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Wheat Midge Forecast For 2016 (06/23/16)

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

Wheat Midge Forecast For 2016

Soil samples in North Dakota showed low levels of overwintering wheat midge larvae (cocoons) for the 2016 season. A total of 183 soil samples were collected from 20 counties in the fall of 2015 to estimate the regional risk for wheat midge in 2016. The distribution of wheat midge is based on unparasitized cocoons found in the soil samples. No soil samples were found with economic population densities of wheat midge (greater than 500 midge larvae per square meter) this past year. Seventy-four percent of the soil samples had zero wheat midge cocoons. This is the lowest population of wheat midge ever recorded since we have been conducting the wheat midge larval soil survey, which started in 1995!

Wheat midge populations decreased by more than half from last year and ranged from zero to 429 midge larvae per square meter, with an average of 25 larvae per square meter in 2015. In 2014, wheat midge populations were higher, ranging from zero to 1,500 midge larvae per square meter, with an average of 61 larvae per square meter. In 2013, wheat midge populations were higher yet and ranged from zero to 3,285 midge larvae per square meter, with an average of 140 larvae per square meter.

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The highest wheat midge numbers ranged from 200 to 500 larvae per square meter in small, localized areas in southeast Burke, northwest Divide, north central Renville, west central Sheridan and northeast Ward counties. These population levels are still considered non-economic and low risk for wheat midge.

Wheat midge populations have declined sharply for several reasons, including multiple field reports of area wide insecticide-fungicide spraying for control of wheat midge and scab disease to minimize wheat losses, and the dry conditions when larvae dropped out of wheat heads in August 2015, causing increased mortality.

It is always good insurance to scout for the orange flies at night when temperatures are greater than 59 F and the winds are less than 6 mph. Scout during the heading to early flowering crop stages. 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. The economic thresholds 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.

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. However, Dow AgoSciences (Source: J. Bloms, Minot) recommends using the following for optimal tank-mixing compatibility:

  • Lorsban Advanced (water-based) formulation with Caramba fungicide;
  • Lorsban 4E formulation or other chlorpyrifos-generic EC formulation (Trade names – Chlorpyrifos 4E AG, Hatchet, Govern 4E, Nufos 4E, Vulcan, Warhawk, Whirlwind, Yuma 4E) with Prosaro fungicide.

Always read and follow label directions. (Note:  Mention of any pesticide product is not considered an endorsement by the author or NDSU.)

Unfortunately, the parasitic wasp, Macroglenes penetrans, which kills wheat midge eggs and larvae, also has decreased considerably from a 3.7 percent parasitism rate in 2015 to an 11 percent parasitism rate in 2014. Ninety-one percent of the larval cocoons had zero incidence of parasitism in 2015, compared with 73 percent in 2014. This is because the parasitic wasp populations are dependent on their host populations, the wheat midge. So, when wheat midge declines, so does the parasitic wasp. This wasp plays an important role in keeping wheat midge controlled naturally. Parasitism rates ranged from zero to 100 percent across the state, with the higher rates occurring in areas where midge populations have been high during the past few years, such as Burke and Divide counties.

NDSU Extension Service county Ag agents collected the soil samples. The North Dakota Wheat Commission supports the annual wheat midge survey.

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Janet J. Knodel

Extension Entomologist

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