Tree protection covers affects microclimate, leaf structural properties and the suitability of leaf wetness sensors to monitor surface wetness in cherry

Surface wetness (SW) is a particularly relevant variable for plant growers as it is related to the incidence of microbial and fungal diseases, as well as to fruit cracking, especially in susceptible species (e.g. Prunus avium). Although knowledge of SW quantity and duration is key to discern and predict its impact on plant health status, monitoring of this variable is still based on sensors of which the output is a simple electrical voltage, rather than a water amount. Furthermore, the intrinsic heterogeneity of canopy conditions seems to play a major role on leaf microclimate and SW.

The presented study analyzes i) the effects of radiative conditions (also affected by the presence of a rain exclusion covers) on the main structural factors affecting SW and SW duration on cherry leaves and ii) the ability of a Leaf Wetness capacitive Sensors (LWS) to represent SW on real leaves. Cherry leaves grown under 4 different environmental conditions (sunlit/shaded x covered/uncovered) were simultaneously artificially wetted to various degrees and their surface water content measured immediately or after variable drying times. The leaf growing conditions appeared to be strongly associated to some leaf structural properties, such as leaf angle, in turn influencing the SW amount and duration. Concerning the LWS, their output signal was first calibrated in respect to their actual SW. Following, the LWS ability to represent the nearby real leaves SW was analyzed. The ability of the LWS to represent real leaves largely depended on the growing conditions of the latter, highlighting the limitations related to using a single sensor type to represent canopy parts affected by intrinsic ecophysiological plasticity. The present analysis provides key findings to support assessments of microclimate, SW, SW duration and its variability on fruit trees, and in particular on cherry.

The study was funded by the PRIN CHOICE project (Optimizing CHerry physiOlogIcal performanCE through the correct choice of multifunctional covers).