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2020 Wheat Midge Forecast (06/25/20)

Male wheat midge are just being captured in pheromone traps located in the northcentral and northwest areas of North Dakota (IPM Crop Survey).

Male wheat midge are just being captured inent.4 pheromone traps located in the northcentral and northwest areas of North Dakota (IPM Crop Survey). The male midge emerges first at 1,100 accumulate degree days and the female starts to emerge at 1,300 ADD using a base temperature of 40 F. Most of northern North Dakota ranges from 1100 to 1200 ADD for wheat midge, so it is mainly the male wheat midge emerging now.

Producers should use the wheat midge degree-day model to predict the emergence of wheat midge, and to determine when to scout and if their wheat crop is at risk. Producers can access the wheat midge degree day model on North Dakota Agricultural Weather Network (NDAWN) at:

https://ndawn.ndsu.nodak.edu/wheat-growing-degree-days.html

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

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If your wheat crop is in the the susceptible crop stage, heading to early flowering (<50% flowering), we recommend scouting fields. Look for tiny, orange adult flies when temperatures are greater than 59 F and the winds are less than 6 mph at night, after 9PM. Use a flashlight 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:

  • Hard red spring wheat - one or more midge observed for every 4-5 heads
  • Durum wheat - one or more midge observed for every 7-8 heads

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The annual soil survey for wheat midge in North Dakota indicated increasing levels of overwintering wheat midge larvae (cocoons) for the 2020 season (Figure 1). A total of 1,900 soil samples was collected from 20 counties in the fall of 2019 to estimate the regional risk for wheat midge in the 2020 field season. The distribution of wheat midge is based on unparasitized cocoons found in the soil samples.

About one percent of the soil samples had very high population densities of wheat midge (greater than 800 midge larvae per square meter) this past year. The hot spots were located in northeast Wells County and southwest Ramsey County. These populations are high enough that an insecticide is usually needed to reduce potential yield loss from wheat midge, if wheat is in the susceptible growth stages during midge emergence and midge populations are at economic threshold levels during field scouting. Another two percent was at a moderate risk level (501-800 midge larvae per square meter) in northeast Bottineau, central Mountrail and northeast McLean County.

The low risk level (201-500 midge larvae per square meter) was also observed in five percent of the samples. Moderate risk areas were scattered in eight counties throughout the state including the northeast area (Nelson County), the central area (Sheridan and Wells Counties), the north central area (McHenry and Rolette Counties), and the northwest area (Divide, Mountrail, Williams Counties). These population levels are still considered non-economic and low risk.

Thirty four percent of the soil samples were at low risk, but it is always a good idea to scout for wheat midge. The majority of the soil samples, 58 percent, had zero wheat midge cocoons, compared to the record low of 84 percent in 2019.

This dramatic increase in wheat midge populations is probably due to the rain in 2019. Plotting out the total rainfall from May through September and total number of wheat midge cocoons for the past eight years showed a strong correlation between precipitation and wheat midge populations. Larvae are susceptible to dryness and require rain to emerge from the soil in late June through mid-July, and to drop out of the wheat heads and to dig into the soil to overwinter as cocoons.

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The good news for 2019 is that the beneficial parasitic wasp, Macroglenes penetrans, which naturally controls wheat midge eggs and larvae, increased to 15 percent of wheat midge cocoons parasitized compared to only 9 percent in 2018 (Figure 2). The average parasitism rate was also higher; 36 percent in 2019 compared to less than five percent for the last four years (2015-2018). The highest parasitism rates were observed in Burke and Ward Counties.

Conserve the parasitic wasp populations by scouting for wheat midge and spraying insecticides only when wheat midge populations are at economic threshold levels. Parasitic wasps fly later than wheat midge, so avoid applying any late insecticide applications (which are not attractive to wheat midge) to prevent killing these ‘good’ insects. This tiny, metallic wasp does an excellent job keeping the wheat midge in check by providing free biological control.

NDSU Extension County ANR agents collected the soil samples. The North Dakota Wheat Commission supports the wheat midge survey. For more information, please read the NDSU Extension publication on IPM of the Wheat Midge in North Dakota E1330.

 

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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