The simulation of pear scab (Venturia pirina) infection periods and epidemics under field conditions

The epidemics of Venturia pirina (Aderh.) observed in 1994, 1996 and 1997 were compared. When the winter was cold and rainy the onset of V. pirina epidemics was earlier in season and disease intensity reached the highest levels. In warm and less rainy winters the onset of epidemics was later and epidemics were less extensive probably due to a late activity of pathosystem. The V. pirina epidemic dynamic was measured by incidence on pears. The disease incidence reached 94% of pears on 12 July 1994, 65% on 25 August 1996 (harvest) and 100% on 11 July 1997. The number of infection periods (IP) was calculated using the scab infection model (SIM). In 1996, 9 IP were monitored and in 1997, 24 TP. The theoretical incidence threshold of V. pirina on pears calculated by SIM for each infection period was probably around 25% under field conditions and it is the most significant result of the model.