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By: Maria Smith, HCS-OSU

Cold is an obvious feature of our Ohio winters, but believe it or not, this month’s sustained cold is an anomaly not seen for nearly the past century. 

Although we’ve had pockets of damaging cold temperatures over the past week (Figure 1), tomorrow morning will be the most widespread and deepest of them all (Figure 2). 

Figure 1. Minimum temperatures for 24 Jan 2026. Note a pocket of tempertures between -5 to -15F in far-NE OH. Temperatures at the Kingsville AARS Research Station logged -9.4F on 24 Jan 2026. Data from https://newa.cornell.edu 

Figure 2. Forecast temperatures for 31 January 2026. Widespread temperatures well below 0F are expected across the state. 

Current bud hardiness models are estimating temperatures for Vinifera such as Chardonnay to have attained a hardiness to nearly -16F (Figure 3). What is interesting, according to the model, is that many of our cold-hardy hybrids are estimated to have less hardiness closer to -11 to -14F (Figure 3). We will show in a follow-up post that many cultivars did lose hardiness following the warm temperatures in early January, although we would expect to regain some hardiness with the recent sustained cold weather pattern

Figure 3. Predicted LT50 (estimated minimum temepratures at which we would expect to sustain 50% primary bud mortality) for Chardonnay (left) and Frontenac (right). 

Based on some initial estimates of injury following temps reaching -9.4F in Kingsville over the past week, I suspect the hardiness is likely over-estimated for Vinifera, at least. However, we will be monitoring injury rates and temperatures over the next several days and will provide more in-depth information once this sustained cold period has passed in the next week or two.

In the meantime, now is a good opportunity to review assessing grapevine winter injury prior to starting or resuming dormant pruning to determine needs for adjusted pruning and yield retention in the 2026 season. 

By: Amaya Atucha, Professor, University of Wisconsin Madison

As we enter the winter season, many growers are once again thinking about the risk of cold injury to grapevines. With increasingly unpredictable weather patterns, including warm spells followed by abrupt cold snaps, it often feels like we are always on alert for potential damage. During the dormant season, freeze injury to buds remains the number one concern, as even the hardiest cultivars can be vulnerable when temperatures fall below their level of cold hardiness.

There has been extensive research on how to measure and understand cold hardiness in grapevines, but the techniques we use, such as laboratory-based bud freezing assays, are not practical for growers to perform on their own. These assessments are typically carried out by researchers and extension specialists at universities and research centers. As a result, growers have had limited ways to know, in real time, how cold hardiness is changing in their own vineyards.

To address this gap, a team from the University of Wisconsin–Madison (Amaya Atucha and Al Kovaleski) partnered with colleagues at Cornell University (Jason Londo and Dan Olmstead), supported by a USDA NIFA CARE grant (2023-68008-39274), to develop a practical, grower-facing prediction tool: the Grape Cold Hardiness Risk Assessment. Built on many years of research, this tool is now available through the NEWA (Network for Environment and Weather Applications) platform and allows growers to monitor predicted cold hardiness of grapevines throughout the dormant season.

In addition to evaluating cold hardiness and helping growers anticipate winter injury risk, the Grape Cold Hardiness Risk Assessment tool can also be used when considering potential vineyard sites. By running the model for a proposed location and cultivar, such as assessing whether Cabernet Sauvignon would regularly fall below its hardiness threshold, growers can make more informed decisions about cultivar selection and site suitability before planting.

Understanding Cold Hardiness in Grapevine Buds

Cold hardiness is a vine’s ability to tolerate freezing temperatures, and it changes continually throughout the dormant season. Buds gain hardiness in the fall as temperatures cool and daylength shortens, reach their peak tolerance in midwinter, and then gradually lose hardiness during late-winter warm spells (Figure 1). Because this process is dynamic, buds can be damaged at several points in the season whenever temperatures fall below what the buds can tolerate at that time.

Figure 1. Seasonal dynamics of cold hardiness in grapevine buds, illustrating fall acclimation (progressive gains in cold tolerance), winter maintenance of maximum hardiness, and spring deacclimation (gradual loss of cold tolerance as buds resume growth).

A vine’s hardiness level is strongly linked to the temperatures it has experienced. Researchers use techniques such as differential thermal analysis to determine the LT50, the temperature at which half of the buds would be expected to die. LT50 serves as a practical threshold for injury risk and changes throughout the winter as buds acclimate and deacclimate.

