The black spot disease already appeared on all oligochitosan-treated pear fruit after inoculation 120 h. Relatively, the IC50 of chitosan and oligochitosan on disease incidence caused by P. piricola was respectively, 1.57 and 7.47 g/L after inoculation 96 h, while 2.05 and 8.79 g/L after inoculation 120 h (Table 3). Therefore, compare to oligochitosan, chitosan was more effective on disease control, especially to that caused by P. piricola.