July Wooster Unit 2 Updates

By: Maria Smith, OSU-HCS

A one-word summary of July: rain.

June/July weather

Precipitation

It has continued raining seemingly non-stop since the growing season kicked off in earnest in May. Contiguous with May, June saw 5.26” of cumulative precipitation at Hort 2 (https://newa.cornell.edu), nearly 0.9” above the 30-year long-term average. To date, Wooster has received 1.21” of precipitation in July. Although July was below the monthly long-term average (4.12”), the frequency of daily rainfall has been high, with measurable rainfall on 13/23 days (57%) so far. The forecast, however, is finally looking sunnier, and just in time for the pre-harvest period. 

Temperature and GDD

We continue tracking similar to the long-term historic average for growing degree day (GDD). We are currently at 1646 GDD (base 50F, Jan 1) as of July 22, versus the long-term average of 1647 GDD. Following a cool May, June heat picked up the slack and bolstered GDD accumulation. The average daily temperature for June 2025 was 3.7F above the historical average, and thus far, July has been a whopping 7F above the historical average. 

Phenology and Cultural Management

Of course, Heat + Moisture = Extra-planetary levels of vegetative growth. 

And once the heat picked up in June, so did the amount of work we’ve had to manage. Shoot positioning, combing, hedging, and leaf removal came on hard and fast. And with the amount of vegetative regrowth, it seems to be a trend that will carry on through the remainder of the growing season (Figure 1). 

Figure 1. Vegetative shoot tip regrowth (left) and recent hedging (right)

At the time of writing this post on July 22, we were at lag phase in berry development, the brief pause before the onset of veraison and have been performing crop estimation to determine final yield potential for harvest. Verasion began kicking off in our early varieties the last week of July, and we are currently beginning to enter veriaion in mid- to late-ripening cultivars. At Hort 2 in Wooster, we are anticipating harvest to begin around the last week of August in our earliest cultivars, though several southern Ohio vineyards have already reported full veraison in early cultivars, which would indicate harvest time beginning as early as next week (the first week of August). 

Notable vine issues for harvest 2025

Fruit set in some cultivars was notably poor this year (Figure 2). Weather conditions during bloom heavily influence fruit set and yield potential. This year, bloom stretched nearly 2 weeks, during which the Wooster vineyard experienced cool temperatures and high rainfall. 

Figure 2. Poor fruit set in V. vinifera Verdelho

In 2024, the Wooster vineyard was hit with 2,4-D herbicide injury prior to bloom, which significantly reduced yields in what was otherwise a very nice growing season. This year, vineyards with reported herbicide injury were impacted much later than in 2024, which allowed most vines to proceed through bloom with less crop loss. However, foliar injury may still limit the ability for full crop maturation. 

Early season disease pressure was very high, particularly for Phomopsis, Anthracnose, and Downy mildew (Figure 3). At this point in the season, our attention turns to foliar downy mildew and bunch rot (Botrytis, Sour Rot, Ripe Rot) concerns. Veraison is one of the final opportunities for systemic fungicide use to manage some of these issues due to pre-harvest intervals and concerns regarding fungicide inhibition of fermentation. 

Figure 3. Late-June foliar downy mildew (top) and fruit infection (bottom) in Vitis hybrid Marquette

Lastly, veraison is when bird deterrents and netting exclusions need to start being applied. The goal is to proactively restrict birds from receiving that first taste of grape that keeps them returning throughout the harvest period (Figure 4). 

Figure 4. Over-the-row netting applied at the onset of veraison to high-wire cordon (HWC) hybrid block at Hort Unit 2.