Effect of spray volume and time of NAA application on fruit size and cropping of Redchief 'Delicious' apple

The effect of naphthaleneacetic acid (NAA) thinning sprays on fruit size of Redchief 'Delicious' apple was studied in relation to spray application volume and time of application. A constant dose of NAA resulted in similar fruit size at harvest when applied in varying spray volumes from high (near full retention, V-x) to V-x/8. NAA applied as a high volume spray (15 mg l(-1)) at various stages of fruit development (4.6 to 22.5 mm king fruit diameter, KFD), indicated that the maximum amount of small fruit was produced following applications at about 11 mm KFD. NAA did not consistently affect growth rate of king fruit immediately after treatment when fruit competition was minimized. NAA reduced fruit size at harvest by about 11% when two competing fruits were present on the same spur, but did not significantly reduce fruit size when a single fruit was permitted to develop per spur.