January 2025 Polar Vortex Update

By: Maria Smith, HCS-OSU

While we anticipate yet another round of arctic air here in Ohio this coming week, we are forecast to be well-above the temperatures we achieved just a few weeks ago (>0F) and not expecting compounding injury from January.

For context: On 22 January 2025, we experienced one of the colder polar vortex events of recent winters, which sent temperatures plunging between -2F and -13F statewide (Figure 1).

With temperatures that cold, some damage (particularly to cold-sensitive Vinifera) is expected. However, spoiler alert, it overall was not nearly as damaging as one might expect.

Figure 1. Minimum temperatures by county on 1/22/2025. Red indicates stations from MRCC (https://mrcc.purdue.edu) and blue indicate NEWA stations (https://newa.cornell.edu). Figure by Fernanda Cohoon.

Bud Injury – Wooster

The station minimum temperatures in the cultivar evaluation blocks of Hort Unit 2 reached -8F. Below is the extent of bud injury experienced among a range of Vinifera and hybrid cultivars (Table 1).

It is important to emphasize that site selection played a critical role in the localized minimum temperatures at Hort 2. Prevailing calm winds (< 2 mph) created radiative conditions, with cold air settling in topographic depressions and lower elevations areas within the site. Across the 45 acres of Hort 2, temperatures from 3 different weather stations ranged between -8F and -10F. The Vinifera grapes (BLK C) and cold hardy hybrid trial (BLK D) are planted on the highest elevation within the site with multi-directional air drainage that inhibits cold air from pooling within the planted grape block.

Why higher mortality among Clarion (MN1220) and NY 06? The higher percentage of bud injury in Clarion (MN 1220) and NY 06 may be related to the herbicide drift injury experienced in the BLK D variety trial vines during the 2024 growing season. BLK D had the highest observed herbicide injury among all 4 planted trial blocks at Hort 2. It’s unknown, however, whether bud mortality was directly caused from herbicide injury or if the observed mortality resulted from lower hardiness and cold injury since bud dissection was not performed until after the January cold event.

Table 1. Bud injury rates of select Vinifera and hybrid cultivars at Hort 2 (Wooster, OH). Data from Fernanda Cohoon and Diane Kinney.

Bud Injury – Ashtabula

Cane samples for several standard and select cold-sensitive Vinifera varieties were collected for bud injury from AARS and commercial vineyards in Ashtabula County to assess damage over a representative range of regional conditions. Overall injury rates from Vinifera at the AARS Kingsville station and commercial vineyards from Grand River Valley (Geneva, OH) and Conneaut Creek (Conneaut, OH) ranged between 2% (AARS Pinot Noir) and 13% (AARS Sauvignon Blanc). Minimum temperatures at AARS reached -5.8F, but temperatures reported from Grand River Valley were reported to be as low as -10F.

Table 2: Overall bud injury (primary, secondary, and tertiary) among of select cultivars and sites within Ashtabula County. Data from Aaron Jaskiewicz, Patrick Turner, and Andy Kirk.

Aligning Wooster DTA information with the Bud Cold Hardiness Model Using Cabernet Franc

The cold hardiness model provided by the Londo lab at Cornell University estimated 50% bud injury for Cabernet Franc at Wooster at -16.78F (Figure 2). DTA (differential thermal analysis – a procedure to collect our own estimates of cold hardiness) from Unit 2 in mid-January estimated LT50 cold hardiness of Cab Franc FPS 11 at -16.55F, which was very close to the model-estimated -16.78F. While it’s possible that hardiness may have been over-predicted (Figure 3), Cab Franc and other Vinifera varieties were able to survive between -5 to -10F actual minimum temperatures without significant injury levels (>15%) in Northeast Ohio.

*Note: the Cornell Bud Cold Hardiness model has been integrated into the NEWA application. For an example of the output, see Figure 4. Only select cultivars are included with the NEWA model integration.   

Figure 2. Predicted cold hardiness of Cabernet Franc using Wooster, OH weather station data. Model-predicted hardiness for Jan 23 was -16.78F and an actual minimum recorded temperature for this station was -9.76F.   

Figure 3. Cabernet Franc cold hardiness data from the Geneva, NY research station that overlays DTA estimated cold hardiness with model-predicted values. LTXX lines indicate estimated temperatures at which 10 (-10.84F), 50 (-14.44F), and 90% (-18.22F) bud injury would occur. LT50 is approximately +2F less hardy than model-estimated values.

Figure 4. An example of the Grape Cold Hardiness Risk Assessment Tool using the Wooster Hort 2 weather station through NEWA.

Recommendations for bud adjustments to accommodate injury rates

We will discuss strategies for adjusted pruning and bud retention at the upcoming Wooster Pruning Workshop on Thursday, March 6.

The best course of action for managing winter cold injury is to 1) assess the amount of injury within your vineyard prior to dormant pruning using a representative sample of 100 buds (10 canes with 10 nodes per cane for each variety/vineyard block to dissect), and 2) adjust bud retention values to appropriately accommodate the amount of sustained injury for your site and varieties.

The additional number of buds to retain is relative to the percentage of damaged primary buds. The following table (Table 3) provides general guidance for how many additional buds to retain with respect to the percent of observed bud injury. Additional information on identifying bud injury and management can be found in the factsheet Assessing and Managing Winter-Damaged Grapevines Part II: Early Spring  

Table 3. Recommended bud retention adjustments based on assessed primary bud injury.

Thankfully, most damage this year thus far appears to be minimal. However, with Buckeye Chuck predicting an early spring, there is still opportunity for injury to occur moving into late winter. Though, to be fair to Chuck’s skills, he currently ranks 8^th among all prognosticating groundhogs and is only right about 55% of the time.