Assessment of a mathematical model to predict spray deposition under laboratory track spraying conditions. II: Examination with further plant species and diluted formulations

Abstract

AbstractMean spray depositions onto leaves of five plant species (Zea mays L., Vicia faba L., Sinapsis alba L., Glycine max (L.) Merr, Vitis vinifera L.) were measured following spraying of an array of 36 solutions of acetone + aqueous “Triton X‐100” varying systematically in composition and properties. The spraying was carried out on five occasions using a standard laboratory track sprayer delivering the equivalent of 600 litre ha−1 onto a plane surface around plant height. The results, plotted as response surfaces, showed that there was little variation in spray deposition with solution composition for V. vinifera, there were some slight decreases in deposition with increase in “Triton X‐100” concentration on V. faba and S. alba, though not with increase in acetone concentration, and that there were slight systematic increases for G. max and large systematic increases for Z. mays with increase in acetone and “Triton X‐100” up to concentrations of 350 ml litre−1 and 0.5 g litre−1 respectively. At higher concentrations of these components, there were no further increases in deposition on these latter species.The results were in agreement with those predicted by a mathematical model derived previously, with the exception of the slight decreases in deposition on V.fana and S.alba and smaller increases in deposition than predicted on G.max. The decreases in deposition on the former species were attributed to slight run‐off from their easy‐to‐wet leaves at the higher “Triton X‐100” concentrations at the spray volume rate (600 litre ha−1) used. The poor fit of the observed and predicted spray depositions on G. max was attributed to the nature of its leaves. These are hairy and it is speculated that the fine hairs, rather than the true leaf surface, played a major role in capturing the small spray drops (115‐130 μm) created by the laboratory sprayer used in this work.The observed and predicted spray depositions with a set of diluted commercial‐type formulations were in good agreement for Setaria viridis (L.) Beauv., Pisum sativum L., Z. mays, with correlation coefficients (r) of 0.985, 0.988 and 0.935 respectively, and also for the more constant depositions on the easy‐to‐wet species Beta vulgaris L., but slightly less so for Triticum aestivum L. (r = 0.886) in this test. Overall the model was well‐behaved, giving a good prediction of the variation in spray deposition on leaves of a range of plant species, provided that these were not extensively hairy, with variation in the dynamic surface tension of the spray solution.