Because cold hardiness is driven by temperature, weather data can be used to model and predict LT50 for many grape cultivars, including both hybrids and vinifera. These predictions help growers judge whether a cold event might cause injury, evaluate potential bud damage after a freeze, and make informed pruning and management decisions. Access to real-time hardiness estimates provides a clearer picture of winter injury risk and supports better vineyard decision-making.

How the Grape Cold Hardiness Risk Assessment Tool Works

The tool, available on the NEWA (Network for Environment and Weather Applications) platform, uses real-time or gridded weather data to estimate bud cold hardiness and identify periods when cold injury is likely for more than fifty grape cultivars.

Step 1: Choose your location

You can run the tool using either a NEWA weather station or gridded climate data.

• Using a NEWA station: Select the station closest to your vineyard and the model will automatically use current and historical weather data from that site.
• Using Grid Data: Enter the coordinates of your vineyard or proposed site. The model will use interpolated weather information from the Northeast Regional Climate Center. This option is ideal for growers without a nearby NEWA station and for evaluating vineyard establishment at new locations.

Step 2: Set model parameters

After selecting the location, choose the settings for your run.

• Choose whether you want temperatures displayed in Fahrenheit or Celsius.
• Select the date you want the model to run through. The model always begins calculations on July 1 of the current season and estimates bud cold hardiness from that date up to the selected day.
  • You can choose a past date to review whether damage may have occurred.
  • You can select today’s date to view current conditions.
  • If your selected date includes forecasted days, the tool will project future LT50 values (temperature at which half of the dormant buds would be expected to be killed by freezing) using the available weather forecast.
• Select the grape cultivar you wish to evaluate. You can run additional cultivars by repeating this step. A downloadable dataset is also available for growers who want to store or analyze the results.

Step 3: View the results

The results panel displays a graph of predicted cold hardiness alongside weather conditions.

• The Y axis shows temperature and the X axis shows dates.
• The solid dark line represents the minimum daily temperature, and the dashed grey line represents the maximum daily temperature.
• The red dashed line labeled LT50 represents the model’s prediction of the temperature at which fifty percent of the buds would be expected to die.
• A vertical blue dashed line marks the current date within the selected period.
• If the minimum temperature line drops below the red LT50 line, this indicates that the air temperature has fallen below the freezing tolerance of the buds at that time, and cold damage is likely to have occurred.

Step 4: Review the cold damage risk forecast

The tool also provides a color coded summary of the predicted freeze risk for the date you selected.

• The risk level is displayed as Low, Medium, or High based on how predicted temperatures compare to the LT50.
• Additional dots on the panel allow you to view up to six future days of risk predictions. Selecting a dot displays the likely risk level for that day based on the weather forecast.

These features allow growers to anticipate upcoming cold events, evaluate recent ones, and make informed management decisions during the dormant season.

Grower Takeaways

• Bud cold hardiness changes throughout the dormant season and depends on the temperatures the vine has recently experienced.
• The LT50 value tells you the temperature at which fifty percent of buds would be expected to suffer cold damage.
• The Grape Cold Hardiness Risk Assessment tool predicts LT50 for more than fifty cultivars using real-time and forecasted temperature data.
• If minimum temperatures fall below the predicted LT50, bud injury is likely.
• The tool works with any NEWA weather station or with gridded climate data by entering your vineyard’s coordinates.
• Forecasted risk levels help growers anticipate upcoming cold events and plan protective actions.
• The model can also be used to assess potential new vineyard sites by comparing cultivar specific hardiness needs with the site’s temperature patterns.

Erdal Ozkan. Professor and Extension State Specialist
The Ohio State University, FABE

Time to give your sprayer some TLC by properly winterizing it.

You probably won't use your sprayer again until next spring. To avoid potential problems, frustration, and major headaches next year, it's wise to give your sprayer some TLC (Tender Loving Care) this time of year. While there may still be other important matters demanding your attention, don’t forget to winterize your sprayer. Don't delay if you haven't done so already. You want to prevent a cracked pump or reduced efficiency caused by not properly winterizing before temperatures drop below freezing. Here are some essential steps to take with your sprayer now.

Rinsing

You probably did the right thing when you last used the sprayer: thoroughly rinsed the entire system (tank, hoses, filters, nozzles). If you didn't, be sure to do this before storing the sprayer. An unrinsed sprayer after each use, especially after the spraying season ends, can lead to cross-contamination of products applied to different crops next spring. Pay special attention to avoiding cross-contamination, which can cause severe crop damage, especially when using some of the newer 2,4-D and Dicamba herbicides. Another issue caused by not properly rinsing all sprayer parts is clogged nozzles. Once nozzles are clogged and remain that way for a long time, it becomes difficult to restore them to their normal working condition, which is what you expect from a properly cleaned nozzle. Leaving chemical residues in nozzles often causes changes in flow rate and spray pattern, resulting in uneven chemical distribution on the target. 

