Trials conducted at HRI-East Malling in the early 1980s showed the benefits of applications of GA4+7 (Regulex) on the skin finish of Cox, Discovery and Golden Delicious (Taylor et al., 1985).
- Four sprays at low concentrations (2.5-10 ppm), commencing at first open flower and applied at 10-day intervals, significantly improved the fruit grade out by reducing the russeting on fruits.
- Only the sprays applied at the highest concentration (10 ppm) had any significant effect on return bloom the following season.
- When pure formulations of GA4 and GA7 were compared the former produced the best response, in terms of russet prevention and also had the least effects upon return bloom.
Trials abroad have shown that sprays of Promalin (16 ppm of a mixture of GA4+7 and benzyl adenine) can reduce russeting on varieties such as Golden Delicious (Eccher and Maffi, 1986).
- Promalin is approved for use on some varieties of apple, especially in the USA.
- These sprays improve fruit shape by increasing the length:diameter ratio of varieties such as Red Delicious (Curray and Williams, 1983; Unrath, 1978) and may also increase fruit weight (Unrath, 1978).
- Applications of Promalin at 25 ppm at full bloom gave the most beneficial effects.
- Trials with Promalin on Cox, conducted at Long Ashton in the late 1970s, showed no effects on fruit length:diameter ratios (Child et al., 1980).
- On varieties such as Cox and Discovery apply sprays of gibberellic acid (e.g. Berelex) at label recommendations (4 times at 5-10 ppm, at 10 day intervals commencing at first open flower) so as to improve skin finish at the time of harvest.