Evaluation of the distribution of spray deposits within a vine canopy from measurements on artificial targets and real leaves

Understanding the distribution of intercepted spray deposits is important for the study of the dose-response relationship of spraying a targeted pathogen and for the optimisation of the spraying process. However, carrying out exhaustive measurements of canopy spray deposits is difficult, particularly in production situations. This new experimental method for use in commercial vineyards was based on the installation of artificial targets (PVC collectors) within the canopy. To evaluate the quality of this experimental method for estimating the statistical distribution of deposition it was compared to an intensive manual method of foliar deposition measurements on real leaves. Intercepted deposition data on the real leaves and artificial targets were collected in a regular grid pattern within 12 non-contiguous vegetation sections. The results showed that although the means were similar, the variance in deposition appeared to differ between the distributions on artificial targets and real foliage, with CV values of between 37.4-52.7 % and 69.4-80.5 % respectively. Therefore, any central statistics must be supplemented with a statistical distribution analysis to account for the dispersion of deposition values within the vegetation. The results from comparisons between the cumulative distributions of intercepted deposition on the real leaves and on the PVC collector sections showed that the deposition estimates averaged over three-vine sections gave relevant, repeatable estimates for both approaches. The results also showed that for low deposition values, the experimental method led to a correct estimation of deposition on real leaves. However, above 230 ng dm2 per 1 g/ha, the experimental method underestimated the deposition on real leaves by 13.6 %. Using these methodological results, it may be possible to develop models capable of predicting the distribution of deposition within the plant canopy. It would thereby be possible to develop an approach for variable-rate sprayer control that takes into account the phytosanitary risk and the site-specific variable structure of the vegetation during the season.

Automated summary

This study compared an experimental method using artificial targets (PVC collectors) in the canopy with a manual method of foliar deposition measurements on real leaves. The results showed differences in the variance of deposition between the artificial targets and real foliage, highlighting the need for statistical distribution analysis.