To assess the potential impact and control options for Monilinia fructicola, the alien stone fruit pathogen in Croatia, development of pre-harvest and post-harvest brown rot was monitored during 2014 and 2015 in a peach orchard where integrated pest management measures are implemented. Two experimental locations, A (younger part of the orchard with a lower elevation) and B (older part with higher elevation) were established, and conditions for infection were monitored using a forecast model for M. fructicola with PinovaSoft ® application. In 2014, symptoms of brown rot in the field were recorded only on fruits at location B, with 6.6% incidence. Monilinia spp. developed on 92.6% of stored fruits from location A and on 20.3% of stored fruits from location B. Out of 40 isolates collected from the fruits at the moment of harvest, 27% were M. fructicola, 30% were Monilinia laxa, and 43% were Monilinia fructigena. Similar percentages of three Monilinia species were determined on stored fruits. In 2015, no fruits affected with brown rot were found at the moment of harvest, but only after 21 days of storage and only on fruits from location B, with low incidence (8% fruits). M. fructicola was found on all fruits with brown rot symptoms, while M. laxa and M. fructigena were detected only on three fruits in mixed infections with M. fructicola. Despite differences in brown rot incidence between years, forecast model recorded seven infections with M. fructicola during the vegetation period in 2014 and 15 infections in 2015. Th e results are indicating that common measures against indigenous M. laxa and M. fructigena may be suitable for the control of invasive M. fructicola, and that all three Monilinia species on peach in Croatia can occur in mixed populations.