Naturally growing apothecia of Monilinia fructicola were collected from two commercial plum orchards near Reedley and Sanger, both in Fresno County, California. Ascospore discharges from 90 (1996) and 86 (1997) apothecia were monitored individually using spore traps at four constant temperatures. The period of discharge decreased as temperature increased from 10 to 25°C. However, daily discharge increased as temperature increased from 10 to 15°C and remained high at 20 and 25°C. The greatest discharge occurred with apothecia at 15°C, followed by those incubated at 20, 10, and 25°C. The germination of ascospores of M. fructicola and the length of germ tubes increased as temperature increased from 7 to 15°C; however, increasing temperatures above 15°C did not increase either ascospore germination or length of germ tubes. This information may help in the development of warning systems and management strategies for brown rot blossom blight of stone fruits.