I was recently asked if it was still necessary to follow the practice of planting winter wheat after the fly-free date. This is a good question because it has been many years since we have had any kind of significant yield losses attributed to the Hessian fly, which is the reason behind the fly-free planting dates. The fall brood of the Hessian fly appears in the later part of September and only lives for a few days. This brood lays its eggs on young grasses which include small grains such as wheat. Maggots hatch from the eggs and the tiny larvae crawl to the crown of the plant and feed on plant juices. The feeding results in stunted plants. After feeding the larvae pupate and overwinter. In the spring adult flies emerge and lay eggs on the leaves of the wheat plant. Maggots hatch and move under the leaf sheath near plant nodes. As they feed they cause the stem to weaken which results in stalks breaking over before wheat harvest. The maggots end their feeding and change to the pupa state about the time of wheat heading and will remain in the stubble until fall when the entire cycle starts over.
The fly-free dates are predictions of when most Hessian fly adults would no longer be alive and able to lay eggs in wheat fields. In Wayne County our fly-free date is September 26. A map showing fly-free dates for Ohio is available at: http://ohioline.osu.edu/iwy/flydates.html. Even if you are not convinced that the Hessian fly remains a threat, it turns out that there are other reasons to stick to that fly-free planting date.
OSU Extension plant pathologist Pierce Paul recently co-authored an article about using the fly-free date for winter wheat planting. He wrote “Another excellent reason to plant wheat after the fly-safe date is to minimize problems with diseases, especially barley yellow dwarf virus (BYDV). BYDV is transmitted by aphids and tends to be most severe when transmission occurs in the fall. Research showed that due to unfavorable weather conditions, the aphid population tends to crash after the fly safe date, leading to fewer problems with BYDV. Planting date studies conducted here at OSU a few years ago showed that BYDV problems and yield loss associated with this disease are much higher when wheat is planted well before the fly-safe date. Planting after the fly-safe date also minimizes early establishment of other diseases such as Stagonospora blotch and leaf rust.”