Emergence times of deutogynes of the pear rust mite,Epitrimerus pyriNalepa, from overwintering sites on branches of pear,Pyrus communisL., were compared between laboratory-stored (constant 1°C)and field-wintered branches at 2–4-wk intervals over 20 wk. Until wk 16, which corresponded to 1 March, 1992, the mean time to 50% emergence of mites declined steadily and was not significantly different between the two groups of branches. After wk 16, the mean time to median emergence of mites from field-wintered branches continued to decline, but there was no further decline in the emergence time of mites from laboratory-stored branches, resulting in a significant difference between the two groups. This divergence of the emergence times of mites from laboratory-stored and field-wintered branches after wk 16 indicated that Reid-wintered mites had begun “post-diapause” development or reactivation after ≍ 1 March. Emergence rates of individual mites from branches held at 1°C for 20 wk were compared at seven constant temperatures: 5.3, 7.8, 10.6, 13.3, 15.5, 17.6, and 20.8°C. Weighted, least squares linear regression was used to describe the relationship between emergence rate and temperature (rate = −0.1008 + 0.0162[temp]) for prediction of emergence in the field.The base threshold temperature for emergence was 6.2°C, as determined by extrapolation of the regression line to thex-axis. The relationship predicted that median (50%) emergence of mites requires 62 ± 1 degree-days (±SE) above the base temperature. The degree-day model was validated using field phenology data collected at one and four sites in 1991 and 1992, respectively. Using a 6.0°C threshold temperature for emergence, and daily minimum-maximum air temperatures beginning 1 March, the model accurately (±2 d) predicted the 50% emergence point. This article discusses the use of the degree-day model to improve current pear rust mite management practices in British Columbia.