Fruit production: The basics of pruning grapes

If a young vine is developed properly from the start, the way is automatically paved for an easier pruning season.

The permanent cordon system and two-bud spur pruning system are used in about 95% of South African vineyards. An advantage of this system is that vintners can be sure of uniform-shaped bunches.

François Viljoen, from wine industry organisation Vinpro, says you should consider the following when pruning:

Pruning is goal-orientated.
The ideal canopy lets in enough light and air for optimum quality. Correct pruning is vital to producing top-class grapes (Diagram 1).
Pruning should not be a challenge if young vines are trellised correctly.
Make sure the trunk is erect.
Choose the bearing canes and space them using pruning shears.
Prune normal and abundant shoots to two-bud bearers and poorly developed shoots to one-bud bearers.
The ideal vine has an upright trunk, balanced cordons with the same strength on both sides, good bearing space, small gibbets and no overlapping of shoot ends.
All shoots should be attached to the wire.

UPRIGHT TRUNK

“If the trunk is skew, you’ve already lost the battle. The vines should be as upright as fence posts,” he says. Skew trunks result in an unequal division of bearers, which means uneven growth (Diagram 2).

Viljoen explains a typical example: 3 bearer positions on one side and 7 bearers on the other. 2 or 3 bearers on one cordon and those at the ends will always be the strongest growers.

Those in the centre of the cordon will be weak shoots and will eventually produce fewer leaves and smaller bunches.

EQUAL SHOOTS

If a cordon is unbalanced, with 2 shoots of different lengths, the bearers and growth will also be uneven.
Viljoen’s tip to ensure they are the same length is to trellis the spurs on the wire in the same year.
He compares this to a pipeline. “If you have one thick and one thin pipe, the thicker one always enjoys preference.”

CORRECT SHOOT THICKNESS

Sometimes farmers get impatient and try to develop a vine too hastily, because this affects growth adversely. If the shoots on the wire are too long, they will bud and grow unevenly.

“If this happens, it is difficult to correct the vine’s development,” says Viljoen.

GOOD BEARING SPACE

The ideal spacing is to leave about 12 cm between bearers. “Leave a space of about the length of a pair of pruning shears between the bearers,” suggests Viljoen.

If there is overlapping at the ends of a cordon, it can create compaction problems. The only way to rectify this is to cut back to the right spacing, he says.

GOOD BUDDING, UNEVEN GROWTH

When a 2- or 3-year-old vine buds well on its cordon shoots, but still shows uneven growth, this is often because the shoots were not topped (cut back by 30 cm or more).

He advises removing all one-bud bearers from the cordon shoots to give the vine another chance to bud and grow.

USING BIOLOGICAL PROTECTION

Viljoen strongly advises the use of trichoderma, a “good” fungus that is sprayed onto pruning wounds shortly after pruning, to form a living protective layer.

Trichoderma colonises the wound faster than Eutypa, which it pushes aside. According to a study by Dr. François Halleen, trichoderma penetrates the shoots even deeper if any unfriendly fungi appear, working even harder to protect the vine.

TIME PRUNING CORRECTLY

In the 1970s, well-known viticulturist and researcher, Prof. Eben Archer and a French colleague, undertook a study to prove that the time of year pruning takes place has an impact on a vineyard’s growth and production.

The earlier final spur pruning takes place in a vineyard, the earlier budding will occur. Conversely, the later this happens, the later in the season the vine will bud. The advantage of later budding is that it creates a better opportunity for the vineyard to flower in warmer weather conditions.

“This is where the secret lies. The hormone citokinine – which determines the harvest for the next year – is formed in the roots. The more active the roots are at this stage, the more citokinine is formed. This sends a message to the buds to produce more bunches. The colder the weather and soil circumstances, the less citokinine is produced, resulting in a smaller harvest.”

Viljoen’s advice is to start pruning only when the vineyard has lost about 80% of its leaves.

TOP PRUNING TIPS

SPACING

Bearer spacing is important in any vineyard.
There is not much one can do if the spacing was too wide at the start, apart from trying a different pruning system.
The Casanave or cane pruning system (4 to 6 buds) could be used as a temporary measure. Two or more canes per vine will also increase the number of buds.

TOO FEW BEARERS

If spacing is too wide because bearers have died back, leaving openings on the vine, you will lose production capacity.
In this case it would be a good idea to fill the wire by plaiting the longer bearers into the openings that are left by the missing bearers.

BEARERS BELOW THE WIRE

According to Viljoen, all bearers growing downwards or below the wire, should be cut off.
The reason for this is that such bearers are usually in the shade and chances are good that that they will die later on in season.
If you discard them early, you will save a great deal of energy for the vine.

SHOOT LENGTH

A common problem is that short bearers are not pruned short enough.
A renewal spur with 3 bud nodules is too long.
The bearer will bud best on the top buds.
The ideal length for most cultivars is bearers with 2 buds (or the length of a matchbox).
For more abundant cultivars, such as Merlot, or young vines, a 1-bud bearer will do (about the length of the short side of a match box).

WEAK VINES

Viljoen says weak vines and/or bearers should be pruned leaving only 1-bud bearers.
He says it is better to give the vine another year to become strong, otherwise production could be permanently harmed and quality will not be great.

VINES GROWING TOO ABUNDANTLY

This could be rectified by cutting down on water and/or fertiliser, but the cane pruning system (7 to 8 buds) could also improve production.

This article first appeared in Farming SA.