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Wheat Midge Populations Lower in 2015 than 2014 (07/02/15)

Soil samples in North Dakota indicate decreased levels of overwintering wheat midge larvae (cocoons) for the 2015 season.

Wheat Midge Populations Lower in 2015 than 2014

Soil samples in North Dakota indicate decreased levels of overwintering wheat midge larvae (cocoons) for the 2015 season. A total of 196 soil samples were collected from 21 counties in the fall of 2014 to estimate the regional risk for wheat midge. The distribution of wheat midge in 2015 is based on unparasitized cocoons found in the soil samples.

Only 7 percent of soil samples statewide are moderate to high risk for wheat midge infestation in contrast to 21 percent last year. These ‘hot’ spots will need to be scouted to determine if fields are above economic thresholds and warrant an insecticide treatment for controlling wheat midge in 2015. Overall, most of the state is at low risk for wheat midge in wheat.

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The high-risk pocket of 800 to greater than 1,200 midge larvae per square meter are concentrated in the northwestern area of North Dakota in Mountrail and Divide Counties. Areas with moderate risk of 501 to 800 midge larvae per square meter are only in Williams County.

Wheat midge populations decreased by more than half from last year and ranged from zero to 1,500 midge larvae per square meter, with an average of 61 larvae per square meter in 2014. In 2013, wheat midge populations ranged from zero to 3,285 midge larvae per square meter, with an average of 140 larvae per square meter. In the remaining counties, 44 percent of the samples had one to 500 larvae per square meter (low risk) and 55 percent had zero larvae per square meter. Although one to 500 midge larvae per square meter is considered low risk, it is good insurance to scout for the orange wheat midge flies at night during the heading to early flowering crop stages. This year we have had good soil moisture with the June rains, which is favorable conditions for wheat midge emergence.

A degree-day model is a good predictor of wheat midge emergence for timing field scouting. The model is based on spring wheat development. It is available on the NDSU North Dakota Agricultural Weather Network website. Select the nearest NDAWN weather station and enter your planting date to get a table that lists accumulated midge degree days and indicates whether your wheat is in the susceptible stage (heading) when wheat midge is emerging. Observations indicate the following degree day accumulations for events in the wheat midge population (base temperature 40°F):

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The map (below) indicates that female wheat midge adults are starting to emerge in areas with higher risks based on the 2014 larval soil samples.

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For field SCOUTING, examine wheat heads at night when temperatures are greater than 59 degrees F and the winds are calm (less than 6 mph) during the heading to early flowering crop stages. The orange adult midge can be seen laying eggs on the wheat heads. Plants are susceptible as the head emerges from the boot. The economic thresholds are when 1 or more midge are observed for every 4 or 5 heads on hard red spring wheat, or when 1 or more midge are observed for every 7 or 8 wheat heads on durum wheat. The critical time to spray is from late heading to early flowering. If wheat scab is a problem due to wet conditions during flowering, most insecticides labeled for wheat midge control can be tank-mixed with a fungicide.

The adult wheat midge is an orange, fragile, very small insect approximately half the size of a mosquito. It is about 0.08 to 0.12 inch (2 to 3 millimeters) long with three pairs of long legs. It has a pair of wings, which are oval, transparent and fringed with fine hairs. Two eyes are conspicuous and black. Be careful not to confuse the lauxaniid fly with wheat midge. The lauxaniid fly is yellowish brown, larger and more robust - about 1/10 to 1/6 inch (2 to 4 mm) in length - than the wheat midge. It also actively flies above the wheat canopy during the day and early evening. In contrast, the wheat midge flutters from plant to plant only in the evening. At night, the lauxaniid can be observed resting in the wheat canopy in a horizontal position with its head pointing down in contrast to the wheat midge, which rests with its head pointing upward.

The soil samples were collected by NDSU Extension Service agents in the fall of 2014. The wheat midge survey is supported by the North Dakota Wheat Commission.

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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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