NEWS for North Dakotans
Agriculture Communication, North Dakota State
University
7 Morrill Hall, Fargo, ND 58105-5665
July 23, 1998
Some localized infestations of the orange wheat blossom midge are proving to be more persistent and mobile than expected, according to North Dakota State University crop expert.
Research and previous experience indicate that after the wheat crop reaches 1,600 growing degree days (a cumulative measure of air temperature) 90 percent of the female wheat midge have emerged. The insects live about four to seven days, so crop specialists expect a gradual decline after that 1,600 growing degree day point. But this year, midge numbers are remaining high for an extended period of time.
"Conditions have been ideal for the insect with frequent thunderstorms causing high dew points," notes Janet Knodel, a crop protection specialist with the NDSU Extension Service in Minot at NDSU's North Central Research Extension Center. "And that's allowed those populations to stay elevated." She says the midge were probably living to the upper end of their possible life span. And June rainfall may have cooled the soil, delaying emergence in some fields so that growing degree days didn't provide an accurate prediction.
Knodel notes that the pest has been more mobile this year as well. Typically, problems are worst where wheat follows wheat in an annual crop rotation and the wheat crop is in the most susceptible stageheading to early flowering.
"This year it didn't seem to really matter what crop was planted. If the field where they emerged wasn't in a susceptible stage, they just moved somewhere else where egg-laying conditions are more favorable," Knodel says. "Although some Canadian research suggests wheat midge adults can move up to 10 miles, we haven't tested that here."
Knodel says the unusual midge activity this year may alter how crop specialists scout and manage crops for the pest. She'll be reviewing data on the midge populations gathered from growers across north central North Dakota to compare it with rainfall, temperature, dewpoint and humidity records.
"Right now our predictions for emergence are all based on growing degree days. Perhaps there's some other factor that's just as important," she says.
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Source: Janet Knodel (701) 857-7682
Editor: Tom Jirik (701) 231-9629