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Wheat Midge Emerging & 2017 Forecast (6/29/17)

Soil samples collected in North Dakota from 2016 indicated low levels of overwintering wheat midge larvae (cocoons) for the 2017 season.

Wheat Midge Emerging & 2017 Forecast

Soil samples collected in North Dakota from 2016 indicated low levels of overwintering wheat midge larvae (cocoons) for the 2017 season. A total of 201 soil samples were collected from 21 counties in the fall of 2016 to estimate the regional risk for wheat midge in 2017. The distribution of wheat midge is based on non-parasitized cocoons found in the soil samples.

Only two percent of the soil samples had economic population densities of wheat midge (greater than 500 midge larvae per square meter) this past year. These higher populations were located in east central Divide County in northwest North Dakota. The majority of the soil samples, 68 percent, had zero wheat midge cocoons.

This is good news for North Dakota wheat producers, as it will reduce the likelihood that insecticide will be needed for wheat midge control in wheat in 2017.

Wheat midge populations ranged from zero to 2,071 midge larvae per square meter, with an average of 42 larvae per square meter in 2016. In 2015, wheat midge populations were slightly lower, ranging from zero to 429 midge larvae per square meter, with an average of 25 larvae per square meter.

Other areas with low wheat midge populations (200 to 500 larvae per square meter) occurred in small, localized areas in northeast Bottineau, southeast Burke, northeast Mountrail, northwest Renville, northwest Towner and central Ward counties. These population levels are still considered non-economic and low risk for wheat midge damage.

knodel wheat midge larval survey

NDSU Extension Entomology recommends scouting any wheat fields that are at risk from heading through early flowering (more than 50 percent flowering) when wheat midge is emerging. A wheat midge degree day model predicts the emergence of wheat midge, and helps producers to determine when to scout.

Producers can access the wheat midge degree day model on the North Dakota Agricultural Weather Network (NDAWN).

Select your nearest NDAWN station and enter your wheat planting date. The output indicates the expected growth stage of the wheat and whether it is susceptible to midge infestation, as well as how far along the wheat midge emergence is.

The current accumulated degree day map (ADD) for wheat midge in North Dakota indicates that 10% of females have emerged at 1300 ADD in most areas (see map). At 1,475 ADD, about 50% of females have emerged. At 1,600 ADD, about 90% of females have emerged. The IPM Scouts have detected low numbers of male wheat midge in pheromone traps, less than 10 midge per trap per week, in Bottineau, Renville, McHenry, Pierce and McLean Counties in the North Central area. No wheat midge was detected in traps located in Ward, Rolette, Sheridan, Divide, Williams, Mountrail and Burke Counties.

knodel midge map DD

Scouting for the orange adult flies is conducted at night when temperatures are greater than 59 F and the winds are less than 6 mph. Use a flash light and slowly scan the heads of wheat plants for wheat midge adults, counting the number of flies per head. The economic thresholds for wheat midge are: one or more midge observed for every four or five heads on hard red spring wheat, or one or more midge observed for every seven

knodel wheat midge photo

or eight heads on durum wheat.

The bad news from the 2016 survey is that the beneficial parasitic wasp, Macroglenes penetrans, which kills wheat midge eggs and larvae, also was low with an average of 4.8% parasitism rate in 2016. Eighty-nine percent of the larval cocoons had zero parasitism in 2016, similar to the level in 2015 with 91 percent. The highest parasitism rates were found in Burke, Bottineau and McLean counties. Since the parasitic wasp is dependent on its host, its populations are usually higher in areas where midge populations have been high the past year.

 

NDSU Extension Entomology recommends conserving the parasitic wasp populations when possible by spraying insecticides only when wheat midge populations are at economic threshold levels, and avoiding any late insecticide applications to minimize the negative impacts on parasitic wasps that are active at that time. This tiny, metallic wasp does an excellent job keeping wheat midge in check by providing free biological control of wheat midge in wheat fields.

knodel wheat midge map 2

The wheat midge soil survey and trapping are supported by the ND Wheat Commission. Please see the NDSU Extension Service E1330 IPM of Wheat Midge in North Dakota for more information and photographs.

Janet J. Knodel

Extension Entomologist

This site is supported in part by the Crop Protection and Pest Management Program [grant no. 2017-70006-27144/accession 1013592] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed are those of the website author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

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