Early budbreak in Ohio – vines at risk again for spring freeze damage

Monday, April 19th, 2021

By: Dr. Maria Smith, HCS-OSU

From Ashtabula to Cincinnati, the growing season is here. Usually, budbreak is a stratified process over several weeks from the south to the north, but not this year. An unusually warm spring has heralded in the start of the season in an uncanny uniform fashion and without regards to cultivar or geographical region (Fig 1). This year’s budbreak pattern, which is anywhere from days to weeks ahead of historical averages, can largely be attributed to the abnormally warm, dry conditions that increase in intensity from south to north (Fig 2).

 

Fig 1. Phenology among several Vinifera and hybrid cultivars at Wooster, Unit 2, Apr 16, 2021 (Photo credit: Diane Kinney).

Fig 2. Temperature (left) and precipitation (right) deviation from the long-term average from March 17 through April 15, 2021 (figures from https://climate.osu.edu)

Despite the recent pleasantly warm weather, Ohio unfortunately remains at risk for below freezing conditions for another 2 to 4 weeks (Fig 3). This week will be a stark reminder of that, as both below freezing temperatures and the chance of snow accumulation are forecasted courtesy of a cold front moving across the state later this week (Fig 4).

Fig 3. Median date of last 32°F for Ohio (figure from www.mrcc.illinois.edu)

Fig 4. Forecast and minimum temperature maps for the week of Apr 19, 2021. (figures from NOAA, www.weather.gov)

Given the upcoming forecasts, let's review some lessons from the 2020 season freezes

Stay calm and optimistic!

Just because temperatures reach < 32°F does not automatically mean that all the shoots will die. Grapes are resilient when it comes to coping with environmental stress, and spring freezes are no exception. The good news over the past few days is that cooler temperatures have slowed growth and development of the vines. This is crucial since we know that buds/shoots that are less advanced can withstand colder temperatures than those which are more developed (Table 1). Additionally, grapes are comprised of compound buds, so that if there is loss of the primary shoots, secondary and tertiary shoots can emerge to resume growth. Although these secondary and tertiary shoots are less fruitful than primary shoots and are developmentally delayed, many common French American and cold-hardy hybrids grown in Ohio have highly fruitful secondary shoots that can temper potential yield losses.

Table 1. Estimated critical temperatures for Pinot noir at different stages of bud/shoot development (Gardea, 1987)

 

Swell

Bud break

First leaf

Second leaf

Third leaf

Pinot noir

26.6

28.0

28.4

28.9

30.0

Review the tools for successfully “weathering” this week’s freeze

One of the first questions that come up when a spring freeze event approaches is “What can I do to protect the vines?”. Once vines have reached budbreak, the options for protection are limited, and the efficacy of the options is highly dependent upon the type of freeze event (Table 2). For many small vineyards, the best options are those that need to be considered and used in advanced of any predicted spring freeze events.  

Table 2: Characteristics of radiation vs advective freeze events. Table from https://www.canr.msu.edu/news/what_is_the_difference_between_a_frost_and_a_freeze

Radiation freeze

Advective freeze

Winds less than 5 MPH

Winds higher that 5 MPH

Clear sky

May be cloudy

Cold air mass 30 to 200 feet thick

Cold air mass 450 to 3,000 feet thick

Inversion develops

No Inversion

Cold air in the low spots

 

White or black frost damage

 

Easier to protect

Difficult to protect

Below is a republishing of methods that can also be found from our OGEN article from APRIL 2020 - Spring Freeze Issue.  Drs. Imed Dami and Michela Centinari (PSU) also discussed these methods in a recent March webinar. Click here to view the presentation.

Methods prior to frost event

  • Delayed pruning: similar to 2020, vines have more advanced phenology than normal and buds are pushing earlier as a result of above average temepratures. Delayed pruning helps with delaying budbreak.
  • Double-pruning: the rationale is similar to delayed pruning. With 1st pruning, you leave extra buds per vine. Due to apical dominance, apical buds push earlier than basal buds. If frost occurs, basal buds (which are delayed in growing) will be less likely to be injured. With the 2nd pruning, apical shoots (injured or not) will be pruned by retaining a final bud count per vine. Note: the 2nd pruning should occur when apical shoots are less than 2" in total growth to avoid potential issues with fruitless shoots developing from the basal buds regardless if you are past the last date of freeze.
  • Row middle and cover crop: bare ground in row middles provide more heat to keep vines warm during a frost event. Mowed grass cover crop will also do the same. So, it is crucial that you mowed your grass as short as possible for added frost protection.
  • Products that delay budbreak: Some products can be effective, but it is too late to apply now if you have not already done so. Please view the recorded webinar presentation with Dr. Imed Dami (link) for an overview of the available budbreak delay products.  
  • KDL (0-0-24) fertilizer: Even though growers would like to use this product, research has shown that KDL does not protect shoots against frost injury once vines resume growth. Therefore, it is not recommended. Dr. Smith researched this product and can be contacted directly for more information.
  • Copper: has been shown to protect young shoots against frost injury by killing ice forming bacteria present on vine foliage. You may start spraying as soon as budbreak and repeat every 5-7 days (washes off easily and must be reapplied after an inch or more of rain) until you’re out of the frost threat period (2 – 3 weeks) in your vineyard. Read the label for the application rate. In CA, 0.75 actual copper per acre was used. Read the label to avoid plant injury. To avoid injury, apply when not cold or wet (slow drying) and use formulation with lime.

Methods during a frost event

  • Wind machines: wind machines, although expensive, are effective against radiative spring frost events (clear, cold nights with temperature inversions).
  • Overhead irrigation (sprinklers): None of our growers in OH has this system. Having said that, DO NOT SPRAY YOUR VINES WITH WATER USING A SPRAYER. You will cause more damage than doing nothing.
  • Heaters: same as above; not a common method in Ohio. When temperature inversion exists, heaters are effective alone and best with wind machines. However, cost of fuel and pollution are main limitations.

Although there are still a couple of days until the predicted freeze event, it is a good idea to also review the recommendations for managing the vineyard if the forecasted freeze causes shoot injury. Those recommendations can be found in the APRIL 2020 OGEN.

April 19, 2021 - 5:00pm -- smith.12720@osu.edu

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