Physical modeling of leaf wetness duration at the tree scale: considering leaf properties and tree architecture to estimate water interception

Fungal disease infection risk in fruit trees strongly depends on the climatic conditions in the orchard and on the microclimate within the tree. The Leaf Wetness Duration (LWD), i.e. the time that free water remains on leaves in relation to rain or dew events is for many fungal species the significant parameter linking the epidemic risk to environment humidity. Our goal is to provide a reliable LWD estimate model for plant protection decision support tools. Since LWD is the combination of two distinct phenomena: water interception and water evaporation, both have to be considered in the model's framework. Water interception is described by two main parameters: canopy gap fraction and leaf water storage capacity. They have been quantified in an experiment on 'McIntosh' apple trees in Quebec (Canada). The gap fraction was measured with a LIDAR detector, which allowed us to choose the desired complexity level of a 3D reconstruction of the canopy. Water storage capacity was measured in orchard on every type of leaf susceptible to apple scab. The obtained data are used to implement a water interception submodel aimed at improving LWD estimation in our physical model.