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By: Maria Smith and Imed Dami, HCS-OSU

It is no surprise to anyone who has been out in the vineyard pruning that hydraulic pressurization and sap flow (“bleeding”) from pruning wounds has been seen earlier than normal due to the above average temperatures over March (Fig 1, photo).

We monitor the warmth of the growing season by recording the growing degree days (GDD). Last Friday (22 March 2024) the GDD at Wooster, Unit 2 was 43, which is higher than the historical average and is about two weeks ahead. However, when we checked the stage of development of the earliest bud breaking varieties, the majority of buds were still at the closed stage with some at the wool stage (see photos). The cool/cold weather we have experienced in the past few days has helped slow bud growth, which is a good thing. Although the recent weather event had no negative impact on bud survival, we are still concerned by the potential for early budbreak this season.  

As an annual reminder, we are freeze prone (< 32F) from roughly April through mid-May, with the latest observed freezes occurring through early-May to early-June, depending on region (Fig 2).

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Figure 1. Temperature departures from the 30-year average for March 1-March 24, 2024. Temperatures have ranged between 5 to 11F above average across Ohio during this period.

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Vine “bleeding” from pruning wound. March 13, 2024, Unit 2 Wooster. Photo from Diane Kinney

Date of Median Last 32°F Freeze

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Figure 2. Median date of last 32F freeze (top) and latest date of observed 32F freeze (bottom). Figures from

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Cabernet franc grapevines grown at the research vineyard in Wooster. Photo taken by Imed Dami on 22 March 2024. 

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Brianna grapevines grown at the research vineyard in Wooster. Photo taken by Imed Dami on 22 March 2024. 

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Itasca grapevines grown at the research vineyard in Wooster. Photo taken by Imed Dami on 22 March 2024. 

Current susceptibility to freeze injury

Several growers reached out this week with concerns about potential bud injury due to temperatures reaching near 20F (Fig 3).

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Figure 3. Minimum low temperatures on 3/21/24. Most regions hit lows in the low-20s, with some areas in the 10s.

Across the Eastern US, buds are undergoing “cold deacclimation”, which is the transition from maximum winter cold hardiness to a cold-sensitive state. With the recent cold temperatures last week, there have been concerns that these temperatures may cause damage, even though buds are still dormant.

The cold hardiness, or LT50 (lethal temperature that kills 50% of primary buds), of the cold sensitive vinifera, Sauvignon blanc, was -1.8F on 12 March 2024. Its cold hardiness was -9.9F on 11 January 2024.  In the past 10 days, the minimum air temperature at Wooster, Unit 2 was 17.8F (on March 21).

A bud cold hardiness model released by Dr. Jason Londo’s lab at Cornell, seeks to provide broader guidance throughout the Eastern US on real-time estimates for bud cold hardiness. This model provides estimated cold hardiness for several key regional wine and juice grape cultivars. Combined with our own bud DTA cold hardiness measurements in Wooster, we are highly confident that buds should not have experienced injury from this past week’s cold temperatures. However, if you remain concerned, it is advised to select a few buds to dissect to verify if any injury occurred at your site.

Planning for another year of spring frost risk and damage

Given that vineyards will be at risk for dormant and/or green tissue injury for several weeks to come, it is important to be prepared for mitigating and responding to injury. We have experienced some level of spring frost in Ohio for the past five years in a row! Be prepared by reading up on some of our previous posts on preparing for spring frosts and managing injury or obtaining a copy of the spring frost bulletin from OSU Extension.

We will be keeping you updated over the next couple of months for the emergence of bud break and any major spring frost events. Although we may not personally enjoy these cold spells, it is helpful for pushing back bud break and our spring frost risks. 

Posted In: Viticulture
Tags: Viticulture, Winter Injury, 2024 season
Comments: 0

By: Maria Smith, HCS-OSU

It’s still winter, but thanks to this El Niño year, it sure hasn’t felt like it in Ohio. Daily average temperatures over the past 30 days have ranged between 6-10 °F above the 30-year mean (Fig. 1). Many of our vineyards are likely taking advantage of this weather to prune the vines for the upcoming year. To those with smaller vineyards (< 10 acres), there is still plenty of time to get your pruning done through March and early April before buds begin to break dormancy. For a year with this mild of a late-winter, delaying your dormant pruning as long as possible can be considered advantageous to staving off bud break among your preferred yield-producing buds.  

