Chemical Thinning of Loquat with Naphthalene Acetic Acid

Loquat ( Eriobotrya japonica ) belongs to the subfamily Pomoideae, and is an evergreen fruit tree which blooms in fall. Its inflorescence is a panicle. To attain commercial fruit size fruit thinning is done by hand. A chemical thinning trial was performed during the 1999-2000 growing season in Peumo, Cachapoal County, Sixth Region, Chile. Sixteen-year-old `Golden Nugget' loquat trees were treated with naphthalene acetic acid (NAA) at rates of 70, 140, and 280 g·ha -1 (1.0, 2.0, and 4.0 oz/acre), split into two or three applications beginning at early fruit set followed with sprays, 13 and/or 28 days later. Each treatment was applied to four randomly selected trees. At harvest, fruit number was measured in four panicles per tree and in the whole tree. NAA produced a thinning effect closely related to dose, with the highest doses inducing both highest flower thinning and the largest size of the fruit, but the lowest yield per tree. Lower doses produced fruit size and yield similar to those of hand-thinned check trees. Fruit load, expressed as trunk cross sectional area (TCSA), reached 1.8 to 9.1 fruit/cm 2 TCSA (11.6 to 58.7 fruit/inch 2 TCSA) in treated trees in comparison to 20 fruit/cm 2 TCSA (121 fruit/inch 2 TCSA) of the nontreated trees. NAA treatments did not affect the number of seeds per fruit. Total dose of 140 g·ha -1 NAA was the most effective in reducing fruit number, whether split into two or three applications. Fruit development seemed to conform to a double sigmoid curve, with a high rate of growth during fall, a lower one through the winter, in order to recover the growth rate in spring until maturity.