The effectiveness of felt egg traps to detect oviposition by the cabbage maggot, Delia radicum (L.), was studied under field conditions for cabbage, Brassica oleracea L. var. capitata L. (Brassicaceae), and rutabaga, Brassica napus L. var. napobrassica (L.) Reichenb. (Brassicaceae), in 1994 and 1995. The numbers of eggs laid on traps were compared with the numbers deposited in the soil next to the plant. Also, the incidence of oviposition (i.e., the percentage of samples with eggs) on soil and traps was compared. A total of 5160 eggs was collected from 5208 samples, but just 16% of all samples had eggs. For cabbage, early in the 1994 season, the incidence of oviposition in soil samples was double that on traps, and the number of eggs per sample was greater also. Oviposition incidence and the number of eggs per sample during the rest of the summer were similar. In the 1995 cabbage trial, the incidence of oviposition early in the season was again higher in soil samples than on traps, and there were fewer eggs per trap than per soil sample. For rutabaga, the number of eggs was similar using both methods early in the second generation, but from mid-August there were more eggs per trap than per soil sample. The incidence of oviposition in the rutabaga trial was similar on traps and in soil through most of the experiment. In this study, felt traps did not adequately detect the timing of cabbage maggot oviposition in the critical early season.