Seasonal patterns of ground beetle activity were examined at six highbush blueberry (Vaccinium corymbosum L.) farms in southwestern Michigan. On each farm, pitfall traps were used to monitor ground beetle activity in two adjacent fields: one managed under a conventional insecticide program (grower standard) and the other with reduced-risk insecticides. Overall, more active ingredient was applied in grower standard than reduced-risk fields, with the greatest amount used in June and July. During the 6-mo sampling period, we collected 11,322 ground beetles comprised of 34 species, with Harpalus pensylvanicus DeGeer representing 70.7% of the total beetles collected. The greatest amount of ground beetle activity occurred in August and September, mostly because of increased captures of the autumn breeding species H. pensylvanicus and H. erraticus Say. Only H. erraticus responded to the different insecticide programs, with eight-fold greater captures in reduced-risk compared with grower standard fields. Because H. erraticus are in the soil as larvae or pupae during June and July, we suggest that greater insecticide use in the grower standard fields resulted in increased mortality of immature H. erraticus. At one farm, where ground cover was absent between blueberry rows, H. erraticus activity did not respond to the difference in insecticide program. This suggests that enhancement of ground beetle activity may require suitable habitat in addition to a reduction in broad-spectrum insecticide use.