Vine Interventions

Pruning usually takes place during dormancy, after leaf fall, once the remaining reserves from the vine leaves have been translocated to the canes, trunk, and roots.

From summer until the following spring, buds pass through several stages of dormancy, influencing pruning timing and the onset of budbreak. During post-dormancy, buds have already regained the ability to burst (after the first autumn cold periods), this process depend solely on climatic conditions.

Overly early pruning trigger early budbreak, leaving shoots vulnerable to late frosts, which are frequent in some areas of the region.

The time available for pruning, approximately three months, is limited for those managing large expanses of vineyards, and it is restricted even further when weather conditions hinder efficient pruning. On the other hand, pruning should be avoided during severe frost, as canes become brittle and the tissues at cut surfaces are exposed to the cold.

Grape varieties differ regarding their budbreak timing. Pruning begins, therefore, with the later-budding varieties (such as the red variety Vinhão and the white variety Trajadura). To minimize the effects of late frosts, two-stage pruning can be carried out. Vines are first pruned “high,” and the bud load is later adjusted to the desired level.

• use healthy plant material, avoiding the use of infected canes for new grafting
• prune diseased vines during the final stage of pruning
• use disinfected pruning shears
• avoid large pruning wounds by adopting less severe pruning methods
• protect wounds with effective fungicidal pastes
• burn dead vines, diseased tissue, and wood older than two years

The pruner must pay careful attention to the sanitary condition of the vines, as the tools used (pruning shears, saws, etc.) can transmit certain diseases and pests, particularly the so-called grapevine trunk diseases.

The pruning of two-year-old or older wood carries greater risk of infection due to the need for larger cuts. Another risk occurs if diseased pruning wood is left to overwinter in the vineyard, where infection can be easily transmitted by the wind. The most significant diseases are Phomopsis cane and leaf spot, Esca, and Eutypa dieback (a fungus associated with the Esca syndrome). More recently, Flavescence dorée has become more widespread in the region, making the destruction of pruning wood increasingly important.

In winter, Phomopsis cane and leaf spot persist at the base of canes in the form of pycnidia (black spots) and in basal buds protected by scales in the form of mycelium. Hence the importance of avoiding very short pruning on infected vines, as this would promote budbreak from infected basal buds.

Esca, traditionally seen as a disease of older vines, is now frequently found in young ones, one to three years after grafting, causing premature vine death. It occurs either in a slow form, in which sap flow becomes impaired and typical leaf symptoms appear due to the release of toxins by the fungi, or in a rapid, apoplectic form, resulting in the death of vines or shoots, with symptoms that can be confused with those of root rot.

Bacterial necrosis can also infect vines via pruning wounds or through direct contamination of buds exposed to sap exuded from pruning wounds.

Grape mealybug is another, if lesser concern, which should be removed during pruning. Trunks should also be scraped, as overwintering forms, such as nymphs and adult females, also use trunk bark as shelter.

Similarly, spider mites overwinter as eggs beneath trunk bark, on canes around buds, on leaf scars, and at the base of spurs, making it equally important to destroy pruning wood.

Training pruning normally covers the first three years of the vine’s development, except in high-trained systems such as the Portuguese cruzeta and cordão sobreposto systems, which may require five years. It is complete when only cane- and spur-based fruiting units are retained.

In this region, where cordons may reach 3.0 m in length, spur pruning is combined with cane pruning using a longer cane, known as a “guide,” which gradually fills the space between vines.

Vertical Cane Phase

All training pruning involves the vertical cane phase, in which a single cane is selected from those arising from the scion, trained vertically, and retained with a limited number of buds depending on vine vigor and the desired trunk height.

It normally consists of four to six buds, which may be positioned higher above ground level by removing some basal buds. In varieties with very short internodes (e.g., Trajadura), buds may be blinded alternately to increase the height of the trunk.

