Inhibition of vegetative growth in red apple cultivars using prohexadione-calcium

Prohexadione-Ca (ProCa) has been evaluated as a growth inhibitor in the vigorous red apple cultivars 'Fuji' and 'Royal Gala'. Greatest inhibition of shoot growth was obtained when ProCa was first sprayed at about 200 mg 1 - 1 from full bloom (FB) up to 12 d after full bloom (DAFB). Shoot regrowth often occured later in the growing season, and a second application of ProCa was then needed to maintain growth inhibition. Inhibition of shoot growth was due mainly to a reduction in internode length. No effects on yield have been found, except for cv. 'Royal Gala', where an increase in crop-load and a decrease in fruit size were recorded. Fruit quality parameters were not affected; but, in cv. 'Fuji', the red colouration of fruit was promoted by ProCa, particularly when repeated sprays of the chemical (at 125 or 250 mg 1 - 1 ) were made. Changes in hue, chroma and lightness were recorded on both the blushed and shaded sides of fruit. No effects on fruit colour were seen in ProCa-treated cv. 'Royal Gala' trees.