Biology of grapevine shoot pinching and practical use of lateral shoots

Pinching: development biology and practical application

Side shoots (laterals) are shoots of the second and subsequent orders that develop from precocious axillary buds in the same year. Contrary to the old opinion about weak photosynthesis in their leaves, practical experiments have proven otherwise. The photosynthetic activity of side shoot leaves is higher than that of the main shoot leaves in the same zone, as the latter are older.

Grape cultivars vary significantly in their ability to form side shoots. In some, they grow actively and are almost as vigorous as the main shoots. In other cultivars, side shoots develop only with intensive nitrogen nutrition on fertile soil, excessive load on the vine, damage by frost, or when shoot polarity is disrupted after pinching.

With an abundance of side shoots, the leaf canopy of the vine increases, which can cause shading of the main shoots. Therefore, at the beginning of growth, the shoots are not removed completely, but only shortened, preserving part of the leaves. On naturally developed side shoots, the harvest forms later and often does not have time to reach standard sugar content by the time of the general harvesting.

• Increase in leaf surface area with an abundance of side shoots — 25%
• Number of leaves left on the main side shoots — 1–2 pcs.
• Number of leaves left on renewal spurs — 6 pcs.
• Yield increase due to last year's side shoots after severe winters — 22%

Side shoots are indispensable for restoring the vine canopy after frosts, hail, or pests. Spring pinching stimulates their growth to form new arms and fruit-bearing units. In southern regions and greenhouses, a second harvest is obtained due to artificially induced side shoots. For this, it is important to carry out pinching on time, increase nutrition, and provide the vines with soil moisture during the period of embryonic inflorescence formation.

When planning winter protection, consider regional characteristics of vine ripening. According to research data, under the conditions of Central Asia, ripened side shoots showed higher frost resistance compared to the main shoots. However, during tests in the Don region, this property was not confirmed.

Girdling: how to accelerate ripening and increase berry size

Girdling is a surgical technique in which the outflow of organic substances to the roots is temporarily suspended on a shoot. To do this, a strip of bark is removed from the basal part of shoots, arms, or the trunk, or the tissues are squeezed with wire. As a result, the upward flow through the xylem is maintained, and photosynthesis products are concentrated in the parts of the vine located above.

This technique is used to reduce the shedding of flowers and fruit set in susceptible cultivars, as well as to increase the size and accelerate the ripening of berries. The procedure also stimulates better formation of fruit-bearing buds for the next year's harvest. It is carried out strictly during phases of high cambium activity for rapid wound healing.

1. Remove a ring of bark 3–10 mm wide or tightly squeeze the shoot with wire at the base.
2. Perform the operation during one of the key periods: before flowering, during berry growth, or at the beginning of harvest ripening.
3. If it is necessary to prolong the effect of the technique, repeat the procedure 2–3 times after the previous wounds have healed.

After girdling, the shoot above the wound thickens due to tissue expansion. Over time, callus grows over the cut site, which restores the conducting paths and the normal outflow of substances. The wound heals fastest in the period from flowering to the beginning of berry ripening.

• Width of the removed bark ring — 3–10 mm
• Time for callus formation and wound healing — 10–30 days
• Optimal temperature for healing — 25–28 °C
• Optimal air humidity for callus formation — 80%
• Maximum lifespan of a vine with trunk girdling — 20 years

Girdling is effective on plants of cultivars with full parthenocarpy (Korinka chernaya, Korinka rozovaya, etc.). At the same time, the shedding of flowers and fruit set is reduced (from 74 to 59%), the mass of the bunch is increased (from 155 to 350 g), the number (by 20%) and mass of berries (by 20–40%) increase, and sugar accumulation in them increases (by 2.5%).

Good results are obtained when girdling plants of individual seedless and table cultivars, in northern regions, in greenhouses (this accelerates berry ripening by 10–15 days), and cultivars prone to poor fruit set and with a functionally female flower type. In years with a cold summer, this accelerates the ripening of the harvest in late cultivars and changes the chemical composition of the berries.

Girdling contributes to better rooting when propagating grapes by layering.

However, it should be borne in mind that in arid regions and in years with low rainfall, the yield of bushes during girdling may decrease due to poor water supply.

Girdling in our country is mainly used for scientific research, on plants of certain table cultivars, and in greenhouses. Its practical significance is minor. Early-ripening cultivars respond weakly to girdling. This technique is used significantly less in Greece, where there are large areas of parthenocarpic grape cultivars.

The grapevine is an optionally self-pollinating and obligately cross-pollinating plant, with its pollen and stigma maturing simultaneously. Therefore, in the presence of wind and optimal temperatures (26–30°C), pollination of flowers and fertilization do not present great difficulties.

