David W. Lockwood, University of Tennessee / University of Georgia
Why is Pruning Necessary?
- eliminate dead, broken, or diseased wood
- eliminate older, non-productive, or marginally productive wood
- encourage development of new wood where the best future crops will be formed
- open the canopy to sunlight, air, and spray penetration
- facilitate the ease of management of the vines (pruning, thinning, harvest)
- keep vines within desired size limits
When to Prune
How early can grapevines be pruned? That will depend on a number of factors. Generally speaking, it would be a good idea to wait as late in the dormant period as possible to start pruning, yet still be able to get it all done. There are considerations and modifications to the above statement.
- By waiting until after the first of the year to begin pruning, there should be no question as to whether the vines are fully dormant. Pruning vines before they are fully dormant could interfere with the ability of the vine to go dormant, thus increasing the potential for cold injury.
- The earlier vines are pruned in winter, the greater the number of buds that should be left as a hedge against cold injury. The down side to this is that if no bud loss occurs, repruning and/or cluster thinning may be necessary to prevent overcropping.
- Varieties that are highly fruitful on secondary buds can be pruned earlier and/or closer to the desired bud count than other varieties. French-American hybrids tend to be more fruitful on secondary buds than American or V. vinifera varieties.
- Pruning wounds remain susceptible to Eutypa or Bot Canker infection much longer early in the season than later. Prune late in the dormant season to promote rapid healing of cuts, especially for varieties that are more susceptible to Eutypa and Bot Canker.
- Delayed pruning may be of value in lessening frost damage. Bud break begins first on the terminals of canes. Waiting until new growth reaches about 3 to 4 inches in length before pruning will set back bud break in the desired areas on canes by several days which may be enough to escape damage by a late frost. A drawback to delayed pruning is the damage that can be done to new growth and buds as prunings are removed from vines.
- Double pruning is a modification of delayed pruning. With it, canes that will not be needed for fruiting are removed while the vine is dormant. Replacement canes and canes that will be cut back for fruiting spurs are pruned after growth has begun, as described above.
Pruning Mature Vines
Before pruning, assess the degree of bud kill. Cross-sectional cuts should be made across numerous buds to see if damage has occurred to the primary bud. The number of buds to be retained at pruning may need to be increased to compensate for different levels of bud mortality.
1. Remove suckers at the base of the vine and canes arising off the trunk below the trellis wires UNLESS these canes are to be used for trunk or cordon replacement. When selecting a cane for trunk replacement on a grafted grapevine, be sure to select one arising from the scion above the graft union as opposed to the rootstock below the graft union.
2. Separate the vine from its neighbor so that pruning cuts will be easier to identify.
3. Remove dead, broken or diseased canes.
STEPS 1 – 3 APPLY TO ALL TYPES OF PRUNING SYSTEMS
4. Identify and remove canes that bore the previous year’s crop. These are easily found as the bark on them tends to be more grayish in color and somewhat shaggy. In addition, newer canes, having smooth, reddish-bronze bark and easily identifiable buds will arise from the old, fruiting canes.
5. Select a healthy cane on each side of the trunk where fruiting is desired to be trained to the trellis wire for cropping in the coming year. Ideally, these canes should arise a few inches (2 – 4) below the trellis wire. Avoid selecting “bull” canes (overly thick and vigorous) as they are too vigorous and the distance between buds is too great to allow leaving enough buds on the cane while keeping the vine within its allotted space.
6. Select another cane arising on each side of the trunk and a few inches below the crop-bearing trellis wire and prune it back to 1 or 2 buds. This is the renewal spur and shoots arising from it may be candidates for fruiting cane selection the following year.
7. Remove all other canes from the vine.
8. Cut each cane back to its desired bud number. This number will depend on type of grape, variety and vine vigor. Cane pruning is used for varieties where the most fruitful buds will be about the 5th to the 10th buds from the base. Do not allow canes to overlap those of a neighboring vine.
4. Remove old fruiting wood from the previous season.
5. Select new canes to be cut back to form spurs. A spur pruned to 2 buds the previous year will have 2 fruiting canes. If the size and quality of the canes are equal, select the cane closest to the cordon to retain and prune it back to 2 to 4 buds. The number of buds to be retained on a spur will depend on the fruitfulness of lower buds. Canes having a diameter about the same as a pencil make the best fruiting spurs.
6. Select canes to be pruned back to form renewal spurs and prune it back to 1 bud. The shoot growing from this bud will develop into a cane that may be selected for pruning to a fruiting spur the next year.
7. Remove old spurs having no 1-year-old wood.
8. Space spurs about 3 to 4 inches apart on the cordon.
9. Spurs should be oriented up or down on cordons depending on the training system being used.
10. The total number of spurs to be retained will depend on vine vigor, variety and the number of buds being left on each fruiting spur.
Important Pruning Terminology
Balanced pruning – adjusting bud number on a vine to allow production of good crops of high quality fruit on a sustainable basis
Bleeding – sap exudate from a woody plant after pruning, usually occurring neat the end of the dormant season. Bleeding will not harm the vine.
Bud – The bud on a grapevine is actually a compound bud containing the primary, secondary and tertiary buds. The primary bud opens first in spring and is, therefore, the most apt to be damaged by a late frost. It is the most fruitfuI bud on the grapevine. If the primary bud is injured or killed, the secondary bud will break and grow. Depending on the type of grape, secondary buds may or may not be fruitful. French-American hybrid varieties tend to be more fruitful on secondary buds than American or vinifera varieties. If the secondary bud is damaged or killed, the tertiary bud will break and grow. Tertiary buds are not fruitful. Buds are located at the intersection of a leaf petiole and the shoot.
Bull cane — shoot growth that is too vigorous. Bull canes typically have very long internodes (5-6 inches or more), large diameter (greater than ½ inch), and generally are somewhat flattened on two sides, giving the cane more of an oval shape in cross-section, as opposed to circular. They are poorly fruitful or unfruitful, less cold-hardy than normal-sized canes, and make poor selections for trunks, to lay down for cordons or to keep for spurs or fruiting canes. Characteristically, they are found on very and overly vigorous vines.
Cane – a mature shoot after leaf fall. Beginning about veraison, a tender, succulent shoot will become woody; color will change from greenish-yellow to bronze.
Cane pruning – system of cutting the vine back to one or more canes that will produce new shoots. The aboveground portion of a cane-pruned vine will have a trunk, one or more canes on which shoots will develop from buds on canes and renewal spurs to be used as sites for new canes for future fruiting sites. Cane pruning is used on grape varieties where the most fruitful buds are located midway on canes.
Cordon (arm) – Semi-permanent horizontal structure on a vine that originates at the head of the trunk and produces shoots and canes.
Shoot – A succulent stem arising from a bud having petioles, leaves, tendrils and fruits.
Spur – short, stubby cane having a few (2 to 4) buds located on the cordon that produces new shoots
Spur pruning – Canes arising on cordons are pruned back to a few buds (2 to 4). Spurs arising from the upper portion of cordons are selected over those on the lower portion of cordons. Spur pruning is used where the most fruitful buds on a cane are found near the base of the cane.
Suckers – shoots arising at the base of the trunk (should be removed unless being used as a replacement trunk)
Feb. 11, 2014