A model of vegetative flush development and its potential use managing macadamia ('Macadamia integrifolia') tree canopies

We examined the relationship between shoot growth and temperature and solar radiation in macadamia ('Macadamia integrifolia' Maiden and Betche, M. 'integrifolia X tetraphylla' Johnson) as an aid to developing pruning strategies for this crop. Trees growing at Alstonville (28.9°S) in northern NSW, Australia, were pruned at various times to promote vegetative flushing under a range of environmental conditions. Flush development in macadamia is cyclic: bud release and stem elongation followed by a period of dormancy, before bud release of the subsequent flush. The rate of bud release after pruning was best correlated with the product of the mean temperature and solar radiation (r² = 0.75, P < 0.0001), whereas the rate of flush development was best correlated with the mean temperature (r² = 0.76, P < 0.0001). The number of buds released per pruned stem was greater under higher temperatures and solar radiation (r² = 0.37, P < 0.001), but the length of the flush after pruning decreased with increasing temperatures (r² = 0.32, P < 0.01). The descriptive models were combined with long-term weather data to predict the duration and characteristics of flushes following pruning at various times of the year along Australia’s eastern seaboard, from Mareeba (17.0°S) to Coffs Harbour (30.38°S). Flush duration and stem length following June pruning were predicted to be greater than following early autumn or September pruning and to vary from year to year, and with location (latitude). We discuss the implications of the model predictions for productivity and propose pruning times intended to optimise flowering and yield. Further research is required to test these proposed pruning strategies.