Seasonal flight activity periods and emergence phenologies of the cabbage maggot, Delia radicum L., and the seedcorn maggot, Delia platura (Meigen), were studied from 2002 to 2004 in canola, Brassica rapa L. and Brassica napus L., in central Alberta, Canada, in relation to degree-days and Julian-days. D. radicum was univoltine in canola. Peak emergence occurred after an accumulation of 345.8 ± 79.4 DD, and 50% flight activity required accumulation of 324.5 ± 46.8 DD (soil base 4°C). D. platura was bivoltine in canola. Peak emergence of the first generation required 339.5 DD, and the second generation required 594.5 ± 38.9 DD (soil base 3.9°C). Peak flight activity occurred after accumulation of 255.0 ± 74.2 and 639.9 ± 69.4 DD for the first and second generations, respectively. A logistic model was used to describe the relationship of degree-days and Julian-days with emergence patterns of adult flies and predicted that 10, 50, and 95% emergence of D. radicum required 213.7 ± 39.9, 324.5 ± 46.8, and 467.2 ± 46.3 DD, respectively. Logistic analysis predicted that 50% emergence of the first generation of D. platura required an average of 255.0 ± 74.2 DD, and the second generation required 526.8 ± 66.6, 639.9 ± 69.4, and 952.8 ± 77.0 DD for 10, 50, and 95% emergence, respectively. Determination of the temporal patterns of abundance of D. radicum and D. platura has potential application for pest management because it can help ensure that phenologies of candidate agents for biocontrol are synchronous with those of the pests they are targeted to control.