Freeze Watch: April 24, 2024

By: Maria Smith, HCS-OSU

Buds are breaking across Ohio and here in Wooster (Fig. 1), but frost risk looms again tonight. A few regions of Ohio reached damaging temperatures for green tissues on the morning of April 22 (Fig. 2), with minor damage observed in some vineyards in Central and Southern Ohio.

Figure 1. Bud status of V. vinifera ‘Cabernet franc’ (top) and Vitis hybrid NY03.06 (bottom) on Monday, April 24. Wooster, Hort Unit 2 minimum temperature for 4/22 was 34.5F (data from https://newa.cornell.edu). Tissue phenology ranges between stages E-L 3-7 throughout both Vinifera and hybrid variety trial blocks. Photo credit: Maria Smith

Figure 2. Minimum low temperatures for Monday, April 22, 2024. Figure from https://mrcc.purdue.edu

However, we are expecting another evening of wide-spread frost potential this evening for Central and Northern Ohio. This blog post is a reminder to visit our resources on spring frost: preparing for spring frosts and managing injury or obtaining a copy of the spring frost bulletin from OSU Extension.

The following is a message from State Climatologist Aaron Wilson about the next predicted frost for this evening.

It looks like we do have one more night tonight to get through this season. Freeze Watches are in place for central and northern Ohio. Skies will clear and winds will relax tonight with widespread frost likely. Lows will fall into the upper 20s to low 30s across northern Ohio (except near Lake Erie which is warm enough to keep temperatures a bit warmer). Traditional cold spots may settle even colder. The timing will likely be about 4-5 hours of sub-freezing temperatures, between 2 and 7am.

Here are the current counties included in the Freeze Watch, but frost across southern Ohio even with official temperatures in the mid to upper 30s is not out of the question tonight.

After tonight, the forecast is promising in terms of freeze potential. Currently, there does not appear to be a threat through the first week of May, which is a good sign that we may be close to the end of our worry!

Our strategy at Hort Unit 2 to prepare for spring freeze in 2024

Delayed (waiting as long as possible) or double (pre-pruning to long spurs) pruning is one of the most reliable strategies for delaying the onset of bud break, thus helping us avoid frost events. Delayed/double pruning works by taking advantage of the strong apical dominance of grapes, whereby the buds on the top of canes open first and the buds on the bottom of the cane that would be retained for fruit production remain closed on the bottom (Fig. 3). This tactic can aid in delaying bud break by up to two weeks. It should be noted that final pruning should be completed by the time the top buds are approximately 1-2” in length to avoid potential impacts on yield from basal buds/blind nodes or excessive delays in fruit ripening. Additionally, delayed/double pruning is best performed in spur-pruned systems.

This year, we have elected to delay pruning, a feasible tactic at Hort Unit 2 given the size of the research vineyard. This method can be a successful strategy in small (< 5-acre) vineyards or for those varieties, such as Marquette, La Crescent, Itasca, etc., that exhibit very early bud break.

Figure 3. Delayed pruning of V. vinifera ‘Chardonnay’ on 4/22. Vines were pruned on 4/23. Note: Apical buds are approximately 1” at E-L stage 5 (middle photo), while basal buds are less developed at E-L stage 3 (bottom photo). All 3 photos were taken of the same vine. Photo credit: Maria Smith