Vinews

No. 6 — April 26, 2021

Contents:

Frost/Freeze Events on April 21 and 22 Result in Damage to Some Grape Cultivars that Had Surpassed Bud Break

Chambourcin branch with shoots that look like the 
                leaf buds curled in and died
Figure 1. Chambourcin shoots killed by frost/freeze events on April 21 and 22, 2021 near Augusta, MO. Photo credit: D.S. Volenberg, Photo taken on April 26, 2021.

Air temperatures fell well below freezing throughout many areas of Missouri last Wednesday (Figure 2) and Thursday (Figure 3). A grape grower in Macon County, MO reported 21 °F on Thursday morning. The Marechal Foch shoots were completely damaged by these low temperatures the grower reported. Other growers have reported damage from the frost/freeze events. After a couple more days pass, most growers will have the opportunity to make a complete assessment. Some vineyard blocks had a very uneven bud break, according to some grape growers. Potentially some of those latent primary buds may have been spared by the cold temperature events. As grape buds progress from winter bud scales, bud swell, wool to bud burst the susceptibility of the bud increases to cold air temperatures. For some grape cultivars damaged by the frost there may be a grape crop produced from both primary as well as secondary buds. This is important to recognize since it will result in an asynchronous bloom or simply an extended bloom period. Primary shoots that escaped frost/freeze damage will bloom first followed by a flush of bloom from secondary shoots. From a disease management standpoint, the most critical disease protection applications are at immediate pre-bloom followed by a post-bloom. Be aware that some grape cultivars damaged by the cold events may necessitate additional protective sprays during the critical period of immediate pre-bloom to post bloom.

On Monday, April 26, I accessed damage to vineyards in the Hermann, New Haven and Augusta areas (Figure 4). In the Hermann area, many of the vineyards came through pretty well with little loss of primary shoots. There was noticeable damage on Catawba, Concord, Traminette, Chambourcin, Valvin muscat. Norton was unscathed by the cold temperatures. In the vineyards I visited in the Hermann area, I estimate that 5 to 7% loss of primary shoots. In the New Haven area, I examined Chambourcin and Vignoles that appeared to have approximately one-inch shoots prior to the frost/freeze events. All shoots were killed by the frost/freeze events. The Augusta area also had all exposed shoots killed by the frost/freeze events (Figure 1). Grower reports from the Ste. Genevieve area also report extensive damage. In contrast, vineyards north of KC had minimal damage based on grower reports.

In some respect we are almost seeing a repeat of the beginning of the 2020 grape growing season. On April 18, 2020, cold temperatures caused damage to some grape cultivars. The difference between this April’s frost/freeze events and last April’s is that in 2021 the minimum air temperatures were 2 to 4 degrees colder and the duration of the cold events were longer. This resulted in some growers thinking their vines survived the first round of the frost/freeze events on Wednesday morning. Unfortunately, for many of these growers, the second evening of frost/freeze events caused severe damage.

Please consider taking this short survey on how the frost/freeze events impacted your vineyard(s). The information from the survey will be provided to the Missouri Wine and Grape Board. The MWGB can then use the data to make an informed decision on issues that impact fruit and juice imports into the state for wineries with domestic winery licenses. The survey is completely confidential. The survey will take less than three minutes to complete.

Frost Freeze Survey:
https://missouri.qualtrics.com/jfe/form/SV_8d1onzKB1Gt5xKS

photo A: aromella branch with new buds brown and shriveled;
                    photo B: Concord branch had buds farther along and leafed, now brown and some leaves wilted; photo C: vignoles branch with brown and shriveled leaf buds; 
                    photo D: vidal blanc branch with brown, shriveled leaf buds
Figure 2. Frost/freeze damage observed on; (A) Aromella near New Haven, MO; (B) Concord near Hermann, MO; (C) Vignoles near New Haven, MO; and (D) Vidal blanc near Augusta, MO on April 26, 2021. Photo credit: D. S. Volenberg.

Map of Missouri with county names labeled, and two numbers highlighted for each callout--the first number is the number of hours with the temperature below 32 degrees F; the second number the low temperature reported by that county. Labels from north to south--Achison: 0, 30.0; Buchanan: 0, 32.2; Linn: 9, 25.0; Monroe: 7, 26.0; Lafayette: 5, 29.7; Boone: 9, 26.2; Lincoln: 6, 28.7; Bates: 6, 29.7; Crawford: 10, 24.6; Lawrence: 10, 24.6; Wright: 10, 24.5; Shannon: 11, 24.9; Cape Girardeau: 6, 29.5
Figure 3. The number of hours average air temperatures were ≤ 32°F for the time period of 10 p.m. on April 20, to 8 a.m. on April 21, 2021, and the low air temperature recorded in selected counties in Missouri.

Map of Missouri with county names labeled, and two numbers highlighted for each callout--the first number is the number of hours with the temperature below 32 degrees F; the second number the low temperature reported by that county. Labels from north to south--Achison: 9, 26.5; Buchanan: 2, 30.2; Linn: 6, 26.5; Monroe: 6, 28.6; Lafayette: 6, 28.2; Boone: 6, 28.3; Lincoln: 4, 27.7; Bates: 8, 27.1; Crawford: 7, 24.0; Lawrence: 5, 27.2; Wright: 6, 25.4; Shannon: ND, ND; Cape Girardeau: 0, 31.8
Figure 4. The number of hours average air temperatures were ≤ 32 °F for the time period of 10 p.m. on April 21, to 8 a.m. on April 22, 2021, and the low air temperature recorded in selected counties in Missouri.

Cumulative Growing Degree Days (Base 50) for the Seven Grape Growing Regions of Missouri from April 1 to April 23, 2021

Region Location by County Growing Degree Days1
2021 2020 30-year Average
Augusta St. Charles 167 147 193
Hermann Gasconade 146 147 184
Ozark Highland Phelps 159 161 205
Ozark Mountain Lawrence 161 165 202
Southeast Ste. Genevieve 170 154 209
Central
Boone 172 141 180
Western Ray 134 136 169

1 Growing degree days at base 50 from April 1 to April 23, 2021. Data compiled from Useful and Useable at https://mrcc.illinois.edu/U2U/gdd/. Click on link below to determine growing degree days in your area.

To determine the number of growing degree days accumulated in your area since April 1, use this tool.

Please scout your vineyards on a regularly scheduled basis in an effort to manage problem pests. This report contains information on scouting reports from specific locations and may not reflect pest problems in your vineyard. If you would like more information on IPM in grapes, please contact Dean Volenberg at 573-882-0476 or 573-473-0374 (mobile) or volenbergd@missouri.edu

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