This phase normally takes place during the second year after planting, whether the vineyard was established with rootlings or bench-grafted vines. However, in this region, in vineyards with high trunks (ramada, cruzeta, cordão sobreposto, and single cordon), the vertical cane phase is often extended by an additional year, until the cane(s) reach the level of the wire. Naturally, this aspect is also related to plant vigor, which may be influenced by soil fertility and irrigation.

Due to the apical dominance of the buds, that is, the greater sap flow to the terminal buds of the vertically oriented cane, budbreak occurs preferentially at these buds, producing the most vigorous canes. This is particularly important because these insertion points form the basis for the subsequent formation of cordons or arms once the trunk height has been established.

Arm Formation Phase

The year in which the arms are formed is by far the most important, as several technical considerations arise simultaneously.

1. Vigorous canes should be selected, arising from buds on the side opposite to that towards which they will be trained. This positioning is for mechanical reasons, as the cane must be bent in the opposite direction to its natural tendency to split. In the case of a double (i.e. divided) cordon, the two sections should cross in opposite directions (a), providing greater stability to the vine and making better use of the available wire by filling more of it with cordon (b).

2. As a rule, the cane from the terminal bud should not be selected, but rather that of the next-to-last bud, provided it is in the position described above. This is because the last internode of the vertical cane is usually thinner and therefore does not contain the same reserves as the preceding one. This avoids a weak point between the previous year’s cane and the base of the cane that will form the arm.

3. Depending on cane vigor and the height of the wire above the ground where the cane will be positioned, several factors must be taken into account:

• if the best, or indeed the only, cane is too close to the training wire (less than 20 cm away), it will result in an overly severe bend with little flexibility. One solution is to delay training the cane onto the wire that year, selecting a weaker cane to form a new vertical cane. If no other cane is available, the cane closest to the wire should be trained, using a slight curvature of the trunk itself to minimize excessive bending.
• If the cane is sufficiently vigorous for the intended extension, that is, able to form the bend at the ideal level and still extend for at least half its final length, the buds located below the wire, including those at the bend, are blinded, and the entire pruning load is concentrated on the horizontal portion of the cane resting on the wire. Under conditions of excellent vigor, with very vigorous canes, each of the following practices should be avoided: retaining pruning load on the vertical current-year cane, blinding the buds at the bend, or retaining additional load on the cane already laid horizontally. To do so would run the risk that the vine would only break buds on the vertical portion of the cane, and not, or only very weakly, on the horizontal portion, a situation referred to locally as “pulling behind.”

4. To ensure regular budbreak from the buds on the horizontal cane laid along the wire, the cane must be tied to the wire carefully. Therefore, sufficient ties should be used to keep the cane well extended along the wire and ensure a smooth curve without kinks. The first tie should always be placed immediately after the first bud on the cane.

5. Spring shoot thinning must be carried out to remove shoots from blinded buds at and below the bends, because cane bending causes preferential sap flow to these shoots at the expense of those arising from the buds retained at pruning. To minimize this tendency, buds must be properly removed by positioning the flatter side of the pruning shears’ blade against the base of the bud; otherwise, removal of the primary bud will leave the secondary buds intact, and they will break in its absence.

For the same reasons, vines should be kept free of watershoots arising from dormant buds on the vine trunk, which at this stage correspond to the former single vertical cane.

Formation of single cordons (CSA, CAR and CSR)

Vigor and trunk height determine the duration of the formation phase. Thus, for a cordão simples ascendente (CSA; ascending single cordon) at a height of 1.10 m, a cordão ascendente e retombante (CAR; ascending and drooping cordon) at a height of 1.35 m, and a cordão simples retombante (CSR; drooping single cordon) at a height of 1.70 m, the starting point is the same: a grafted vine with a two-bud scion in the first year, from which two canes emerge, followed by selection of the single cane that will retain between four to six buds, according to its vigor.

