Preliminary tests were carried out using ammonium thiosulphate as a chemical thinning agent for apple ('Cox's Orange Pippin' and 'Braeburn') blossoms. Ethephon and NAA (1-napthylacetic acid) were included for comparison. Whole tree sprays of 37g/l ammonium thiosulphate over-thinned 'Cox's Orange Pippin' blossoms and severely scorched blossoms, foliage, and apical meristems. Ethephon at 0.35 g/l also over-thinned, and NAA thinned to an intermediate extent when compared with the controls. When the lower concentration of 3.7 g/l ammonium thiosulphate was directly applied to stamens and styles of 'Braeburn' blossoms by brush, initial fruit set was only 30% that of untreated blossoms. When 0.35 g/I ethephon was directly applied by brush to spur leaves or petals of 'Braeburn' blossoms at pink bud, initial fruit set was only 23% that of untreated blossoms. lt is concluded that ammonium thiosulphate has the potential to thin apple blossoms. Further experiments to define optimum concentrations and spray volumes are needed.

. The growth retardants paclobutrazol (3-[(4-chlorophenyl)methyl]-a-(1,1-dimethylethyl)-IH-1,2,4-triazole-l-ethanol)and RSW 0411 ((3-(cyclohexyl methylene)-a-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol) were tested on two-year-old trees of Granny Smith and Fuji apple . RSW 0411 at 100 mg/L did not cause any growth reduction in Granny Smith, while 500 and 1000 mg/L significantly reduced growth below that of the control between 27 and 40 days after application . Paclobutrazol at 100 mg/L had a small effect on growth of Granny Smith shoots ; however 500 mg/L significantly reduced shoot growth between 27 and 55 days after application, and 1000 mg/L reduced shoot growth between 27 and 82 days after application . By 100 days after application, there were no longer differences between treatments . Shoot growth on Fuji trees was reduced below that of the control as follows : between 14 and 27 days following a single application of 500 mg/L RSW 0411 ; between 27 and 55 days following two applications ; between 14 and 72 days following three applications ; and between 14 and 82 days following four applications . Treatments were applied 14 days apart . Paclobutrazol was a more active growth retardant than RSW 0411 at the same rate, and the growth-retarding effects of RSW 0411 were short-lived .In recent years, trees in many New Zealand apple orchards have been planted intensively ; 3-5 m between rows and 1-3 m within rows . In Europe, most trees at these spacings are planted on the dwarfing M 9 or M 26 rootstocks ; however, in New Zealand, trees continue to be planted on the semi-dwarfing MM 106 rootstock .Growers and advisors thought that height and spread of trees on MM 106, at close spacings, would be adequately controlled through early cropping . How-

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