NDSU Extension - Mercer County

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2020 Wheat Midge Forecast

wheat midge

Submitted by Craig Askim, Extension Agent/Agriculture and Natural Resources

Rainfall has finally arrived in Mercer County. While this is good news, producers must now be on the lookout for wheat midge. The midge require rain to emerge from the soil in late June through mid-July, so producers are encouraged to scout their fields. The article below explains the life cycle of midge, the correct time to scout for them, and when a chemical application is needed. 

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.  If your wheat crop is in 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 9 PM. 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 and for durum wheat - one or more midge observed for every 7-8 heads. The annual soil survey for wheat midge in North Dakota indicated increasing levels of overwintering wheat midge larvae (cocoons) for the 2020 season. 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.

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.

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 Integrated Pest Management of the Wheat Midge in North Dakota E1330.

Source: Janet Knodel, NDSU Extension Entomologist, janet.knodel@ndsu.edu

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