By the third year, the selected cane is able to reach and be trained onto the wire in the 1.10 m and 1.35 m training systems, but not in the 1.70 m system. In the latter case, a single vertical cane should therefore be retained again to increase trunk height and reach the wire in the following year (fourth year).

Formation of cordão sobreposto systems (CSOB and Lys systems)

In the formation pruning of cordão sobreposto systems, that is, systems with two trunk heights, formation of the lower cordon is faster and formation of the upper cordon takes longer. There is therefore a period during which production pruning is carried out on the cordon established at the lower height while formation pruning continues on the higher cordon. This difference requires careful selection of canes according to the vigor conditions involved, as in the case of Cordão Sobreposto (CSOB), with trunk heights of 1.10 m and 2.10 m and with both canopies drooping.

In the case of the Lys system, the recommended trunk heights are 1.10 m and 1.45 m, respectively, for a drooping canopy and an ascending canopy.

Whenever possible, similar pruning loads should always be retained on the upper and lower cordons, to avoid the vine preferentially responding to the lower cordon's load. For this reason, in the Lys system, it is preferable to form both cordons or arms simultaneously rather than over two years.

Once the vine has been formed and its perennial structure with one or more arms has been established, fruiting pruning is carried out on the canes produced in the previous year.

Not all buds on a cane are capable of producing fruit; the buds in the middle third are usually the most fruitful. However, bud fertility varies according to grape variety, so it is important to understand the fruiting habits of each variety, as these determine the appropriate pruning intensity.

Three pruning types differ according to the number of buds retained.

Short pruning

Short pruning leaves two or three fruitful buds on a cane that are known by various names, including spurs (talões), polegares, talicões, tornos, among others.

Short pruning has traditionally been avoided in this region due to the vigor of the regional grape varieties, as well as to climatic conditions contributing to a certain degree of vegetative exuberance. Nevertheless, trials of short pruning on regional grape varieties have revealed some advantages, without significant production losses. By creating more concentrated production zones, it facilitates green operations, plant protection treatments, and subsequent pruning. It is also the most commonly used approach in mechanical pruning.

Long pruning

Long pruning retains at least four buds on the cane.

In this type of pruning, two important aspects must be considered: the orientation of the canes and whether or not they are left free. It does not make sense to leave long, upward-growing canes without also retaining spurs (mixed pruning). Since they tend to produce shoots mainly from the distal buds, the following year's pruning would have to rely on canes located too far from the main axis of the cordon.

Mixed pruning

Mixed pruning, in which both canes and spurs are retained on the same vine, is the most common in this region, both in traditional training systems such as ramada (a pergola-type system) and in more recent systems such as cordons. The spurs encourage renewal, ensuring high-quality canes for the following year's pruning, while the canes are intended for current-year production, making use of the most fruitful buds.

Cane and spur pruning

This is probably the most widespread system. Initially applied to cruzeta (a Portuguese high-trunk training system), it was later adopted for various types of cordons. It consists of retaining 4–5-bud canes spaced along the cordon, with renewal spurs in between. Upward-directed canes predominate, even in fully drooping canopy systems (cruzeta, CSR, CSOB), because the shoots arising from the canes naturally bend downward under their own weight. This practice is justified by the better quality of canes that grow in an upward direction.

However, some grape varieties prefer longer drooping training systems (more than five buds): Loureiro, in particular, due to its susceptibility to shoot breakage; in vigorous varieties such as Avesso; in varieties with low fruitfulness, such as Arinto; or in varieties in which fruitfulness is concentrated in the middle third of the cane, such as Padeiro.

In an attempt to create more gaps (“holes”) in the canopy, the spur should always be retained next to the cane whenever possible. This is, in fact, the principle behind Guyot pruning, rather than alternating spurs with canes.

Sylvoz pruning

Sylvoz is a long pruning system based on long, arched canes, that are bent downward and tied to a wire below the level of the cordon, perpendicular to the direction of the wire. The same cane functions as both a fruiting and a renewal cane, as bending it downwards allows the basal buds to perform the role normally fulfilled by spurs.