The goal of this post is to remind you and your crew about pruning best practices following last week’s Wooster grapevine pruning workshop. In 2023, we published a pruning primer article about the what, when, and whys of pruning. In this companion article, we’ll touch on vineyard sanitation and a few routine pruning errors so that you can maximize the long-term health and productivity of your vines.

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Fig 1. 30-day Average temperature departure from mean Feb 9, 2024 – March 9, 2024. Photo from

Vineyard Sanitation:

Did you have grape diseases in the vineyard during 2023? Fungal diseases such as Anthracnose, Phomopsis, and black rot are well-known to overwinter on woody tissues (canes, cordons, trunks) and persistent mummified fruit that was left in the vineyard overwinter (Fig. 2). These infected tissues go on to serve as a source of pathogen propagules for infecting new, healthy tissue over the next growing cycle. Similarly, crown gall bacteria (Agrobacterium vitis, Fig. 3) can persist for years in infected tissues and is managed through renewal of vine parts during pruning.

Vineyard sanitation, or the act of removing and destroying dormant, infected tissues while pruning can aid in the reduction of pathogen populations available to infect in subsequent seasons. If disease was a significant issue in your vineyard, it is best practice to destroy tissue by burning, burying, or removing completely from the vineyard rather than composting, since inadequate temperatures during composting can fail to kill propagules. Sanitation should also extend to tools through regular cleaning and sharpening (sharp-cut pruning wounds heal quicker) of pruning tools.

Fig 2. Phomopsis lesions (left) will persist on shoots that lignify and become canes; black rot mummy berries (right)

Fig. 3 Grape trunk infected with crown gall, a bacterium that causes tumor-like growths (galls) on infected woody tissues (trunks, cordons, roots).

HOWEVER, if your vineyard was clean of disease, cuttings may be mulched using a flail mower or brush hog (Fig. 4) directly in the row. Avoid using a regular lawn mower deck to chop up pruned wood, especially larger pieces of trunks or cordons. 

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Fig. 4 Flails on a rotating drum. Flail mowers and brush hogs can chop up small diameter woody materials. Photo from:

Routine pruning and training issues:

Grape pruning and training are not intuitive, and even experienced practitioners make mistakes in the process. Here are a few of the most common issues that I encounter when out assessing vineyards in the late-winter:

  • Training weak wood: healthy wood is 1) ¼ to ½” in diameter, 2) sun exposed in the previous year, 3) has dark brown periderm (outer bark). Canes that are small and weak or large and vegetative are less cold hardy and less productive than optimal wood quality.
  • Retaining excessive bud numbers after final pruning: Pruning should remove approximately 80-90% of the vine growth from the previous season. Retaining too many buds after final pruning sets the vine up to produce shoots with smaller clusters and less shoot growth than vines with an “optimal” number of buds. Refer to the Midwest Grape Production Guide for guidance on balanced pruning practices.
  • Training cordons that are too long: Cordons are best established in segments of 12 to 15” in length, especially in Vinifera cultivars. This is to encourage all buds along the cane to develop into healthy shoots. Leaving excessively long cane segments while training or retraining cordons can result in blank regions where shoots do not develop, thus leading to canopy gaps and a less productive vineyard.
  • Making poor pruning cuts: Wounding on the vine is an entry to pathogen infections. This includes pruning wounds. Avoiding large flush cuts on older (2+ year-old wood), using sharp pruning shears, and pruning in dry conditions are important to reducing risks for spur/cordon/trunk infections and dieback.
  • Consider the spur, cane, and bud position: We want to select canes, buds, and spurs that help us best conform to and maintain our training system. When training young vines, bud positioning should be considered when making cuts to ensure that shoots and subsequent canes are positioned along our fruiting wires without strong bends or breaks at the base that can restrict sap flow through the vascular tissues. Selecting shoots/canes along the trunk that can be easily arched upwards from under the fruiting wire or those that conform to the fruiting wire when extending/replacing cordons are preferred to shoots/canes that emerge from buds positioned above the fruiting wire. 
Posted In: Disease mangement, Viticulture
Tags: Viticulture, pruning
Comments: 0

By: Melanie L. Lewis Ivey, Associate Professor, Extension Fruit Pathologist, Department of Plant Pathology

This article can be found in the January 2024 issue of Ohio Fruit News.

