Leaves and twig sections of boxwood infected with Calonectria pseudonaviculata were incubated in sand at two moisture levels (36% [carrying capacity] and 5% water [vol/vol]) and at five temperatures (-10, 0, 10, 20, and 30°C). Percent sporulation from monthly tissue samples plated on glucose yeast-extract tyrosine media declined to zero after 5 months at 30°C and after 7 months at -10°C. At 0, 10, and 20°C, sporulation was observed through 30 months. Statistical analysis of data collected over 16 months of sampling showed a significant effect for temperature in all sample types, with maximum survival at 10°C. For discrete microsclerotia grown on cellophane sheets, sporulation was not observed after 2 months at 30°C or after7 months at -10°C. At all other temperatures, they continued to germinate over the 30 months of sampling. Statistical analysis showed significant effects for temperature and moisture level, with maximum survival at 0°C in moist soil over 16 months. These results suggest that extremes of heat and cold will kill the pathogen in plant debris but, at moderate temperatures, it will remain in soil for long periods, making replanting in affected sites in well-moderated climates difficult.