Over the years, the fruiting unit tends to become longer, so pruning should be renewed using true spurs or water shoots located close to the base of the unit. This pruning system is recommended for training systems in which the canopy is divided into an upward-growing section and a drooping section.

Guyot pruning

This pruning system is typical for low, exclusively upward-growing training systems. As recommended in its simple form—one 2-bud spur and one long cane with 5 to 8 buds—in this region, it is not compatible with the usual vine spacing (1.25–2.50 m) and, consequently, with the pruning loads practiced (25–35 buds/vine). However, if, instead of being laid out along the wire (single Guyot), the cane is bent to form an arch in the same direction as the wire (Guyot with an arched cane), and the system is bilateral or double, it can be adapted provided that vine spacing is increased.

Single Guyot is one of the pruning systems that most limits vine expansion. A good balance must be maintained between the vigor of shoots arising from the spur and the cane to avoid an uneven growth response between the two. Each year, a new cane is formed from the shoot arising from the upper bud of each spur, while the shoot from the lower bud becomes the new spur.

In the region, training on high bardos (traditional Portuguese training systems) consists of overlapping Guyot systems with bent canes.

Cazenave pruning

This is a mixed pruning system consisting of 4–5-bud canes spaced 30–40 cm apart and inclined at approximately 45° to prevent excessive shoot growth from the terminal buds. Spurs must also be retained for vigorous varieties, which tend to produce shoots preferentially from the terminal buds.

For the canes to be maintained at this angle, they must be tied to an upper wire, which makes the pruning operation less efficient.

This system is only applicable to upward-growing canopy systems.

Royat pruning

This short pruning system consists of only 2–3-bud spurs spaced 15–18 cm apart and is applicable to fertile varieties.

Once established, the main advantage of this system lies in the ease and speed of execution. In addition, the clusters are well exposed and accessible for treatments. It is only used with upward-growing canopy systems.

Disadvantages include that it requires careful, time-consuming formation pruning, and it is difficult to achieve balanced growth along the entire cordon due to differences in vigor.

Pruning systems such as Single Guyot, Cazenave, and Royat are applicable to exclusively upward-growing training systems, which in this region are only recommended for moderately to poorly fertile mid-slope sites.

Water shoots compete for vine reserves with shoots produced from the canes retained at pruning, increasing canopy density and consequently having negative effects on production quality.

The removal of these shoots, which develop in unwanted positions, should be carried out as early as possible to prevent the vine from investing reserves in non-productive growth and to avoid making the operation more difficult as the shoot bases harden.

This canopy management practice is not usually given the importance it deserves, particularly in a region such as this, where there is a diversity of training systems with upward-growing and/or downward-growing canopies, and where climatic conditions favor both vigorous growth and fungal diseases.

As the name suggests, this practice consists of positioning shoots according to the intended layout of the training system. This operation is now facilitated in upward-growing canopies by the use of double wires, between which the shoots are inserted. These wires may be movable, occupying more than one height position and thereby reducing the investment in wire.

Shoot positioning is increasingly necessary as the number of canopies increases, particularly when they are downward-growing and overlapping, as in the case of cordões sobrepostos and lys. This is because the canopies must remain independent, so that the shoots do not intertwine and leave open space between the canopies. Therefore, shoots growing from the lower cordon must be separated from the upper one, as they tend to attach themselves to it.

With exclusively downward-growing canopies, shoots naturally bend downwards as they acquire sufficient weight, but in an uncontrolled manner. They should subsequently be combed, i.e. arranged in parallel, untangled from one another and positioned vertically downward, to improve air circulation and prevent them from growing horizontally and shading the vegetation below.

This operation has a maximum time window of approximately eight days after flowering, after which the tendrils begin to lignify, making it impossible to position the shoots manually without the use of pruning shears. Some grape varieties have brittle shoots, so that positioning them overly early presents a risk of desnoca. This is the case with Loureiro, which only allows unrestricted handling after fruit set, leaving a very short window for carrying out this operation. Moreover, this intervention should only be performed on days with good weather, to reduce the risk of shoot breakage.

