Sprays containing the trace element zinc are often recommended for improving fruit quality of harvested apples.
- Trials conducted at East Malling in the 1980s showed that zinc sprays applied during flowering reduced fruit set but, as applications in the previous year also increased flower bud abundance, this negative effect was cancelled out (Yogaratnam and Greenham, 1982).
More recent trials, conducted at East Malling (Hipps, personal communication), indicate that sprays applied during the stage of active cell division in fruitlets (i.e. in the few weeks following petal fall) can, on occasions, stimulate thinning.
- Sprays of 1.0 g l-1 zinc (as 4.4 g ZnSO4.7H2O l-1 mixed with a proprietry wetting agent), applied in 1998 at high volume to semi-mature Bramley’s Seedling apple trees on M.9 rootstock, reduced initial fruit set by 17%.
- However, similar sprays in 1999 had no effect on fruit set. Further research is needed to understand this variable effect of zinc on fruit abscission
- The thinning potential of sprays of zinc products needs further investigation.