EFFECT OF GIBBERELLIC ACID AND CPPU ON COLOUR AND BERRY SIZE OF ´REDGLOBE´ GRAPES IN TWO SOIL TYPES

The effect of different cultivation practices on the colour and berry size of grapes, was investigated in a field experiment in ‘Redglobe’ vineyards, grafted onto Ramsey, on two soil types, in the Hex River Valley in South Africa. Cultivation practices include application of different concentrations and combinations of gibberellic acid, CPPU and a seaweed extract. Data with regard to berry colour, size and quality were collected. Clay-loam soil is considered more suitable than sandy loam soil for production of red table grapes with the colour required by the Far Eastern markets. More grapes of the required colour were obtained from the vineyard on clay-loam soil, but the occurrence of partially coloured grapes was also increased. Irrespective of site (soil type), 20 mg L^-1 GA₃ plus 5 mg L^-1 CPPU plus 1.5% seaweed extract applied at 12 mm berry size, combined with 1.5% seaweed extract at 16 mm berry size and 1.5% seaweed extract at véraison, yielded the highest percentage of bunches with the required colour. However, on clay-loam soil, the highest percentage of partially coloured berries occurred. The combination of GA3 and CPPU, delayed sugar accumulation (ripening), but improved berry firmness. CPPU applied at véraison can be used to obtain more grapes of the required colour, as well as improving berry firmness. The risk of occurrence of partially coloured grapes, as well as delaying sugar accumulation and ripening, is also increased.