This practice promotes fruit set and improves leaf exposure, preventing poorly ventilated canopy areas and consequently premature senescence of mature leaves.

Shoot topping, or summer pruning, consists of cutting off the ends of shoots. It is perhaps the most common canopy management practice and is essential in intensive, high-density vineyards, particularly to facilitate mechanization, among other vineyard management considerations. In this region, shoot topping is carried out when necessary, after the period of most active growth. Normally, it immediately follows the positioning of downward-growing canopies; otherwise, tractor access through the inter-rows becomes impossible.

In addition to this practical aspect, by reducing shading, shoot topping improves cluster exposure and reduces the incidence of diseases and pests. However, it alters vine physiology by stimulating the production of lateral shoots. In upward-growing canopies, shoot topping becomes necessary when shoots extend beyond the top wire and bend back over themselves. In addition, the production of lateral shoots at the top of the canopy considerably increases exposed leaf area, with notable photosynthetic benefits. In downward-growing canopies, shoot topping has the effect of improving air circulation within the canopy by preventing shoots from reaching ground level.

Shoot topping intensity can vary. It is considered severe when only four leaves are retained above the last cluster, and moderate when seven leaves are retained. More severe shoot topping should be carried out in vineyards with excessive vigor and consequently fruit set problems due to flower and young berry drop, because severe topping removes many mature leaves, the loss of which will negatively affect lower vigor vines.

In general, shoot topping should not be carried out either too early or too late, and should never be performed before flowering, because the production of lateral shoots triggers competition that disrupts the vegetative and reproductive balance of the vine. Recent trials at EVAG on the optimum timing of shoot topping have highlighted the importance of the vigor of the grape variety × rootstock × soil fertility combination. The more vigorous the system, the more important it is to perform shoot topping at flowering.

Late shoot topping is detrimental, particularly when carried out close to veraison. At this stage, it mainly causes a substantial reduction in active leaf area, with negative effects on grape quality.

Shoot topping is one of the most easily mechanized canopy management operations in vineyards planted in orderly rows. Various models of mechanical toppers are available on the market, with preference given to those capable of adjusting cutting height and width during operation.

This operation removes leaves, generally those below the clusters, to improve air circulation and sunlight exposure in the fruit zone, thereby improving berry color development and ripening under good sanitary conditions.

However, of all canopy management practices, leaf removal is the one that should be applied with the greatest caution, both in terms of intensity and timing.

It should be carried out mainly in dense canopies and should primarily involve leaves that are no longer active. Performing it too early during the ripening period, particularly on days with high solar radiation, can lead to sunburn with negative effects on yield and quality. Although it is normally performed by hand, it can also be carried out mechanically.

Leaf removal should be delayed until the clusters have accumulated high sugar levels, thereby avoiding the risk of sunburn that may result from earlier exposure. When performed at this stage, it also provides better control of rot and increases harvest efficiency by facilitating access to the clusters.

For highly productive grape varieties and in years of high yields, cluster thinning may be useful to regulate production and improve quality. It can be carried out on part or all of the cluster; in the latter case, the second- and third-position clusters should be removed. The intensity of thinning should be at least 30% to achieve a reduction in excessive production, as well as increases in average cluster weight and sugar content, together with a decrease in total acidity.

The operation should be carried out between fruit set and veraison, that is, before sugar begins to accumulate in the berries. When performed after veraison, it reduces yield but does not improve quality. Cluster thinning is normally carried out manually using pruning shears, making it an expensive operation in large vineyards. An alternative is chemical thinning about one week after fruit set, although the desired level of crop reduction is more difficult to control.

Cluster thinning is also recommended during the first year after grafting, or in the year grafted vines are planted, as a means of improving vine vigor.