REDUCING SPRAY VOLUMES AND DOSAGES ON CONVENTIONAL AIRBLAST ORCHARD SPRAYERS USING LOW-VOLUME NOZZLE SYSTEMS

Low volume, fine-droplet hollow cone (HC) Delavan nozzles were fitted to a conventional airblast machine in an attempt to reduce both the vo lume of spray and the dosage of chemical to thin apples. Red 'Deliciou s' trees at the Grove Research Station in southern Tasmania were thinn ed with ethephon at full bloom and the post-bloom thinner 6-benzyladen ine at 20 days after full bloom. An unthinned control was compared wit h a treatment hand-thinned at 20 days after full bloom and chemically thinned treatments. The chemical sprays were applied with an airblast sprayer at high volume using conventional nozzles or Delavan HC nozzle s at 50, 100, 200, 400 or 800 L/ha at 50, 75 or 100% of the dosage use d at high volume. Most chemical treatments had some effect on the para meters measured when compared with the unthinned control while some we re as effective as the hand-thinned treatment. The most consistent tre atments were at 200 L/ha at the 75 and 100% dosages. Higher or lower v olumes tended to be less effective, however, this could have been caus ed by either spray drift or evaporation of the smaller droplets used a t these volumes. Although reducing the dosage to 75% did not reduce th inning effects, reduction of dosage to 50% resulted in significantly l ess thinning. These results offer a breakthrough for many orchardists to convert to low volume spray application very economically using the Delavan HC nozzles which produce a better droplet size than tradition al high volume hydraulic nozzles. It also offers possibilities to sign ificantly lower chemical usage by reducing dosage of chemical applied per hectare. Even more important is the reduction of wastage and pollu tion.