The Hessian fly (HF), Mayetiola destructor (Say), has historically been a significant pest of wheat throughout the Great Plains, including Kansas. However, it has been many decades since the flies’ activity has been monitored in the field. This paper presents research on the activity of the HF throughout the year in Kansas, i.e., examining when the fly is active and how moisture events may play a role. Results of a newer technology, pheromone trapping, in four counties in Kansas shows that HF males are active in the fall, at least 6 wk later than the historical fly-free dates established nearly 100 yr ago. Therefore, the ‘Hessian Fly-Free Date’ is not as valid as previously thought and might be better referred to as the ‘Best Pest Management Planting Date’. Using pheromones for fall and spring trapping also indicated that HF is more active throughout the spring than previously thought, with almost continuous fly emergence and numerous emergence peaks in both spring and fall. Pheromone traps were also used to determine if fly emergence peaked after moisture events as previously thought. Fly emergence could not be positively correlated with any moisture event.