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.
Without scouting eggs, you will be just guessing as to whether or not Hessian fly is in your field. Our NC State recommendations are that you should only spray if you’ve had historical problems with Hessian fly, planted early, did not use an insecticidal seed treatment, and have a susceptible variety. You can find a list with varietal susceptibility at this link (click here). In the vast majority of these cases, using one of these management tactics will effectively manage Hessian fly. There are certain situations where multiple tactics are needed to prevent yield loss. These are only under the heaviest pressure situations and should be based on your past experience with this pest.
Also remember the point of the spray is kill to adult flies, with the hope of some residual to kill flies that may attack in the future. Sprays may have some efficacy on larvae as they hatch from the eggs, but this has never been demonstrated with research and is open to question. Once larvae reach the base of the plant, they remain protected from foliar insecticide sprays. Results are best when sprayed at the 2-3 leaf stage of wheat, or slightly before. Use the highest labeled rate of your choice of pyrethroid.
Finally, you can link to a web version of the management publication here and can download a free .pdf with interactive links to web-based data here. A video on Hessian fly biology management is below.