Management of polarity and productivity of grapevine bushes using pruning methods

How to manage polarity: short pruning and spatial arrangement

The polarity of a grapevine directly determines the nature of its growth and fruiting. To manage longitudinal polarity in viticulture, four methods are used: short pruning of shoots, forming of fruiting units, bending of canes, and pruning to base buds. The choice of a specific technique depends on the biological characteristics of the cultivar and cultivation technology.

Fruiting shoots can be oriented in space in various ways. They are left as a cane (directed vertically or slanted upward, horizontally, vertically, or slanted downward), a half-arch, an arch, a ring, a spiral, or a hanging shoot. Such positioning allows for the redistribution of nutrients to the necessary buds.

Short pruning to a spur is the simplest and historically earliest method of formation. When using it, the vine arms elongate slowly, and the wounds inflicted remain small. This method simplifies maintenance and allows for the full mechanization of pruning, which is especially relevant for modern high-trunk vineyards.

• Short pruning length — 1–4 buds
• Annual arm growth — 1–2 internodes
• Pruning of greenhouse cultivars — 2–3 buds
• Yield reduction of oriental cultivars — 2–3 times or more

Short pruning is practiced for greenhouse cultivars such as Foster's Seedling and Frankenthal, as well as for Royat and AZOS cordon forms. With good growing conditions — regular irrigation and fertilizer application — it is possible to shift the zone of maximum fertility lower along the shoot. In some cases, short pruning leads to further differentiation of inflorescences in the remaining buds.

Mixed pruning for a fruiting unit and vine restoration schemes

Pruning for a fruiting unit, or mixed pruning, entered global practice in the 19th century and remains the primary method today. It combines short pruning of a replacement spur and medium or long pruning of a fruiting cane. Every year, new shoots grow from the spur buds to renew the unit, while the long cane ensures a high-quality harvest by preserving the most productive middle zone of the vine.

When pruning a replacement spur, it is important to consider the spatial orientation of the buds and regional characteristics of the vineyard. An incorrect choice of pruning length can lead to underloading the vine with shoots or their inconvenient arrangement. To accurately adjust the load on the vine, proven practical schemes are used.

In practice, ideal shoot development on a replacement spur does not always occur. To maintain the shape of the vine and the planned yield, agronomists use an individual approach to pruning each fruiting unit. The choice of scheme depends on the actual condition of the vine and the presence of viable buds:

• One good shoot on the spur, two on the cane: the shoot on the spur is pruned to 2–3 buds for a new replacement spur. A strong basal shoot of the old cane is pruned medium or long for fruiting, and the rest of the cane is removed.
• Weak shoot on the spur or its absence: the old replacement spur is cut off completely. A new fruiting unit is formed from two strong shoots at the base of the old cane.
• One good shoot on the spur, shoots only at the end of the cane: the old cane with all shoots is removed. The only shoot on the replacement spur is pruned long, to 4–5 buds, to restore the unit the following year.
• Use of suckers: if the main shoots have been damaged, but there are well-matured suckers with developed buds, the fruiting unit is formed from them.

The bending method is used for forms like the Kakhetian (Georgian), where the shoot is bent into a ring; the Sylvoz cordon, where shoots are bent into an arch; and when tying fruiting shoots in a half-arch or arch, etc. This utilizes an important property — longitudinal polarity, thanks to which vigorous shoots develop on the part of the fruiting shoot furthest from the soil surface. Buds in the bend zone start growing earlier, the central buds within them are more differentiated, there is a greater influx of nutrients to them, and they are more fruitful. At the same time, this method causes rapid elongation of perennial branches. It is also important to consider the varying reactions of different cultivars to shoot bending.

The method of polarity regulation by pruning to latent buds — according to Marconi — is used in Italy and in greenhouses. It consists of artificially creating conditions for the development of latent buds during very short pruning (to 2 buds) and removing the lower buds on a fruit-bearing shoot pruned to 4 buds. Fruit-bearing shoots are formed from the upper buds (3rd and 4th). The shoots that developed from the latent buds are pruned again the following year to 2–4 buds. The disadvantage of the method is that, in this case, a large number of shoots are removed, the wounds are large, and sometimes the latent buds do not develop, so the upper shoots are left, which lengthens the spurs.

Fig. 46. Head-shaped forms:

/ — on rootstock cultivar mother plantations; 2 — trunk-based (Turkmen); 3 — USA, Germany, France.