In December 2023, the Environmental Protection Agency (EPA) proposed an interim decision for the registrations for thiram, ferbam and ziram. Despite updates and recommendations for ziram, presented during the public comment period for the 2021 proposed interim decision, changes were not made to the previous risk picture and proposal.

Thiram, ferbam and ziram are critical to the successful management of fruit diseases and the prevention of fungicide resistance development. Final decisions on the proposed interim decisions are scheduled for April-June 2024. An open 60-day public comment period is planned for the beginning of 2024. Once the comment period opens, comments can be submitted on-line or by mail. Open comment periods are announced at

Representatives from the EPA have emphasized that without new data or significant numbers of comments, the proposed interim decision on these products is unlikely to change.

The EPA will only announce final changes to the registrations of all pesticides through the “Bulletins Live – 2” website. However, the OSU Extension Specialty Crop Team will make every effort to keep fruit producers in the state updated.

Figure 1. Peach leaf curl is most effectively controlled using Ferbam or Ziram. Image courtesy of K. Peter, Penn State University.

Docket EPA-HQ-OPP-2015-0433

Risks of Concern: There are risks of concern for “fish (both freshwater and estuarine/marine), aquatic invertebrates, mammals, terrestrial invertebrates, birds, and aquatic and terrestrial plants.” In addition, there are “exposure concerns to occupational handlers and post application risks”.

Proposed Mitigation: To address the risks of concerns for thiram the following mitigation strategies were proposed.

  • Cancellation of all non-seed treatment uses such as strawberries, peaches, non-bearing trees, shrubs, nursery stock, ornamentals.

  • Cancellation  for  all  commercial  seed treatment uses.

  • Only on-farm seed treatment for liquid formulations and use of a PF10 respirator for some crops (snap bean, rice, soybean, and wheat).

  • Limit animal repellency use in nursery settings (ornamentals, vegetables, trees, container stock) to 84178-1 only. This product is also registered for other use sites and those uses must be removed from the label. Applications must be made with a manually pressurized handgun. All other products must remove their animal repellency use from the label.


Risks of Concern: There are risks of concern for “fish (both freshwater and estuarine/marine), aquatic invertebrates, mammals, terrestrial invertebrates, and birds.” In addition, there are “exposure concerns to occupational handlers and occupational post application risks for workers”.

Proposed Mitigation: To address the risks of concerns for ferbam the following mitigation strategies were proposed.

  • Cancellation of all uses on apple, pear, citrus, mango, and cranberries.

  • Restrict the application method to only be applied by a mechanically pressurized handgun on peach and nectarine for dry flowable formulations and require the use of a PF50 respirator.

  • Only dormant period applications for peaches and nectarines.


Risks of Concern: There are risks of concern for “fish (both freshwater and estuarine/marine), aquatic invertebrates, mammals, birds, and terrestrial invertebrates”. In addition, there are “dermal and inhalation exposures to occupational handlers, post-application occupational risks (dermal), and bystander (non-occupational) risks to adults (dermal) and children (combined dermal and incidental oral)”.

Proposed Mitigation: To address the risks of concerns for ziram the following mitigation strategies were proposed.

  • Cancellation of all uses on all crops.

  • Cancellation of uses for paint preservatives.

  • Engineering controls for the non-paint materials preservative uses.

  • Reducing the maximum application rate in all ziram-preserved building materials.

  • Limiting application to the dry-end of the paper preservation process.

Posted In: Disease mangement
Comments: 0

By Imed Dami and Diane Kinney, HCS-OSU

This article summarizes the 2023 dormant and growing seasons and the impact of weather on grape varieties grown on the research vineyard at the OSU-OARDC in Wooster, Ohio.

