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April 8, 2005 Wheat Midge Outlook Good for North Dakota A soil survey conducted last year detected low levels of overwintering wheat midge larvae, according to Janet Knodel, North Central Research Extension Center crop protection specialist. “This is good news for wheat and durum producers,” Knodel says. “Wheat midge populations ranged from 0 to less than 500 midge larvae per square meter, with most of the state having less than 200 midge larvae per square meter during 2004.” Fields with more than 1,200 midge larvae per square meter are considered high risk. At that point, some control tactic must be used to reduce midge populations. Although a few fields sampled in 2004 had populations close to 1,000 midge larvae per square meter, a tiny, black parasitic wasp kept the wheat midge in check. This wasp, Macroglenes penetrans, parasitizes the larvae of wheat midge and will emerge the following spring and kill the wheat midge larvae. Parasitism can range from 0 percent to 100 percent, with the higher rates occurring in areas where midge populations have been high for a few years. With the wheat midge population being low for the last few years, producers unfortunately may see a slow decline in the parasitic wasp population in the future. “Weather conditions and the stage of wheat will be important in determining if sporadic outbreaks of wheat midge will cause economic damage this year,” Knodel says. “Environmental conditions favoring wheat midge development include moist soil conditions prior to emergence in late June to early July, warm, high humidity and light wind conditions during egg laying.” Economic injury still can occur if wheat or durum is in the susceptible stage (heading to 50 percent flowering) during wheat midge emergence and egg laying. Damage can reduce crop yields and lower the grade of harvested grains. Wheat midge was detected in 1994 in the northeast counties bordering Manitoba, Canada. Wheat midge continued to expand its distribution into the north-central region and eventually moved westward into northwestern North Dakota and even Montana. Economic damage was common in 1995 and 1997 through 2001. However, for the past several years there has been a general decline in wheat midge populations, causing less economic damage to wheat and durum fields. The wheat midge degree-day model developed by Canada has helped predict emergence and peak activity periods, as well as when field monitoring should take place. “Careful, regular monitoring of wheat and durum fields is good insurance if your crop is susceptible after wheat midge have emerged and are active,” Knodel says. “Scout fields after 9 p.m., when the temperature is above 59 degrees Fahrenheit and the wind speed is less than 6 mph. Count the number of adult wheat midge present on four or five heads at several locations and then use an average per field.” Economic thresholds are one midge per four to five wheat heads for hard red spring wheat and one midge per seven to eight heads for durum. At these levels of infestation, wheat yields will be reduced by 15 percent if the midge is not controlled. Not every small fly in the crop will be a wheat midge. Wheat midge is a small, fragile orange-colored fly about the 2 to 3 millimeters in size. Another small fly that is common in wheat fields is the lauxanid, which is larger (2.5 to 4 millimeters), more robust and yellowish-brown in color. The wheat midge tends to flutter from plant to plant and rests with its head pointing skyward, while the lauxanid flies and rests in a horizontal position with its head pointing toward the ground. The wheat midge survey is conducted by the NDSU Extension Service and supported by the North Dakota Wheat Commission. ### Source:
Janet Knodel, (701) 857-7682, jknodel@ndsuext.nodak.edu
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