Late-March Freeze and Spring 2024 Wooster Vineyard Updates

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).

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.

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

Figure 2. Median date of last 32F freeze (top) and latest date of observed 32F freeze (bottom). Figures from https://mrcc.purdue.edu

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

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

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).

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.