THE EFFECT OF HYDROGEN CYANAMIDE (DORMEX) ON FLOWERING AND CROPPING OF DIFFERENT APPLE CULTIVARS UNDER TROPICAL CONDITIONS OF SUBOPTIMAL WINTER CHILLING

The effects of pre-bud-break application of 1.5% hydrogen cyanamide (3% Dormer) on the flowering and cropping of 12 apple cultivars were determined over the years 1988/89 to 1991/92 in tropical Zimbabwe, at a site with less than 300 h of winter chilling below 7.2 degrees C per year. Control trees, other than those of 'Mutsu' and 'Goldjon' which were indistinguishable from the treated trees, showed varying degrees of delayed flowering and low yield in comparison with the cyanamide-treated trees. The latter, irrespective of cultivar, attained full bloom within 4-5 weeks of the common date of treatment, so that blossoming of the different cultivars, as well as that of the different trees of each cultivar, was synchronized, and all cropped heavily in relation to tree size. Very satisfactory yields of 'Mollies Delicious', 'Canvada', 'Drakenstein', 'Golden Delicious', 'NJ46', 'Marjorie Pye', 'Spartan', 'Starking', 'Granny Smith' and 'Ohinemuri' were thus obtained by the use of cyanamide in an environment otherwise unsuitable for them, especially for the later cultivars on this list.