Weather: Temperature

Our 2023 growing season was greatly affected by a freeze event on December 23, 2022 to -7 F. Bud injury was higher than normal due to warmer (3F) than a typical December. The early part of the year was significantly warmer than both the long-term average and 2022 temps. This did not hold true for the early growing season though as temperatures were below in both areas. In Wooster, we missed a frost event in mid-May that greatly affected other grape growing regions in the state. Our last date for temperatures below freezing in the spring was April 27th which coincided with bud break. Phenological progress was slow due to cool, dry temperatures. During fruit ripening in early fall, temperatures followed closely to both long-term and 2022. Cumulatively, as year end, we are only slightly above 2022. We did have an earlier fall frost date of October 31st resulting in a lower-than-average FFD of just 187 in comparison to 201 in 2022.

Weather: GDD

Nearly 40 GDD units were gained during early winter from the 1st of January through 1st of April. April continued to be slightly above both 2022 and the long-term averages but things drastically dropped off for the entire growing season May through September. By years’ end, we are at only 2734 GDD vs 3104 in 2022 which was already significantly lower than 2021. In relation to the long-term 30-year average of 3058 GDD, we are 324 GDD lower at this time. This is the first time that yearly GDD dropped below 3000 in 10 years.

Weather: Precipitation

Annual precipitation was above the long-term average but significantly below 2022 (34.53” vs 41.03”). That being said, we did have near drought like conditions during the early growing season mid-May through mid-June with nearly no rainfall at all. This early drought ended with nearly 3” the last two weeks of June alone. July and September were also very dry. A 5-day period in early August recorded 2.69” with another near 3” the last week of the month. In September, we only recorded 0.32” with November at 1.36”. In general, and except August, we had a drier than normal summer-fall, which impacted disease pressure in 2023.

Vineyard Notes:

2023 Winter freeze injury:  The deep freeze of December 23, 2023 caused significant bud injury. Vinifera varieties (15) sustained 85-100% primary bud injury; Table grapes (8): 55-100%; hybrids (19): 15-82%. The causal claims, that the temperature dropped very fast, are not accurate. In our vineyard, temperature dropped about 50F in 24 hrs or 2F/hr. That is considered a normal “freezing rate”. It is the mild December that led to “deacclimation” of vines. Also, the freeze-thaw cycle (45F/-7F) just before the event exacerbated the extent of damage. However, the crop loss in some varieties was not as severe as expected due to our pruning adjustment. For example, Chardonnay sustained 85% bud injury but produced 3 tons/acre after hedge (or minimal) pruning.

Diseases and insects: With the drier weather, diseases were also less of a problem this year. Bird and racoon damage was nearly non-existent, but yellow jacket damage was fair which led to high sour rot incidence. Dr. Ivey confirmed a new disease, called ripe rot, for the first time in Ohio that we found in some of the varieties in Wooster. More information regarding this will be shared at a later time.

Fruit quality:  Sour rot continues to be our biggest challenge in fruit quality. Harvest began on August 23rd for Briana and our final harvest occurred on October 5th for Cabernet franc. Despite a very low GDD, we were able to ripen fruit of most varieties and fruit composition was appropriate. For example, in 2023, sugars in 14 varieties averaged 19.9 Brix. In 2022, the average was almost the same at 19.8 Brix. Acidity was also below 10g/L in general despite a cool season. TA averaged 7.5 g/L in 2023 and 7.9 g/L in 2022. It is possible that fruit chemistry was not impacted negatively (based on low GDD), because we had a low crop load due to winter injury. So there was less fruit to ripen in most varieties. We also like to think that our group did a good job with canopy management that enhanced fruit quality even in a cool year!

Table: 2023 Harvest fruit composition of selected grape varieties at the Wooster research vineyard: (2022 data)



Posted In: Viticulture
Tags: 2023 season, Vineyard Update
Comments: 0

***This factsheet can be found on Ohioline at or as a printable PDF online via the OSU Buckeye Appellation or Fruit Pathology websites.***

By: Melanie L. Lewis Ivey, Associate Professor, Department of Plant Pathology, OSU CFAES-Wooster Campus

Ripe Rot of Grape

Ripe rot is a late-season disease that primarily occurs in warm, moist, growing regions in the southeastern United States. However, outbreaks in Ohio and other states in the Midwest and Northeast occur when conditions are warm and wet during fruit maturation. The disease is caused by multiple species of the fungus Colletotrichum. Ripe rot reduces fruit yield and adversely affects the chemical composition and quality of grapes and wine, leading to undesirable flavors and color.

