Control of tree size and vigour in custard apple (Annona spp. hybrid) cv. African Pride in subtropical Australia

Five methods of controlling tree size, viz. growth retardant (foliar-sprayed and trunk-injected paclobutrazol), root-restriction bags, cherimoya rootstock and sugar apple (Annona squamosa) interstock, were evaluated for their effects on growth, yield and fruit quality of custard apple (Annona spp. hybrid cv. African Pride) in subtropical Australia. Compared with trees on their own roots, sugar apple interstock was highly effective in dwarfing 'African Pride' trees, reducing tree canopy volume by 72-90%. Root-restriction bags (woven fibreglass) proved to be only partially effective in controlling tree size due to growth of major roots through the seams. Compared with trees on their own roots, cherimoya rootstock alone, and sugar apple interstock increased fruit weight per unit canopy volume by a maximum of 3- and 5-fold, respectively. Sugar apple interstock reduced the severity of fruit disorders 'woodiness' and 'brown pulp' by about 75 and 50%, respectively.