Ethephon, NAA and NAD as chemical thinners of pear fruitlets

The thinning ability of Ethephon, NAA and NAD was tested on two pear cultivars (Conference and Rosada) in 1997 and 1998 at Caorle (NE Italy). Ethephon, NAA, and NAD were applied five and ten days after full bloom (DAFB). Chemicals were used at concentrations ranging between 200 – 800, 5 – 40, and 7.5 - 30 ppm for Ethephon, NAA, and NAD, respectively. The results showed that the tested chemicals display a varying ability in thinning pear fruitlets depending upon time of application, concentration and fruit load. The two cultivars showed different reactions to the chemicals, ‘Conference’ being the most sensitive. With ‘Rosada’, NAA at the tested concentrations underthinned, while Ethephon gave erratic results. NAD treatments at both spraying times were the most effective in reducing the fruitlet population with beneficial effects on fruit size at harvest. With ‘Conference’, all the chemicals showed the ability to promote fruit abscission at both spraying times, although the thinning effect varied according to chemical type and concentration, and fruit load