Many viticultural management decisions are based on tradition and habit. I find this to be particularly true with pruning systems. Even though we in the East are relatively new to growing grapes, most of us have quickly settled on a pruning technique and are not interested in making changes. I know, because until fairly recently, I was adamant about only using cordon/spur pruning in my vineyard. My vineyard is now over 80% cane pruned. In the following paragraphs I would like to explain why I have made the change.
I would like to define the two systems. Cane pruning requires an annual replacement or renewal of one year old wood (canes) on the fruiting wire. These canes typically contain 6 to 10 buds and are 1 to 2 feet long. The buds from these canes will produce fruitful shoots that support that year's crop. The subsequent winter that cane will be removed and replaced by a new one year old cane.
Cordon pruning leaves a permanent horizontal extension of the trunk in place year after year. Cordons can be decades old and achieve diameters of several inches or more. The cordons themselves do not usually produce fruitful shoots. The fruitful shoots come from spur positions located along the cordon. These spur positions typically support one cane that is pruned short, usually to two buds. This short cane is called a spur. Spurs are usually only a few inches long.
For many years I was very satisfied with cordon pruning. However, once my vines started entering their second decade I was beginning to see problems with the cordons. Spurs were disappearing, wood was rotting, and disease and mite pressures were increasing. Then the infamously cool, wet 2003 growing season resulted in serious cordon and trunk winter damage to these older vines. I was forced into cane pruning as the majority of my cordons were damaged beyond repair. Over the subsequent two years most of my old vine cordons had to be replaced by new canes. I saw many advantages of cane pruning over cordon and have continued cane pruning these vines for the last four years.
On a trip to France many years ago, as we where driving through a cane pruned vineyard for a meeting, a friend asked me why I didn't cane prune. My reply was that it was too difficult. The vineyard owner was subsequently asked to explain why he didn't cordon prune. "Too difficult" was his reply. I now know that it is all simply a matter of what you are used to. I don't find that one system is easier than another. There are however, distinct labor and timing issues with both.
The first several years of a vineyard's establishment the two pruning systems have more or less the same skill and labor requirements. I do find however, that in years 4 through 10, cordon pruning is more labor efficient. Unskilled pruners can systematically pre-prune all spurs to a certain length and pull brush (this can also be done mechanically). Skilled pruners can then follow quickly making key cuts. If frost is a concern, spurs can be left tall (4 or 6 buds) and then cut after the threat of a late spring frost. Dormant tying only involves the occasional securing of a cordon or replacement cane.
Life is good for "middle aged" cordon pruned vines. The problem that I eventually ran into was the previously mentioned wood diseases and winter damage. This eventually required an enormous amount of time with saws, and often futile attempts at cordon replacement with poorly positioned renewal canes. Eventually cordon pruning required very experienced labor and took a lot more time to complete.
Cane pruning can be very fast. If I am pressed for time, I will quickly make the key cuts and have unskilled labor pull brush behind me. It is really not feasible to pre-prune because of the need to save long canes. We make an additional pass to tie canes to the fruiting wire in March and April when the temperatures warm and fingers function without gloves. As much as we all enjoy tying canes on a drop dead gorgeous spring day, it is very labor intensive. Dormant tying is where cane pruning can have a distinct economic disadvantage compared to cordon pruning, at least when the cordons are still healthy and well behaved.
I have found that cane pruning has a distinct advantage over cordon pruning in two areas. The first is with mite damage. For years my vineyards have had a problem with early season mites. Just after bud break, dozens of mites could be found on every newly emerging shoot. The damage would stunt growth and often destroy the basal leaves. Dormant oils were ineffective as the mites eggs were protected by the bark of old spur positions. I had to resort to mitacides. This was not a good way to start the growing season. I did however, observe that where I had put down new replacement canes, there were few, if any mites. Ever since I switched to cane pruning, early season mites have not been much of an issue.
The second advantage is with phomopsis. This fungus disease was a major problem in my older mountain vineyards as the combination of old, previously infected cordon wood with prolonged wetting periods (mountain fogs and misty rains), often required numerous preventive fungicide sprays before the young shoots reached 6" in length. Cane pruning has all but solved the problem. I do still get some phomopsis lesions on shoots coming from renewal spurs or other basal buds, but the problem is much more manageable
Other wood diseases have contributed to old cordon decline. I have to be honest that I cannot say definitively what organisms have caused these wood diseases, but there are plenty of options to choose from (esca, botrysphaeria, eutypa). Up until 2003 we were making numerous large pruning cuts (spur and cordon renewals) without treating the wounds. I can only conclude that this practice accelerated the incidence of rotting cordons and trunks. We now apply Dreft on all pruning cuts, and also find that cane pruning greatly reduces the number and size of pruning wounds. Wood diseases are much less of an issue now.
My vineyard is one big experiment, but conclusions are based on anecdotal evidence rather than more objective data analysis. Having stated this, I do believe that the incidence of late season bunch rots has declined when I changed from cordon to cane pruning. I attribute this to two things: increased air flow in the fruit zone and reduced inoculum originating from old cordon wood.
I did find, when switching from cordon to cane pruning, that I needed to change some of my canopy management strategies. This was especially true in the period between bud break and bloom. Shoot thinning actually became easier, requiring only one pass. Whereas with cordon pruning, certain varieties such as Seyval, Sauvignon Blanc, Cabernet Franc and Petit Verdot, needed multiple passes as new blind buds continued to produce shoots along the cordon up until bloom. Shoot thinning with cane pruning is fast, but requires workers who understand vine training and pruning. This is because the head region is naturally too vigorous and crowded. It needs to be thinned in a way that reduces crowding, but leaves key shoots in position to develop into next year's fruiting canes.
Timing with shoot tying/positioning has to be very precise with cane pruning as the entire cane can twist downward (we are on VSP and Lyre) if the shoots are not secured soon enough. This did require us to install a new catch wire just 8" above the fruiting wire so that we could tie tender shoots before they "flopped".
In wide spaced vineyards (6' or more between vines), cane pruning may lead to very uneven shoot development. If canes are allowed to carry too many shoots (more than 6 has been my experience), strong development by basal and apical shoots suppress mid-cane shoots. These mid-cane shoots remain stunted and are not capable of ripening high quality grapes.
If shoots are relatively uniform, I have not noted any differences in uneven ripening between cane and cordon pruning. In this case I base my conclusions on visual observations of color changes during veraison.
Typically cluster sizes are larger with cane pruning than cordon pruning. This can be a quality disadvantage, especially in red wine grapes. I feel that large clusters have a greater percentage of interior, buried berries that taste less ripe. I see this notably with Cabernet Franc in some years. We frequently have to resort to some cluster wing or shoulder removal in large clustered red wine varieties in order to reduce cluster size and remove less ripe berries. I have not observed any differences in berry size between the two pruning systems. Finally, as was mentioned previously, I do feel that there are less late season bunch diseases with cane pruning as opposed to cordon pruning.
In many situations cordon pruning has more benefits than cane pruning. Young to middle aged vineyards that are widely spaced, less labor intensive, and pleased with their yields probably should not consider cane pruning. On the other hand, certain varieties such as Sauvignon Blanc, Nebbiolo and many native American vines are not very fruitful in their basal buds and require cane pruning. In Bordeaux they say that cane pruned vines enjoy longer, productive lives than cordon pruned. If you are not sure which system to choose, I can tell you that it is much easier to start with cane pruning and then switch to cordon than the other way around.