van Zyl J.G., Sieverding E.G., Viljoen D.J., Fourie P.H.
Department of Plant Pathology, Stellenbosch University, Private Bag X1, Stellenbosch 7602, South Africa; Citrus Research International, P.O. Box 28, Nelspruit, South Africa; Evonik Africa (Pty) Ltd, P.O. Box 3739, Somerset West 7129, South Africa; Evonik Industries AG, Goldschmidtstraße 100, 45127 Essen, Germany
van Zyl, J.G., Department of Plant Pathology, Stellenbosch University, Private Bag X1, Stellenbosch 7602, South Africa, Citrus Research International, P.O. Box 28, Nelspruit, South Africa; Sieverding, E.G., Evonik Industries AG, Goldschmidtstraße 100, 45127 Essen, Germany; Viljoen, D.J., Evonik Africa (Pty) Ltd, P.O. Box 3739, Somerset West 7129, South Africa; Fourie, P.H., Department of Plant Pathology, Stellenbosch University, Private Bag X1, Stellenbosch 7602, South Africa, Citrus Research International, P.O. Box 28, Nelspruit, South Africa
van Zyl, J.G., Sieverding, E.G., Viljoen, D.J., Fourie, P.H., 2014. Evaluation of two organosilicone adjuvants atreduced foliar spray volumes in South African citrus orchards of different canopy densities Crop Protection 00:0000-0000.Citrus producers in South Africa generally use high spray volumes (6000 to 16,000lha-1) to control pests and diseases adequately for the fresh fruit market. In order to study the benefit of organosilicone adjuvants at reduced spray volumes, trials were conducted with two organo tri-siloxane adjuvants. Two separate spray trials were conducted in the Western and Eastern Cape provinces of South Africa in uniform navel orange orchards. Break-Thru S240 (super-spreader) and Break-Thru Union (spreader-sticker), at recommended dosages per hectare (300mlha-1, respectively), were sprayed separately in combination with a yellow fluorescent pigment (1mll-1) at a high (20l tree-1≈9600 to 12,100lha-1, depending on tree and inter-row spacing), medium (14l tree-1≈6500 to 8500lha-1) and low (8l tree-1≈3700 to 4800lha-1) spray application volumes. Sprays consisting of the fluorescent pigment in water alone were used as control treatments. Trees were sprayed from both sides with a commercial multi-fan tower sprayer (BSF-Multiwing) at a constant tractor speed (2.4kmh-1) and spray pressure (1500kPa). The different spray volumes were achieved by using different spray nozzles (TeeJet Disc-Core type; full and hollow cone nozzles D3-DC56/46, D4-DC56/46, D5-DC56/46). Leaves were sampled from six canopy positions (inner and outer canopy position at bottom, middle and top of the tree). Deposition quantity and quality of fluorescent pigment were determined on upper and lower leaf surfaces using fluorometry, digital photomacrography and image analyses. Spray uniformity and efficiency were also compared among treatments. Deposition quantity generally increased with increasing spray volume, but normalised values showed better spray efficiency at lower volumes. In pruned and less dense canopies, a beneficial effect of adjuvants was observed in terms of deposition quantity, efficiency and uniformity, especially at reduced volume applications (14l tree-1) on the inside and outside of the canopy. Little improvement in deposition quality was generally observed with the use of adjuvants. These benefits were not as evident in very dense canopies, illustrating the importance of canopy management when spraying at reduced volumes. Data obtained from the study is valuable for future improvement in spray application methodology in South Africa and other developing countries. © 2014 Elsevier Ltd.