Comparison of the biological effectiveness of controlled droplet application sprayers and high-volume sprayers in thinning apple trees

Abstract

SummaryTwo trials at the Grove Research Station in southern Tasmania compared the thinning effects of high (HV), low (LV) and ultra low volume (ULV) sprays. A “Micron” sprayer applying 25, 50, 100 and 200 1 ha−1 was compared with HV spray application of 6 000 1 ha−1 of ethephon at 300 mg l−1 on mature red ‘Delicious’ trees. A similar comparison was made using a “Micronair” sprayer in applying NAA to ‘Golden Delicious’ trees at 10 mg l−1. In all cases the LV and ULV sprays were equilibrated to apply the same dosage of chemical per hectare to that applied at H V. All sprays removed significantly more fruit when compared with unsprayed controls. There was no consistent or wide ranging differences in thinning effects between HV and LV or ULV sprays. In the “Micron” trial using ethephon on red ‘Delicious’ the thinning effects were reflected in better mean fruit weight and to a lesser extent increased fruit size. In the “Micronair” trial using NAA on ‘Golden Delicious’, a late spray of NAA produced pygmy fruit ...