Schmidt: 2016 Wheat Midge Survey Results, 2017 Forecast
Results of the fall 2016 wheat midge survey are in and soil samples in North Dakota indicate low levels of overwintering wheat midge larvae (cocoons) for the 2017 season. This is a good indication that less insecticide will be needed by North Dakota wheat producers to control wheat midge during the 2017 growing season.
NDSU Extension Agriculture Agents in 21 counties from the northern half of North Dakota collected a total of 201 soil samples during the fall of 2016. The distribution of wheat midge is based on unparasitized cocoons found in the soil samples.
Only two percent of the soil samples had economic population densities of wheat midge (greater than 500 midge larvae per square meter) this past year. The higher populations were located in east central Divide and southeast Burke counties in northwest North Dakota. The majority of the soil samples, 68 percent, had zero wheat midge cocoons present.
Wheat midge populations ranged from zero to 2,071 midge larvae per square meter, with an average of 42 larvae per square meter in 2016. In 2015, wheat midge populations were slightly lower, ranging from zero to 429 midge larvae per square meter, with an average of 25 larvae per square meter.
Other areas with low wheat midge populations (200 to 500 larvae per square meter) occurred in small, localized areas in northeast Bottineau, southeast Burke, central Divide, central McLean, northeast Mountrail, northwest Renville, northwest Towner and central Ward counties. These population levels are still considered non-economic and low risk for wheat midge.
While the 2017 wheat midge forecast is low, Janet Knodel, North Dakota State University Extension Service entomologist, recommends scouting any wheat fields that are at risk from heading to early flowering (more than 50 percent flowering) when wheat midge is emerging. A wheat midge degree day model predicts the emergence of wheat midge, and helps producers to determine when to scout.
Producers can access the wheat midge degree day model on the North Dakota Agricultural Weather Network (NDAWN) at “https://ndawn.ndsu.nodak.edu/wheat-growing-degree-days.html”>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 is susceptible to midge infestation, as well as how far along the wheat midge emergence is, such as, 50 percent females emerged.
Scouting for the orange adult flies is conducted at night when temperatures are greater than 59 F and the winds are less than 6 mph. Use a flash light 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.
While the 2017 wheat midge forecast is low for most of northern ND, soil samples collected during the fall of 2016 indicated that the beneficial parasitic wasp, Macroglenes penetrans, which kills wheat midge eggs and larvae, also was low with an average of 4.8 percent parasitism rate in 2016. Eighty-nine percent of the larval cocoons had zero incidence of parasitism in 2016 which was similar to the level in 2015 with 91 percent.
The highest parasitism rates were found in Burke, Bottineau and McLean counties. Since the parasitic wasp is dependent on its host, wheat midge, its populations are usually higher in areas where midge populations also have been high the past year.
Although the parasitic wasp and wheat midge populations are cyclic, wasps play an important role in keeping wheat midge controlled naturally it is still important to continue use best pesticide application practices 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. This tiny, metallic wasp does an excellence job keeping the wheat midge in check by providing free biological control of wheat midge in wheat fields.
For more information on wheat midge, check out NDSU publication E-1330 “Integrated Pest Management of the Wheat Midge in North Dakota” available online at www.ag.ndsu.edu/pubs/plantsci/pests/e1330.pdf.
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