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

SummaryProhexadione-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 l–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 l–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.