Fly-free Date and Wheat Planting

Hessian Fly larvae

by Glen Arnold, Putnam County 

Many farmers are visiting the Farm Science Review this week before fall harvest starts in earnest. In addition to harvesting soybeans and corn, will also be planting soft red winter wheat. Most soybean fields are still not close to harvesting so wheat planting will likely be a bit later than normal.

Wheat should never be planted prior to the Hession fly-free date of September 25th in Putnam County because of the possibility of severe damage by virus such as Barley Yellow Dwarf  and by the larvae of the Hessian Fly.

The fly-free date is September 23 for Henry, Wood, and Sandusky counties; September 24 for Seneca County; September 25 for Hancock and Putnam counties; and September 26 for Allen, Hardin, and Wyandot counties. These dates have been selected and determined from years of research for wherever wheat is grown in the county.

The Hessian fly can be one of the most destructive pest species in wheat. This insect originated from Russia and was accidentally introduced into North Americawhen Hessian troops imported straw bedding during the American Revolutionary War. Hessian flies were first observed on Long Island, New Yorkaround 1779. Today, they are present in most wheat growing areas of the United States. Around the turn of the 20th century, this insect destroyed millions of bushels of wheat in Missouri.

In late summer and early fall, Hessian fly adults begin to emerge from wheat stubble and the “fly-free date” is set to occur after the peak emergence of Hessian fly adults. When wheat is planted after the fly-free date, there is not a suitable host for females to lay eggs on. These females will then die without laying their full complement of eggs. If these eggs are laid and then hatch, the larvae will feed between leaf sheaths and stems until they pupate in mid-autumn. Infected plants become weakened and fail to “tiller” (sprout new stems).  Plants may also “lodge” (plant falls/lies down) during grain fill, which is usually where the damage is noticed the most.

Research has also shown that farmers, by planting after this fly-free date, are not only controlling the Hessian fly – but also aphids that carry a harmful virus called Barley Yellow Dwarf, and also other foliar wheat diseases.

It is certainly a win-win situation when a farmer is able to control harmful insects and diseases merely by planting after a certain date as opposed to applying pesticides.

Research has also determined that long-term average yields are actually higher for wheat planted during a 10-day period after the fly-free date.

There has also been new genetics developed in wheat varieties to be more resistant to the Hessian fly; but like any other fly, changing biotypes of the Hessian fly have overcome some of this resistance over the years.

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