Reducing spray volumes and dosages on conventional airblast orchard sprayers using low volume nozzle systems

Abstract

Summary.Low volume, fine-droplet hollow cone (HC) Delavan nozzles were fitted to a conventional airblast machine in an attempt to reduce both the volume of spray and the dosage of chemical to thin apples. Red ‘Delicious’ trees at the Grove Research Station in southern Tasmania were thinned with ethephon at full bloom and the post-bloom thinner 6-benzyladenine at 20 days after full bloom. An unthinned control was compared with 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 nozzles at 50, 100, 200, 400 or 800 L/ha at 50, 75 or 100% of the dosage used at high volume. Most chemical treatments had some effect on the parameters measured when compared with the unthinned control while some were as effective as the hand-thinned treatment. The most consistent treatments were at 200 L/ha at the 75 and 100% dosages. Higher or lower volumes tended to be less effective, however, this could have been caused by either spray drift or evaporation of the smaller droplets used at these volumes. Although reducing the dosage to 75% did not reduce thinning effects, reduction of dosage to 50% resulted in significantly less 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 traditional high volume hydraulic nozzles. It also offers possibilities to significantly lower chemical usage by reducing dosage of chemical applied per hectare. Even more important is the reduction of wastage and pollution.