Optimising crop load and fruit quality of 'Packham's Triumph' pear with ammonium thiosulfate, ethephon and 6-benzyladenine

Trials were conducted at Nubeena in Tasmania (Australia) over a two year period to develop chemical thinning programs for the European pear cultivar ‘Packham’s Triumph’ and to assess the impact of thinning chemicals on fruit quality. Chemicals examined were 80 mgL⁻¹ ethephon and 1.0% v/v ammonium thiosulphate (ATS) applied during the bloom period, and 6-benzyladenine (BA) applied at 100 or 150 mgL⁻¹ from 10 to 40 days after full bloom (dAFB). The desiccating agent ATS was an effective bloom thinner, and two applications at 25% and 80% bloom stage would be recommended. The post-bloom thinner BA was a consistent thinner of ‘Packham’s Triumph’, and can be applied as early as 10 dAFB to as late as 40 dAFB as a post-bloom thinner after a bloom application of either ethephon or ATS. BA was also an effective thinner when used alone. Two applications of BA did not increase the thinning effect. All chemicals examined maintained or improved fruit quality measured as size, flesh firmness and total soluble solids content, but ATS caused a slight increase in skin russet. BA ameliorated the russeting effect of ATS.