ENHANCING ABSCISSION OF MATURE MACADAMIA NUTS WITH ETHEPHON

The effect of (2-chloroethyl)phosphoric acid (ethephon) on the absciss ion of mature 'Beaumont' macadamia nuts (Macadamia integrifolia x M. t erraphylla) was investigated in two experiments. In 1988, 6-year-old t rees were treated with 200 or 400 mg/litre of ethephon, with and witho ut pH neutralisation or a surfactant, 2 weeks after nut maturity. Nut abscission increased from 6% on untreated trees to a maximum of 87% on trees treated with a 400 mg/litre neutralised solution of ethephon wh ich included a surfactant. Trees treated with 400 mg/litre ethephon sp rays showed a large but nonsignificant reduction in yield in the follo wing season. A second experiment in 1990 determined the effects of thr ee ethephon rates (400, 500, and 600 mg/litre) applied on three separa te dates (nut maturity, nut maturity + 2 weeks, and nut maturity + 4 w eeks). In this study 70% of nuts abscissed after the final application compared to only 7% on untreated trees. However ethephon applied 2 or 4 weeks after the nuts matured caused significant flower damage and c rop loss in the following season. Despite the enhancement of abscissio n rates, ethephon cannot be recommended for application to 'Beaumont' macadamia trees in New Zealand because of the loss of subsequent yield s.