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By: Imed Dami and Maria Smith, HCS-OSU

Freeze advisories were issued the week of May 15 and temperature dropped below freezing on May 18. The lowest temperatures ranged between 28 oF and 31 oF. These freeze events were thankfully not widespread and occurred mainly in northeast Ohio (see map below). Note that this was the latest freeze since 26 May 2013 for Wooster and the second latest freeze on record since 1997. 

At the time of freeze occurrence, stages of development in grapevines ranged between 3” and 12” shoot growth. Expected killing temperatures at those stages vary between 29 oF and 30 oF. Therefore, shoot injury was sustained in some vineyards. Overall, damage was sporadic and reported in only few vineyards that have less than ideal site locations or have varieties that budded out very early.  Those who have wind machines turned them on in northeast Ohio. At our research vineyard in Wooster, budbreak took place mid- to late April; however, temperature dropped to only 35 ºF on May 18. Several growers reported minimum injury to Dr. Smith. For those who experienced damage, they may refer to a previous article posted by Dr. Smith that discusses how to deal with injured vines.

We assume that we’re done with cold events between winter and spring for now, and we hope not to worry about it until next year.  

Posted In: Viticulture
Tags: 2023 season, Spring Frost
Comments: 0

By: Maria Smith, HCS-OSU

With the frost risks largely in the rear-view of April, we are starting to see new shoot growth bolt ahead under warming temperatures of the past week (Figure 1). Keep in mind, if you did have damage from those late-April freeze events, you may just be starting to see the emergence of secondary and tertiary shoots (Figure 2).


Figure 1. Shoot growth Chardonnay 4-May 2023 (top) at E-L stages 3-4 and 16-May 2023 (bottom) at E-L stages 11-12.

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Figure 2. Primary and secondary shoot emergence from single node position


Cumulative GDD in Wooster is near the historic average for this time of year (Figure 3) as warm early- and mid-April temperaturs have been buffered with a cool down in late-April through early-May. As mentioned in the last post, we saw two late spring frost events that contributed to wide-spread injury to many vineyards in the northern portions of the state.

April precipitation (4.0”) was 0.6” above the 10-year average rainfall (3.4”), but we are currently on track for a drier than average May, with only 1.3” of accumulated rainfall in the first 2 weeks of the month.

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Figure 3. Wooster, OH cumulative GDD (base 50F) as of May 16 = 372, historic GDD for May 16 = 383. Chart from CFAES Weather System (

Timely vineyard management:

Below are some considerations for cultural management of your vines at this early stage of the growing season:

  • New vineyard plantings: Now through early June is when we need to get our new vineyard plantings completed. If dry weather persists, new vines should be irrigated. 1 and 2-yr-old vines should receive around 0.5” to 1” of water per week through rainfall and irrigation while root systems are being established.
  • 2 and 3-yr-old vines: retain the 2-3 shoots required for continued trunk and/or cordon establishment and remove the remaining shoots from the trunk. Remove inflorescences (flower clusters) from the remaining shoots. The goal of these tasks is to encourgage robust vegetative growth of young vines.
  • Mature vines: Shoot thin vines when shoots are between 6-12” in growth. For details on shoot thinning and suckering mature vines, visit our blog post from May 2022 and review our video on canopy management here. *Note: shoot thinning for vines that were adjusted for bud counts following winter injury is critical, as canopies will be denser with greater bud retention.
  • The process of de-hilling soil around grafted vines should be completed to prevent scion rooting

Disease management

With the rapid rate of shoot growth along with the increase of average daily temperatures, it’s important to ensure your shoots stay protected against early season diseases, including Phomopsis, Anthracnose, Black Rot, Downy Mildew, and Powdery Mildew. Remember that disease management should be preventative beginning around 1” of shoot growth and combined with best canopy management practices.  

For successful control, it’s important to understand the disease, cultivar susceptibility, and management options. There are several resources available for disease management such as the Midwest Fruit Pest Management Guide, Developing an Effective Fungicide Spray Program for Grapes in Ohio, and NY/PA Pest Management Guide. Fact sheets on important grape diseases can be found here. Read and follow all label guidelines and ensure proper fungicide rotation and sprayer coverage/calibration to reduce risks for fungicide resistance.

Vineyard insects

During the warm stretch of April, I was hearing from several growers about the prevalence of grape flea beetles in vineyards seen brazenly snacking on swollen buds. Adult beetle damage to newly developing buds can be economically damaging to yield if not adequately controlled. Flea beetles tend to be most concentrated along vineyard boarders in proximity to wood lines, so treatment may only need to be targeted in certain portions of the vineyard. Thresholds for spraying flea beetle have been suggested at 2 to 4% (or 2 to 4 injured buds per 100 buds checked), and broad-spectrum insecticides work well against flea beetles if necessary to use. Be aware that flea beetles go through one lifecycle per season and that their larvae can cause damage and skeletonization to leaves through June (though rarely in sufficient quantity to be considered economically important), and control of larvae may help reduce future populations of this insect.

Herbicide drift injury

Rapid shoot growth in vineyards generally coincides with planting time for row crops, and with that comes the risk for herbicide drift injury. The most effective way to reduce the risk for herbicide drift injury is to develop relationships with neighboring farmers and applicators and inform them about the proximity of your vineyard. However, drift injury may still happen, and it’s best to be prepared since drift events are sporadic and difficult to predict.  

An early, subtle symptom of auxinic herbicide (2,4-D, dicamba, etc.) injury is shoot epinasty, which can be mistaken for other abiotic stresses like drought (Figure 4). Other symptoms including leaf cupping, curling, and chlorosis (leaf yellowing) may take additional time to develop and depend on the amount of herbicide exposure (Figure 5).