The ease of properly rinsing a tank's interior depends on its type. It is very simple if the tank is relatively new and has special rinsing nozzles and mechanisms inside. If not, manual rinsing becomes more difficult and can pose safety risks, such as inhaling fumes from leftover chemicals during the process. To avoid these issues, you can either replace the tank with one that has interior rinse nozzles or install an interior rinse system in your current tank. 

For effective rinsing of all sprayer parts, circulate clean water through the entire sprayer for several minutes first with the nozzles off, then flush out the rinsate through the nozzles. Rinsing should ideally be done in the field or on a concrete chemical mixing/loading pad with a sump to recover rinse water. In any case, dispose of the rinsate following the instructions on the pesticide labels you have used. Always check the label for specific directions. Most labels recommend the following procedure: if rinsing on a concrete rinse pad with a sump, return the collected rinsate to the tank, dilute it with water, and spray it in the field where it cannot reach ditches or other water bodies. If rinsing is done in the field, make sure you are not flushing rinsate in one area. It’s best to dilute the rinse water in the tank further and spray it on the field in places where it won’t contaminate nearby water bodies or ditches. 

Cleaning

Rinsing the system with water, as explained earlier, may not completely remove chemicals from the sprayer. This could lead to cross-contamination issues. Residues of certain pesticides left in the sprayer might cause serious problems when applying a spray mixture containing those residues to a crop highly sensitive to that pesticide. To prevent such issues, it's best to thoroughly clean and rinse the entire spraying system with a cleaning solution. Usually, a mixture of 1 part household ammonia to 100 parts water works well for cleaning the tank. However, if the tank hasn't been cleaned for weeks or immediately after the last spraying, you might need to start with a detergent solution. Some chemicals require specific rinsing solutions. Always check the product label for the latest cleaning instructions.

Cleaning the outside of sprayer components deserves equal attention. Remove compacted deposits with a bristle brush. Then flush the exterior parts of the equipment with water. A high-pressure washer can be used if available. Wash the exterior of the equipment either in the field, away from ditches and nearby water sources, or on a specially constructed concrete rinse pad with a sump. Again, the rinsate should be disposed of according to the label recommendations. As I mentioned earlier, most labels recommend the same practice: put the rinsate collected in the sump back into the tank, dilute it with water, and spray it in the field where there is no potential for the rinsate to reach ditches or other nearby water bodies. 

Winterizing

Recheck to ensure no liquid remains inside any of the sprayer parts to prevent freezing. The pump, as the core of a sprayer, needs special attention. You don’t want a cracked pump or one that isn’t working properly due to inadequate winterization before temperatures drop below freezing. After draining the water, add a small amount of oil, then turn the pump four or five revolutions by hand to coat the inside. Ensure this oil won’t harm rubber rollers in a roller pump or rubber parts in a diaphragm pump. Refer to the operator's manual. If oil isn't recommended, pouring one tablespoon of radiator rust inhibitor into the pump's inlet and outlet can also help prevent corrosion. Alternatively, use automotive antifreeze with rust inhibitor in the pump and other sprayer parts. This helps protect against corrosion and freezing if any water remains. To prevent corrosion, remove nozzle tips and strainers, dry them thoroughly, and store them somewhere dry. Another option is to submerge them in a can of light oil, such as diesel fuel or kerosene. 

Storage

Find ways to protect your sprayer from the harmful effects of snow, rain, sun, and strong winds. Moisture in the air, whether from snow, rain, or soil, causes rust on the metal parts of all types of unprotected equipment. This is especially true for a sprayer, which has various hoses, rubber gaskets, and plastic components. While the sun can help reduce moisture in the air, it can also cause damage. Ultraviolet light weakens and softens rubber parts like hoses and tires, and degrades some tank materials. The best way to protect your sprayer is to store it in a dry building. Keeping sprayers inside also allows you to work on them anytime during the off-season, regardless of the weather. If storing inside isn't possible, cover the sprayer with a material that shields it from sun, rain, and snow. For trailer-style sprayers, place blocks under the frame or axle and reduce tire pressure during storage. 

Finally, double-check all sprayer parts before leaving it behind. Identify parts that may need repairs or replacement. Inspect the tank and hoses for any signs of cracks or damage. Check the painted surfaces for scratches and touch up with paint to prevent corrosion. Also, remember to cover openings to prevent birds from nesting in the sprayer and to keep insects, dirt, and other debris out of the system.

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.