PLANT-GROWTH REGULATORS CANNOT BE USED TO ALTER SIGNIFICANTLY THE COMMERCIAL HARVEST DATE OF BORONIA-HETEROPHYLLA F MUELL. (RUTACEAE)

Harvest of the cut flower crop, Boronia heterophylla F. Muell., is res tricted to a 2-week period in early spring. Extension of the flowering period by plant growth regulators was examined in plants growing in t he field under standard, commercial production conditions. Flowering t ime, and hence harvest date, were delayed by 6-9 days following the ap plication of gibberellic acid and benzyl adenine (GA(4+7)+BA). High co ncentrations of GA(4+7)+BA (40, 80 mg/L) delayed flowering longer than 20 mg/L, but reduced flower number. BA alone (4 applications of 20, 5 0, or 100 mg/L) reduced flower number and did not affect harvest date. GA(3) (4 applications of 20 mg/L) prevented flowering. Paclobutrazol (100 mg/L) reduced flower number and delayed flowering by 4 days. The timing of applications at the commencement of flower-promoting conditi ons, when plants had been exposed to 10-20 nights of temperatures <10 degrees C (mid autumn), appeared to be critical. A delay of harvest of 6 days is a 40% extension of the harvest period but this may not be s ufficient for commercial production.