Disease Development and Symptoms
Ripe rot is caused by multiple species of the fungus Colletotrichum. In the spring, warm (77–86 degrees Fahrenheit /25–30 degrees Celsius) rains initiate the production and release of spores from tissues infected the previous season. Berries are susceptible to infections from bloom through harvest, but symptoms first appear just after veraison (the onset of ripening) and close-to-fruit maturity. Symptoms on berries of white-fruited cultivars first appear as reddish-brown circular lesions (Figure 1A) that can be mistaken for sunburn or chemical injury. The lesions expand in concentric circles until they cover the entire berry. As the berries rot, they become covered with black spots (fungal fruiting bodies or acervuli). During wet weather, the berries become covered with salmon-colored spore (conidia) masses (Figure 1B and 1C). Symptoms on red-fruited berries can be difficult to discern without the presence of spores and can be confused with sour rot (see PLPATH-FRU-50 Sour Rot Disorder of Grape). Rain spreads spores to other berries and clusters. The berries eventually shrivel into hard raisin-like structures called mummies, which usually remain attached to the berry cluster. Disease symptoms on the leaves, shoots, peduncles (cluster stems), or pedicels (berry stems) are not common. The fungus primarily overwinters on mummified berries and infected pedicels or peduncles, but also overwinters in woody tissues and dormant buds.

Figure 1. Ripe rot of white-fruited grape. Reddish- brown circular lesions on berries are the first symptoms of ripe rot (A). Berries covered in fruiting bodies of the ripe rot fungus (B). Salmon colored spores on the surface of a berry (C).


Cultivar Selection

All cultivated grape (North American, V. vinifera, and interspecific hybrids of V. vinifera) varieties are susceptible to infection by the ripe rot fungus. However, some varieties appear to be more susceptible than others (Table 1). Susceptibility can vary from season to season.

Table 1. List of ripe rot susceptibility of common varieties grown in the Midwest and Northeastern United States1.

Resistant Chardonel, Concord, Delaware, Ontario, Syrah
Susceptible Chambourcin, Chardonay, Marquette, Merlot, Niagara, Neptune, Sauvignon blanc, Seyval
Highly Susceptible Cabernet Franc, Cabernet Sauvignon, Carlos, Flame, Muscat, Golden Muscat, Petit Verdot, Vidal Blanc

1Data from Shiraishi et al. 2007

Cultural Practices

Dormant season pruning to remove mummies can reduce the number of spores produced and released in the spring. Pruning debris should be removed from the vineyard before bud break, especially vineyards with a history of ripe rot.

Chemical Control

Fungicides applied early in the season, from bloom to three to four weeks after bloom, are effective at preventing infections and limiting late-season rot. If weather conditions favor disease development close to harvest (i.e., warm, wet, high humidity), additional fungicide applications are recommended. For late-season fungicide applications, always check the pre-harvest interval (PHI) of the fungicide to confirm that it can be used close to harvest.

Commercial growers can consult the Midwest Fruit Pest Management Guide (Bulletin 506) and/or Developing an Effective Fungicide Spray Program for Wine Grapes in Ohio (Plant Pathology Series No. 147) for current fungicide recommendations.

Backyard growers should integrate early-season fungicide application with cultural practices to control ripe rot disease. Ripe rot disease can be confused with other fruit rots, such as sour rot or black rot. Backyard growers are encouraged to contact the C. Wayne Ellett Plant and Pest Diagnostic Clinic ( or 330-263-3721) for disease confirmation before making late-season fungicide applications.

Post-harvest Storage Practices

Grape clusters with ripe rot can negatively affect the quality and color of wine or juice. Fruit infected with ripe rot fungus that have not developed symptoms may develop symptoms during storage. To prevent rotting while in storage, sort out cracked, discolored, and rotting berries; place the berries in a breathable container; and store them at 30–32 F (-1–0 C).

