Crop Load Control of 'Fuji' Apple in Central Italy

Alternate bearing of Fuji apple is an increasing problem in high density planting systems. In a commercial orchard (Ascoli Piceno, central Italy) with 4329 trees/ha (3.3x0.7 m), several substances (ammonium thiosulphate, lime sulphur, olive oil and benzyladenine), potentially active in blossom thinning, were investigated in comparison to hand thinning and untreated control. Fruit set was evaluated in four different positions of the canopy (bottom, high, North and South). At harvest the number of fruits per tree was counted and their size measured. All substances were active but only benzyladenine was able to almost completely substitute the hand thinning in all the canopy positions. Ammonium thiosulphate and olive oil showed a positive result only in the bottom part of the South side of the tree. In the same orchard, bud extinction before flowering and hand flower thinning were performed in a second comparison trial between "taille longue" and heading back pruning. Heading back and flower thinning was able to create a different crop load with a final production ranging from 50 to 80 t per hectare and significant differences of return bloom, suggesting that an appropriate number of fruit buds and flowers per cluster removal is necessary to moderate alternate bearing in Fuji apple.