Wheat alert: Be aware of the fly

Planting date is one of the critical management practices that affect wheat yields in our area. The other two are variety selection and planting depth. Farmers have the power to control variety selection and planting depth, but planting date is weather dependent. In our area, wheat is generally planted after soybean. Weather will determine how soon soybean fields may be harvested and will determine how soon fields are suitable for wheat planting after the bean harvest. However, farmers also are aware that wheat should not be planted until after the "fly-free date." This date is the time that the main fall brood of adult Hessian flies have completed their life cycle and died before emergence of susceptible wheat seedlings. The adult Hessian fly is a tiny, dark-colored insect about one-eighth inch long that resembles a large gnat or small mosquito. Females lay eggs on the seedling leaves, which hatch in three to seven days. Newly emerged maggots will move down to the crown of the plant and reside in the grooves of the leaf sheath and stem. They will feed on plant tissue by using their mouthparts like sandpaper and lap up juices that seep out. Larvae are the only stage that damage wheat; adult flies do not feed. Maggots usually feed on the lower leaves and stems and reduce plant vigor. Infested plants become stunted and stiffly erect, and leaves are thickened with a bluish green color. A single maggot feeding on a plant for three days can stunt a young plant or tiller. Heavily damaged plants usually die during the winter. Outbreaks of the Hessian fly have caused severe losses in wheat for the past 230 years in this country. It also may damage barley and rye, but not oats. Its damage was first observed in North America in the Long Island, New York area in the late 1770s. The fly was found in the vicinity where Howe's British troops were encamped. It was thought that Hessian soldiers in his army brought the pest from Europe in straw used for bedding; thus, its name — Hessian fly. The Hessian fly moved from Long Island approximately twenty miles annually until it reached the wheat growing region of the Great Plains. Problems associated with the pest and possible control methods are discussed at length in Thomas Jefferson's agricultural writings. Hessian fly caused a US shortage of wheat in 1836 that caused economic problems for farmers prior to the Panic of 1837. It was reported in Ohio agricultural reports as early as 1847. In the latter part of the 1800s Hessian fly infestations were specifically reported in Crawford, Defiance, Seneca and Wood counties. Serious outbreaks occurred in Ohio in 1895 and 1920. Parts of Indiana had serious outbreaks as late as the early 1960s. A "fly free" date was observed as a possible control practice as early as the late 18th century in the Mid-Atlantic States. The Ohio Agricultural Experiment Station started using fly free dates for Ohio from 1911 to 1919. Nation-wide fly-free dates were established from studies conducted from 1918 to 1935. The dates used today in Ohio and other states were a result of this research. In addition to the management research, resistant variety programs were initiated in our region in the 1940s. New varieties with Hessian fly-resistant genes were heavily introduced between 1950 and 1983. The low incidence of damage from Hessian fly in Ohio today can be attributed to both host-plant resistance and planting date. However, over the past decade surveys have shown that the genes are no longer effective against a new emerging biotype of Hessian flies. With the loss of plant resistance, planting date will once again be our main defense against devastating yields losses to Hessian fly. With global warming, new research may be required, and the dates adjusted as our climate changes. Currently, the fly free dates are Sept. 26 for Hardin and Wyandot counties, Sept. 25 for Hancock and Putnam, Sept. 24 for Seneca and Sept. 23 for Wood. The fly free date may not be much of an issue for farmers this year. Soybean fields may not be ready for harvest until after the fly free date. Most of our wheat is planted into harvested soybean fields. However, with climate change, the fly free date may be moving into October for Northwest Ohio. Research will be needed to ensure that farmers truly are planting after the fly free date. So, an old nemesis may once again become the scourge of wheat production and just like a movie sequel, we can see a new headline: Return of the Fly. Lentz is agriculture and natural resources educator with Ohio State Extension Office — Hancock County.