Effects of ethephon on macadamia racemes

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Abstract
Ethephon sprays applied to Macadamia integrifolia trees caused the abortion of elongating racemes. The critical concentration of ethephon for early raceme damage was between 400 and 800 mg l−1. Dormant racemes were less sensitive, and rapidly elongating racemes more sensitive to ethephon damage. Raceme and floret death and abscission occurred between two and five weeks after application, and a second flush of racemes subsequently occurred four to seven weeks after application. The final numbers of racemes produced were similar, regardless of ethephon concentration. Initial nut set was reduced but more nuts were set on later racemes. Final nut set and yield were unaffected by ethephon treatments. This apparent compensating mechanism may have practical application in crop management strategies.