Results obtained on the efficacy of 6-BA alone, and in combination with other thinning agents from different apple producing areas of Northern Italy

The thinning efficacy of 6-BA alone, and in combination with other chemicals, relating to fruit size and climate conditions, was investigated in different apple producing areas of Northern Italy. In two different areas of the Emilia-Romagna region (Bologna and Ferrara), 150 ppm of 6-BA alone, and in combination with Carbaryl or NAA, were applied to fruits at different phenological stages (12 to 14 mm of the king fruit diameter) on “Galaxy” and “Fuji” orchards. In the Piedmont region (Cuneo district area), 150 ppm of 6-BA alone, and in combination with Carbaryl, NAD or Ethephon, were applied to three cultivars (Schniga Schnitzer, Nagafu 6 and Scarlet) at different phenological stages, namely between 12.7 and 14 mm of the king fruit’s diameter. During the growing season, and at the time of application, the minimum and maximum temperatures were monitored daily. The number of flower clusters at full bloom, fruitlets at fruit set, and fruits before and after the June drop, were assessed. At harvest, the productive performance, (fruit number, fresh weight and the distribution of fruit in the commercial size classes) was measured. During the trial performed in the Bologna district area, the biometric (diameter and length), and the quality parameters (fresh weight, soluble solid content, flesh firmness and starch), were also measured at harvest. The thinning efficacy of 6-BA alone, and in combination with other chemicals, appeared to relate more to king fruit size than to climate conditions. Moreover, 6-BA alone induced similar thinning efficacy, comparable to “Standard thinning” methods, on “Gala” and “Fuji”, when king fruit diameter and climate conditions were appropriate. The efficacy of the chemicals tested alone, and in combination, with the exception of Carbaryl, produced results which were more dependent upon the time of application rather than the climatic conditions.