REGULATIONS OF GROWTH AND FRUITING OF A HIGH DENSITY APRICOT ORCHARD
The meadow orchard system has not succeeded on the Kanino apricot, mainly due to slow regeneration. Summer pruning has a prolonged effect on apricot trees compared to winter pruning. Therefore, we preferred a training system with a modified central leader, with 3–6 limbs pruned back alternatively, after 1–3 bearing seasons.
Three year old trees reached the height of 2 – 2.5 m with winter pruning, or 1.5 – 2 m after additional summer pruning.
Their yield was 3–5 kg per tree, or 26.5 – 33.3 tons per hectare.
At the narrow spacing, the tree canopy became too dense, leading to failure of the lower parts to initiate flower clusters, while the fruits of central parts grew slower, and were inferior at harvest. Fruit set was poor in the following spring, due to a hail-storm during blossom in spite of a dense and uniform flowering. Yield per tree reached 2.8 kg in the fourth season, after an alternate winter pruning, but only 1.7 kg in winter topped or summer pruned trees, the yield per hectare being 19 and 13 tons, accordingly.
Growth retardants were sprayed on the upper part of the trees at the end of the second season. The apricots were found very susceptible to various chemicals.
Vegetative growth was stunted after Alar and CCC treatments, but Ethrel, Morphactin or Off-shoot-O caused die-back of apices, yellowing of mature leaves and partial leafdrop. Otherwise, laterals were not damaged, and blossom was profound in the following spring. After Alar or CCC treatment, yield was 15 % higher. Different treatments were applied after harvest in the third season. Na-Dikegulac or PP 528 sprayed on the upper third of the tree canopy, did not cause phytotoxic symptoms. Both had only a slight retardation effect on terminal shoots, with more lateral branching. Na-Dikegulac brought about a 20 % increase of yield in the fourth season, while PP 528 caused a decrease by the same amount. Fruit maturation was advanced, especially by Dikegulac.
Tree spacing of the first plot was found unsuitable for standard mechanical cultivation or harvest, and raised problems of density and shade within the multishoot system.
A second plot was planted in 1978, where spacing expanded to 2 x 1 – 1.25 m, with 4000 – 5000 trees per hectare. Potted seedlings were planted in spring or autumn in the plot, and should be budded after about 6 months. Within 2 years