Grape and Wine Institute

University of

Vinews

No. 1 — Feb. 15, 2021

Contents:

Determining Cold-Injury to Grape Buds

The recent extreme cold-temperature events resulting from the “Polar vortex” should have you thinking about grape bud injury. A brief primer on the anatomy of a grape bud will help you further understand the evaluation process. The primary bud is in the center, the secondary bud is above the petiole leaf scar and the tertiary bud is on the opposite side of the primary bud directly across from the secondary bud. The longitudinal cross section of a grape bud clearly shows the three buds of a compound grape bud (Figure 1).

cross-section of a bud with arrows pointing to the different parts--The primary bud is in the center and is more fleshy green; the secondary bud is to the right and is a slightly smaller bud shape; the tertiary bud is to the left of the primary bud and is the smallest bud shape in the cross-section; the bud cushion extends below all three buds in the cross-section and looks like the border leading to the rest of the vine
Figure 1. Longitudinal cross-section of a grape bud showing the primary, secondary, and tertiary buds as well as the bud cushion. Photo credit: D.S. Volenberg

Inset A: A black line diagonal in the center of the cross-section is labeled--Black line represents cross-sectional cut with a razor blade; directly below this is an arrow pointing to inset B: the cross-section here offers a much more narrow of a view of the plant
Figure 2. Cross section cut above in A is to shallow and does not allow you to determine if the primary bud is injured in B. Photo credit: D.S. Volenberg

Inset A: shows a diagonal line in the center that indicates where the cut for the cross section was made; two arrows below it point to the sections shown in Inset B--the left arrow points to the center of the primary bud, a large green and brown swirl; the right arrow points to the smaller secondary bud, not really visible
Figure 3. A deeper cross-sectional cut (A) reveals the primary bud being uninjured (B). Notice that the cross-sectional cut still does not reveal if the secondary bud is injured. Photo credit: D.S. Volenberg

Inset A: shows a diagonal line in the center that indicates where the cut for the cross section was made; two arrows below it point to the sections shown in Inset B--the left arrow points to the center of the secondary bud; the right arrow points to the tertiary bud. Both look like healthy green swirls.
Figure 4. Another cross-sectional cut (A) reveals the secondary bud uninjured (B). The tertiary bud is still not visible. Photo credit: D.S. Volenberg

Inset A: shows a diagonal line closer to the bud cushion that indicates where the cut for the cross section was made; three arrows below it point to the sections shown in Inset B--the left arrow points to a very small tertiary bud; the middle arrow points to the center of the healthy large green swirl of a bud; the right arrow points to the slightly smaller bud next to it, also healthy
Figure 5. Another cross-sectional cut (A) reveals the tertiary bud uninjured (B). Photo credit: D.S. Volenberg

Inset A: shows a diagonal line at the bud cushion that indicates where the cut for the cross section was made; one arrow below it points to the sections shown in Inset B--the arrow points to a large fleshy green cross-section that doesn't indicate injury
Figure 6. Another cross-sectional cut (A) reveals the bud cushion (B). The bud cushion does not reveal any information of the health of the buds. The only thing the bud cushion reveals is that you have cut to deep into the bud. Photo credit: D.S. Volenberg

Inset A shows damage to a primary bud that looks like a black switl in the center of distant green in mainly grown; Inset B shows a healthier cross-section that is still all green swirls amidst the brown barky areas
Figure 7. Cold damaged primary bud (A). Notice the brown discoloration of the primary bud. Compare to healthy primary bud (B). Photo credit: D.S. Volenberg

Items You Will Need to Determine Bud Injury

  • Razor blades
  • 10X hand lens helps to view cut buds
  • Grape canes
    • Collect 10 canes with 10 buds. Take a single cane from a vine. The cane should represent the buds you would keep during dormant pruning. Select vines randomly throughout the vineyard. If the vineyard block you are sampling has different terrain (i.e. vines on a bluff and vines on the bottom of the slope) then consider collecting two different samples.
    • Keep cultivars separate.
    • Place canes indoors at approximately 70°F for 24 to 48 hours prior to evaluating the buds. This time period allows injured grape buds to oxidize.
  • Data collection
    • Consider location of bud on the cane. Buds closest to the cordon would be bud 1 and the distil bud would be bud 10. The buds closest to the cordon are more cold hardy.
    • Initial assessment of buds may just be primary buds. If bud injury to primary buds is 60% or greater, then consider evaluating secondary buds.

Please do not rely on data of bud damage that your neighbor has collected or data that I may post. Each vineyard block is a separate unit and cultivars respond differently to cold injury. Additionally, past management practices play a large role in the cold sensitivity of the grape buds.

What to do with your bud injury data:

  • Realize that even in a “normal” year primary bud damage can be near 15%. If your data is 15% or less primary bud damage then you will not need to adjust your dormant pruning.
  • Based on bud damage percentages, you can adjust your bud counts to reflect the damage.
  • You need to know your grape cultivars fruitfulness. Does the cultivar produce fruit on secondary buds? Does the cultivar produce fruit on basal buds? There is not a lot of data on these two topics for individual cultivars. Most of this information comes from other grape growers who have experienced cold weather events in the past. So reach out to other growers that are growing the same cultivars as you. A simple unwritten rule is that secondary buds produce approximately 1/3 of crop compared to primary buds.

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 (office) 573-473-0374 (mobile) or volenbergd@missouri.edu


Map of Missouri with county names labeled, and the lowest reported Feb. 16, 2021 temperatures for the state indicated by county. Labels from north to south--Achison: -26.2; Buchanan: -13.9; Linn: -12.6; Monroe: -12.9; Lafayette: -14.6; Boone: -10.8; Lincoln: -6.7; Bates: -15.6; Morgan: -14.9; Craword: -7.8; Lawrence: -16.1; Wright: -12.4; Shannon: -7.8; Cape Girardeau: -4.9
The lowest recorded air temperatures for 2021 occurred in Missouri on Feb. 16, 2021. Most counties experienced below zero temperatures for the period of Feb. 13-16, 2021. Data from http://agebb.missouri.edu/weather/stations/