However, in certain years, under conditions that prevent pollen grains from reaching the stigma, supplementary pollination is carried out on plants of cultivars with perfect flower types. The reasons for this are:

• absence of wind or low wind speed (less than 2–3 m/s);
• heavy rainfall, which washes away the secretory fluid from the stigma and the pollen;
• deterioration of nutrient supply to inflorescences and flowers and their high shedding rate.

The goal of this technique is to increase fruit set, as well as the number and mass of berries and clusters. Grape productivity increases by 15–45% as a result.

For supplementary pollination during the flowering stage of plants, machines that create good air circulation are used: helicopters and dusters. Supplementary pollination is combined with dusting plants with sulfur against powdery mildew.

Artificial pollination is the pollination of cultivars with a functionally female flower type, as their pollen is sterile, using fertile pollen from other cultivars. It is carried out on plants of the following cultivars:

• Moldavsky (Moldova);
• Tavkveri (Azerbaijan);
• Chaush Bely (Crimea);
• Madeleine Angevine (RSFSR and Ukrainian SSR);
• Plechistik, Pukhlyakovsky (Don region);
• Nimrang, Katta-Kurgan, Charas Muscat (Central Asia), etc.

Even when establishing a plantation with alternating rows of pollinator cultivars and pollinated cultivars at a ratio of 1:1 or 1:2 (for example, Tsimlyansky Cherny and Plechistik in the Don region), the yield of cultivars with a functionally female flower type is not always stable, since favorable conditions for cross-pollination are often absent (pollen spreads to a distance of up to 2–5 m — to one inter-row space). A major role in obtaining stable high yields in plants of these cultivars is played by the selection of pollinator cultivars, which must biologically correspond to the pollinated cultivar, coincide with it in flowering time and rate, produce a large amount of pollen, release it easily, and be fertile. The most effective method is using a mixture of pollen from different cultivars whose flowering periods coincide with the flowering period of the pollinated cultivar.

For artificial pollination, pollen (inflorescences) is harvested from pollinator cultivars with perfect flowers or from rootstock cultivars with male flowers. Up to 900 g of pollen per 1 hectare is required. It is collected before 12 o'clock in the afternoon. Pollen is stored in a dry, cool room, less often in desiccators over calcium chloride for up to 20 days.

Pollination is carried out on sunny mornings 2–5 times using the following methods:

• handheld pollinators;
• dusters;
• helicopters.

This technique allows for regulating the number of berries in a cluster, which contributes to an increase in their mass and improved aeration. It has limited application. The best time for thinning is after the end of flowering and natural fruit set drop, once the berries reach the size of a pea.

During this process, less valuable berries are removed from the cluster:

• at its apex;
• at the ends of the branches;
• the outermost of the three at a fork.

In case of a very dense cluster, 10–30% of the berries are thinned out. This technique is of particular importance for table cultivars in greenhouse conditions, where severe berry damage is observed. Forming looser clusters improves their aeration and increases the inflow of nutrients to the remaining berries, and also:

Thinning is performed manually using special blunt scissors. For these purposes, preparations such as ethephon, DNOC, alpha-naphthylacetic acid, and gibberellin have also been tested, but due to inconsistent effects, they have not found application, except for ethephon.

Fig. 57. Pollinators, their design and application for pollination (dimensions in millimeters).

Grape Defoliation: Biological Significance and Technique

Defoliation is the artificial removal or thinning of grapevine leaves. This technique has long been used in traditional winemaking regions: in the south of Russia, in Transcaucasia, Uzbekistan, and Ukraine. On fruit-bearing plantations, it helps to redirect the flow of plastic substances to the berries and improve the aeration of the bushes. In nurseries, defoliation is necessary to accelerate the ripening of the vine and prepare nursery plants for digging.

• Treatment time for fruiting bushes — 7–15 days before harvesting berries
• Defoliation time in the nursery — 2–3 weeks before digging up nursery plants
• Increase in berry juice sugar content — by 2.8–5.6%
• Magnesium chlorate application rate in the nursery — 7 kg/ha

In commercial vineyards, leaf removal solves several technological tasks at once. It reduces the susceptibility of berries to diseases during the ripening period and decreases the bush's transpiration. This practice also improves bunch exposure to light, which contributes to the appearance of a beautiful "tan" on the berries and enhances their marketability.

• shortening of the growing season;
• improvement of bush ventilation and reduction of bunch rot;
• increase in berry juice sugar content;
• facilitation of harvesting, including machine harvesting.

This agricultural practice yields excellent results in northern viticulture regions with low photosynthetically active radiation (PAR). In recent years, scientists have been actively studying the possibility of performing defoliation in the bunch zone during mechanized harvesting. This is because the harvesters' vibrators inevitably knock off some leaves during operation.