Guidelines for the preparation of table grapes in SA for export 2025/2026_ND

Tipping of bunches This involves manually removing the bottom (± 5 cm) part of the bunch to improve the set, especially in the lower part of the bunch. Tipping is usually done just before or during flowering. Shortening This is the final shortening of the bunches to the desired length, achieved by cutting off the unwanted portion. Shortening is usually done just after set. Different measurements apply, for example, the length of snipping scissors, a cigarette lighter, or a hand’s breadth. Sometimes the bunch is shortened to a number of laterals. The modern trend in the table-grape industry is to aim for an optimal number of berries per bunch for a given cultivar (Table 3). See page 98. Shatter or abortion Shatter refers to the abortion and dropping of flowers or small berries (2–5 mm) just after flowering during set. The cultivars that are most prone to shatter are Alphonse Lavallée, Sugrathirteen (Midnight Beauty ® ), Sugrathirtyfour (Adora Seedless ® ) and IFG Ten (Sweet Globe™). A tendency to shatter is likely to be genetic. Experience with Alphonse Lavallée 30–40 years ago suggested that levels of carbohydrates and other nutrients during flowering and setting played an important role. The number of bunches per vine is also important. When there are too many bunches, plant growth regulators such as cytokinins and auxins are diluted, and levels in any given bunch are not high enough to prevent shatter. By removing bunches, growers can increase the available carbohydrates, nutrients, and plant growth regulators per bunch, and therefore the opportunity for berries to set. Set has been extensively researched in Alphonse Lavallée. The resulting recommendations for improved set apply to other cultivars and are summarised below. Before flowering Retain one bunch per shoot. Reducing bunches increases the carbohydrate levels in the remaining bunches. Leaving all the bunches, especially in very fertile cultivars, risks excessive shatter. At 5% flowering Remove leaves around bunches and shoulder bunches, especially large bunches. At this stage, the basal leaves don’t contribute much to carbohydrate levels through photosynthesis. Making bunches smaller elevates the carbohydrate levels in the remaining parts of the bunches. At 10% flowering Top shoots. Actively growing shoots compete with bunches for available carbohydrates and nutrients. The severity of topping is determined by vigour and temperature. The more vigorous the plants and the warmer the weather, the bigger the section that should be topped. At 50%–80% flowering Vines can be girdled at 50%–80% flowering in extreme conditions (high temperatures and vigorous growth). By interrupting the phloem, the downward flow of carbohydrates is stopped, which increases the carbohydrate levels in the bunch zone. Since the research on Alphonse Lavallée, plant growth regulators such as cytokinins have become available. These can enhance set when applied at 1-2 ppm during 50%–80% flowering. However, note that cytokinins are not registered for this use in South Africa. Cytokinins only promote set when applied preventively. It doesn’t reduce shatter when used at a berry size of 3–4 mm (set). Cytokinins have disadvantages when used during flowering. Small shot berries may remain, and berries become rounder. Colour development may also be adversely affected.

6 SATI GUIDELINES FOR THE PREPARATION OF TABLE GRAPES IN SOUTH AFRICA FOR EXPORT