EFFECT OF CONCENTRATION, APPLICATION VOLUME AND ADDITION OF A SURFACTANT ON RESPONSE TO BENZYLADENINE AS THINNING AGENT IN 'WILLIAMS' PEARS

Benzyladenine (BA) is an effective thinning agent for ‘Williams’ pear, the most important cultivar in Argentina. The aims of this research were: to find the minimum effective BA rate for increasing fruit size in ‘Williams’ pear, and to improve application efficiency by modifying volume rate and adding a silicone surfactant. Trials were carried out over three seasons (2007-2010). In the two first seasons different rates were evaluated: 50, 100, 150 and 200 mg/L. Applications were made when fruit diameters were 10-12 mm. In the third season, two application volumes (450 and 1300 L/ha) and the addition of a silicone surfactant (Silwet^®) were evaluated with BA at a rate of 100 mg/L. Variables determined were: coverage percentage, fruit drop, fruit number per 100 flower clusters (fruit set), fruit number per branch cross sectional area, fruit number per tree, fruit weight and distribution of yield depending on fruit size. No significant differences between 150 and 200 mg/L BA were found. These treatments reduced fruit set by 20-40% and fruit number per tree by 10-35% compared to the control. At harvest, fruit weight was improved by 10-20%, yield of small fruit (diameter <65 mm) was reduced by 40-65% and the yield of large fruit (diameter >70mm) increased by 60-100%. The 100 mg/L BA rate was less effective with only 10-20% reduction in fruit set. At harvest, this treatment showed 5% higher fruit weight, 10% less yield of small fruit and up to 30% higher yield of large fruit. The lowest BA rate (50 mg/L) did not stimulate a thinning effect and/or increase fruit size at harvest. In the third season, the surfactant addition improved the percentage coverage and efficacy of BA on fruit size at harvest.