Useful Resources

To learn more, check out Ohio State University Extension resources on ripe rot of grapes and related topics:

Developing an Effective Fungicide Spray Program for Wine Grapes in Ohio from Fruit Pathology Laboratory website from Ohio State University Extension at

Sour Rot Disorder of Grape, (2021) from Ohio State University Extension’s Ohioline, at

Midwest Fruit Pest Management Guide (OSU Bulletin 506) from Purdue Extension Education Store at


Shiraishi, M., Koide, M., Itamura, H., Yamada, M., Mitani, N., Ueno, T., Nakaune, R., and Nakano, M. 2007. Screening for resistance to ripe rot caused by Colletotrichum acutatum in grape germplasm. Vitis 46:196-200

By: Maria Smith, HCS-OSU

The new USDA plant hardiness zone maps have been updated for 2023 and were released this week. These updates occur approximately every 10 years, with the last maps released in 2012. The following press release from the USDA provides explanation for how the new zones are calculated and the 30-year timespan of winter minimum temperatures used to calculate the new zones.

These maps provide general guidance to new and existing grape growers to match vine cold tolerance with site conditions. HOWEVER, it should be noted that these zones are based on averages of winter minimum temperature, and mesoclimate conditions need to be accounted for in cultivar selection. As it is also stated in the press release and instructions for map use, winter extreme temperatures are variable and do dip below zone averages. In my 5 years at OSU, we have seen varying levels of winter injury in Vinifera in 2022, 2021, and 2019. And that does not include the polar vortex years of 2014 and 2015. All that to say, just because most of the state is now considered Zone 6a and 6b, does not necessarily indicate that Vinifera will survive at every site in every year. Choosing to plant Vinifera comes with significant risk of winter injury.

It is still best practice to track weather at your site to understand annual variation in weather conditions, be judicious in your cultivar selection, and plan to protect your grafted vines from winter injury.

You can use the interactive map to find your zone based on Zip code or download high-resolution copies of the map at
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Figure 1. Ohio’s cold hardiness zones now include 5b (-15 to -10F), 6a (-10 to -5F), 6b (-5 to 0F), and 7a (0 to 5F).

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Figure 2. Updated national map of USDA cold hardiness zones for 2023


USDA Unveils Updated Plant Hardiness Zone Map

Contact: Jan Suszkiw

WASHINGTON, DC, Nov. 15, 2023—The U.S. Department of Agriculture (USDA) today released a new version of its Plant Hardiness Zone Map (PHZM), updating this valuable tool for gardeners and researchers for the first time since 2012. USDA’s Plant Hardiness Zone Map is the standard by which gardeners and growers can determine which plants are most likely to thrive at a location. The new map—jointly developed by USDA's Agricultural Research Service (ARS) and Oregon State University's (OSU) PRISM Climate Group—is more accurate and contains greater detail than prior versions.

It is available online at In addition to the map updates, the Plant Hardiness Zone Map website was expanded in 2023 to include a “Tips for Growers” section, which provides information about USDA ARS research programs of interest to gardeners and others who grow and breed plants.

The 2023 map is based on 30-year averages of the lowest annual winter temperatures at specific locations, is divided into 10-degree Fahrenheit zones and further divided into 5-degree Fahrenheit half-zones. Like the 2012 map, the 2023 web version offers a Geographic Information System (GIS)-based interactive format and is specifically designed to be user-friendly. Notably, the 2023 map delivers to users several new, significant features and advances. The 2023 map incorporates data from 13,412 weather stations compared to the 7,983 that were used for the 2012 map.

Furthermore, the new map’s rendering for Alaska is now at a much more detailed resolution (down from a 6 ¼ -square-mile area of detail to a ¼ square mile). "These updates reflect our ongoing commitment to ensuring the Plant Hardiness Zone Map remains a premier source of information that gardeners, growers and researchers alike can use, whether they’re located in the continental United States, Alaska, Hawaii or Puerto Rico,” said ARS Administrator Dr. Simon Liu.

Approximately 80 million American gardeners and growers represent the most frequent users of the USDA Plant Hardiness Zone Map. However, they’re not the only ones with a need for this hardiness information. For example, the USDA Risk Management Agency refers to the map’s plant hardiness zone designations to set certain crop insurance standards. Additionally, scientists incorporate the plant hardiness zones as a data layer in many research models, such as those modeling the spread of exotic weeds and insects.

The 2023 Plant Hardiness Zone Map is now available as a premier source of information that gardeners, growers and researchers alike can use.

