Timely Viticulture Timeline: Dormant
Updated: April 30, 2021
By Joseph Fiola, Ph.D.

Assessing Grapevine Bud Damage

Damage from low winter temperatures is arguably the greatest risk to sustainable profitable winegrape production in the eastern US. The majority of Maryland vineyards have not experienced a significant amount of low-temperature damage over the past decade or so, however some vineyards have experienced damage this winter (2013/2014). The following “Timely Vit” will give an overview of how to assess the damage and how to modify your pruning based on the assessment. Please see the previous “Timely Vit” in the series on “Understanding Grapevine Bud Damage” for an overview of how vines attempt to prevent damage, the conditions which influence the level of damage, and types of damage.

When temperatures below 0˚ F take place, it is prudent for growers to collect canes and assess bud damage prior to pruning. Here are some guidelines for bud damage assessment and pruning adjustment.

How to assess the amount of low-temperature damage to buds (Handle sharp objects with CARE!!)

1)

Collect enough canes so that you have about 100 buds from the block or variety that you are checking.

  • Collect buds for damage assessment for each variety separately and for each block of the same variety separately (for example Cabernet Sauvignon on top of hill and Cabernet Sauvignon on the bottom of the hill.)
  • The first 2-10 buds from the bottom of the cane (closest to the cordon/head) are critical.

2)

 Bring the canes indoors and allow them to warm at room temperature for a minimum of 24 hours. This allows the damage to develop and makes it easier to differentiate between healthy and injured buds.

3)

Use a sharp razor blade to cut cross-sections of the bud until you can tell if the large primary bud is healthy (green) or injured (brown) (all green in figure 5.)

  • First, cut about 1/3 down from the top of the bud (figure 2.)
    • Use this to assess primary bud damage (large bud in the center of figure 3.)
  • Second, cut about 2/3 down from the top of the bud (figure 4.)
    • Use this to assess secondary bud damage (secondary left of primary; tertiary right of the primary.)

4)

Count the number of dead or injured buds, and divide by the total number of buds sampled to get the percentage of injury.

  • Use a data sheet to record and compute bud mortality by variety and block.
Figure 1. Side view before cut
Figure 1. Side view before cut
Figure 2. First cut in yellow
Figure 3. Top view after first cut
Figure 3. Top view after first cut
Figure 4. Second cut in yellow
Figure 4. Second cut in yellow
Figure 5. Top view after second cut
Figure 5. Top view after second cut

To see a VIDEO of how this is done, please check the following:

Bud Injury Testing Part 1, Hans Walter-Peterson, Viticulture Specialist with Cornell Cooperative Extensions Finger Lakes Grape Program teaches you how to test grape buds for injury prior to pruning.

Bud Injury Testing Part 2, Hans Walter-Peterson, Viticulture Specialist with Cornell Cooperative Extensions Finger Lakes Grape Program teaches you how to test grape buds for injury prior to pruning.

If there is damage to buds you can modify your normal pruning practices and leave proportionately more buds to try to compensate for the damage and get back to a “normal” or desired crop level.

How to adjust pruning based on an assessment of low temperature damage to buds.

  • 0-15% dead primary buds – Do not change normal pruning practices.
  • 15-35% dead primary buds – Increase the number of buds retained by 35%.
  • 25-50% dead primary buds – Increase the number of buds retained by 50%.
  • >50 dead primary buds – Minimally prune. Prune away only those nodes which will intrude into the space of adjacent vines or which will produce fruit so low that it hangs to the ground.
    • If damage is >50% there is a high likelihood of cordon and cane/trunk damage.
    • There will also be a higher likelihood of Crown Gall damage to the graft union area
    • Watch those vines closely in mid-spring to assess the extent of cane/trunk damage and Crown Gall.

The following resources were utilized for the information in this “Timely Vit.”  For more information on assessing bud injury:

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