As wheat has become less common as a crop, it is harder to find the "fly free date" in publications. For those who are not familiar with the term, this comes from the date after which damage from the Hessian fly is negligible. It is also the planting date range which typically gives the best yields of wheat for a variety of reasons, including less damage from Septoria leaf spot and Barley yellow dwarf virus. Below is the table of dates for Illinois counties:
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