Farm Progress

Drought likely caused decline in overwintering wheat midge larvae.

March 23, 2018

2 Min Read
MIDGE GONE: An orange blossom wheat midge rests on a wheat head. Due to a record larvae population, there will likely be far few midges to worry about this year.

Soil samples in North Dakota indicate record low levels of overwintering wheat midge larvae for the 2018 season, reports Janet Knodel, North Dakota State University Extension Service entomologist.

A total of 201 soil samples were collected from 21 counties in the fall of 2017 to estimate the regional risk for wheat midge this year. The distribution of wheat midge is based on nonparasitized cocoons found in the soil samples.

“Less than 1% of the soil samples had economic population densities of wheat midge (greater than 500 midge larvae per square meter) this past year,” Knodel says. “The hot spot was located in one soil sample in northeastern Rolette County in north-central North Dakota. The majority of the soil samples, 75%, had zero wheat midge cocoons, which is a record low for the wheat midge larval survey since its inception in 1995.”

The dry weather was extremely detrimental to wheat midge in 2017, Knodel says. Larvae require dew or rain to drop out of the wheat heads and dig into the soil to overwinter as cocoons.

Still scout
But even with the low-risk forecast for wheat midge, it is wise to scout any wheat fields that are at risk from heading to early flowering (less than 50% flowering) when wheat midge is emerging, Knodel advises.

A wheat midge degree day model predicts the emergence of wheat midge, and helps producers determine when to scout and if their wheat crop is at risk. The model is on the North Dakota Agricultural Weather Network website.

If you select your nearest NDAWN station and enter your wheat planting date, the program shows you 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, such as 50% females emerged.

Scouting for the orange adult flies is conducted at night when temperatures are greater than 59 degrees F and the winds are less than 6 mph. 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 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 or eight heads on durum wheat.

Also at record lows is the population of parasitic wasps, which naturally control wheat midge eggs and larvae.

“We need to continue to conserve 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,” Knodel says.

Source: NDSU

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