Plant hardiness zone designations represent what’s known as the “average annual extreme minimum temperature” at a given location during a particular time period (30 years, in this instance). Put another way, the designations do not reflect the coldest it has ever been or ever will be at a specific location, but simply the average lowest winter temperature for the location over a specified time. Low temperature during the winter is a crucial factor in the survival of plants at specific locations.

As with the 2012 map, the new version has 13 zones across the United States and its territories. Each zone is broken into half zones, designated as “A” and “B.” For example, zone 7 is divided into 7a and 7b half zones. When compared to the 2012 map, the 2023 version reveals that about half of the country shifted to the next warmer half zone, and the other half of the country remained in the same half zone. That shift to the next warmer half zone means those areas warmed somewhere in the range of 0-5 degrees Fahrenheit; however, some locations experienced warming in the range of 0-5 degrees Fahrenheit without moving to another half zone.

These national differences in zonal boundaries are mostly a result of incorporating temperature data from a more recent time period. The 2023 map includes data measured at weather stations from 1991 to 2020. Notably, the 2023 map for Alaska is “warmer” than the 2012 version. That’s mainly because the new map uses more data representing the state’s mountain regions where, during winter, warm air overlies cold air that settles into low-elevation valleys, creating warmer temperatures.

The annual extreme minimum temperature represents the coldest night of the year, which can be highly variable from year to year, depending on local weather patterns. Some changes in zonal boundaries are also the result of using increasingly sophisticated mapping methods and the inclusion of data from more weather stations. 

Temperature updates to plant hardiness zones are not necessarily reflective of global climate change because of the highly variable nature of the extreme minimum temperature of the year, as well as the use of increasingly sophisticated mapping methods and the inclusion of data from more weather stations.  Consequently, map developers involved in the project cautioned against attributing temperature updates made to some zones as reliable and accurate indicators of global climate change (which is usually based on trends in overall average temperatures recorded over long time periods).

Although a paper version of the 2023 map will not be available for purchase from the government, anyone may download the new map free of charge and print copies as needed.

The Agricultural Research Service is the U.S. Department of Agriculture's chief scientific in-house research agency. Daily, ARS focuses on solutions to agricultural problems affecting America. Each dollar invested in U.S. agricultural research results in $20 of economic impact.

Posted In: Viticulture
Comments: 0

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.

A bunch of grapes on a vine

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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.

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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 (

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.

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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.
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Tags: 2023 season
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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.

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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 (

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.

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Fig 3. Ohio drought status, 27 June 2023. From

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.

A bunch of bugs on a vine

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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!

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Fig. 6 Air quality from 28 June 2023. Figure from

Posted In: Viticulture
Tags: 2023 season
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By: Imed Dami and Maria Smith, HCS-OSU

Freeze advisories were issued the week of May 15 and temperature dropped below freezing on May 18. The lowest temperatures ranged between 28 oF and 31 oF. These freeze events were thankfully not widespread and occurred mainly in northeast Ohio (see map below). Note that this was the latest freeze since 26 May 2013 for Wooster and the second latest freeze on record since 1997. 

At the time of freeze occurrence, stages of development in grapevines ranged between 3” and 12” shoot growth. Expected killing temperatures at those stages vary between 29 oF and 30 oF. Therefore, shoot injury was sustained in some vineyards. Overall, damage was sporadic and reported in only few vineyards that have less than ideal site locations or have varieties that budded out very early.  Those who have wind machines turned them on in northeast Ohio. At our research vineyard in Wooster, budbreak took place mid- to late April; however, temperature dropped to only 35 ºF on May 18. Several growers reported minimum injury to Dr. Smith. For those who experienced damage, they may refer to a previous article posted by Dr. Smith that discusses how to deal with injured vines.

We assume that we’re done with cold events between winter and spring for now, and we hope not to worry about it until next year.  

Posted In: Viticulture
Tags: 2023 season, Spring Frost
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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.

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


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.

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Figure 3. Wooster, OH cumulative GDD (base 50F) as of May 16 = 372, historic GDD for May 16 = 383. Chart from CFAES Weather System (

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.

Posted In: Viticulture
Tags: 2023 season, Vineyard Update
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