A COMPARISON OF AIR-SHEAR AND ELECTROSTATIC SPRAY TECHNOLOGY WITH A CONVENTIONAL AIR-BLAST SPRAYER TO THIN APPLES

Red Delicious apple trees at Spreyton in northwest Tasmania were thinn ed with ethephon using an air-shear-electrostatic sprayer (low volume: 100 or 200 L/ha with or without electrostatics) or a commercial air-b last sprayer (high volume: 2000 or 4000 L/ha). Treatments were applied at 2 and 10 days after full bloom. Also included were an unsprayed co ntrol and a hand-thinned treatment (15-20 days after full bloom). Carb aryl + Thiram was also applied 3 times (20, 32 and 40 days after full bloom) using the same spray treatments. All dosage rates were equilibr ated to apply the same amount of active ingredient/ha. The spray treat ments thinned fruit more than the controls when compared for fruit num ber and all size variables measured except percentage of fruit greater -than-or-equal-to 80 mm. There were significant differences for fruit number between the hand-thinned, 4000 L/ha high volume and 200 L/ha ai r-shear treatments, and all the remaining treatments. This applied to both total numbers of fruit set or numbers of fruit hand-thinned at 80 -90 days after full bloom. This late hand-thinning had the effect of e vening up the fruit size but the control still had significantly small er fruit than all the other treatments due to the larger number of fru it carried through to hand-thinning.