Efforts to understand and improve crop load of 'Hass' avocado

Avocado (Persea americana Mill.) yields are low compared to other fruit crops, commonly less than 10 t ha-1 in Australia, prompting our research into improving productivity through understanding and improving crop load capacity. When we removed varying percentages of inflorescences on 3-year-old ‘Hass’ trees in a trial at Childers, central Queensland, Australia, we found clear relationships between number of inflorescences and yield, yield and vegetative growth, as well as yield and fruit size. In a second trial, we removed the whole or part of the vegetative tip of indeterminate inflorescences on 3-(then 4-)year-old ‘Hass’ trees to reduce vegetative competition with fruit growth. Spring fruit set increased in these tipping treatments in one of two years of the trial, but final fruit set did not differ from the control in either year. In the same trial, foliar application of “Cytolin” (®Sumitomo Chemicals, 19 g L-1 6-benzyladenine and 19 g L-1 gibberellins4+7) at the end of the extension of the spring flush to increase increasing axillary branching and thus fruiting sites, increased the total length of summer vegetative growth of shoots but not branchin