The cold temperatures this week reminded us that we are approaching our fly-free date for Ohio. These
dates are based on predictions on when most Hessian fly adults would no longer be alive to lay eggs on
emerging wheat. Planting winter crops after this date is a good practice to prevent infestations. Areas
of Northern Ohio can safely plant wheat after September 22, whereas the dates in southern Ohio extend
to October 4 and 5.
The fly free date can also be used for both cover crops and to manage diseases. Hessian fly can infest
certain types of cover crops such as rye and triticale. While we may not worry about yield loss in cover
crops, high populations in the winter may provide for infestations in the following spring. For diseases,
the biggest advantage and most important benefit of planting after the fly-safe date is reduction in fall
establishment of Barley Yellow Dwarf Virus (BYDV), Stagonospora blotch, and Septoria leaf spot.
Populations of the aphids that transmit BYDV are usually much lower after the fly-safe date, thus
reducing the level of transmission of the disease to the new crop. BYDV tends to be more damaging and
causes the greatest yield loss when it becomes established in the fall. For leaf diseases such as
Stagonospora and Septoria, planting after the fly-safe date also reduces the risk of fall infections. When
Stagonospora- and Septoria-causing fungi overwinter in the leaves, this usually gives both diseases a
head-start in the spring, leading to great and earlier damage of the flag leaves before grain-fill is
complete, and consequently, greater yield loss if a susceptible cultivar is planted and diseases are not
managed with a fungicide.