The leaf wetness duration (LWD) is an important parameter to monitor the epidemiology of apple diseases, like apple scab, the most common disease of the crop. The regional climate and management conditions of the orchards are determinant factors for the occurrence of leaf wetness. And, depending on the canopy microclimate it is important to know the position with greater LWD, for use in forecasting models of disease. Few studies have evaluated LWD on apple orchards and none in the cropping conditions of southern Brazil, particularly in the producing region of Vacaria, in the state of Rio Grande do Sul, Brazil. This study aimed to characterize the spatial variation of LWD in canopies of apple trees in open sky and under hail net covering, in Vacaria, Brazil. The experiment was carried out in orchards of 'Royal Gala' apple cultivars, conducted in central leader with support (spacing 1m x 3m), being one in open sky and other under hail net. The LWD was monitored in the upper, middle and lower strata of the plant canopy. The LWD was higher in the lower part of the canopy in both apple orchards. Tendency to greater LWD in the covered orchard was observed for all strata of the canopy, with significant differences for the upper and middle strata of canopies. LWD values were more similar between portions of the canopy under hail net than in the open sky.
Malus domestica; wetness; diseases; microclimate
