Main content area

Evaluating the use of NAA to thin 'Barouni' olives in the "on" year to increase fruit size and decrease alternate bearing under South African conditions

Crous, J. J., Schmeisser, M., Steyn, W. J.
Acta horticulturae 2014 no.1057 pp. 81-87
alternate bearing, cultivars, flowering, fruit quality, fruit set, naphthaleneacetic acid, olives, prices, trees, California, South Africa
High fruit set in an “on” season decreases olive flower initiation, resulting in a subsequent “off” season with little fruit. Early fruit thinning in an “on” season with naphthalene acetic acid (NAA) is used to reduce fruit numbers and increase fruit size in the current “on” season, and to ensure adequate fruit numbers in what otherwise would have become the subsequent “off” season. However, NAA has not been used for olive thinning in South Africa and the effective concentrations for local conditions and cultivars are not known. ‘Barouni’ olives are grown for table purposes only and therefore fruit size is the main fruit quality parameter. In this study, NAA was applied to ‘Barouni’ trees at 100, 150 and 200 mg L-1 in the 2007/08 season. NAA on average decreased the estimated total fruit number by 19.1% and reduced yield by 11.8%. The decrease in fruit numbers resulted in a significant increase in fruit size – the percentage fruit in the jumbo (>5.4 g) category was 9.9% higher compared to the control. Although there was no differential payment according to fruit size in the 2007/2008 season, the increase in fruit size is important since larger ‘Barouni’ olives generally sell for higher prices. Despite a significant decrease in yield and increase in fruit size compared to the control, the subsequent “off” season yield (2008/09) was not affected by any of the treatments. This was probably due to the mild thinning effect of the NAA concentrations evaluated. It appears that effective NAA concentrations for optimal thinning of ‘Barouni’ under South African conditions might be higher compared to optimal concentrations (120-150 mg L-1) used in California.