Assessing and Responding to Winter Cold Injury to Grapevine Buds

There are three ways to deal with cold:

1. Avoid the cold stress

a. Find a warm place to grow grapes - this is site selection

b. Protect the buds or tissues from exposure to cold by burial or other means.

2. Tolerate the cold

a. Grow a variety with sufficient cold hardiness to tolerate the expected temperatures.

b. Maximize the maturity of the tissues you grow by applying excellent viticulture.

3. Tolerate the cold injury

If all the above ground vine tissues are killed, there is little you can do except replant or retrain from below the gound, but partial vine death is much more common.

Delay pruning as long as feasible so that the danger of cold injury is reduced. (If December, January and February have passed without extreme cold, the danger is reduced. March may still produce damaging temperatures, but your odds of avoiding injury have increased.)

If you suspect possible cold damage, examine the buds and proced on the basis of actual injury.

Assessing cold injury of grape buds

Choose buds similar to those you will save during pruning. This means the lower nodes of canes of the better quality on the vine.

Sample based upon differences in your vineyard. This can be by variety, rootstock or based upon site and soil differences (lower vs upper sections, better or less well drained, etc.)

Collect at least 100 nodes from each section.

If the freeze event was recent and the buds may not have thawed since exposure to potentially harmful temperatures, the bring the canes into a warm room, keep the canes moist and wait fro 24-48 hours before examining the buds. This allows damaged cells to thaw and the oxidative reactions which reveal damage to happen.

Cut the buds and record the number of live and dead primary buds. People often also record the status of secondary and tertiary buds. This is worthwhile information, but not as important as primary bud survival.

This is a longitudinal section of a grape bud - note the three growing points or buds

This is the region of the bud which should be examined to assess primary bud injury. The colored area is the compressed primary shoot for the next season.

This is the region of the bud which should be examined to assess secondary bud inujury. It adjacent to the leaf scar.

This is the region of the bud to examine to assess damage to the potential tertiary shoot.

The examination

On the left is an intact grape bud. The leaf scar is to the left. The bulge on the left side of the bud is the secondary bud. The righthand picture shows a longitudinal view. In the series below the top view of a bud having successive horizontal slices removed is shown (click on the thumbnails to see the bigger picture). The line on the right shows the approximate level of the horizontal cut.

Below are a series of thumbnails showing progressive

Intact bud

First cut. This is too shallow only the tips of the bud scales have been cut. The secondary bud is just beginning to be revealed at the lower left quadrant of the cut.

Second cut. This cut is still too shallow. The secondary bud is better defined, but only the tips of bud scales have been cut.

Third cut This cut shows a life primary bud. The cut has been through what will become a shoot internode. People often worry about whether the color is bright green, olive green or sort of gray. Just so long as the bud is not blackened, it is alive.

The tertiary bud can now be seen, but only bud scales of the secondary and tertiary buds have been cut.

Fourth cut

This is a good level to assess the health of the secondary and teritary buds, but it is too deep to assess primary bud health. Once the cut moves to the base of the shoot (the bud cushion), the status cannot be assessed. Dead buds will often be found on live bud cushions.

Fifth cut

This cut is too deep. Only bud cushion is revealed. There may be dead primary, secondary and tertiary buds on top of a live bud cushion. Deep cuts may give a false sense of security.

The primary bud of this bud has died. The secondary bud is alive. The tertiary bud cannot be evaluated at this level of cut.

The above series shows why a single cut will not reveal the complete status of the buds nor even allow certainty as to the status of the primary bud. A series of shallow cuts is recommended.

This bud reveals the imact of injury and multiple shoots per node. Note that only a partial prophyll (incompletely formed first leaf) survived from the primary bud (shoot in the middle). The secondary and tertiary buds formed shoots.

Compensating for bud injury

If you know buds have been injured, you can retain more to compensate for the proportion of dead buds. Remember even when there is no cold damage, it is not uncommon for 10% or more of the buds not to develop.

© Copyright 2000 Robert Pool