Abstract :
[en] A model predicting the spray droplet interception and retention by a single virtual plant has been developed. The
model was based on three main experimental inputs: the 3D architecture of a barley plant, the spray quality and
the droplet impact behavior. Two contrasted formulation scenarios, limits of the common range covered by
pesticide application in terms of surface tension, were tested by changing the droplet behavior at impact in the
model. Simulations were undertaken for studying the variability of spray retention resulting from spray quality,
applied volume and plant size for a difficult-to-treat target. Results showed that the spray retention efficiency
ranged from 6.8% to 96.6% of a theoretical full adhesion scenario, where all intercepted droplets were captured,
according to spray quality for the two formulation scenarios tested. Average retention increased with increasing
spray fineness, applied volume per hectare and plant size. Variability of deposits, evaluated using the coefficient
of variation of simulated retentions, was found to be a function of the mean droplet density according to
CV∝N^(-0.68), where CV is the coefficient of variation and N the number of droplet per square centimeter.
Variability was also found to be a function of the plant size according to a relation CV∝S^(-0.5), where S is the
total leaf area of the plant model. The variability of deposits increased with decreasing spray fineness, applied
volume per hectare and plant size because of the reduced number of droplets contributing to retention. Wetting
properties greatly influenced retention but surprisingly poorly influenced the variability of deposits. Such a
modeling approach that is capable of an independent investigation of the influence of various parameters on
spray retention can be used to improve understanding of application methods and adjuvants that could help
minimizing development of resistance in problematic weed species.
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