PENDLETON - An Oregon State University research project on nematodes has unexpectedly revealed a major infestation of wheat by a tiny, destructive fly.

More than 90 percent of the spring wheat in test plots in Umatilla County, and 30 percent in Sherman County, were infested by Hessian flies, said Richard Smiley, research scientist and former superintendent of the OSU Extension Service's Columbia Basin Agricultural Research Center near Pendleton.

Smiley said his research project at three locations, grown last spring, was not on Hessian flies but on whether root lesion nematodes cause economic damage to annual fields planted without summer fallow.

However, when researchers noted the Hessian flies in the test plots of the nematode study they realized they had an opportunity to study how much damage the infestation had caused and what wheat varieties and chemical treatments had proved the most resistant.

"Sometimes scientists are opportunists," Smiley said. "We had no thought that the Hessian fly was going to damage this wheat, but it was a great opportunity to quantify the damage caused through the flies' activity."

They found that wheat with genetic resistance to Hessian flies had little infestation and damage, and so did wheat that had been treated with a pesticide that targets Hessian flies. However, combining these controls did not seem to significantly improve control.

The Hessian fly has been a bane to cereal grain farmers since it was brought to North America by German soldiers hired to fight for England during the Revolutionary War. It resembles a mosquito, except that it is smaller, black and lacks the mosquito's blood-sucking stinger. Hessian fly larvae are not much larger than a grain of salt, but their effect is powerful. The almost-transparent larvae simultaneously suck nutrients from the emerging wheat and inject a growth-inhibiting toxin.

The larvae can kill a plant or stunt its growth, which lowers both the wheat yield and its quality, or grade, scientists say.

Adult flies, which live only two days, usually appear three times during the year - twice in the spring and once in the fall. However, unusual rains in early September in Eastern Oregon apparently gave the fly a second autumn flight, which may have contributed to the infestation, Smiley said.

The scope and cost of the infestation is still being calculated, but it appears now that it primarily affected wheat in Umatilla and Sherman counties, said Mary Corp, a cereal crop specialist with the OSU Extension office in Umatilla County.

"A 50 percent yield loss is possible," Corp said. "That's significant."

In terms of cost and yield, Smiley said it appears the infestation in his plots at two Umatilla County locations reduced the value of spring wheat production by $70 an acre, not taking into account losses from lowering of the wheat's grade.

Representatives for the Oregon Wheat Grower's League and the Oregon Wheat Commission said they are aware of Smiley's report of the infestation. They are monitoring reports of additional infestations and plan to compile more specific, detailed information as it becomes available.

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Richard Smiley, 541-278-4397