Removal of Off-Season Inflorescences Improves Fruit Retention, Kernel Quality, and Source–Sink Balance in Macadamia ‘O.C’

The effects of removing off-season inflorescences on retained fruit performance and whole-tree yield in macadamia remain insufficiently understood. To assess whether flower-removal timing influences reproductive and fruit development, we evaluated five treatments in seed-propagated macadamia trees using a randomized complete block design with five blocks and 25 trees. At the beginning of full bloom, all inflorescences of the designated October, January, February, or March flowering flush were manually removed from the whole tree; control trees received no flower removal. We measured the persistence of fruit-bearing tagged inflorescences, individual fruit growth, kernel traits, whole-tree yield, and leaf and branch carbohydrate status. Compared with the control, October flower removal increased the percentage of fruit-bearing tagged inflorescences before harvest from 12.9% to 18.3% (a 41.9% relative increase) and reduced their relative loss from 81.1% to 69.2% (an 11.9 percentage-point difference). These percentages describe inflorescence-level retention rather than flower-level fruit set. Individual fruit fresh weight at 180 days after flowering increased from 20.1 to 25.5 g, and kernel dry weight increased from 1.48 to 1.73 g. However, mean whole-tree fresh fruit yield with green husk was 35.98 kg tree−1 under October flower removal, compared with 54.75 kg tree−1 in the control (34.28% lower). By comparing removal of four flowering flushes, this study shows that favorable responses in retained inflorescences and sampled fruits do not necessarily translate into higher whole-tree yield. Flower removal also altered leaf and branch carbohydrate status, but these measurements do not demonstrate that carbohydrate competition caused the observed reproductive responses.