PPDL Picture of the Week for
March 16, 2015
Rejuvenating winter injured grapevines
Bruce Bordelon, Professor, Department of Horticulture and Landscape Architecture
The winter of 2014 was unusually cold, causing significant damage to grapevines (and other cold tender woody plants) across the Midwest. One of the most notable forms of damage was death of woody portions of the vines: the cordons and trunks. Trunk damage is very rare in our region, but because the damaging temperatures occurred over such a prolonged period last winter, damage was extensive. Many vines failed to leaf out normally last year, or leafed out, but then showed damage later in the summer (Picture 1). Most varieties produced very little, if any, fruit. If your vines are in this situation, don’t give up. There is a way to bring them back.
What can be done?
Grapevines are very resilient. They have the ability to regrow from beneath the soil surface. The root system is insulated from cold temperatures and remains alive. Shoots from the base of the trunk will grow (Picture 2). These “suckers” (as they are called) are normally removed each year. But if they are retained, they can be used to replace the old woody portions that were damaged. It will take a couple of years to get vines back to full production, but that is much faster than removing the old vine and replanting a new vine.
How to retrain a grapevine.
Hopefully the grower saved several shoots that grew from the base last year (Figure 2). If not, they should be able to do that this year. The green shoots mature into canes over the winter and will make future trunks and cordons. The best canes for renewing trunks are moderately vigorous, about pencil to finger diameter with 4-6 inch internodes. Larger, excessively vigorous canes are called “bull canes” and usually do not make good trunks. They tend to be more cold tender and less productive than the moderately vigorous canes. The grower can remove the old trunk and save from 2 to 6 canes this spring (Figure 4). That will allow the vine to produce some fruit this year, which will help offset the high vigor of the large root system. If more than two canes are retained for this growing season, the extras can be removed at the end of the season and the best two canes can be retained to be the permanent trunks. Be sure to remove the shoots that develop on the lower portion of the new trunks. Keep the shoots that develop at the top of the canes beneath the training wire and along the training wire. Each of these shoots will produce clusters of fruit. The vine will probably not be able to fully ripen all the fruit that develops, so it is best to remove some of the clusters to improve fruit quality and avoid excess stress on the vine. Leaving one cluster per shoot is a good rule of thumb.
Once the vine has been rejuvenated with new trunks and cordons, try to maintain the vine structure by pruning to short 3-5 node spurs along the cordon each spring. That will provide enough shoots to produce a good crop of fruit each year.
You can learn much more about grape growing on our website at www.ag.purdue.edu/HLA/extension.Click the Fruit crops icon.