This information was assembled in poster form in response to questions following the "Halloween Freeze" of 2002 in Eastern Washington.

The source of much of this information is from the Cornell University website Dealing with Winter Injury to Grapevine Canes and Trunks.

Cost for providing this information was provided in part by the Washington Association of Wine Grape Growers.

 

Factors Influencing Damage

Age:
Vineyards less than 5 years old sustain more damage, possibly due to less protective bark.

Site:
Cold pockets, low-lying areas, latitude, and elevation can all affect the local temperatures.

Yield:
Reasonable crop loads do not appear to affect bud survival.

Fluctuating Weather:
Brief periods of warm weather during mid-winter can decrease a vine's cold-hardiness.

Grow Tubes:
Vines in grow tubes seem to fair worse, possibly due to greater temperature fluctuations inside the tubes.

Harvest Date:
Grower observations indicate that cold hardiness is NOT influenced by an early or late harvest.

Viruses:
Vines infected with at least 2 strains of the leaf roll virus may suffer greater damage.

Disease:
Severe late-season infections of powdery mildew, especially on young vines, may put vines at higher risk.

Freezing: What Do You See?

Buds

Freezing results in dried, black and discolored buds.

 

 

 

Plant Tissue: Phloem and Xylem

Phloem is the nutrient-conducting tissue, while Xylem is the water-conducting tissue.

Destruction of either tissue can result in reduced shoot growth and smaller leaves.

Numbers 1-4 show varying levels of damage after tissue freezing.

Numbers 5-6 are normal growth.

Phloem damage heals more readily than xylem damage, which often results in death of the vine.

Trunk

Damage to the trunk can result in both the previous pictures and...

 

Assessment of Damage

Initial Step

To properly assess damage, divide the vineyard into blocks or regions based upon characteristics of the lancscape.

Determinative factors include: changes in elevation, structures inhibiting airflow (windbreaks, roads, surrounding agriculture), soil variation, grape varieties, and vineyard size.

With this in mind, decide how many sections within the vineyard are necessary to provide a good representation of the potentially different temperature zones.

Bud

Buds contain 3 or more growing points. The primary bud is central to and larger than the other buds.

Cutting the buds properly will ensure accurate diagnosis of damage....

 

Cane

Damage can be in patches throughout the cane.

Collect numerous samples and assess on different aras of the same cane.

A series of thin longitudinal slices will reveal the extent of damage. The first slice should remove only the bark and expose the phloem. Another deeper slice will expose the xylem.

Thin slice removes bark and exposes dead, brown phloem

Young vine: Deep cut into the xylem (green) which is surrounded by dead phloem (brown)

Series of thin cuts showing dead phloem and slightly damaged xylem

Trunk

Trunk damage is the most difficult to assess. Like the cane, damage can be patchy on the trunk and throughout the vineyard!

Vary the location of sampling on the bark, but BE CAREFUL not to girdle the vine.

Use a series of thin longitudinal slices, as described in assessment of canes.

 

Concentric circles showing bark, dead phloem, and live xylem.

Entire trunk is brown and dead.

 

Since damage is patchy and samples must be limited, accurate assessment of damage on trunks is difficult!