If you suspect your vineyard has experienced an herbicide drift event, document your evidence as soon as possible and consider taking action by contacting the Ohio Department of Agriculture to file a complaint.

Figure 4. Shoot epinasty, or the downward growth of shoot tips. 48-hrs following low-concentration herbicide exposure.

Figure 5. Leaf cupping patterns 48-hrs following high-concentration dicamba exposure.

Posted In: Viticulture
Tags: 2023 season, Vineyard Update
Comments: 0

By: Imed Dami and Maria Smith, HCS-OSU

Statewide frost events occurred on April 24-27 (Table 1). Early budding varieties had already broken buds or were at a more advanced shoot development, and thus sustained frost damage. At the OSU research vineyard in Wooster, temperatures in a shielded logger at 5ft high measured 32F on April 25 and 34F on April 27. However, when we measured the temperatures in proximity to the fruiting spurs, we recorded temperature between 27.5 °F and 30.2 °F, i.e., below freezing. As a result, frost injury was minimal, causing only burning of leaf margins (Figure 1).   

Table 1. Ohio regional minimum temperatures (°F) from 25 April and 27 April. Weather data from CFAES Weather System and NEWA

Weather Station

25 April min temps (°F)

27 April min temps (°F)

Ashtabula (Northeast)



Avon Lake (North Central)



Caldwell (Southeast)



Cincinnati (Southwest)



Columbus (Central)



Fremont (Northwest)



Piketon (Southcentral)



Wooster (Northeast)




Figure 1. Leaf margins burned after a frost event, bus the shoot is still alive (photo by Dami).

Factors affecting frost injury:

Phenological (developmental) stage: During deacclimation (March-April), grapevines become increasingly sensitive to temperature below freezing (32 oF) and critical temperatures (CT) vary with the stage of bud development. That is, buds become more sensitive as they grow in early spring. CT of buds or young shoots is defined as the air temperature that causes 50% damage after exposure for 30 minutes. The following is an example of CT of Pinot noir at different stages of bud/shoot development:

Stage of development

Critical Temperature (CT)




Dormant bud



Swollen bud stage



Bud burst (break)



First unfolded leaf



Second unfolded leaf



Fourth unfolded leaf



Weather conditions: CT also varies with weather conditions including air relative humidity and corresponding dew point. Dew point (DP) is the temperature at which water condenses out of the air as dew or the temperature that corresponds to 100% relative humidity.  Condensation releases heat and slows the drop of air temperature. Thus, if DP is higher than CT, heat will be released before reaching damaging temperatures and may provide some protection.  If the air is dry, DP is low and temperature will drop rapidly and may reach CT and thus cause more damage. 

Early budding varieties are also more susceptible to spring frost. For example, Marquette, La Crescent, Concord, Chardonnay break buds early in Ohio and thus tend to be sensitive to spring frost. Late budding varieties such as Vidal rarely sustain frost damage. Further, varieties bear fruit on shoots originated from primary buds. Some bear fruit from secondary and base buds. Secondary and base buds of Vinifera and Native grapes are not as fruitful and thus may sustain more crop loss than Hybrids. Secondary buds may produce 30-50% of the crop potential. Tertiary buds typically are not fruitful regardless of variety.

Figure 2. Frosted shoot and new shoot emergence from spur base bud (Archive photo by Dami)

What to do after a frost event?

  • First, do not give up! Grapevines have an amazing way of recovering and compensating for yield. Also, the percent of damage does not equate the percent of crop loss.
  • Whether the damage is severe or not, you should not discontinue your disease and insect management program. You need to keep the vine canopy healthy.
  •  Fertilization: if the damage is severe and only fruitless shoots recovered, this situation may lead to excessive shoot growth and vigor. You should avoid nitrogen fertilization. If the damage is minimum and a normal crop is expected, continue a normal fertilizer program. If you practice split application of nitrogen (N), skip the first one and then, based on the fruit to shoot growth, decide whether to apply the post-fruit set N application. 
  • Canopy management: due to excessive foliage and resulting shading you may need to be more aggressive with your canopy management practices. This practice will vary with the level of frost damage and variety. Like any other vineyard operation, it comes down to practice cost and the “well-being” of the grapevine. Sometime, the two factors do not go together. It is up to the grower to decide which way to proceed. Since there are many scenarios to consider that are dependent on the type of frost damage (partial or complete) and variety.
  • Provided below are two specific examples of canopy management based on reported research in Indiana and California.
    1. Our colleague, Dr. Bruce Bordelon at Purdue University, conducted a trial to manage several hybrids after a frost event that caused partial frost damage. Damaged shoots were either pruned (shoot or spur) or left intact (untreated control). With Marquette, pruning damaged shoots resulted in increased yield and better cane quality (size) the following year.
    2. Glenn McGourty, past OGWC speaker and viticulturist at UC Davis, conducted a similar trial with Chardonnay. He also found that removal of damaged shoots resulted in higher yield. Fruit ripening was delayed, but fruit quality was unaffected. In both situations, there was added labor to remove damaged shoots (20 to 30 hrs/acre). However, the extra cost in the year of frost damage was justified with less labor for pruning the following season and better cane quality. Basically, a severe frost year was a good year to “clean up” old cordons for new spur development. If you have a specific situation and undecided how to proceed, please do not hesitate to contact me.   
  • Disaster Assistance: Contact your local USDA-FSA (Farm Service Agency) and report your crop loss. It is important that you record the extent of damage you have, in case some assistance program becomes available.



Posted In: Viticulture
Tags: 2023 season, Spring Frost
Comments: 0