Keywords: carbaryl, NAA (naphthalenacetic acid), ethephon, promaline (GA4+7+benzyladenine), urea, fruit abscission.
The investigation was carried out in the Practice Fields of the Superior Technical School of Agricultural Engineers, Polytechnic University of Madrid in 1993, in an apple orchard of ‘Starkrimson’/M-26 and /MM-106 and ‘Golden Spur’/MM-111, at 10,000 and 13,000 tree·ha-1, respectively, using different products for the chemical thinning of fruits, and sprayed when the fruits had around 25 mm of diameter. The area of the trunk, height of the tree and number of vegetative shoots bigger than 10 cm of length, had a positive effect with the total number of fruits, number and weight of the commercial fruits per tree, as effect of the chemical thinning of fruits in the two apple cultivars. The maximum number of commercial fruits per tree and the maximum yield of the same quality of fruits, was bigger in ‘Starkrimson’, with the products ethephon (0.18 and 0.60 g·litro-1), carbaryl (2.55 g·litro-1) and urea (6 %); in ‘Golden Spur’ the products that induced the best results were NAA (16 mg·litro-1) and carbaryl (1.27 and 2.55 g·liter-1). The ethephon in the used concentration induced a high abscission of fruits. The reddest and uniform, less yellow colors and with smaller brightness in ‘Starkrimson’, were induced by the treatments with ethephon (0.30 g·liter-1) and hand thinning; in ‘Golden Spur’ the fruits from hand thinning and with ethephon, were with more yellow coloration of fruit peel and more brightness. The firmness of the pulp of the fruits, in ‘Starkrimson’ didn’t have effect by the chemical products; contrarily in ‘Golden Spur’, the control, hand thinning and NAA (16 mg·liter-1), were more consistent in relation to the fruits with ethephon (0.30 g·liter-1). The quantity of total soluble solids of the fruits (TSS; ºBrix) in ‘Starkrimson’ was higher only in the hand thinning, and in ‘Golden Spur’ the maximum of TSS was found it the fruits with hand thinning and with ethephon (0.18 g·liter-1); only in this cultivar the higher content of TSS was present in the commercial fruits (³65 mm of diameter).