's pruning workshop, let’s go down the reminders of when, what, and whys of pruning.

Why prune?

In young vines (< 3yo), pruning is intended to build the vine to conform to the intended training system. This means, selecting healthy wood for trunk and/or cordon establishment.

For mature vines (>3 yo), the main goal of pruning is to adjust the vine size and yield potential to produce a healthy crop in the upcoming season (i.e., create a balanced vine). For new grape growers, this seems dramatic, but in “normal” years, this means removing more than 90% of the 1 yo wood that is on the vine (Fig 1).

Figure 1. Vine before pruning (left) and after pruning (right). High wire, bilateral cordon-trained Vitis hybrid.

What to prune? Or how many buds to retain?

Normally, we suggest a method called “balanced pruning”, or retaining bud numbers according to vine size based on the pruning weight of 1-year-old canes.

Table 1. Balanced pruning formulas for different grape types. Adapted from Midwest Grape Production Guide. The formula follows the number of buds to leave for the 1 lb of pruning weight + the number for each additional lb of pruning weight.

A general rule of thumb: this should equate to approximately 4-6 buds per foot of vine spacing (e.g., if the vine spacing is 5-8’, retain 20-50 buds per vine). *Note, buds on hybrid and Vinifera wine grape varieties are typically more fruitful on the basal nodes. Therefore, when retaining buds, it is often best to leave more 2-3 bud spurs instead of fewer, longer spurs. This is not the case with Concord, Niagara, and other American varieties where the most fruitful buds are nodes 3-6.

But winter 2022-2023 wasn’t “normal”. The Christmas Eve polar vortex may have caused significant bud injury to your vines, especially in the most cold-sensitive varieties or in the colder locations in the state (see: Pre-Christmas Freeze and Impact on Grapevines). In Ohio where we have a propensity for winter injury, it’s important to check your bud injury and adjust pruning accordingly to maintain cropping levels (Fig. 2, Table 2). At Wooster, we assess bud injury as a % of 100 buds (10-bud canes). This is performed by variety.

Figure 2. Assessing bud mortality by cross-sectioning buds using a sharp razor blade. Notice the alive (left) vs. dead (right) status of the primary buds in the figure above.  

Table 2: Adjusted pruning based on % bud mortality.

Why minimal prune? Yes, it’s a pain to shoot thin, but what we have noticed is that hedge pruning can aid in maintaining yield levels despite extensive (70-80%) primary bud injury. We have observed in the past that the rates of bud injury tend to be higher on node positions in the middle and end of canes vs. towards the base of canes. This means that buds retained from minimal hedge-styled pruning tend to be more alive than leaving more buds through cane pruning modifications (e.g., double-wrapping canes, quad-cane pruning).

Wood quality. Healthy, sun-exposed, reddish-brown wood that is approximately ¼ to ½” in diameter is optimal (think: Sharpie™, Pencil, Pen; Figure 3). This wood will contain buds with better cold hardiness, higher fruitfulness, and have the carbohydrate availability to support the development of 2-3 shoots. AVOID: bull wood (large, vegetive wood > ½” in diameter) and weak (< ¼” diameter).

Figure 3. Healthy, optimal wood selection for spurs and trunk and cordon training

When to prune? We acknowledge that larger vineyards are time-constrained and likely begin pruning earlier in the winter. However, if possible, small vineyards should wait as long as possible into spring. This is to allow compensation in case of winter injury, but can also help stave off early bud break by suppressing the development of the most basal buds on the cane (explained in our 2019 OGEN article: Grapevine Dormant Pruning). If waiting is not possible, begin with the most cold hardy varieties first, then proceed to the most cold sensitive varieties last (note* If you’re growing cold hardy MN hybrids, prioritize the later breaking varieties like Frontenac to prune first and prune the most early bud break varieties prone to spring freeze like Marquette and La Crescent last).

Pruning should be completed by the beginning of bud swell. Although bud break timing depends on numerous factors, we typically see signs of bud swell in mid to late-April in Wooster (may be 2-3 weeks different in southern and northern parts of Ohio). If you are double or delayed pruning as a spring frost avoidance strategy, final pruning needs to be completed no later than 1” in apical shoot growth. This is to avoid potential yield losses associated with basal bud break delays.  

By: Imed Dami, HCS-OSU

On December 23-24, Ohio experienced the coldest temperatures of the year 2022. Temperature lows ranged between 3F and -13F (see map). Statewide, the lowest temperatures occurred in West central Ohio and ranged between -9 F and -13F. In central Ohio, minimum temperatures ranged between -5F and -10F. In southwest, temperature dropped to -7F to -12F. In southeast, 3F to -6F were recorded. In Northwest, temperatures ranged between -3F and -11F. Northeast (majority of vinifera grape acreage) experienced the mildest temperatures ranging between -2F and -6F. At our research vineyard in Wooster, we recorded -7F on December 23, 2022.

To have a preliminary assessment of cold injury, we collected canes from our most cold sensitive vinifera varieties. We also collected a cold hardy hybrid, Frontenac blanc for comparison. Our findings were disappointing with higher-than-expected cold damage across the board. Table 1 summarizes cold injury of primary and secondary buds from 8 varieties. In vinifera primary bud injury ranged between 87% and 100%. Frontenac blanc sustained only 5% primary bud injury. Our results suggest that cold damage of vinifera varieties could be more severe than expected across the state. Hybrids (with LT50 of -13F or lower) should have minimum to no injury from this cold event. 

The extensive cold damage of vinifera varieties is puzzling. In late November, buds showed a good level of cold hardiness. For example, Chardonnay had LT50 = -7.7F. In December, low temperature of -7F was recorded in that vineyard in Wooster. So, at that temperature, we should have 50% or more bud survival. But, that was not the case and we had 10% primary bud survival (see Table 1). One way to explain this discrepancy is that vines lost cold hardiness in December. This is possible since we had a mild December with mean temperature 3F above the 30-year average (Figure 2).  

We still have a few weeks to go with winter weather and potential damaging temperatures are still possible.  Growers should be mindful of that and bud assessment, before pruning, is recommended. Pruning adjustment is definitely needed this year.  

Figure 1. Minimum temperatures on December 23-24, 2022. Note that minimum temperatures ranged between 3F and -13F. Source: Dr. Aaron Wilson, OSU state climatologist.

Table 1. Bud injury of 8 grape varieties exposed to -7F on December 23, 2022. Wooster, OH.

Figure 2. Monthly mean temperature deviation from the 30-year average in 2022 in Wooster.  Bars above 0F means temperature was above the 30-year average. Bars below 0F means temperature was below the 30-year average.