Abstract: Brown spot of pear (Pyrus communis) is a fungal disease caused by Stemphylium
vesicarium. This disease may result in high economical losses in several pear growing areas in Europe. Infection and necrosis occur on leaves and fruits. Infected fruits are unmarketable. It is assumed that the susceptibility of pear to S. vesicarium decreases with the physiological age of the fruit. In a series of trials, the influence of fruit age of ‘Conference’ pear on susceptibility and disease severity was evaluated in the orchard and laboratory. To this end, a method was developed to inoculate pears in the orchard. The results showed that pear fruits are most susceptibility within approximately the first 3 months after fruit set. However, these early infections do not result in decayed pears. However, shortly before harvest the pears are also susceptible to infection. These infections result in large lesions.