Looking at Trunk Damage
Lake Erie Regional Grape Program
The rising temperatures have helped kick-start sap movement and allowed us to get the first good chance to inspect for damage. Over the past week I have been out cutting the outer layer of trunks and cordons and looking for freeze damage. Much like the earlier bud cuttings the damage varies from cultivar, location, and the low temp at vineyard site.
To assess trunk and cane damage, make a shallow cut into the trunk or cane deep enough to expose the outer layer of the vascular tissues (about 1/8 inch deep). Examine the vascular tissue for freeze damage by the amount of oxidation (browning) in the various tissues. Trunk damage occurs in this order; phloem, xylem, and then cambium. Damage to the phloem (A-E outer ring) will prevent the flow of carbohydrates needed for shoot development, but will most likely not kill the trunk. Damage to xylem will restrict flow from the roots to the canopy resulting in stunted, chlorotic (yellowed), or dead shoots and can cause vines to collapse under stress. To learn more on how to evaluate trunk damage see the 2015 March Newsletter http://lergp.cce.cornell.edu/newsletter.php.
As you evaluate trunk damage keep in mind the severity and location of the damage. This will help you plan herbicide treatments in specific areas where trunk renewal is needed. Suckers should be retained with the purpose of vine or trunk renewal when trunk damage looks like B, C, and D in the figure below. Severe trunk damage in figure A shows the trunk has no sap flow signaling it is dead. Although the trunk in figure B has sap flow the damage is severe enough that the vine will not be able to function and will most likely die to the ground. Figure E shows minimal damage and should be able to grow out of the minor vascular damage. Both F.1 and F.2 are examples of healthy trunks with no vascular damage.