Effects of temperature on premature nut drop in macadamia

Abstract

Five-year-old Macadamia integrifolia (cultivars Keauhou, Keaau and Kau) trees in pots were grown in a controlled environment for 10 weeks after nut set. High temperatures of (a) 30 and 35 deg C, compared with (b) 20 and 25 deg , induced a larger number of nuts to drop early. After the initial nut drop period, temperature maintained at, or returned to 25 deg , resulted in little additional nut drop. When temperatures at (b) were increased to 25 and 30 deg , respectively, further nut drop occurred. When the temperature was increased from 30 to 35 deg , the rate of drop was intermediate between treatments (a) and (b). It is suggested that 30 deg might be critical in promoting unacceptable levels of nut drop. By avoiding extreme day temperatures, the proportion of the potential crop which is lost through premature nut drop may be reduced.