Around this time of the year, Hessian fly adults begin to become active.
The time of peak activity can vary from year to year. For example, in the fall of 2010, Hessian fly was active from mid-November to mid-December. Last year (2012), Hessian fly pressure was heaviest around the end of November to the beginning of December.
For details concerning scouting and treatment thresholds for Hessian fly click here.