July and August Vineyard Updates
By: Maria Smith, HCS-OSU
In Wooster and throughout much of Ohio, we’re here: veraison (Fig. 1), the onset of the ripening period. During veraison, the berries will begin to change color, soften in texture, and expand in size. This is also the time when grower efforts earlier in the season will pay off in yield and quality outcomes of the mature grapes. Today in Wooster also marks our first harvest of the season with very early ripening Brianna (Fig. 1).
Once again, our program is providing weekly cultivar maturity updates through OGEN. These updates can be found on the front page of the OSU Buckeye Appellation website.
Figure 1. Marquette at veraison (left) 3 August 2023 in central OH and Brianna at harvest (right) 21 August 2023. Brianna photo from Diane Kinney, Wooster Unit 2.
Growing degree days: As of August 20, we are at 2,074 GDD (Fig. 2). This is still below the long-term average (2,271). If we continue along the current trajectory, this will be the coolest season we have had in Wooster in the last 6 years.
Figure 2. Wooster, OH cumulative GDD (base 50F) as of August 20 = 2,074, historic GDD for August 20 = 2,271. Chart from CFAES Weather System (https://weather.cfaes.osu.edu)
Precipitation: Although rain picked up in June, precipitation continues to be below or near average for July and August. Precipitation for July was 2.5” and 3.7” to-date for August. The long-term averages are 4.1” and 3.1” inches for July and August, respectively. Cumulative precipitation for the 2023 growing season (1-Apr through 20-Aug) is approximately 4” below the long-term average (18.7”).
Disease and Insects:
- Midseason: When rain events resumed in late June/early July, so did disease infections. While many canopies were looking very clean during bloom, failure to continue protecting developing berries during the 4 to 5-week post-bloom period may now start to make an appearance. This has been most observed for black rot and anthracnose, which have begun appearing in infected fruit over the past few weeks (Fig. 3). Unfortunately, once infection symptoms appear in fruit, they cannot be retroactively treated. Vineyard sanitation practices to remove and destroy mummified berries and clusters should be performed to reduce black rot inoculum for the next season. Unlike previous seasons, downy mildew (DM) has not been as prevalent of an issue this year.
- Pre-harvest: Weather (temperature, precipitation) and canopy microclimate are major determinants of pre-harvest diseases, particularly bunch rots (sour rot, Botrytis, ripe rot) and foliar downy mildew. Skipping out on a protective spray at veraison may cause several of these diseases to pop up unexpectedly once grapes begin reaching 15+ Brix in susceptible cultivars. Keep in mind, following veraison low-PHI fungicides and those without adverse effects on fermentation should be used. A few examples include Captan, Phosphrous acids (Rampart, ProPhyt, Phostrol), OSO 5%, and Oxidate. Always consult the label for PHIs.
- For more disease-specific resources, see:
Figure 3. Black rot in Chambourcin (left) and Anthracnose in Vidal blanc (right).
- Midseason: Japanese beetles, emerging in early July, are finally subsiding. Some feeding damage was observed in shoot tips during July, but control using Carbaryl (Sevin XLR) prevented severe defoliation (Fig. 4).
- Pre-harvest: Several insect species can be problematic during grape ripening, especially wasps, fruit flies, brown marmorated stink bugs, and multi-colored lady Asian beetles, which can all negatively impact fruit and wine quality.
Figure 4. Japanese beetles (left) and leaf skeletonization of new cordon (right).
July Phytotoxicity: Many pesticides can cause phytotoxicity, depending on tank mix compatibility, cultivar sensitivity to active ingredients, and vineyard conditions (temperature, leaf wetness). Captan, in particular, can cause foliar burn and scarring on green berries when applied in conjunction with other pesticides that contain oil.
This year we have noticed difenoconazole, an active ingredient in Revus Top and Inspire Super to cause foliar phytotoxicity in UMN cold hardy cultivars at several vineyard sites. This was observed in commercial plantings of La Crescent and Frontenac, and in unreleased trials of UMN cultivars at Unit 2 in Wooster (Fig 5).
Berry splitting and bruising: I will be putting out a second blog post that discusses the various causes of berry splitting, bruising, and scarring. However, it has been observed in several vineyards throughout the state from various causes including hail and phytotoxicity. In some cases, damaged berries may shrivel up and be unproblematic, while in others the damaged berries may become a source for late-season bunch rot infections.
Figure 5. Difenoconazole injury and berry splitting in MN 1241. August 2, 2023. Photo from Diane Kinney.
Cultural management and harvest decisions:
- Crop estimation. Mid-season crop estimation provides a good indication of final yield, which can be used to assist winemakers with volume estimates or with the amount of grapes available to sell. Crop estimation is best done at lag-phase, which may still be ongoing in late-ripening cultivars or in cooler regions of the state.
- Veraison nutrient management. Verasion is the last time during the growing season that vine nutrition should be adjusted and is the optimal time to check for most nutrients. Veraison adjustments using low-dose (5 lbs N/acre) applications of nitrogen may increase yeast assimilable nitrogen (YAN) in fruit with low N-availability without excessive increases in vegetative growth (Gutierrez-Gamboa 2022, Tian 2022).
- Crop thinning. Although major yield adjustments are best made from pea-size to bunch-closure, removing green clusters that lag behind ripening fruit during version can help in producing uniform fruit at harvest. Given the late spring frost in May, it is a good year to evaluate fruit uniformity and make the decision to either drop green clusters or possibly consider a second harvest of late-emerging secondary clusters.